Artifacts in portable electrocardiographic monitoring A. Z. Krasnow D. K. Bloomfield, M.D.* Urbana-Champaign, Ill.
This article describes a series of artifacts encountered in 466 cases of portable electrocardiographic monitoring by a technique known as dynamic electrocardiography (DCG). Although standard 12-lead electrocardiographic artifacts have been documented repeatedly, ~-6 there have been only scattered reports of DCG artifacts, 7.H and physicians are generally less familiar with their characteristics. Since artifacts always enhance the possibility of improper diagnosis, which leads to improper therapy, we believe that our experience will be useful to those who use portable ECG monitoring techniques. Methods
The equipment used in these studies was the Avionics Model 350 "Electrocardiocorder," and the Avionics Model 650 "Composite Electrocardioscanner." Patients were unselected individuals who were referred for monitoring by their private physicians; the patients' complaints were varied, the most prominent being chest pain, palpitations, and dizziness-syncope. Subjects ranged in age from 14 to 89 years. Some patients were ambulatory at home, work, or within a hospital; others were at bed rest. Electrodes were positioned with the exploring electrode at the V5 position and the reference electrode over the manubrium, All tapes were scanned by a single technician who printed out suspicious areas of the recording.
From the University of Illinois. College of Medicine, School of Basic Medical Sciences. Urbana-Champaign, Ill. Received for publication Dec. 11. 1974. Reprint requests: D, K. Bloomfield, M.D., Medical Sciences Bldg., Urbana, Ill. 61801. *Dean, University of Illinois, College of Medicine, School of Basic Medical Sciences.
March, 1976, Vol. 91, No. 3, pp. 349-357
No effort was made to quantify the incidence of specific artifacts except in general terms of rare, occasional, or common. Results
Artifacts discovered were divided into two general categories, pseudo-arrhythmias and nonarrhythmias. A classification of the artifacts, their relative frequency, probable cause, and potential seriousness, is shown in Table I. Some were trivial, whereas others created serious problems in interpretation, and in two instances almost caused the unnecessary implantation of an artificial cardiac pacemaker. Pseudo-arrhythmias mimicking supraventricular rhythms are shown in Figs. 1, 2, and 3. Fig. 1 shows pseudo-premature atrial contractions. They are identified as an artifactual, intermittent slowing of the recorder for brief periods, with normal operation thereafter. The complexes appear smaller and compressed in time, as if there were a transient excess load placed on the battery-driven mechanism. T h a t this was not due to battery failure per se is seen by the fact t h a t tracing a of Fig. 1 shows the same artifact recorded 9 hours before tracing b, in which the artifact continues; the same battery was in continuous use. Replacement of the "Electrocardiocorder" motor eliminated the artifact. The Fig. 1 artifact might also be interpreted as pseudopremature junctional beats since the P-wave is distorted and the P-R interval is reduced to less than 0.12 second. Fig. 2, pseudo-sinus or atrial tachycardia, is a relatively common artifact associated with battery- or electric-motor failure and has been described by others. 1~ 11 Characteristically, it appears toward the end of the recording tape, is of gradual onset, and is accompanied by gradual
American H e a r t Journal
349
K r a s n o w and Bloomfield
Table I. Classification of artifacts
Type of artifact
1. Pseudo-arrhythmia a. Supraventricular 1. Pseudo-PAC 2. Pseudo-PAT 3. Pseudo-atrial fibrillation b. Ventricular 1. Pseudo-PVC 2. Pseudo-fusion beat 3. Pseudo-ventricular tachycardia c. Junctional or dissociative l. Pseudo-junctional rhythm 2. Pseudo-Mobitz II A-V block 3. Pseudo--sinusarrest 2. Non-arrhythmia a. Voltageor frequency response disturbance 1. Pseudo-aberrancy 2. Pseudo-lowvoltage b. Tape and polarity reversal 1. Tape reversal 2. Polarity reversal c. Pseudo-alternans {"Siamese twins") d. Alteration of QRST (pseudo-primary T-wave changes)
Figure number in text
Relative frequency
Probable cause*
Potential effect on diagnosis and treatment
1 2 3
Occasional Occasional Rare
A B U-1
Possible Serious Serious
4 5 6
Occasional Common Rare
C-1 C-1 U-2
Possible Minimal Serious
7 8 9
Rare Occasional Rare
A C-1 D
Possible Serious Serious
10 11
Occasional Occasional
C-1 B
Minimal Minimal
12 13 14 15
Occasional Occasional Rare Common
E E E C-2
Serious Serious Possible Serious
*A, Electrical or mechanical artifact of recording device; cause unknown.B, Electrical artifact of recordingdevicedue to battery or electric-motor failure. C-1, Bodymovementor disturbance of skin electrode contact. C-2, Bodymovementcausing a changein the recordingdipole. D, Mechanical artifact of playbackdevice. E, Technician error. U-l, Unknowncause; probably a loose or broken wire connection. U-2, Unknowncause; probably exercise.
diminution, and often cessation, of the signal. T h e characteristics m a y vary depending u p o n w h e t h e r the cause is a loss of b a t t e r y charge or a m o t o r which draws excessive current, the f o r m e r being of shorter d u r a t i o n before c o m p l e t e loss of signal. Fig. 3 shows pseudo-atrial fibrillation, p r o b a b l y associated with a loose connection or broken lead. TM P a r t s of the tracing {Fig. 3, a) m i g h t be confused with Parkinsonian tremor, b u t this was n o t consistent t h r o u g h o u t . Fig. 3, b shows a brief period w i t h o u t artifact, revealing the basic sinus r h y t h m . T h e p r e m a t u r e ventricular systole at beat No. 7 of Fig. 3 a also suggests t h a t t h e s e strips are artifactual, since it has a full and exact c o m p e n s a t o r y pause, u n u s u a l in atrial fibrillation. P s e u d o - v e n t r i c u l a r a r r h y t h m i a s are shown in Figs. 4, 5, and 6. Fig. 4 is an example of a pseudop r e m a t u r e ventricular c o n t r a c t i o n p r o b a b l y due to jostling of an electrode. I t shows basically a sinus r h y t h m with mild sinus a r r h y t h m i a . Base-
350
line disturbances are present t h r o u g h the first four beats. B e a t No. 3 is an artifactual distortion of a n o r m a l l y conducted beat because: (1) Despite the m a r k e d Q R S distortion, there is no secondary T - w a v e change. (2) T h e T - T interval between beats No. 2 and No. 3 shows only a 0.04second shortening, well within the sinus a r r h y t h mia variation. (3) T h e S-wave of beat No. 3 can be identified as a n o r m a l segment of the otherwise distorted QRS. Its timing in relation to preceding and following S-waves is well within the sinus a r r h y t h m i a limits. (4) T h e S-T segment following the S-wave, like the T-wave, has n o r m a l configuration. Fig. 5 shows a pseudo-fusion beat. T h e complex is characterized by a sudden loss of frequency response noted in b o t h the P-wave and the Q R S complex. Electrical recovery is not entirelY complete until the second beat after the pseudofusion beat. F o r a period of 0.24 second before the a b e r r a n t Q R S t o immediately thereafter, there is a high-frequency cut-off disturbance which
March, 1976, Vo!. 91, No. 3
Artifacts in portable ECG monitoring
Fig. 1. Pseudo-atrial or pseudo-junctional premature contractions associated with Electrocardiocorder battery failure.
