J. ELECTROCARDIOLOGY, 9 (2) 99-102
Editorial:
Electrocardiographic Diagnosis of Myocardial Infarction in Patients with Transvenous Pacemakers
MI during sinus rhythm in patients with complete LBBB. The studies of Walston et al 2 suggest that in LBBB the first half of the QRS is related mostly to depolarization of the septum from right to left and, to a lesser extent, to depolarization of the thinner RV wall. The electrical forces of septal depolarization predominate and the net vector produces an initial positive deflection in leads 1, V5 and Vs. Thus, in extensive damage of the interventricular septum, loss of normal septal forces will leave the RV forces unopposed. The initial forces will, therefore, point to the right and cause q waves in leads 1, AVL, V5 and Vs. This initial q wave is followed by a larger R wave, resulting from propagation of activation across the non-infarcted part of the interventricular septum in a leftward and posterior direction. Because the QRS during endocardial RV apical pacing resembles the QRS of spontaneously occurring LBBB (except for initial forces), Cardenas et al 3 and Castellanos et al 4 investigated the diagnosis of anteroseptal MI during ventricular pacing by applying the criteria of Sodi-Pallares ~ for the diagnosis of anteroseptal MI in LBBB. During RV apical pacing, (in the absence of MI) the left chest leads display R, Rs, rS or QS complexes, but never an initial q wave. An extensive anteroseptal MI, close to the site of the stimulating electrodes, changes the initial QRS vector in the same way as in LBBB with anteroseptal MI. Initial forces will, therefore, point to the right because of unopposed activation of the RV wall. This causes an initial q wave in leads 1, AVL, V5 and Ve, producing what Castellanos et al a have called the St-qR pattern. We have encountered this pattern in seven patients with obvious extensive anteroseptal MI during apical ventricular pacing and believe it is specific for this diagnosis. A small anteroseptal MI is almost invariably masked because viable myocardium on the right
The electrocardiographic diagnosis of myocardial infarction (MI) in patients with transvenous right ventricular (RV) pacemakers has become an important subject because it involves a large and relatively old patient population prone to coronary artery disease. The clinician must appreciate the various patterns of ventricular depolarization in the absence of MI to properly interpret the electrocardiogram (ECG) in patients with suspected MI. A positive diagnosis of MI may be difficult or impossible in the presence of intraventricular conduction disturbances, such as left bundle branch block (LBBB), fascicular block or WolffParkinson-White (WPW) Syndrome. Ventricular pacing is no exception and, therefore, many infarctions remain completely masked during ventricular pacing. Conversely, all these conduction disorders, including ventricular pacing, simulate infarction when initial forces are oriented in such a way as to mimic pathologic Q waves. 1. ANTERIOR WALL MYOCARDIAL INFARCTION Sodi-Pallares et al 1 have emphasized the diagnostic significance of small q waves in leads 1, AVL, V5 and V~ in the diagnosis of anteroseptal
From the Division of Cardiology, Department of Medicine, The Genesee Hospital, and the University of Rochester School of Medicine and Dentistry, Rochester, New York. Reprint requests to: Dr. S. Serge Barold, The Genesee Hospital, 224 Alexander Street, Rochester, NY 14607. 99
100
BAROLD ET AL
side of the septum will produce sufficiently large forces to direct the initial vector to the left. The St-qR pattern is useful in the diagnosis .of anteroseptal MI during RV endocardial pacing, but the following points should be borne in mind.
d. Unipolar pacing with large spikes may distort the QRS complex so much that the onset of the QRS may be difficult to determine. 5 Thus, initial q waves (otherwise seen in bipolar pacing) may be absent. Conversely, the overshoot of the unipolar spike may also cause a pseudo Q wave not due to ventricular depolarization.
