METHODS
Precordial Electrocardiographic Mapping After Exercise In the Diagnosis of Coronary Artery Disease
KIM FOX, MRCP ANDREW SELWYN, MRCP JOHN SHILLINGFORD.FRCP, FACC London, England
A technique is described for recording the precordial electrocardiographic body surface map before and after exercise. The technique provides an extra dimension to the conventional exercise electrocardiogram because a measurement can be made of the area and severity of S-T segment changes that are projected onto the front of the chest. Sixteen lead isopotential surface maps were recorded before and after exercise in 109 patients with angina who subsequently underwent coronary arteriography. In addition, exercise electrocardiograms were obtained in 53 of these patients using three orthogonal leads and in all patients using a single chest unipolar chest lead. Precordial surface mapping after exercise was found to have a greater sensitivity (95 percent) than electrocardiography using either the orthogonal leads (66 percent) or a single chest lead (64 percent) (P 0.05). The technique of precordial surface mapping after exercise improves the ability to diagnose coronary artery disease and can easily be applied to clinical practice.
The aim of exercise or stress testing is to increase myocardial oxygen demand in order to elicit the electrocardiographic manifestations of ischemia (S-T segment changes) that are absent at rest. The ability to elicit these alterations in the S-T segment depends on the degree of narrowing of the coronary arteries, the amount of work performed and the accuracy with which areas of myocardial ischemia can be detected. It is usually accepted that 70 percent luminal narrowing of a major coronary vessel is necessary before the blood supply to the myocardium can be compromised by exertion, l-3 and the modern multistage stress tests aiming at maximal heart rates ensure that an adequate work load is nearly always achieved.4 The principal limiting factor of these tests is the detection of myocardial ischemia. Although multiple lead and orthogonal systems are adequate in most cases,5,6 they are not sufficiently sensitive. This paper describes a technique for recording serial precordial surface maps after exercise that has proved superior to other methods in the diagnosis of coronary artery disesse. Methods From the Division of Cardiovascular Disease, Royal Postgraduate Medical School, Hammersmlth Hospital, London, England. This work was supported by a grant from the t3ritish Heart Foundation, London, England. Manuscript received July 24, 1978; revised manuscript received September 29, 1978, accepted October 5. 1978. Address for reprints: Kirr Fox, MRCP, Cardiovascular Research Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London, W12 OHS, England.
Electrocardiographic mapping: One hundred nine consecutive patients (93 men and 16 women with a mean age of 48 years) were studied before undergoing diagnostic coronary arteriography. They were referred from the outpatient department and all were sufficiently fit to undergo an exercise test. In all patients a 16 point precordial electrocardiogram was recorded using a direct writing ink jet Mingograf (Elema Schonander) recording on four channels simultaneously. The gain employed was 10 mm for 1 mv, and the paper speed was 25 mm/set. The 16 points were distributed evenly over the left hemithorax, and the boundaries were the angle of Louis, the right sternoclavicular joint, the posterior axillary line and 6 cm below the xiphisternum (Fig. 1). Disposable press stud electrodes7 were used and then secured into position using adhesive tape
March 1979
The American Journal of CARDIOLOGY
Volume 43
541
ELECTROCARDIOGRAPHIC MAPPING AFTER EXERCISE-FOX
ET AL.
FIGURE 1. Patient with 16 press stud electrodes evenly distributed over the left hemithorax. The electrodes are secured in position with adhesive tape and connected to the four channel electrocardiograph by means of a four-way switching system.
sufficiently tight to keep the electrodes stable without interfering with respiration. Screened electrode cable was used and the 16 electrodes were connected to the electrocardiograph using a four-way switching system (Fig. 1). The 16 precordial leads were unipolar V leads connected to a central Wilson terminal. One of the positions (C3, Fig. 2) corresponded exactly to lead Vs and was selected to act as the single chest lead. Exercise testing: Graded maximal exercise tests were performed using a bicycle ergometer.8 Patients cycled at a constant speed (50 revolutions/min), and the work load was increased by 25 watts each minute. Exercise was performed for 6.04 f 2.23 minutes (mean f 1 standard deviation). The exercise tests were limited by the appearance of chest pain, dyspnea, fatigue or multiple ventricular ectopic complexes.9 All recordings were made with the patient sitting comfortably
-+--v---+-+---
with the arms extended resting on the handlebars. A recording was taken from the 16 positions before exercise, immediately after and then 1,3,5,8 and 10 minutes later. Recordings were then continued at 3 minute intervals, as necessary, until the electrocardiogram had returned to the pre-exercise state. Connecting the electrodes to the patient in preparation for the test took 10 to 15 minutes, and usually 15 to 20 minutes was required for the exercise test and postexercise recordings. Each 16 lead precordial map took about 10 seconds to record, and about 10 minutes was required to analyze a series of maps from a patient. Fifty-three of these patients were randomly selected to undergo, in addition, a graded maximal exercise test using a treadmill.‘0 All these patients had orthogonal three lead electrocardiograms using the Frank lead system6 recorded before, during and at regular intervals after exercise using a
-+--+---k-b
4
Before Exercise
ST Segment Depression
542
March 1979
The American
Immediately
FIGURE 2. Example of recording of the 16 positions before and after exercise. The precordial area of S-T segment depression drawn as a contour map is shown on the left.