distorts the baseline, the P-wave, and the QRS. T h e baseline t h r o u g h o u t the strip shows small high-frequency irregularities, except during the period in question. T h e 50 per cent reduction in QRS voltage occurs toward the end of the artifactual period, and it is likely t h a t the peak of the artifactual disturbance obliterated the n o r m a l Pwave. T h e artifact is probably caused by some type of electromechanical disturbance affecting the frequency response of the recorder. It is an incomplete form of the artifacts seen in Fig. 8. Fig. 6, a continuous strip, is a d r a m a t i c example of pseudoventricular tachycardia, cause unknown. T h e initial sinus r h y t h m is n o t e d to be gradually engulfed by an u n d u l a t i n g artifact which gradually poses as a ventricular t a c h y c a r dia. T h e R - R interval of the n o r m a l QRS complexes can be followed t h r o u g h o u t , as indicated b y the time intervals n o t e d on top of the strips. T o w a r d the end of the episode (Fig. 6, d), the QRS complexes can be identified as the process concludes. Several artifgcts (Figs. 7, 8, and 9) mimicked j u n c t i o n a l r h y t h m , a n d c o n d u c t i o n or p a c e m a k e r disturbances. Fig. 7 is really an example of a frequency response disturbance simulating a j u n c t i o n a l r h y t h m . Fig. 8 shows t w o extreme examples of t e m p o r a r y i m p a i r m e n t of electrode contact, posing as advanced A-V block. T h e "blocked P-wave" in Fig. 8, a is a c t u a l l y a diminutive QRS complex, since it is n o t s y n c h r o n i z e d with the preceding P-wave and is of a different configuration. T h e P-wave preceding and the T-wave following t h a t complex are c o m p l e t e l y lost, Figs. 8, b and c come from a different p a t i e n t
American Heart Journal
Fig. 2. Pseudo-sinus or atrial tachycardia due to battery failure. At 15:15 (a) the record shows normal sinus rhythm at a rate of 94 per minute. At 19:00 (b) the artifactual rate is 144, but there is compression of the entire PQRST complex, including a loss of voltage.
whose electrocardiogram showed atrial fibrillation and left bundle b r a n c h block. T r a c i n g b was originally interpreted as a reversion to n o r m a l sinus r h y t h m with advanced A-V block requiring p a c e m a k e r insertion. This was in error because the complexes m a s q u e r a d i n g as P-waves are irregular and are actually compressed QRS complexes reflecting n o r m a l l y c o n d u c t e d beats in the presence of atrial fibrillation. Fig. 9 shows u n u s u a l artifacts related to the playback process. T h e y resulted when the c o m p a n y which m a n u f a c t u r e d the recording tape (3 M C o m p a n y - 200 Tape) discontinued its line and replaced it with a new product (178 Tape), to give higher recording fidelity. T h e result was not a success for the D C G method. T h e new tape tended to adhere to the slow-speed scanning head of the "Electrocardioscanner." T h e combination~ of the tape slowing with the strip-chart recorder running at 25 mm. per second p r o d u c e d the effects seen in Fig. 9. In each instance the slowing or t e m p o r a r y stoppage of the tape caused by its
351
K r a s n o w and Bloomfield
Fig. 3. Pseudo-atrial fibrillation. The artifact persisted throughout the recording except for brief periods of clarity (b). The patient did not suffer from Parkinson's disease or have any other observable tremor. A 12-lead electrocardiogram was free of artifact {time interval in seconds).
Fig. 4. A pseudo-premature ventricular contraction. The aberrant complex appears to be premature, but it is an artifact obscuring a normal QRS which can be identified by its relatively normal S-wave, S-T segment, and T-wave (time intervals in seconds).
Fig. 5. Pseudo-fusion beat. The designated complex is an incomplete form of the examples shown in Fig. 8. Note the change in P-wave configuration preceding the complex (time interval in seconds).
sticking to the scanning head produced artifacts t h a t resembled either m a r k e d sinus a r r h y t h m i a , bradycardia, or sinus arrest. In some instances the artifact is readily identified by the obvious broadening of the t o t a l P Q R S T complex {Fig. 9, b), b u t this was not always possible since t h e stoppage occasionally occurred a b r u p t l y b e t w e e n complexes {Fig. 9, a). W h e n the t a p e was released, the recording of n o r m a l sinus r h y t h m reappeared. Misinterpretation of these artifacts has also led to the improper r e c o m m e n d a t i o n o f insertion of a cardiac pacemaker. S e v e r a l artifacts were noted t h a t did not fall into the category of pseudo-arrhythmias. Fig. 10 is closely related to Figs. 2 and 8. T h e complexes seem to be similar to a b e r r a n t QRS c o n d u c t i o n
352
seen c o m m o n l y with atrial p r e m a t u r e contractions. Fig. 11 relates to the b a t t e r y failure noted in Fig. 2, except t h a t the d o m i n a n t effect is loss of signal. T h e loss of signal has obliterated the P waves so t h a t a n y atrial a r r h y t h m i a would be difficult to diagnose. F o r example, the loss of Pwave signal in the presence of sinus a r r h y t h m i a could lead to the erroneous diagnosis of atrial fibrillation. Occasionally, the technician c o n f u s e s t h e beginning and the end of the tape, so t h a t the DCG p r i n t o u t appears as a mirror image (Fig. 12). T h e reversal is simple to identify in Fig. 12, a, b u t when the T-waves are less p r o m i n e n t (Fig. 12, b), the reversal m a y go unnoticed. Failure to identify the reversal can lead to the diagnosis of a misleading Q-wave. This was p a r t i c u l a r l y evident from a second case, Fig. 12, c, in which the broad S-waves of an episode of p a r o x y s m a l atrial t a c h y cardia appear as b r o a d Q-waves suggestive of myocardial damage. Similar problems can arise if the recording electrodes are transposed, leading to polarity reversal (Fig. 13). T h i s is usually evident, b u t again misleading "Q-waves" can be seen. A most interesting artifact, and one previously reported,10, 11 is the presence of a double imprint on the recording tape. Fig. 14 is an example of two independent r h y t h m s on a single t a p e which
March, 1976, Vol. 91, No. 3
Artifacts in portable ECG monitoring
c}
9
Fig. 6, Pseudo-ventricular tachycardia. The cause of the rhythmic artifact is unknown but the normal QRS
complexes can be followed throughout most of the tracing. (The tracing is a continuous strip. R-R intervals are noted in seconds.)