a. The St-qR pattern must be present in leads V5 and V6 to be confident of the diagnosis. During pacing of the mid-outflow of the RV (in the absence of MI) paced beats not uncommonly exhibit a normal qR or Qr configuration in leads 1 and AVL 5,6. In this situation the inferior leads (2, 3 and AVF) show a dominant R wave suggesting catheter displacement, but we have never observed significant initial q waves in the left precordial leads which register R, Rs or QS patterns. We have, however, observed .pseudo-infarction patterns with a qR complex m leads 1 and AVL and predominantly negative forces in leads 2, 3 and AVF in three patients with slight displacement of a bipolar pacing catheter (inserted by the transfemoral route) into RV outflow tract. 7 None of these patients had coronary artery disease or myocardial infarction. It seems that further work is necessary to clarify in detail the various patterns of depolarization seen with pacing different parts of the RV. Consequently, the position of the pacemaker electrode should always be checked when a qR pattern is seen only in leads 1 and AVL, even if the forces in leads 2, 3 and AVF are negative.
2. I N F E R I O R W A L L MYOCARDIAL INFARCTION
b. Lead placement in the left precordial leads should be carefully explored. If the electrodes are placed one intercostal space too low (or ? too high), the St-qR pattern may not be seen. Conversely, if the electrodes are at the proper level and the diagnosis of anteroseptal MI is suspected, they should be placed one space higher, or perhaps lower, to search for the initial q wave. c. Sodi-Pallares et aP also suggested that an S wave in V6 in LBBB may be due to infarction of the LV free wall and a QS pattern in V5 and V~ suggests extensive anterior wall MI. This diagnosis is not always easy and lead placement always remains a problem. The same reasoning cannot be applied to the QRS generated during endocardial pacing of the RV as rS, RS or QS patterns are very common and normal manifestations of uncomplicated endocardial pacing. On this basis, no significance should be attributed to an S wave or a QS complex in the left precordial leads during ventricular pacing.
Ventricular pacing almost invariably masks an inferior wall MI by producing QS complexes in the inferior leads. Cardenas et al 3 have emphasized the usefulness of an initial or "intermediate" R wave in AVR in the diagnosis of inferior wall MI. We cannot agree with Cardenas et al 3 regarding the specificity of a rS pattern in AVR for the diagnosis of inferior wall MI, because this pattern may occasionally occur during uncomplicated RV apical pacing. We feel, however, that the presence of a rS pattern in AVR necessitates careful deductive analysis of the entire ECG to evaluate its significance, as this pattern may occasionally occur in anteroseptal MI as shown in Fig. 5 in the paper of Cardenas et al. 3 Clockwise rotation of the frontal plane VCG is uncommon, but not necessarily abnormal, during transvenous ventricular pacing, s-ll However, when the afferrent part of a clockwise frontal loop vectorcardiogram is situated inferiorly below the X axis, there will be marked inferior shift of the late forces and, in this situation, the ECG may show QR or Qr complexes in the inferior leads.12,13 The rare sign would appear to be specific for inferior wall MI, as it is never seen during uncomplicated ventricular pacing. 3. P O S T E R I O R W A L L MYOCARDIAL INFARCTION A posterior wall MI should shift the QRS loop in the horizontal plane anteriorly, producing a dominant R wave in the right precordial leads. This diagnosis can rarely be made with confidence during ventricular pacing because there are so many other causes of a dominant R wave in V1 in the absence of infarction. 6 A clear cut example of marked anterior displacement of the horizontal loop due to a true posterior wall MI was recently published by Kulbertus and DeLeval-Rutten, 14 suggesting that this diagnosis could occasionally be made.15 4. ST-T WAVE C H A N G E S Sodi-Pallares et al 1 have emphasized the distinction b e t w e e n primary and secondary J. ELECTROCARDIOLOGY, VOL. 9, NO. 2, 1976
