12-Lead Vectorcardiography in Ischemic Heart Disease
Peter W. Macfarlane, PhD, FESC, and 1. Edenbrandt, MD, PhD
Abstract: The conventional approach to recording the vectorcardiogram is to use a speciallydesigned set of electrodes that derive 3-orthogonalleads, ideally corrected with respect to lead strength and direction. This has disadvantages in that it entails a separate recording as opposed to the use of the 12-lead ECG that is universally used. On the other hand, recently developed equations allow the vectorcardiogram to be derived from the 12-lead ECG, and although there is not a one-to-one correspondence with the vectorcardiogram derived using a corrected orthogonal lead system, it has been shown that there is a high degree of similarity between the two derivations. This article discusses the advantages of utilizing the "derived 12-lead vectorcardiogram," which is claimed to have information that is complementary to that of the scalar 12-lead ECG display. It is suggested that using the combination of the 12-lead ECG and the vectorcardiogram derived therefrom, provides the optimum approach to ECG interpretation as compared to using either method alone. Key words: 12-lead ECG, vectorcardiography, computer analysis, ischemic heart disease.
Without question, the 12-lead electrocardiogram (ECG) remains the dominant form of electrocardiographic investigation in use at the present time. For routine purposes, the only other electrocardiographic technique that showed any likelihood of challenging 12-lead ECG was vectorcardiography. With the use of 3-orthogonalleads derived using one of several lead systems but most notably that of Prank,' suitable display equipment could be used to produce the vectorcardiogram that effectively was a projection of the spatial resultant electrical force on to three mutually perpendicular planes. Vectorcardiography did not succeed in replacing From the University Department of Medical Cardiology. Royal Infirmary. Glasgow. Scotland.
Dr. Edenbrandt wassupported during his research work inGlasgow in partbya grantfrom the Swedish Medical Research Couneil.
Reprint requests: Dr. P.W. Macfarlane, University Department of Medical Cardiology. Royal Infirmary. Glasgow. G31 2ER Scotland.
12-lead ECG for many reasons. First, it required the use of either a completely different set of electrodes or else additional electrodes to supplement those in use for recording the 12-lead ECG from the same patient. Second, interpretation of vectorcardiograms was in itself a skill that many physicians did not acquire. Third, there was the added complexity, at least in the early days, of producing the vector loops using photographic techniques that were somewhat timeconsuming. Other attempts were made to simplify the procedure, notably the use of the hybrid lead system" whereby, with the addition of two extra electrodes compared to those required for the 12-lead ECG. it was possible to record both the 12 and the 3-orthogonal lead ECG simultaneously. Such a system was used routinely for many years in Glasgow Royal Infirmary. Again, however, this approach and others were never adopted commercially because of the extra hardware involved and because the enthusiasts
188
12-Lead Vectorcardiography •
failed to convince the cardiologic community at large that additional benefit was to be gained from using the vectorcardiogram. Nevertheless. the proponents of vectorcardiography maintained that the technique still provided information which was complementary. if not supplementary, to that of the 12-lead ECG. In 1968. Dower? suggested that the 12-lead ECG could be derived from the 3-orthogonal leads of Frank, and he introduced a series of equations based on studies of Frank's image surface." Subsequently, Dower modified these equations slightly." However, this approach to recording the 12-lead ECG via a 3orthogonal lead system was not accepted because of morphologic differences between the derived 12lead ECG and the actual 12-lead ECG. More recently, however, there has been increasing interest in the reverse process. namely, the derivation of the XYZ leads from the 12-lead ECG. Different methods have been proposed":" but one introduced in our own laboratories was first proposed by Edenbrandt and Pahlm.? These authors essentially inverted the matrix of co-efficients that Dower had proposed for deriving the 12-lead ECG from the orthogonalleads. This approach has the advantage that no additional leads are required compared to those for recording the 12-lead ECG, and with modern computer techniques, the derivation of the 3-orthogonalleads is essentially a trivial task. Many electrocardiographs now incorporate thermal array printers that facilitate production of vectorcardiographic loops at no additional cost in hardware compared to that required for displaying the conventional 12-lead ECG. The advantages of the vectorcardiogram basically revolve around the phase relationships between the 3-orthogonal leads which, when combined to produce vectorcardiographic loops, show additional information that is essentially hidden in the scalar display even of the 3-orthogonal lead ECG itself. This article summarizes the advantages of the vectorcardiographic display for the diagnosis of ischemic heart disease.