Fig. 7. Pseudo-junctional rhythm. This is an example of a low-frequency cut-off disturbance of the recording equipment.
could easily be mistaken as a sign ot serious h e a r t disease manifested as electrical alternans. T h e independence of the r h y t h m s is evident by noting t h a t the coupling i n t e r v a l between the large and the small complexes is c o n s t a n t l y changing, indicating two i n d e p e n d e n t rates. At the beginning of the strip the small complex a p p e a r s coupled to the large one, whereas at the end of the strip the reverse is true. T h e tracing appears to be from two separate individuals; and, indeed, we have seen similar tracings from Siamese twins. T h e most likely cause of this artifact is the re-use of an incompletely erased tape. A l t h o u g h we did not knowingly re-use tapes, this could have h a p p e n e d inadvertently. It is also possible t h a t the artifact could have been caused by a particularly strong
American Heart Journal
signal imprint affecting adjacent sections of the thin, 0.5-mil tape wound upon the spool. In any event, it can be identified as an artifact by its parasystolic nature. It is differentiated from true parasystole by its complete independence from r e f r a c t o r y periods. A final artifact, one t h a t is perhaps the most difficult to deal with, is the change in complex configuration associated with body m o v e m e n t or position. An example is seen in Fig. 15, in which a p p a r e n t T-wave inversions are recorded. These T - w a v e inversions are probably secondary to positional changes a b o u t the recording dipole. It should be noted t h a t the S-wave in Fig. 15, a, is incorporated into a late slur in t h e R-wave of tracing b; the more p r o m i n e n t the S-wave in Fig.
353
K r a s n o w a n d Bloomfield
Fig. 8. a, Pseudo-sec0nd-degree A-V block. The small complex after the fourth QRS is not a P-wave, but is actually a normal QRS incompletely recorded (time intervals in seconds), b and c, Artifactual pseudo-advanced A-V block in the presence of atrial fibrillation and bundle branch block.
Fig. 9. Four examples of pseudo-sinus arrest (sinus bradycardia or arrhythmia): In example a, the tape stoppage occurred between two successive complexes; examples b, c, and d are variations of tape slowing or stoppage noted from a single patient whose basic rhythm was regular.
15, t h e m o r e " n o r m a l " is t h e T - w a v e . S i m i l a r l y , the S-T segments tend to follow the positional Tw a v e c h a n g e s . T h e s e a r e v e r y c o m m o n f i n d i n g s in the records of patients who were later considered to have normal hearts, as well as those with known abnormalities.
Discussion ECG interpretation has always required knowledge o f a n d a b i l i t y t o r e c o g n i z e a r t i f a c t s . T h e
354
s a m e skills a r e r e q u i r e d for D C G i n t e r p r e t a t i o n , t o g e t h e r w i t h a n e w s e t of p r o b l e m s a s s o c i a t e d with battery-operated equipment. The early D C G r e p o r t s o f G i l s o n a n d a s s o c i a t e s '~ s u m m a r i z e d a r t i f a c t u a l p a t t e r n s as s e e n b y o s c i l l o s c o p e , but pseudo-arrhythmias were not described. Hinkle and associates ~ studied the physical limit a t i o n s of t h e D C G s y s t e m , a n d c a u t i o n e d p a r t i c ularly against overinterpretation of S-T segment and T-wave changes, a warning recently repeat-
March, 1976, Vol. 91, No. 3
Artifacts in portable ECG monitoring
Fig. 10. Pseudo-aberrancy due to a temporary change in frequency response (time intervals in seconds).
Fig. 11. Pseudo-low voltage and tachycardia associated with partial battery failure. The changes noted are similar
to those in Fig. 2, but the predominant effect is a loss of voltage with less prominent development of a pseudotachycardia.
Fig. 12. Two strips from a reversed tape (a, b). The second strip, at 19:30, suggests A-V dissociation. In c, a second example of tape reversal demonstrates, in mirror image, an episode of paroxysmal atrial tachycardia and a PVC. ed 13 a n d denied? ~, 1~ P s e u d o - a r r h y t h m i a s h a v e been described infrequently. 1~ 11 Aside from the intellectual challenge of identifying the a r r h y t h m i c and n o n - a r r h y t h m i c artifacts of T a b l e I, the effect of m i s i n t e r p r e t a t i o n can be p o t e n t i a l l y dangerous. As n o t e d in the table, failure to correctly identify artifacts could lead to serious consequences in 8 of the 15 e x a m ples. A m o n g the s u p r a v e n t r i c u l a r pseudoa r r h y t h m i a s , the false sinus or atrial t a c h y c a r d i a could lead to u n n e c e s s a r y digitalization. Conversely, the false atrial fibrillation shown in Fig. 3, with the regular R - R intervals, could be m i s t a k e n for a j u n c t i o n a l r h y t h m in the presence of atrial fibrillation a n d digitalis intoxication. T h e pseudo-PVC's a n d a r t i f a c t u a l fusion b e a t s are relatively trivial, b u t the p s e u d o v e n t r i c u l a r t a c h y c a r d i a of Fig. 6 m i g h t lead to drastic a n d unnecessary measures. T h e p s e u d o - a r r h y t h m i a s
American Heart Journal
seen in b o t h Figs. 8 and 9 could be i n t e r p r e t e d as indicating a need for the i m p l a n t a t i o n of an artificial p a c e m a k e r , a n d in 2 cases this a l m o s t happened. T h e m a i n danger p r e s e n t e d by n o n - a r r h y t h m i c artifacts is the t e n d e n c y to o v e r i n t e r p r e t the changes. T h e e x a m p l e s of t a p e reversal and polarity reversal (Figs. 12 and 13) b o t h demonstrate large Q-waves t h a t would ordinarily be a b n o r m a l in the V~ electrode position. More c o m m o n and m o r e i m p o r t a n t are the m a n y S T - T changes t h a t are observed during the course of D C G monitoring. T h e m o n i t o r i n g dipole lies between the m a n u b r i u m a n d the V~ position, and is relatively sensitive to changes in b o d y position. T h u s it is c o m m o n to see the S-waves wax a n d wane as in Fig. 15, with associated s e c o n d a r y Twave changes. Similarly, the S - T s e g m e n t s shown in Fig. 15 change f r o m concave u p w a r d and
355
K r a s n o w a n d Bloomfield
Fig. 13. Reversedpolarity resulting from incorrect electrode placement.
Fig. 14. Pseudo-electricalalternans, or the "Siamese-twin"effect.There is dissociationbetween the two sets of complexes (time intervals in seconds).