ECG DIAGNOSIS OF MI
ST-T wave abnormalities in the diagnosis of myocardial ischemia and infarction in LBBB and the WPW Syndrome. The diagnosis of MI or ischemia during ventricular pacing (as in the WPW Syndrome or LBBB) is never certain when based on ST-T wave changes alone, when only a few ECGs are available. Indeed, relatively stable ST-T wave abnormalities suggestive of primary changes may occasionally be seen during uncomplicated ventricular pacing. 16 Despite these limitations, serial ECGs with evolving primary ST-T wave abnormalities, may, however, provide important clues of underlying ischemia or MI as illustrated by the report of Bodenheimer et al, 17 who recently observed striking transient primary ST-T wave abnormalities during ventricular pacing in episodes of "Prinzmetal's" angina. The electrical overshoot of the large unipolar spike of a ventricular triggered pacemaker may extend into the ST segment and the resulting ST-T wave changes (pseudo-current of injury) should not be attributed to injury due to coronary a r t e r y disease. 5 Such overshoot into the ST segment may occasionally be seen with unipolar ventricular-inhibited pacemakers. 5. ANALYSIS OF THE U N D E R L Y I N G SPONTANEOUS QRS COMPLEX Suppression of ventricular-inhibited pacemakers by chest wall stimulation TM (or ventricular triggered pacemakers by shorting their output TM) may reveal diagnostic Q waves. In this respect, it must be remembered that abnormalities of repolarization may occur secondary to pacing per se and cause quite prominent ST depression and T wave inversion, which should not be interpreted as ischemia or subendocardial infarction. 2~ S. SERGE BAROLD, MB, FRACP, FACC LING S. ONG, M.D. ROBERT A. H E I N L E , M.D., FACC
REFERENCES 1. SODI-PALLARES, D, CISNEROS, F, MEDRANO, GA, BISTENI, A, TESTELLI, MR AND DEMICHELI: Electrocardiographic diagnosis of myocardial infarction in presence of bundle branch block (right and left), ventricular premature beats and Wolff-Parkinson-White Syndrome. Prog in Cardiovas Dis 6:107, 1963 2. WALSTON,A, BOINEAU,J B, SACH, M S, AVERS, C R, ESTES, EH: Relationship between ventricular depolarization and QRS in right and left bundle branch block. J of Electrocardiol 1:155, 1968 J. ELECTROCARDIOLOGY, VOL. 9, NO. 2, 1976
3. CARDENAS,
101
M L, SANZ, G, LINARES,
J C,
ZAMORA, C, MEDRANO, GA, ESTANDRIA, A: Diagnostico electrocardiographico de infarto del miocardio en pacientes con estimulacion endocardica del ventriculo derecho par marcapasos. Archovos del Institute de Cardiologia de Mexico 42:345, 1972
4. CASTELLANOS,A, ZOBLE, R, PROCACCI, PM, MYERBURG, R J, BERKOVITS, BV: St-qR pattern: New sign for diagnosis of anterior myocardial infarction during right ventricular pacing. Br Heart J: 35:1161, 1973 5. CASTELLANOS,A JR, ORTIZ, J M, PASTIS, N, CASTILLO, C: The electrocardiogram in patients with pacemakers. Progr Cardiovasc Dis 13: 190, 1970 6. BAROLD, S S: Clinical problems with temporary pacing. In Modern Cardiac Pacing, A Clinical Overview, S FURMANANDD J W ESCHER, eds. Charles Press, Bowie, Maryland, 1975, p 115 7. BAROLD, S S ANDONG, L S: Electrocardiographic diagnosis of myocardial infarction in patients with transvenous ventricular pacemakers. In Proceedings of Colloquium on Cardiac Pacing, J NORMAN AND A RICKARDS, eds. Arnheim, The Netherlands, 1975 (in press) 8. THURMANN, M: Vectorcardiographic and electrocardiographic findings of hearts with electrical pacemakers. Am J Med Sci 94:578, 1967 9. BUCHNER, C, BELGER, R, OVERBECK, W, STREICHAN, C AND REINDELL, N: DaN elektrokardiogramm und vektorkardiogramm nach implantation eines elektrischen Schrittmachers. Ztschr ffir Kreislauff 54:861, 1965 10. CASTELLANOS,A, LEMBERG,L, SALHAMICK,L, BERKOVITS, B V: Pacemaker vectorcardiography. Am Heart J 75:6, 1968 11. ZONERAICH,O, ZONERAICH, S, AND DOUGLAS, A: The vectorcardiographic findings in patients with artificial pacemakers. Diseases of the Chest 53:436, 1968 12. ZONERAICH,0 AND ZONERAICH, S: Pacemaker vectorcardiography in patients with myocardial infarction and intraventricular conduction defects. J of Electrocardiol. 