Methods The equations for the derivation of the XYZ leads from the 12-lead ECG are as follows": X = -O.I72VI - 0.074V2 + 0.122V3 + 0.231 V4 + O.239V5 + 0.194V6 + 0.1561 - 0.01 II Y = 0.057VI - 0.019V2 - 0.106V3 - 0.022V4 + 0.041 V5 + 0.048 V6 - 0.227 I + 0.887 II Z = -0.229Vl - 0.31OV2 - 0.246 V3 - 0.063 V4 + 0.055V5 + 0.108V6 + 0.0221 + 0.10211
Macfarlane and Edenbrandt
189
For the purposes of the present study, 12-lead ECGs were recorded using methods already described for ECG analysis using the Glasgow Program. 10 The software incorporated the above equations so that the XYZ leads were derived from the 12-lead ECG. Previously within the Glasgow Program, the XYZ leads were those derived from the hybrid ECG and so the software already had the capability of coping with IS-lead ECG analysis. The Glasgow Program calculated a median beat from which all amplitudes and durations could be equated but also from which vectorcardiographic measurements and loops could be produced. The output is essentially for research purposes and each illustration in this brief report is a collage designed to simplify the presentation.
Poor R Wave Progression A difficult diagnostic problem in electrocardiography is that of poor R wave progression in the anteroseptal leads Vr V 4 • Indeed, the Bethesda Conference of 1978 discouraged the use of this particular term although it has persisted in clinical practice in certain areas. Figure lA shows a 12-lead ECG recorded from a 44-year-old woman with a QS in V2 and a low R wave in V3 • Cardiac catheterization revealed normal coronary arteries. The 12-lead vectorcardiogram on the horizontal plane shows an essentially normal counterclockwise inscription of the loop. In this case, therefore, it is suggested that the poor R wave progression is essentially a normal variant. On the other hand, Figure IB shows the 12-lead ECG and the 12-lead vectorcardiogram from a 44year-old male with a clinical history of myocardial infarction. It can be seen that the R waves, V2, and V3 • in particular, are low. However. the transverse loop of the vectorcardiogram shows that there is clockwise inscription of the first 30 ms. of the vectorcardiographic loop. This is abnormal and is consistent with anteroseptal myocardial infarction. Thus, the vectorcardiogram provides additional information to that of the 12-lead ECG and confirms the suggestion that there is myocardial infarction.
as Complexes V2 , V3 The differential diagnosis of QS complexes in leads V2 and V3 in the presence of tall R waves with a left ventricular strain pattern can often be extremely difficult. Figure 2A shows the 12-lead ECG from a 59-
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Peter W. Macfarlane, PhD, FESC, and 1. Edenbrandt, MD, PhD
Abstract: The conventional approach to recording the vectorcardiogram is to use a speciallydesigned set of electrodes that derive 3-orthogonalleads, ideally corrected with respect to lead strength and direction. This has disadvantages in that it entails a separate recording as opposed to the use of the 12-lead ECG that is universally used. On the other hand, recently developed equations allow the vectorcardiogram to be derived from the 12-lead ECG, and although there is not a one-to-one correspondence with the vectorcardiogram derived using a corrected orthogonal lead system, it has been shown that there is a high degree of similarity between the two derivations. This article discusses the advantages of utilizing the "derived 12-lead vectorcardiogram," which is claimed to have information that is complementary to that of the scalar 12-lead ECG display. It is suggested that using the combination of the 12-lead ECG and the vectorcardiogram derived therefrom, provides the optimum approach to ECG interpretation as compared to using either method alone. Key words: 12-lead ECG, vectorcardiography, computer analysis, ischemic heart disease.
Without question, the 12-lead electrocardiogram (ECG) remains the dominant form of electrocardiographic investigation in use at the present time. For routine purposes, the only other electrocardiographic technique that showed any likelihood of challenging 12-lead ECG was vectorcardiography. With the use of 3-orthogonalleads derived using one of several lead systems but most notably that of Prank,' suitable display equipment could be used to produce the vectorcardiogram that effectively was a projection of the spatial resultant electrical force on to three mutually perpendicular planes. Vectorcardiography did not succeed in replacing From the University Department of Medical Cardiology. Royal Infirmary. Glasgow. Scotland.
Dr. Edenbrandt wassupported during his research work inGlasgow in partbya grantfrom the Swedish Medical Research Couneil.
Reprint requests: Dr. P.W. Macfarlane, University Department of Medical Cardiology. Royal Infirmary. Glasgow. G31 2ER Scotland.