Fig. 15. Positionalchanges which lead to an apparent changein QRST conduction,and which simulate primary T-wave changes.These changeswere present throughout the traciag. T-waveinversionsalwaysaccompaniedthe loss or diminutionof the S-wave. isoelectric to concave downward and slightly depressed. These changes also appear secondary to QRS changes associated with the variable representation of the cardiac vector on the
dipole. Recently, Stern and Tzivoni 14, 4~challenged the work of Hinkle and associates 8 and concluded that the DCG system reliably recorded the ST-T segment for the evaluation of dynamic changes induced by ischemia. We cannot agree with their conclusion. Although proof is lacking, we have seen numerous S-T-segment and T-wave changes by DCG monitoring that appeared to be inconsistent with the diagnosis of ischemic heart disease. It is of interest t h a t in Fig. 4 of one of Stern and Tzivoni's papers, 1~ the changes reported as "deterioration of ST-T changes" during sleep are almost identical with our Fig. 15, the Twave inversions shown being inversely proportional to the depth of the S-wave. Furthermore, there is a vast literature which indicates that STT changes alone must be evaluated in terms of the physiologic status of the subject. ",-2~ The ST-T-wave changes on DCG monitoring are also greatly exaggerated in the presence of left
356
ventricular hypertrophy and/or digitalis. As with all ST-T-wave changes observed by this technique, they are interpreted with extreme caution as positional artifacts, unless there are compelling facts to the contrary. The diagnosis of artifacts requires, above all, a high index of suspicion. The only diagnostic rule we can advise is to assume that all anomalies detected by portable monitoring are artifactual until proved otherwise by careful measurements, logic, or confirming diagnostic tests. DCG complexes from a single pair of electrodes should always be compared to a reference 12-lead electrocardiogram. Some artifacts are obvious (Figs. 7, 11, and 13), whereas others are extremely subtle (Figs. 6, 8, and 15). The incidence of artifacts during 8 hours of recording will necessarily exceed the incidence of artifacts recorded during the 1 minute of recording represented by the standard ECG. The patient's diary, recording subjective symptomatology during the recording, may complicate interpretation, particularly with respect to subtle changes of the S-T segments and Twaves. A number of patients who were monitored for symptoms of bizarre chest pain recorded
March, 1976, Vol. 91, No, 3
Artifacts in portable ECG monitoring
symptoms throughout the recording period; some of these symptoms occurred simultaneously with S T - T c h a n g e s , a n d s o m e o c c u r r e d in t h e a b s e n c e of s u c h c h a n g e s . T h e p i c t u r e w a s o f t e n so c o n fusing that additional diagnostic tests, such as exercise tolerance tests or coronary angiography, were recommended. The causes of monitoring artifacts were not always obvious nor subject to proof. We have i n d i c a t e d t h e p r o b a b l e c a u s e in T a b l e I, o m i t t i n g t h e m o s t ~common a n d o b v i o u s a r t i f a c t s , b a c k g r o u n d noise, a n d b a s e l i n e m o v e m e n t . T h e s e a r tifacts can be reduced or eliminated by careful t e c h n i q u e in p r e p a r i n g t h e s k i n a n d c a r e f u l l y attaching the electrodes. Battery-failure artifacts (Figs. 2 a n d 11) a l w a y s o c c u r t o w a r d t h e e n d o f monitoring, but mechanical and movement artifacts can occur at any time. The pseudo-sinus a r r e s t a r t i f a c t s o f Fig. 9 w e r e r e a l l y a p l a y b a c k , rather than a recording, artifact. In general, a r t i f a c t s c a n b e c a u s e d a t a n y p o i n t in t h e monitoring sequence from the time of attachment of the electrodes until final interpretation.
Summary The development of portable ECG monitoring techniques has brought with it new insights into the electrical activity of the heart, and new p r o b l e m s in i n t e r p r e t a t i o n o f a r t i f a c t s . T h i s a r t i c l e s u m m a r i z e s a n d classifies 15 d i f f e r e n t types of artifacts observed from dynamic electroc a r d i o g r a p h y . T h e a r t i f a c t s a p p e a r p a r t l y as pseudo-arrhythmias mimicking supraventricular, ventrictflar, junctional, and dissociative rhythms. T h e r e a r e also n o n - a r r h y t h m i c a r t i f a c t s w h i c h c a n b e m i s l e a d i n g in t h e i n t e r p r e t a t i o n o f Qwaves, S - T - s e g m e n t s , a n d T - w a v e s . E i g h t o f t h e 15 a r t i f a c t s h a v e p o t e n t i a l l y s e r i o u s c o n s e q u e n c e s if n o t u n d e r s t o o d , a n d in 2 i n s t a n c e s a n a r t i f a c t almost led to the unnecessary implantation of an artificial cardiac pacemaker.
2. Berson, A. S., and Pipberger, H. V.: The low frequency response of electrocardiographs, a frequent source of recording errors, AM. HEART J. 71:779, 1966. 3. Meyer, J. L.: Some instrument-induced errors in the electrocardiogram, J.A.M.A. 201:351, 1967. 4. Yurchak, P. M.: Artifacts resembling cardiac arrhythmias, Postgrad. Med. 53:79, 1973. 5. Duke, M.: Artifacts in the electrocardiogram, Med. Trial Tech. Q. 17:377, 1971. 6. Riseman, J. E. F., and Sagall, E. L.: Diagnostic problems resulting from improper electrocardiographic technique, J.A.M.A. 178:806, 1961. 7. Gilson, J. S.: Electrocardiorecorder AVSEP patterns in 37 normal adult men, Am. J. Cardiol. ] 6:789, 1965. 8. Hinkle, L. E., Jr., Meyer, J., Stevens, M., and Carver, S. T.: Tape recordings of the ECG of active men, Circulation 36:752, 1967. 9. Shumak, K. H., and Brown, K. W. G.: Continuous portable electrocardiography, Can. Med. Assoc. J. 98:139, 1968. 10. Malek, J., and Glushien, A.: Artifacts in portable ECG monitoring, Ann. Intern. Med. 77:1004, 1972. 11. Hansmann, D. R., and Sheppard, J. J.: ECG monitor artifacts, Ann. Intern. Med. 78:619, 1973. 12. Gilson; J. S., Holter, N. J., and Glasscock, W. R.: Clinical observations using the Electrocardiocorder - AVSEP continuous electrocardiographic system, Am. J. Cardiol. ] 4:204, 1964. 13. Iyengar, R., Castellanos, A., and Spence, M.: Continuous monitoring of ambulatory patients with coronary disease, Prog. Cardiovasc. Dis. 13:392, 1971. 14. Stern, S., and Tzivoni, D.: The reliability of the HolterAvionics system in reproducing the ST-T segment, AM. HEART J. 84:427, 1972. 15. Stern, S., and Tzivoni, D.: Dynamic changes in the ST-T segment during sleep in ischemic heart disease, Am. J. Cardiol. 32:17, 1973. 16. Rubenfire, M., and Rosenzweig, S.: Electrocardiographic artifacts simulating atrial flutter, J.A.M.A. 220:1130, 1972. 17. Iglesias, R., Echenique, R., and Gonzalez, G.: T-wave inversion of the ECG of healthy individuals with vagotonia, Aerosp. Med. 40:318, 1969. 18. Mari0tt, H. J. L.: Normal electrocardiographic variants simulating ischemic heart disease, J.A.M.A. 199:325, 1967. 19. Mari0tt, H. J. L.: Coronary mimicry: normal variants and physiologic, pharmacologic and pathologic influences that simulate coronary patterns in the electrocardiogram, Ann. Intern. Med. 52:411, 1960. 20. Mayerson, H. S., and Davis, W. D.: The influence of posture on the electrocardiogram, AM. HEART J. 24:593, 1942.
REFERENCES 1. Dower, G. E., et al.: On QRS amplitude and other errors produced by direct-writing electrocardiographs, AM. HEART J. 65:307, 1963.