After Exercise
Journal of CARDIOLOGY
Volume
43
ELECTROCARDIOGRAPHIC
Hewlett-Packard 1513EI three channel electrocardiograph. X and Z leads were placed in the fourth intercostal space. All exercise tests were recorded before the coronary arteriograms were obtained. The criteria of the Scandinavian committee on electracardiographic classification were used to interpret the exer-
cise tests.11 S-T segment changes were measured from the P-Q segment, and the segment was considered depressed if there was a change of 1 mm or more lasting 0.08 second or longer. S-T segment elevation was measured 0.06 second from the end of the QRS complex and was considered significant if the value was 1 mm or more. Contour maps of the area of S-T segment change were drawn for each precordial surface map.12 Coronary arteriography: All patients had left ventricular angiography and coronary arteriogaphy performed with the and cardiologists who Judkins technique. l3 The radiologists performed the investigation also interpreted the coronary arteriograms without knowledge of the exercise tests. Statistical analysis was performed using a chi square test
TABLE
MAPPING AFTER EXERCISE-FOX
ET AL.
I
Results of Coronarv
Arteriosraphv
in 109 Patients Patients (no.)
Single vessel disease Left anterior descending artery (LAD) Circumflex artery (LCx) Right coronary artery (RCA) Total
14 1 2:
Two vessel disease Left main stem LAD + LCx LAD + RCA RCA + LCx Total
:: 4 29
Three vessel disease Left main stem + RCA LAD + LCx + RCA Total
:: 36
4
and paired t tests.
Results It was possible to obtain satisfactory recordings permitting measurement of the S-T segment changes in all patients. Figure 2 shows a typical example of the quality of recording obtained before and after exercise in a patient with a significant narrowing of the left anterior descending coronary artery. Also shown is the contour map drawn of the area of S-T segment depression. It can be seen that the baseline is stable even immediately after severe exertion when a heart rate of 150 beatslmin has been achieved. It was not necessary to shave the chests of the men to obtain a satisfactory tracing, and no difficulties were experienced obtaining good tracings in the 116women.
immediately
we-exercise
FIGURE 3. Sequence of contour maps (with a sample electrocardiographic complex taken from position C2 below) recorded before and after exercise in a patient with significant narrowing of the left anterior descending coronary artery. S-T segment depression is present immediately after the end of exercise and increases in both area and severity during the first minute after the end of exercise.
3 mins after
The maximal heart rate achieved with use of the bicycle ergometer ranged from 111 to 167 beats/min (mean 148). In the 53 patients who also had an orthogonal lead stress test, the maximal heart rate was 123 to 167 beats/min (mean 152) on the bicycle ergometer and 130 to 167 beats/min (mean 152) on the treadmill (P >0.05). Sequence of S-T changes in surface maps: Eighty-five of the 109 patients were found to have significant (70 percent or greater) luminal narrowing of at least one major coronary artery (Table I). Figure 3 shows the sequence of contonr maps obtained before and after exercise in a patient with significant narrowing of the left anterior descending coronary artery. S-T segment
exercise
5 mins
ST Segment
Depression
March 1979
after exercise
after
cl
exercise
lmm
1 min after exercise
10 mins
after
exercise
32 mm
The American Journal of CARDIOLOGY
Volume 43
543
ELECTROCARDIOGRAPHIC MAPPING AFTER EXERCISE-FOX
ET AL.