4:1, 1971 13. BAROLD,SS, ONG, LS, BANNER, RL: Diagnosis of inferior wall myocardial infarction during right ventricular apical pacing. Chest (in press). 14. KULBERTUS, HE AND DELEVAL-RUTTEN, F: Vectorcardiographic study of QRS in patients with transvenous pacemakers and myocardial infarction. J of Electrocardiol 7:27, 1974 15. ROTHFELD, E L, ZUCKER, I R, ANDAHUJA, V: Electrical diagnosis of myocardial infarction in the paced dog heart. J Electrocardiol 6:27, 1973 16. LYON, L J: T wave inversions. Arch Int Med 135:745, 1975 17. BODENHEIMER, M, LIPSKI, J, DONOSO, E, AND DACK, S: Prinzmetal's variant angina: A clinical and electrocardiographic study. Am Heart J 87:304, 1974 18. BAROLD, SS, PUPILLO, GA, GAIDULA, J J, AND LINHART, J W: Chest wall stimulation in evaluation of patients with implanted ventricularinhibited demand pacemakers. Br Heart J 32: 783, 1970
1 02
BAROLD ET AL
19. CENTER, S, BERGER, R A, AND TARJAN, P: The diagnosis of acute myocardial infarction in patients with permanent pacemakers. Arch Int Med 127:932, 1971 20. CHATTERJEE, K, HARRIS, A, DAVIES, G, LEATHAM,A: Electrocardiographic changes subsequent to artificial ventricular depolarization. Br Heart J 31:770, 1969
21. GOULD, L, VENKATARAMAN, K, GOSWAMI, M K, ANDGOMPRECHT,R F: Pacemaker induced electrocardiographic changes simulating myocardial infarction. Chest 63:829, 1973 22. NEVINS, MA: Electrocardiographic diagnosis of acute myocardial infarction in patients with implanted pacemakers. Br Heart J 36:609, 1974
J. ELECTROCARDIOLOGY, VOL. 9, NO. 2, 1976
Editorial:
Electrocardiographic Diagnosis of Myocardial Infarction in Patients with Transvenous Pacemakers
MI during sinus rhythm in patients with complete LBBB. The studies of Walston et al 2 suggest that in LBBB the first half of the QRS is related mostly to depolarization of the septum from right to left and, to a lesser extent, to depolarization of the thinner RV wall. The electrical forces of septal depolarization predominate and the net vector produces an initial positive deflection in leads 1, V5 and Vs. Thus, in extensive damage of the interventricular septum, loss of normal septal forces will leave the RV forces unopposed. The initial forces will, therefore, point to the right and cause q waves in leads 1, AVL, V5 and Vs. This initial q wave is followed by a larger R wave, resulting from propagation of activation across the non-infarcted part of the interventricular septum in a leftward and posterior direction. Because the QRS during endocardial RV apical pacing resembles the QRS of spontaneously occurring LBBB (except for initial forces), Cardenas et al 3 and Castellanos et al 4 investigated the diagnosis of anteroseptal MI during ventricular pacing by applying the criteria of Sodi-Pallares ~ for the diagnosis of anteroseptal MI in LBBB. During RV apical pacing, (in the absence of MI) the left chest leads display R, Rs, rS or QS complexes, but never an initial q wave. An extensive anteroseptal MI, close to the site of the stimulating electrodes, changes the initial QRS vector in the same way as in LBBB with anteroseptal MI. Initial forces will, therefore, point to the right because of unopposed activation of the RV wall. This causes an initial q wave in leads 1, AVL, V5 and Ve, producing what Castellanos et al a have called the St-qR pattern. We have encountered this pattern in seven patients with obvious extensive anteroseptal MI during apical ventricular pacing and believe it is specific for this diagnosis. A small anteroseptal MI is almost invariably masked because viable myocardium on the right