American Heart Journal
35 7
This article describes a series of artifacts encountered in 466 cases of portable electrocardiographic monitoring by a technique known as dynamic electrocardiography (DCG). Although standard 12-lead electrocardiographic artifacts have been documented repeatedly, ~-6 there have been only scattered reports of DCG artifacts, 7.H and physicians are generally less familiar with their characteristics. Since artifacts always enhance the possibility of improper diagnosis, which leads to improper therapy, we believe that our experience will be useful to those who use portable ECG monitoring techniques. Methods
The equipment used in these studies was the Avionics Model 350 "Electrocardiocorder," and the Avionics Model 650 "Composite Electrocardioscanner." Patients were unselected individuals who were referred for monitoring by their private physicians; the patients' complaints were varied, the most prominent being chest pain, palpitations, and dizziness-syncope. Subjects ranged in age from 14 to 89 years. Some patients were ambulatory at home, work, or within a hospital; others were at bed rest. Electrodes were positioned with the exploring electrode at the V5 position and the reference electrode over the manubrium, All tapes were scanned by a single technician who printed out suspicious areas of the recording.
From the University of Illinois. College of Medicine, School of Basic Medical Sciences. Urbana-Champaign, Ill. Received for publication Dec. 11. 1974. Reprint requests: D, K. Bloomfield, M.D., Medical Sciences Bldg., Urbana, Ill. 61801. *Dean, University of Illinois, College of Medicine, School of Basic Medical Sciences.
March, 1976, Vol. 91, No. 3, pp. 349-357
No effort was made to quantify the incidence of specific artifacts except in general terms of rare, occasional, or common. Results
Artifacts discovered were divided into two general categories, pseudo-arrhythmias and nonarrhythmias. A classification of the artifacts, their relative frequency, probable cause, and potential seriousness, is shown in Table I. Some were trivial, whereas others created serious problems in interpretation, and in two instances almost caused the unnecessary implantation of an artificial cardiac pacemaker. Pseudo-arrhythmias mimicking supraventricular rhythms are shown in Figs. 1, 2, and 3. Fig. 1 shows pseudo-premature atrial contractions. They are identified as an artifactual, intermittent slowing of the recorder for brief periods, with normal operation thereafter. The complexes appear smaller and compressed in time, as if there were a transient excess load placed on the battery-driven mechanism. T h a t this was not due to battery failure per se is seen by the fact t h a t tracing a of Fig. 1 shows the same artifact recorded 9 hours before tracing b, in which the artifact continues; the same battery was in continuous use. Replacement of the "Electrocardiocorder" motor eliminated the artifact. The Fig. 1 artifact might also be interpreted as pseudopremature junctional beats since the P-wave is distorted and the P-R interval is reduced to less than 0.12 second. Fig. 2, pseudo-sinus or atrial tachycardia, is a relatively common artifact associated with battery- or electric-motor failure and has been described by others. 1~ 11 Characteristically, it appears toward the end of the recording tape, is of gradual onset, and is accompanied by gradual
American H e a r t Journal
349
K r a s n o w and Bloomfield
Table I. Classification of artifacts
Type of artifact
1. Pseudo-arrhythmia a. Supraventricular 1. Pseudo-PAC 2. Pseudo-PAT 3. Pseudo-atrial fibrillation b. Ventricular 1. Pseudo-PVC 2. Pseudo-fusion beat 3. Pseudo-ventricular tachycardia c. Junctional or dissociative l. Pseudo-junctional rhythm 2. Pseudo-Mobitz II A-V block 3. Pseudo--sinusarrest 2. Non-arrhythmia a. Voltageor frequency response disturbance 1. Pseudo-aberrancy 2. Pseudo-lowvoltage b. Tape and polarity reversal 1. Tape reversal 2. Polarity reversal c. Pseudo-alternans {"Siamese twins") d. Alteration of QRST (pseudo-primary T-wave changes)
Figure number in text
Relative frequency
Probable cause*
Potential effect on diagnosis and treatment
1 2 3
Occasional Occasional Rare
A B U-1
Possible Serious Serious
4 5 6
Occasional Common Rare
C-1 C-1 U-2
Possible Minimal Serious
7 8 9
Rare Occasional Rare
A C-1 D
Possible Serious Serious
10 11
Occasional Occasional
C-1 B
Minimal Minimal
12 13 14 15
Occasional Occasional Rare Common
E E E C-2
Serious Serious Possible Serious
*A, Electrical or mechanical artifact of recording device; cause unknown.B, Electrical artifact of recordingdevicedue to battery or electric-motor failure. C-1, Bodymovementor disturbance of skin electrode contact. C-2, Bodymovementcausing a changein the recordingdipole. D, Mechanical artifact of playbackdevice. E, Technician error. U-l, Unknowncause; probably a loose or broken wire connection. U-2, Unknowncause; probably exercise.
diminution, and often cessation, of the signal. T h e characteristics m a y vary depending u p o n w h e t h e r the cause is a loss of b a t t e r y charge or a m o t o r which draws excessive current, the f o r m e r being of shorter d u r a t i o n before c o m p l e t e loss of signal. Fig. 3 shows pseudo-atrial fibrillation, p r o b a b l y associated with a loose connection or broken lead. TM P a r t s of the tracing {Fig. 3, a) m i g h t be confused with Parkinsonian tremor, b u t this was n o t consistent t h r o u g h o u t . Fig. 3, b shows a brief period w i t h o u t artifact, revealing the basic sinus r h y t h m . T h e p r e m a t u r e ventricular systole at beat No. 7 of Fig. 3 a also suggests t h a t t h e s e strips are artifactual, since it has a full and exact c o m p e n s a t o r y pause, u n u s u a l in atrial fibrillation. P s e u d o - v e n t r i c u l a r a r r h y t h m i a s are shown in Figs. 4, 5, and 6. Fig. 4 is an example of a pseudop r e m a t u r e ventricular c o n t r a c t i o n p r o b a b l y due to jostling of an electrode. I t shows basically a sinus r h y t h m with mild sinus a r r h y t h m i a . Base-
350
line disturbances are present t h r o u g h the first four beats. B e a t No. 3 is an artifactual distortion of a n o r m a l l y conducted beat because: (1) Despite the m a r k e d Q R S distortion, there is no secondary T - w a v e change. (2) T h e T - T interval between beats No. 2 and No. 3 shows only a 0.04second shortening, well within the sinus a r r h y t h mia variation. (3) T h e S-wave of beat No. 3 can be identified as a n o r m a l segment of the otherwise distorted QRS. Its timing in relation to preceding and following S-waves is well within the sinus a r r h y t h m i a limits. (4) T h e S-T segment following the S-wave, like the T-wave, has n o r m a l configuration. Fig. 5 shows a pseudo-fusion beat. T h e complex is characterized by a sudden loss of frequency response noted in b o t h the P-wave and the Q R S complex. Electrical recovery is not entirelY complete until the second beat after the pseudofusion beat. F o r a period of 0.24 second before the a b e r r a n t Q R S t o immediately thereafter, there is a high-frequency cut-off disturbance which
March, 1976, Vo!. 91, No. 3
Artifacts in portable ECG monitoring
Fig. 1. Pseudo-atrial or pseudo-junctional premature contractions associated with Electrocardiocorder battery failure.