depression is present immediately after the end of exercise, and the area continues to increase over the first 1 minute after exercise with a large central area of maximal S-T segment depression present. Thereafter, both the area and severity gradually decrease, returning to the resting state at 8 minutes. Sequential changes in the S-T segment similar to those seen in this patient were present in 75 patients. In a further eight patients S-T segment depression was present only in the recording made immediately after exercise. In 63 patients
differences were present in the amount of S-T depression recorded in adjacent electrode sites. Correlation with coronary arteriographic findings: In 95 percent (81 of 85) of the patients with sig-
nificant narrowing of a major coronary artery, a correct diagnosis was made using exercise precordial mapping (S-T depression in 61 patients, S-T elevation in 8 patients and both S-T elevation and depression in 12 patients). By comparison, the diagnosis was correct in only 64 percent (54 patients) when the single chest lead (Vs)
TABLE II
Details of the 11 Patients With a Positive Precordial Exercise Map and a Negative Orthogonal Lead Stress Test Heart Rate Achieved (beatsimin) Precordial Orthogonal Test Test
Age (yr) & Sex
Case no. 1
55F 49F 50M SOM
150 140 160 135
150 150 167 125
;
45M 35M 45M 52M
130 150 145 160
130 125 145 167
9
36M
130
111
62M 57M
160 130
150 130
z 4
:
:‘:
Site of Precordial lschemia High High Inf High Inf High High High Low Inf Low Inf High Inf
ant = anterior; CAD = vessel narrowing on coronary arteriography; LCx = left circumflex coronary artery; RCA = right coronary artery.
exercise
ST Segment
544
March 1979
5 mins Depression
m
after
3 4
ant,
;
ant lat ant lat,
4 2 5
LAD LCX LAD RCA, LCx
lat,
4
RCA, LCx
ant
2 1
LAD LAD, RCA
LAD LCX RCA RCA, LAD, LCx
inf = inferior; LAD = left anterior descending coronary artery; lat = lateral;
1 min 5 mins after after exercise exercise exercise IRE 4. Patient with severe narrowing of the left anterior descending coronary artery. Exercise on both the bicycle ergometer (precordial mapping, left) and the treadmill (orthogonal leads, rlghi) was stopped because severe chest pain developed. An area of S-T segment depression in the high anterior part of the surface map was recorded after exercise. A sample complex recorded from position 82 is shown below each map. No S-T segment changes were seen using the Frank system of three orthogonal leads. X and Z leads were placed in the fourth intercostal space.
exercise
1 mm
The American Journal of CARDIOLOGY
Coronary Vessel(s) CAD
ant lat
preexercise
1 min after
Positions Showing S-T Segment Change (no.)
Volume 43
immediately after
ELECTROCARDfOGRAPHlC
was used (P
Precordial Electrocardiographic Mapping After Exercise In the Diagnosis of Coronary Artery Disease
KIM FOX, MRCP ANDREW SELWYN, MRCP JOHN SHILLINGFORD.FRCP, FACC London, England
A technique is described for recording the precordial electrocardiographic body surface map before and after exercise. The technique provides an extra dimension to the conventional exercise electrocardiogram because a measurement can be made of the area and severity of S-T segment changes that are projected onto the front of the chest. Sixteen lead isopotential surface maps were recorded before and after exercise in 109 patients with angina who subsequently underwent coronary arteriography. In addition, exercise electrocardiograms were obtained in 53 of these patients using three orthogonal leads and in all patients using a single chest unipolar chest lead. Precordial surface mapping after exercise was found to have a greater sensitivity (95 percent) than electrocardiography using either the orthogonal leads (66 percent) or a single chest lead (64 percent) (P 0.05). The technique of precordial surface mapping after exercise improves the ability to diagnose coronary artery disease and can easily be applied to clinical practice.
The aim of exercise or stress testing is to increase myocardial oxygen demand in order to elicit the electrocardiographic manifestations of ischemia (S-T segment changes) that are absent at rest. The ability to elicit these alterations in the S-T segment depends on the degree of narrowing of the coronary arteries, the amount of work performed and the accuracy with which areas of myocardial ischemia can be detected. It is usually accepted that 70 percent luminal narrowing of a major coronary vessel is necessary before the blood supply to the myocardium can be compromised by exertion, l-3 and the modern multistage stress tests aiming at maximal heart rates ensure that an adequate work load is nearly always achieved.4 The principal limiting factor of these tests is the detection of myocardial ischemia. Although multiple lead and orthogonal systems are adequate in most cases,5,6 they are not sufficiently sensitive. This paper describes a technique for recording serial precordial surface maps after exercise that has proved superior to other methods in the diagnosis of coronary artery disesse. Methods From the Division of Cardiovascular Disease, Royal Postgraduate Medical School, Hammersmlth Hospital, London, England. This work was supported by a grant from the t3ritish Heart Foundation, London, England. Manuscript received July 24, 1978; revised manuscript received September 29, 1978, accepted October 5. 1978. Address for reprints: Kirr Fox, MRCP, Cardiovascular Research Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London, W12 OHS, England.