The electrocardiographic diagnosis of myocardial infarction (MI) in patients with transvenous right ventricular (RV) pacemakers has become an important subject because it involves a large and relatively old patient population prone to coronary artery disease. The clinician must appreciate the various patterns of ventricular depolarization in the absence of MI to properly interpret the electrocardiogram (ECG) in patients with suspected MI. A positive diagnosis of MI may be difficult or impossible in the presence of intraventricular conduction disturbances, such as left bundle branch block (LBBB), fascicular block or WolffParkinson-White (WPW) Syndrome. Ventricular pacing is no exception and, therefore, many infarctions remain completely masked during ventricular pacing. Conversely, all these conduction disorders, including ventricular pacing, simulate infarction when initial forces are oriented in such a way as to mimic pathologic Q waves. 1. ANTERIOR WALL MYOCARDIAL INFARCTION Sodi-Pallares et al 1 have emphasized the diagnostic significance of small q waves in leads 1, AVL, V5 and V~ in the diagnosis of anteroseptal
From the Division of Cardiology, Department of Medicine, The Genesee Hospital, and the University of Rochester School of Medicine and Dentistry, Rochester, New York. Reprint requests to: Dr. S. Serge Barold, The Genesee Hospital, 224 Alexander Street, Rochester, NY 14607. 99
100
BAROLD ET AL
side of the septum will produce sufficiently large forces to direct the initial vector to the left. The St-qR pattern is useful in the diagnosis .of anteroseptal MI during RV endocardial pacing, but the following points should be borne in mind.
d. Unipolar pacing with large spikes may distort the QRS complex so much that the onset of the QRS may be difficult to determine. 5 Thus, initial q waves (otherwise seen in bipolar pacing) may be absent. Conversely, the overshoot of the unipolar spike may also cause a pseudo Q wave not due to ventricular depolarization.
a. The St-qR pattern must be present in leads V5 and V6 to be confident of the diagnosis. During pacing of the mid-outflow of the RV (in the absence of MI) paced beats not uncommonly exhibit a normal qR or Qr configuration in leads 1 and AVL 5,6. In this situation the inferior leads (2, 3 and AVF) show a dominant R wave suggesting catheter displacement, but we have never observed significant initial q waves in the left precordial leads which register R, Rs or QS patterns. We have, however, observed .pseudo-infarction patterns with a qR complex m leads 1 and AVL and predominantly negative forces in leads 2, 3 and AVF in three patients with slight displacement of a bipolar pacing catheter (inserted by the transfemoral route) into RV outflow tract. 7 None of these patients had coronary artery disease or myocardial infarction. It seems that further work is necessary to clarify in detail the various patterns of depolarization seen with pacing different parts of the RV. Consequently, the position of the pacemaker electrode should always be checked when a qR pattern is seen only in leads 1 and AVL, even if the forces in leads 2, 3 and AVF are negative.
2. I N F E R I O R W A L L MYOCARDIAL INFARCTION
b. Lead placement in the left precordial leads should be carefully explored. If the electrodes are placed one intercostal space too low (or ? too high), the St-qR pattern may not be seen. Conversely, if the electrodes are at the proper level and the diagnosis of anteroseptal MI is suspected, they should be placed one space higher, or perhaps lower, to search for the initial q wave. c. Sodi-Pallares et aP also suggested that an S wave in V6 in LBBB may be due to infarction of the LV free wall and a QS pattern in V5 and V~ suggests extensive anterior wall MI. This diagnosis is not always easy and lead placement always remains a problem. The same reasoning cannot be applied to the QRS generated during endocardial pacing of the RV as rS, RS or QS patterns are very common and normal manifestations of uncomplicated endocardial pacing. On this basis, no significance should be attributed to an S wave or a QS complex in the left precordial leads during ventricular pacing.