distorts the baseline, the P-wave, and the QRS. T h e baseline t h r o u g h o u t the strip shows small high-frequency irregularities, except during the period in question. T h e 50 per cent reduction in QRS voltage occurs toward the end of the artifactual period, and it is likely t h a t the peak of the artifactual disturbance obliterated the n o r m a l Pwave. T h e artifact is probably caused by some type of electromechanical disturbance affecting the frequency response of the recorder. It is an incomplete form of the artifacts seen in Fig. 8. Fig. 6, a continuous strip, is a d r a m a t i c example of pseudoventricular tachycardia, cause unknown. T h e initial sinus r h y t h m is n o t e d to be gradually engulfed by an u n d u l a t i n g artifact which gradually poses as a ventricular t a c h y c a r dia. T h e R - R interval of the n o r m a l QRS complexes can be followed t h r o u g h o u t , as indicated b y the time intervals n o t e d on top of the strips. T o w a r d the end of the episode (Fig. 6, d), the QRS complexes can be identified as the process concludes. Several artifgcts (Figs. 7, 8, and 9) mimicked j u n c t i o n a l r h y t h m , a n d c o n d u c t i o n or p a c e m a k e r disturbances. Fig. 7 is really an example of a frequency response disturbance simulating a j u n c t i o n a l r h y t h m . Fig. 8 shows t w o extreme examples of t e m p o r a r y i m p a i r m e n t of electrode contact, posing as advanced A-V block. T h e "blocked P-wave" in Fig. 8, a is a c t u a l l y a diminutive QRS complex, since it is n o t s y n c h r o n i z e d with the preceding P-wave and is of a different configuration. T h e P-wave preceding and the T-wave following t h a t complex are c o m p l e t e l y lost, Figs. 8, b and c come from a different p a t i e n t
American Heart Journal
Fig. 2. Pseudo-sinus or atrial tachycardia due to battery failure. At 15:15 (a) the record shows normal sinus rhythm at a rate of 94 per minute. At 19:00 (b) the artifactual rate is 144, but there is compression of the entire PQRST complex, including a loss of voltage.
whose electrocardiogram showed atrial fibrillation and left bundle b r a n c h block. T r a c i n g b was originally interpreted as a reversion to n o r m a l sinus r h y t h m with advanced A-V block requiring p a c e m a k e r insertion. This was in error because the complexes m a s q u e r a d i n g as P-waves are irregular and are actually compressed QRS complexes reflecting n o r m a l l y c o n d u c t e d beats in the presence of atrial fibrillation. Fig. 9 shows u n u s u a l artifacts related to the playback process. T h e y resulted when the c o m p a n y which m a n u f a c t u r e d the recording tape (3 M C o m p a n y - 200 Tape) discontinued its line and replaced it with a new product (178 Tape), to give higher recording fidelity. T h e result was not a success for the D C G method. T h e new tape tended to adhere to the slow-speed scanning head of the "Electrocardioscanner." T h e combination~ of the tape slowing with the strip-chart recorder running at 25 mm. per second p r o d u c e d the effects seen in Fig. 9. In each instance the slowing or t e m p o r a r y stoppage of the tape caused by its
351
K r a s n o w and Bloomfield
Fig. 3. Pseudo-atrial fibrillation. The artifact persisted throughout the recording except for brief periods of clarity (b). The patient did not suffer from Parkinson's disease or have any other observable tremor. A 12-lead electrocardiogram was free of artifact {time interval in seconds).
Fig. 4. A pseudo-premature ventricular contraction. The aberrant complex appears to be premature, but it is an artifact obscuring a normal QRS which can be identified by its relatively normal S-wave, S-T segment, and T-wave (time intervals in seconds).
Fig. 5. Pseudo-fusion beat. The designated complex is an incomplete form of the examples shown in Fig. 8. Note the change in P-wave configuration preceding the complex (time interval in seconds).
sticking to the scanning head produced artifacts t h a t resembled either m a r k e d sinus a r r h y t h m i a , bradycardia, or sinus arrest. In some instances the artifact is readily identified by the obvious broadening of the t o t a l P Q R S T complex {Fig. 9, b), b u t this was not always possible since t h e stoppage occasionally occurred a b r u p t l y b e t w e e n complexes {Fig. 9, a). W h e n the t a p e was released, the recording of n o r m a l sinus r h y t h m reappeared. Misinterpretation of these artifacts has also led to the improper r e c o m m e n d a t i o n o f insertion of a cardiac pacemaker. S e v e r a l artifacts were noted t h a t did not fall into the category of pseudo-arrhythmias. Fig. 10 is closely related to Figs. 2 and 8. T h e complexes seem to be similar to a b e r r a n t QRS c o n d u c t i o n
352
seen c o m m o n l y with atrial p r e m a t u r e contractions. Fig. 11 relates to the b a t t e r y failure noted in Fig. 2, except t h a t the d o m i n a n t effect is loss of signal. T h e loss of signal has obliterated the P waves so t h a t a n y atrial a r r h y t h m i a would be difficult to diagnose. F o r example, the loss of Pwave signal in the presence of sinus a r r h y t h m i a could lead to the erroneous diagnosis of atrial fibrillation. Occasionally, the technician c o n f u s e s t h e beginning and the end of the tape, so t h a t the DCG p r i n t o u t appears as a mirror image (Fig. 12). T h e reversal is simple to identify in Fig. 12, a, b u t when the T-waves are less p r o m i n e n t (Fig. 12, b), the reversal m a y go unnoticed. Failure to identify the reversal can lead to the diagnosis of a misleading Q-wave. This was p a r t i c u l a r l y evident from a second case, Fig. 12, c, in which the broad S-waves of an episode of p a r o x y s m a l atrial t a c h y cardia appear as b r o a d Q-waves suggestive of myocardial damage. Similar problems can arise if the recording electrodes are transposed, leading to polarity reversal (Fig. 13). T h i s is usually evident, b u t again misleading "Q-waves" can be seen. A most interesting artifact, and one previously reported,10, 11 is the presence of a double imprint on the recording tape. Fig. 14 is an example of two independent r h y t h m s on a single t a p e which
March, 1976, Vol. 91, No. 3
Artifacts in portable ECG monitoring
c}
9
Fig. 6, Pseudo-ventricular tachycardia. The cause of the rhythmic artifact is unknown but the normal QRS
complexes can be followed throughout most of the tracing. (The tracing is a continuous strip. R-R intervals are noted in seconds.)