12-lead ECG for many reasons. First, it required the use of either a completely different set of electrodes or else additional electrodes to supplement those in use for recording the 12-lead ECG from the same patient. Second, interpretation of vectorcardiograms was in itself a skill that many physicians did not acquire. Third, there was the added complexity, at least in the early days, of producing the vector loops using photographic techniques that were somewhat timeconsuming. Other attempts were made to simplify the procedure, notably the use of the hybrid lead system" whereby, with the addition of two extra electrodes compared to those required for the 12-lead ECG. it was possible to record both the 12 and the 3-orthogonal lead ECG simultaneously. Such a system was used routinely for many years in Glasgow Royal Infirmary. Again, however, this approach and others were never adopted commercially because of the extra hardware involved and because the enthusiasts
188
12-Lead Vectorcardiography •
failed to convince the cardiologic community at large that additional benefit was to be gained from using the vectorcardiogram. Nevertheless. the proponents of vectorcardiography maintained that the technique still provided information which was complementary. if not supplementary, to that of the 12-lead ECG. In 1968. Dower? suggested that the 12-lead ECG could be derived from the 3-orthogonal leads of Frank, and he introduced a series of equations based on studies of Frank's image surface." Subsequently, Dower modified these equations slightly." However, this approach to recording the 12-lead ECG via a 3orthogonal lead system was not accepted because of morphologic differences between the derived 12lead ECG and the actual 12-lead ECG. More recently, however, there has been increasing interest in the reverse process. namely, the derivation of the XYZ leads from the 12-lead ECG. Different methods have been proposed":" but one introduced in our own laboratories was first proposed by Edenbrandt and Pahlm.? These authors essentially inverted the matrix of co-efficients that Dower had proposed for deriving the 12-lead ECG from the orthogonalleads. This approach has the advantage that no additional leads are required compared to those for recording the 12-lead ECG, and with modern computer techniques, the derivation of the 3-orthogonalleads is essentially a trivial task. Many electrocardiographs now incorporate thermal array printers that facilitate production of vectorcardiographic loops at no additional cost in hardware compared to that required for displaying the conventional 12-lead ECG. The advantages of the vectorcardiogram basically revolve around the phase relationships between the 3-orthogonal leads which, when combined to produce vectorcardiographic loops, show additional information that is essentially hidden in the scalar display even of the 3-orthogonal lead ECG itself. This article summarizes the advantages of the vectorcardiographic display for the diagnosis of ischemic heart disease.
Methods The equations for the derivation of the XYZ leads from the 12-lead ECG are as follows": X = -O.I72VI - 0.074V2 + 0.122V3 + 0.231 V4 + O.239V5 + 0.194V6 + 0.1561 - 0.01 II Y = 0.057VI - 0.019V2 - 0.106V3 - 0.022V4 + 0.041 V5 + 0.048 V6 - 0.227 I + 0.887 II Z = -0.229Vl - 0.31OV2 - 0.246 V3 - 0.063 V4 + 0.055V5 + 0.108V6 + 0.0221 + 0.10211
Macfarlane and Edenbrandt
189
For the purposes of the present study, 12-lead ECGs were recorded using methods already described for ECG analysis using the Glasgow Program. 10 The software incorporated the above equations so that the XYZ leads were derived from the 12-lead ECG. Previously within the Glasgow Program, the XYZ leads were those derived from the hybrid ECG and so the software already had the capability of coping with IS-lead ECG analysis. The Glasgow Program calculated a median beat from which all amplitudes and durations could be equated but also from which vectorcardiographic measurements and loops could be produced. The output is essentially for research purposes and each illustration in this brief report is a collage designed to simplify the presentation.
Poor R Wave Progression A difficult diagnostic problem in electrocardiography is that of poor R wave progression in the anteroseptal leads Vr V 4 • Indeed, the Bethesda Conference of 1978 discouraged the use of this particular term although it has persisted in clinical practice in certain areas. Figure lA shows a 12-lead ECG recorded from a 44-year-old woman with a QS in V2 and a low R wave in V3 • Cardiac catheterization revealed normal coronary arteries. The 12-lead vectorcardiogram on the horizontal plane shows an essentially normal counterclockwise inscription of the loop. In this case, therefore, it is suggested that the poor R wave progression is essentially a normal variant. On the other hand, Figure IB shows the 12-lead ECG and the 12-lead vectorcardiogram from a 44year-old male with a clinical history of myocardial infarction. It can be seen that the R waves, V2, and V3 • in particular, are low. However. the transverse loop of the vectorcardiogram shows that there is clockwise inscription of the first 30 ms. of the vectorcardiographic loop. This is abnormal and is consistent with anteroseptal myocardial infarction. Thus, the vectorcardiogram provides additional information to that of the 12-lead ECG and confirms the suggestion that there is myocardial infarction.
as Complexes V2 , V3 The differential diagnosis of QS complexes in leads V2 and V3 in the presence of tall R waves with a left ventricular strain pattern can often be extremely difficult. Figure 2A shows the 12-lead ECG from a 59-
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