Electrocardiographic mapping: One hundred nine consecutive patients (93 men and 16 women with a mean age of 48 years) were studied before undergoing diagnostic coronary arteriography. They were referred from the outpatient department and all were sufficiently fit to undergo an exercise test. In all patients a 16 point precordial electrocardiogram was recorded using a direct writing ink jet Mingograf (Elema Schonander) recording on four channels simultaneously. The gain employed was 10 mm for 1 mv, and the paper speed was 25 mm/set. The 16 points were distributed evenly over the left hemithorax, and the boundaries were the angle of Louis, the right sternoclavicular joint, the posterior axillary line and 6 cm below the xiphisternum (Fig. 1). Disposable press stud electrodes7 were used and then secured into position using adhesive tape
March 1979
The American Journal of CARDIOLOGY
Volume 43
541
ELECTROCARDIOGRAPHIC MAPPING AFTER EXERCISE-FOX
ET AL.
FIGURE 1. Patient with 16 press stud electrodes evenly distributed over the left hemithorax. The electrodes are secured in position with adhesive tape and connected to the four channel electrocardiograph by means of a four-way switching system.
sufficiently tight to keep the electrodes stable without interfering with respiration. Screened electrode cable was used and the 16 electrodes were connected to the electrocardiograph using a four-way switching system (Fig. 1). The 16 precordial leads were unipolar V leads connected to a central Wilson terminal. One of the positions (C3, Fig. 2) corresponded exactly to lead Vs and was selected to act as the single chest lead. Exercise testing: Graded maximal exercise tests were performed using a bicycle ergometer.8 Patients cycled at a constant speed (50 revolutions/min), and the work load was increased by 25 watts each minute. Exercise was performed for 6.04 f 2.23 minutes (mean f 1 standard deviation). The exercise tests were limited by the appearance of chest pain, dyspnea, fatigue or multiple ventricular ectopic complexes.9 All recordings were made with the patient sitting comfortably
-+--v---+-+---
with the arms extended resting on the handlebars. A recording was taken from the 16 positions before exercise, immediately after and then 1,3,5,8 and 10 minutes later. Recordings were then continued at 3 minute intervals, as necessary, until the electrocardiogram had returned to the pre-exercise state. Connecting the electrodes to the patient in preparation for the test took 10 to 15 minutes, and usually 15 to 20 minutes was required for the exercise test and postexercise recordings. Each 16 lead precordial map took about 10 seconds to record, and about 10 minutes was required to analyze a series of maps from a patient. Fifty-three of these patients were randomly selected to undergo, in addition, a graded maximal exercise test using a treadmill.‘0 All these patients had orthogonal three lead electrocardiograms using the Frank lead system6 recorded before, during and at regular intervals after exercise using a
-+--+---k-b
4
Before Exercise
ST Segment Depression
542
March 1979
The American
Immediately
FIGURE 2. Example of recording of the 16 positions before and after exercise. The precordial area of S-T segment depression drawn as a contour map is shown on the left.
After Exercise
Journal of CARDIOLOGY
Volume
43
ELECTROCARDIOGRAPHIC
Hewlett-Packard 1513EI three channel electrocardiograph. X and Z leads were placed in the fourth intercostal space. All exercise tests were recorded before the coronary arteriograms were obtained. The criteria of the Scandinavian committee on electracardiographic classification were used to interpret the exer-
cise tests.11 S-T segment changes were measured from the P-Q segment, and the segment was considered depressed if there was a change of 1 mm or more lasting 0.08 second or longer. S-T segment elevation was measured 0.06 second from the end of the QRS complex and was considered significant if the value was 1 mm or more. Contour maps of the area of S-T segment change were drawn for each precordial surface map.12 Coronary arteriography: All patients had left ventricular angiography and coronary arteriogaphy performed with the and cardiologists who Judkins technique. l3 The radiologists performed the investigation also interpreted the coronary arteriograms without knowledge of the exercise tests. Statistical analysis was performed using a chi square test
TABLE
MAPPING AFTER EXERCISE-FOX
ET AL.
I
Results of Coronarv
Arteriosraphv
in 109 Patients Patients (no.)
Single vessel disease Left anterior descending artery (LAD) Circumflex artery (LCx) Right coronary artery (RCA) Total
14 1 2:
Two vessel disease Left main stem LAD + LCx LAD + RCA RCA + LCx Total
:: 4 29
Three vessel disease Left main stem + RCA LAD + LCx + RCA Total
:: 36
4
and paired t tests.