Fig. 7. Pseudo-junctional rhythm. This is an example of a low-frequency cut-off disturbance of the recording equipment.
could easily be mistaken as a sign ot serious h e a r t disease manifested as electrical alternans. T h e independence of the r h y t h m s is evident by noting t h a t the coupling i n t e r v a l between the large and the small complexes is c o n s t a n t l y changing, indicating two i n d e p e n d e n t rates. At the beginning of the strip the small complex a p p e a r s coupled to the large one, whereas at the end of the strip the reverse is true. T h e tracing appears to be from two separate individuals; and, indeed, we have seen similar tracings from Siamese twins. T h e most likely cause of this artifact is the re-use of an incompletely erased tape. A l t h o u g h we did not knowingly re-use tapes, this could have h a p p e n e d inadvertently. It is also possible t h a t the artifact could have been caused by a particularly strong
American Heart Journal
signal imprint affecting adjacent sections of the thin, 0.5-mil tape wound upon the spool. In any event, it can be identified as an artifact by its parasystolic nature. It is differentiated from true parasystole by its complete independence from r e f r a c t o r y periods. A final artifact, one t h a t is perhaps the most difficult to deal with, is the change in complex configuration associated with body m o v e m e n t or position. An example is seen in Fig. 15, in which a p p a r e n t T-wave inversions are recorded. These T - w a v e inversions are probably secondary to positional changes a b o u t the recording dipole. It should be noted t h a t the S-wave in Fig. 15, a, is incorporated into a late slur in t h e R-wave of tracing b; the more p r o m i n e n t the S-wave in Fig.
353
K r a s n o w a n d Bloomfield
Fig. 8. a, Pseudo-sec0nd-degree A-V block. The small complex after the fourth QRS is not a P-wave, but is actually a normal QRS incompletely recorded (time intervals in seconds), b and c, Artifactual pseudo-advanced A-V block in the presence of atrial fibrillation and bundle branch block.
Fig. 9. Four examples of pseudo-sinus arrest (sinus bradycardia or arrhythmia): In example a, the tape stoppage occurred between two successive complexes; examples b, c, and d are variations of tape slowing or stoppage noted from a single patient whose basic rhythm was regular.
15, t h e m o r e " n o r m a l " is t h e T - w a v e . S i m i l a r l y , the S-T segments tend to follow the positional Tw a v e c h a n g e s . T h e s e a r e v e r y c o m m o n f i n d i n g s in the records of patients who were later considered to have normal hearts, as well as those with known abnormalities.
Discussion ECG interpretation has always required knowledge o f a n d a b i l i t y t o r e c o g n i z e a r t i f a c t s . T h e
354
s a m e skills a r e r e q u i r e d for D C G i n t e r p r e t a t i o n , t o g e t h e r w i t h a n e w s e t of p r o b l e m s a s s o c i a t e d with battery-operated equipment. The early D C G r e p o r t s o f G i l s o n a n d a s s o c i a t e s '~ s u m m a r i z e d a r t i f a c t u a l p a t t e r n s as s e e n b y o s c i l l o s c o p e , but pseudo-arrhythmias were not described. Hinkle and associates ~ studied the physical limit a t i o n s of t h e D C G s y s t e m , a n d c a u t i o n e d p a r t i c ularly against overinterpretation of S-T segment and T-wave changes, a warning recently repeat-
March, 1976, Vol. 91, No. 3
Artifacts in portable ECG monitoring
Fig. 10. Pseudo-aberrancy due to a temporary change in frequency response (time intervals in seconds).
Fig. 11. Pseudo-low voltage and tachycardia associated with partial battery failure. The changes noted are similar
to those in Fig. 2, but the predominant effect is a loss of voltage with less prominent development of a pseudotachycardia.
Fig. 12. Two strips from a reversed tape (a, b). The second strip, at 19:30, suggests A-V dissociation. In c, a second example of tape reversal demonstrates, in mirror image, an episode of paroxysmal atrial tachycardia and a PVC. ed 13 a n d denied? ~, 1~ P s e u d o - a r r h y t h m i a s h a v e been described infrequently. 1~ 11 Aside from the intellectual challenge of identifying the a r r h y t h m i c and n o n - a r r h y t h m i c artifacts of T a b l e I, the effect of m i s i n t e r p r e t a t i o n can be p o t e n t i a l l y dangerous. As n o t e d in the table, failure to correctly identify artifacts could lead to serious consequences in 8 of the 15 e x a m ples. A m o n g the s u p r a v e n t r i c u l a r pseudoa r r h y t h m i a s , the false sinus or atrial t a c h y c a r d i a could lead to u n n e c e s s a r y digitalization. Conversely, the false atrial fibrillation shown in Fig. 3, with the regular R - R intervals, could be m i s t a k e n for a j u n c t i o n a l r h y t h m in the presence of atrial fibrillation a n d digitalis intoxication. T h e pseudo-PVC's a n d a r t i f a c t u a l fusion b e a t s are relatively trivial, b u t the p s e u d o v e n t r i c u l a r t a c h y c a r d i a of Fig. 6 m i g h t lead to drastic a n d unnecessary measures. T h e p s e u d o - a r r h y t h m i a s
American Heart Journal
seen in b o t h Figs. 8 and 9 could be i n t e r p r e t e d as indicating a need for the i m p l a n t a t i o n of an artificial p a c e m a k e r , a n d in 2 cases this a l m o s t happened. T h e m a i n danger p r e s e n t e d by n o n - a r r h y t h m i c artifacts is the t e n d e n c y to o v e r i n t e r p r e t the changes. T h e e x a m p l e s of t a p e reversal and polarity reversal (Figs. 12 and 13) b o t h demonstrate large Q-waves t h a t would ordinarily be a b n o r m a l in the V~ electrode position. More c o m m o n and m o r e i m p o r t a n t are the m a n y S T - T changes t h a t are observed during the course of D C G monitoring. T h e m o n i t o r i n g dipole lies between the m a n u b r i u m a n d the V~ position, and is relatively sensitive to changes in b o d y position. T h u s it is c o m m o n to see the S-waves wax a n d wane as in Fig. 15, with associated s e c o n d a r y Twave changes. Similarly, the S - T s e g m e n t s shown in Fig. 15 change f r o m concave u p w a r d and
355
K r a s n o w a n d Bloomfield
Fig. 13. Reversedpolarity resulting from incorrect electrode placement.
Fig. 14. Pseudo-electricalalternans, or the "Siamese-twin"effect.There is dissociationbetween the two sets of complexes (time intervals in seconds).