Ventricular pacing almost invariably masks an inferior wall MI by producing QS complexes in the inferior leads. Cardenas et al 3 have emphasized the usefulness of an initial or "intermediate" R wave in AVR in the diagnosis of inferior wall MI. We cannot agree with Cardenas et al 3 regarding the specificity of a rS pattern in AVR for the diagnosis of inferior wall MI, because this pattern may occasionally occur during uncomplicated RV apical pacing. We feel, however, that the presence of a rS pattern in AVR necessitates careful deductive analysis of the entire ECG to evaluate its significance, as this pattern may occasionally occur in anteroseptal MI as shown in Fig. 5 in the paper of Cardenas et al. 3 Clockwise rotation of the frontal plane VCG is uncommon, but not necessarily abnormal, during transvenous ventricular pacing, s-ll However, when the afferrent part of a clockwise frontal loop vectorcardiogram is situated inferiorly below the X axis, there will be marked inferior shift of the late forces and, in this situation, the ECG may show QR or Qr complexes in the inferior leads.12,13 The rare sign would appear to be specific for inferior wall MI, as it is never seen during uncomplicated ventricular pacing. 3. P O S T E R I O R W A L L MYOCARDIAL INFARCTION A posterior wall MI should shift the QRS loop in the horizontal plane anteriorly, producing a dominant R wave in the right precordial leads. This diagnosis can rarely be made with confidence during ventricular pacing because there are so many other causes of a dominant R wave in V1 in the absence of infarction. 6 A clear cut example of marked anterior displacement of the horizontal loop due to a true posterior wall MI was recently published by Kulbertus and DeLeval-Rutten, 14 suggesting that this diagnosis could occasionally be made.15 4. ST-T WAVE C H A N G E S Sodi-Pallares et al 1 have emphasized the distinction b e t w e e n primary and secondary J. ELECTROCARDIOLOGY, VOL. 9, NO. 2, 1976
ECG DIAGNOSIS OF MI
ST-T wave abnormalities in the diagnosis of myocardial ischemia and infarction in LBBB and the WPW Syndrome. The diagnosis of MI or ischemia during ventricular pacing (as in the WPW Syndrome or LBBB) is never certain when based on ST-T wave changes alone, when only a few ECGs are available. Indeed, relatively stable ST-T wave abnormalities suggestive of primary changes may occasionally be seen during uncomplicated ventricular pacing. 16 Despite these limitations, serial ECGs with evolving primary ST-T wave abnormalities, may, however, provide important clues of underlying ischemia or MI as illustrated by the report of Bodenheimer et al, 17 who recently observed striking transient primary ST-T wave abnormalities during ventricular pacing in episodes of "Prinzmetal's" angina. The electrical overshoot of the large unipolar spike of a ventricular triggered pacemaker may extend into the ST segment and the resulting ST-T wave changes (pseudo-current of injury) should not be attributed to injury due to coronary a r t e r y disease. 5 Such overshoot into the ST segment may occasionally be seen with unipolar ventricular-inhibited pacemakers. 5. ANALYSIS OF THE U N D E R L Y I N G SPONTANEOUS QRS COMPLEX Suppression of ventricular-inhibited pacemakers by chest wall stimulation TM (or ventricular triggered pacemakers by shorting their output TM) may reveal diagnostic Q waves. In this respect, it must be remembered that abnormalities of repolarization may occur secondary to pacing per se and cause quite prominent ST depression and T wave inversion, which should not be interpreted as ischemia or subendocardial infarction. 2~ S. SERGE BAROLD, MB, FRACP, FACC LING S. ONG, M.D. ROBERT A. H E I N L E , M.D., FACC