Results It was possible to obtain satisfactory recordings permitting measurement of the S-T segment changes in all patients. Figure 2 shows a typical example of the quality of recording obtained before and after exercise in a patient with a significant narrowing of the left anterior descending coronary artery. Also shown is the contour map drawn of the area of S-T segment depression. It can be seen that the baseline is stable even immediately after severe exertion when a heart rate of 150 beatslmin has been achieved. It was not necessary to shave the chests of the men to obtain a satisfactory tracing, and no difficulties were experienced obtaining good tracings in the 116women.
immediately
we-exercise
FIGURE 3. Sequence of contour maps (with a sample electrocardiographic complex taken from position C2 below) recorded before and after exercise in a patient with significant narrowing of the left anterior descending coronary artery. S-T segment depression is present immediately after the end of exercise and increases in both area and severity during the first minute after the end of exercise.
3 mins after
The maximal heart rate achieved with use of the bicycle ergometer ranged from 111 to 167 beats/min (mean 148). In the 53 patients who also had an orthogonal lead stress test, the maximal heart rate was 123 to 167 beats/min (mean 152) on the bicycle ergometer and 130 to 167 beats/min (mean 152) on the treadmill (P >0.05). Sequence of S-T changes in surface maps: Eighty-five of the 109 patients were found to have significant (70 percent or greater) luminal narrowing of at least one major coronary artery (Table I). Figure 3 shows the sequence of contonr maps obtained before and after exercise in a patient with significant narrowing of the left anterior descending coronary artery. S-T segment
exercise
5 mins
ST Segment
Depression
March 1979
after exercise
after
cl
exercise
lmm
1 min after exercise
10 mins
after
exercise
32 mm
The American Journal of CARDIOLOGY
Volume 43
543
ELECTROCARDIOGRAPHIC MAPPING AFTER EXERCISE-FOX
ET AL.
depression is present immediately after the end of exercise, and the area continues to increase over the first 1 minute after exercise with a large central area of maximal S-T segment depression present. Thereafter, both the area and severity gradually decrease, returning to the resting state at 8 minutes. Sequential changes in the S-T segment similar to those seen in this patient were present in 75 patients. In a further eight patients S-T segment depression was present only in the recording made immediately after exercise. In 63 patients
differences were present in the amount of S-T depression recorded in adjacent electrode sites. Correlation with coronary arteriographic findings: In 95 percent (81 of 85) of the patients with sig-
nificant narrowing of a major coronary artery, a correct diagnosis was made using exercise precordial mapping (S-T depression in 61 patients, S-T elevation in 8 patients and both S-T elevation and depression in 12 patients). By comparison, the diagnosis was correct in only 64 percent (54 patients) when the single chest lead (Vs)
TABLE II
Details of the 11 Patients With a Positive Precordial Exercise Map and a Negative Orthogonal Lead Stress Test Heart Rate Achieved (beatsimin) Precordial Orthogonal Test Test
Age (yr) & Sex
Case no. 1
55F 49F 50M SOM
150 140 160 135
150 150 167 125
;
45M 35M 45M 52M
130 150 145 160
130 125 145 167
9
36M
130
111
62M 57M
160 130
150 130
z 4
:
:‘:
Site of Precordial lschemia High High Inf High Inf High High High Low Inf Low Inf High Inf
ant = anterior; CAD = vessel narrowing on coronary arteriography; LCx = left circumflex coronary artery; RCA = right coronary artery.
exercise
ST Segment
544
March 1979
5 mins Depression
m
after
3 4
ant,
;
ant lat ant lat,
4 2 5
LAD LCX LAD RCA, LCx
lat,
4
RCA, LCx
ant
2 1
LAD LAD, RCA
LAD LCX RCA RCA, LAD, LCx
inf = inferior; LAD = left anterior descending coronary artery; lat = lateral;
1 min 5 mins after after exercise exercise exercise IRE 4. Patient with severe narrowing of the left anterior descending coronary artery. Exercise on both the bicycle ergometer (precordial mapping, left) and the treadmill (orthogonal leads, rlghi) was stopped because severe chest pain developed. An area of S-T segment depression in the high anterior part of the surface map was recorded after exercise. A sample complex recorded from position 82 is shown below each map. No S-T segment changes were seen using the Frank system of three orthogonal leads. X and Z leads were placed in the fourth intercostal space.
exercise
1 mm
The American Journal of CARDIOLOGY
Coronary Vessel(s) CAD
ant lat
preexercise
1 min after
Positions Showing S-T Segment Change (no.)
Volume 43
immediately after
ELECTROCARDfOGRAPHlC
was used (P