Fig. 15. Positionalchanges which lead to an apparent changein QRST conduction,and which simulate primary T-wave changes.These changeswere present throughout the traciag. T-waveinversionsalwaysaccompaniedthe loss or diminutionof the S-wave. isoelectric to concave downward and slightly depressed. These changes also appear secondary to QRS changes associated with the variable representation of the cardiac vector on the
dipole. Recently, Stern and Tzivoni 14, 4~challenged the work of Hinkle and associates 8 and concluded that the DCG system reliably recorded the ST-T segment for the evaluation of dynamic changes induced by ischemia. We cannot agree with their conclusion. Although proof is lacking, we have seen numerous S-T-segment and T-wave changes by DCG monitoring that appeared to be inconsistent with the diagnosis of ischemic heart disease. It is of interest t h a t in Fig. 4 of one of Stern and Tzivoni's papers, 1~ the changes reported as "deterioration of ST-T changes" during sleep are almost identical with our Fig. 15, the Twave inversions shown being inversely proportional to the depth of the S-wave. Furthermore, there is a vast literature which indicates that STT changes alone must be evaluated in terms of the physiologic status of the subject. ",-2~ The ST-T-wave changes on DCG monitoring are also greatly exaggerated in the presence of left
356
ventricular hypertrophy and/or digitalis. As with all ST-T-wave changes observed by this technique, they are interpreted with extreme caution as positional artifacts, unless there are compelling facts to the contrary. The diagnosis of artifacts requires, above all, a high index of suspicion. The only diagnostic rule we can advise is to assume that all anomalies detected by portable monitoring are artifactual until proved otherwise by careful measurements, logic, or confirming diagnostic tests. DCG complexes from a single pair of electrodes should always be compared to a reference 12-lead electrocardiogram. Some artifacts are obvious (Figs. 7, 11, and 13), whereas others are extremely subtle (Figs. 6, 8, and 15). The incidence of artifacts during 8 hours of recording will necessarily exceed the incidence of artifacts recorded during the 1 minute of recording represented by the standard ECG. The patient's diary, recording subjective symptomatology during the recording, may complicate interpretation, particularly with respect to subtle changes of the S-T segments and Twaves. A number of patients who were monitored for symptoms of bizarre chest pain recorded
March, 1976, Vol. 91, No, 3
Artifacts in portable ECG monitoring
symptoms throughout the recording period; some of these symptoms occurred simultaneously with S T - T c h a n g e s , a n d s o m e o c c u r r e d in t h e a b s e n c e of s u c h c h a n g e s . T h e p i c t u r e w a s o f t e n so c o n fusing that additional diagnostic tests, such as exercise tolerance tests or coronary angiography, were recommended. The causes of monitoring artifacts were not always obvious nor subject to proof. We have i n d i c a t e d t h e p r o b a b l e c a u s e in T a b l e I, o m i t t i n g t h e m o s t ~common a n d o b v i o u s a r t i f a c t s , b a c k g r o u n d noise, a n d b a s e l i n e m o v e m e n t . T h e s e a r tifacts can be reduced or eliminated by careful t e c h n i q u e in p r e p a r i n g t h e s k i n a n d c a r e f u l l y attaching the electrodes. Battery-failure artifacts (Figs. 2 a n d 11) a l w a y s o c c u r t o w a r d t h e e n d o f monitoring, but mechanical and movement artifacts can occur at any time. The pseudo-sinus a r r e s t a r t i f a c t s o f Fig. 9 w e r e r e a l l y a p l a y b a c k , rather than a recording, artifact. In general, a r t i f a c t s c a n b e c a u s e d a t a n y p o i n t in t h e monitoring sequence from the time of attachment of the electrodes until final interpretation.
Summary The development of portable ECG monitoring techniques has brought with it new insights into the electrical activity of the heart, and new p r o b l e m s in i n t e r p r e t a t i o n o f a r t i f a c t s . T h i s a r t i c l e s u m m a r i z e s a n d classifies 15 d i f f e r e n t types of artifacts observed from dynamic electroc a r d i o g r a p h y . T h e a r t i f a c t s a p p e a r p a r t l y as pseudo-arrhythmias mimicking supraventricular, ventrictflar, junctional, and dissociative rhythms. T h e r e a r e also n o n - a r r h y t h m i c a r t i f a c t s w h i c h c a n b e m i s l e a d i n g in t h e i n t e r p r e t a t i o n o f Qwaves, S - T - s e g m e n t s , a n d T - w a v e s . E i g h t o f t h e 15 a r t i f a c t s h a v e p o t e n t i a l l y s e r i o u s c o n s e q u e n c e s if n o t u n d e r s t o o d , a n d in 2 i n s t a n c e s a n a r t i f a c t almost led to the unnecessary implantation of an artificial cardiac pacemaker.
2. Berson, A. S., and Pipberger, H. V.: The low frequency response of electrocardiographs, a frequent source of recording errors, AM. HEART J. 71:779, 1966. 3. Meyer, J. L.: Some instrument-induced errors in the electrocardiogram, J.A.M.A. 201:351, 1967. 4. Yurchak, P. M.: Artifacts resembling cardiac arrhythmias, Postgrad. Med. 53:79, 1973. 5. Duke, M.: Artifacts in the electrocardiogram, Med. Trial Tech. Q. 17:377, 1971. 6. Riseman, J. E. F., and Sagall, E. L.: Diagnostic problems resulting from improper electrocardiographic technique, J.A.M.A. 178:806, 1961. 7. Gilson, J. S.: Electrocardiorecorder AVSEP patterns in 37 normal adult men, Am. J. Cardiol. ] 6:789, 1965. 8. Hinkle, L. E., Jr., Meyer, J., Stevens, M., and Carver, S. T.: Tape recordings of the ECG of active men, Circulation 36:752, 1967. 9. Shumak, K. H., and Brown, K. W. G.: Continuous portable electrocardiography, Can. Med. Assoc. J. 98:139, 1968. 10. Malek, J., and Glushien, A.: Artifacts in portable ECG monitoring, Ann. Intern. Med. 77:1004, 1972. 11. Hansmann, D. R., and Sheppard, J. J.: ECG monitor artifacts, Ann. Intern. Med. 78:619, 1973. 12. Gilson; J. S., Holter, N. J., and Glasscock, W. R.: Clinical observations using the Electrocardiocorder - AVSEP continuous electrocardiographic system, Am. J. Cardiol. ] 4:204, 1964. 13. Iyengar, R., Castellanos, A., and Spence, M.: Continuous monitoring of ambulatory patients with coronary disease, Prog. Cardiovasc. Dis. 13:392, 1971. 14. Stern, S., and Tzivoni, D.: The reliability of the HolterAvionics system in reproducing the ST-T segment, AM. HEART J. 84:427, 1972. 15. Stern, S., and Tzivoni, D.: Dynamic changes in the ST-T segment during sleep in ischemic heart disease, Am. J. Cardiol. 32:17, 1973. 16. Rubenfire, M., and Rosenzweig, S.: Electrocardiographic artifacts simulating atrial flutter, J.A.M.A. 220:1130, 1972. 17. Iglesias, R., Echenique, R., and Gonzalez, G.: T-wave inversion of the ECG of healthy individuals with vagotonia, Aerosp. Med. 40:318, 1969. 18. Mari0tt, H. J. L.: Normal electrocardiographic variants simulating ischemic heart disease, J.A.M.A. 199:325, 1967. 19. Mari0tt, H. J. L.: Coronary mimicry: normal variants and physiologic, pharmacologic and pathologic influences that simulate coronary patterns in the electrocardiogram, Ann. Intern. Med. 52:411, 1960. 20. Mayerson, H. S., and Davis, W. D.: The influence of posture on the electrocardiogram, AM. HEART J. 24:593, 1942.
REFERENCES 1. Dower, G. E., et al.: On QRS amplitude and other errors produced by direct-writing electrocardiographs, AM. HEART J. 65:307, 1963.
American Heart Journal
35 7