REFERENCES 1. SODI-PALLARES, D, CISNEROS, F, MEDRANO, GA, BISTENI, A, TESTELLI, MR AND DEMICHELI: Electrocardiographic diagnosis of myocardial infarction in presence of bundle branch block (right and left), ventricular premature beats and Wolff-Parkinson-White Syndrome. Prog in Cardiovas Dis 6:107, 1963 2. WALSTON,A, BOINEAU,J B, SACH, M S, AVERS, C R, ESTES, EH: Relationship between ventricular depolarization and QRS in right and left bundle branch block. J of Electrocardiol 1:155, 1968 J. ELECTROCARDIOLOGY, VOL. 9, NO. 2, 1976
3. CARDENAS,
101
M L, SANZ, G, LINARES,
J C,
ZAMORA, C, MEDRANO, GA, ESTANDRIA, A: Diagnostico electrocardiographico de infarto del miocardio en pacientes con estimulacion endocardica del ventriculo derecho par marcapasos. Archovos del Institute de Cardiologia de Mexico 42:345, 1972
4. CASTELLANOS,A, ZOBLE, R, PROCACCI, PM, MYERBURG, R J, BERKOVITS, BV: St-qR pattern: New sign for diagnosis of anterior myocardial infarction during right ventricular pacing. Br Heart J: 35:1161, 1973 5. CASTELLANOS,A JR, ORTIZ, J M, PASTIS, N, CASTILLO, C: The electrocardiogram in patients with pacemakers. Progr Cardiovasc Dis 13: 190, 1970 6. BAROLD, S S: Clinical problems with temporary pacing. In Modern Cardiac Pacing, A Clinical Overview, S FURMANANDD J W ESCHER, eds. Charles Press, Bowie, Maryland, 1975, p 115 7. BAROLD, S S ANDONG, L S: Electrocardiographic diagnosis of myocardial infarction in patients with transvenous ventricular pacemakers. In Proceedings of Colloquium on Cardiac Pacing, J NORMAN AND A RICKARDS, eds. Arnheim, The Netherlands, 1975 (in press) 8. THURMANN, M: Vectorcardiographic and electrocardiographic findings of hearts with electrical pacemakers. Am J Med Sci 94:578, 1967 9. BUCHNER, C, BELGER, R, OVERBECK, W, STREICHAN, C AND REINDELL, N: DaN elektrokardiogramm und vektorkardiogramm nach implantation eines elektrischen Schrittmachers. Ztschr ffir Kreislauff 54:861, 1965 10. CASTELLANOS,A, LEMBERG,L, SALHAMICK,L, BERKOVITS, B V: Pacemaker vectorcardiography. Am Heart J 75:6, 1968 11. ZONERAICH,O, ZONERAICH, S, AND DOUGLAS, A: The vectorcardiographic findings in patients with artificial pacemakers. Diseases of the Chest 53:436, 1968 12. ZONERAICH,0 AND ZONERAICH, S: Pacemaker vectorcardiography in patients with myocardial infarction and intraventricular conduction defects. J of Electrocardiol. 4:1, 1971 13. BAROLD,SS, ONG, LS, BANNER, RL: Diagnosis of inferior wall myocardial infarction during right ventricular apical pacing. Chest (in press). 14. KULBERTUS, HE AND DELEVAL-RUTTEN, F: Vectorcardiographic study of QRS in patients with transvenous pacemakers and myocardial infarction. J of Electrocardiol 7:27, 1974 15. ROTHFELD, E L, ZUCKER, I R, ANDAHUJA, V: Electrical diagnosis of myocardial infarction in the paced dog heart. J Electrocardiol 6:27, 1973 16. LYON, L J: T wave inversions. Arch Int Med 135:745, 1975 17. BODENHEIMER, M, LIPSKI, J, DONOSO, E, AND DACK, S: Prinzmetal's variant angina: A clinical and electrocardiographic study. Am Heart J 87:304, 1974 18. BAROLD, SS, PUPILLO, GA, GAIDULA, J J, AND LINHART, J W: Chest wall stimulation in evaluation of patients with implanted ventricularinhibited demand pacemakers. Br Heart J 32: 783, 1970
1 02
BAROLD ET AL
19. CENTER, S, BERGER, R A, AND TARJAN, P: The diagnosis of acute myocardial infarction in patients with permanent pacemakers. Arch Int Med 127:932, 1971 20. CHATTERJEE, K, HARRIS, A, DAVIES, G, LEATHAM,A: Electrocardiographic changes subsequent to artificial ventricular depolarization. Br Heart J 31:770, 1969
21. GOULD, L, VENKATARAMAN, K, GOSWAMI, M K, ANDGOMPRECHT,R F: Pacemaker induced electrocardiographic changes simulating myocardial infarction. Chest 63:829, 1973 22. NEVINS, MA: Electrocardiographic diagnosis of acute myocardial infarction in patients with implanted pacemakers. Br Heart J 36:609, 1974
J. ELECTROCARDIOLOGY, VOL. 9, NO. 2, 1976
