Left Anterior Fascicular Block and Masking of Inferior Wall infarction

JAY BROWN, M.D., F.A.C.C. ANTHONY KING, M.D.

New York. New York

From the Division of Cardiology, Department of Medicine, Harlem Hospital Center, Columbia University College of Physicians and Surgeons, New York, New York. Requests for reprints should be addressed to Dr. Jay Brown, Division of Cardiology, Department of Medicine, Harlem Hospital Center, 506 Lenox Avenue, New York, New York 10037. Manuscript submitted Decem- ber 27, 1985, and accepted January 28, 1986.

A case of inferior wall myocardial infarction that was obscured by left anterior hemiblock is presented. This report illustrates that changes in the sequence of electrical activation of the left ventricle resulting from this conduction disturbance may lead to a missed electrocardiographic diagnosis.

Left anterior fascicular block may conceal or produce a variety of electrocardiographic abnormalities. Anteroseptal Q waves consistent with infarction [l-3], augmentation of the R wave in lead AVL mimicking left ventricular hyper-trophy [4], and masking of right bundle branch block [5,6] have been attributed to this conduction abnormality. Left anterior fascicular block may also mask previous myocardial infarction, including anteroseptal infarction and inferior wall infarction [ 1,7,8].

In this report, we describe a patient with prior inferior wall infarction that was obscured by left anterior fascicular block.

CASE REPORT

A 49-year-old diabetic, hypertensive man with previously documented inferior wall myocardial infarction was admitted to the hospital because of several episodes of retrosternal chest pain lasting 20 to 30 minutes. The pain was unresponsive to sublingual nitroglycerin tablets.

An electrocardiogram recorded on the first hospital day (Figure 1) revealed sinus tachycardia at 120 beats/minute and QS waves in leads Ill and aVF confirmatory of old inferior wall infarction. QS waves were present in precordial leads VI and VP, a finding consistent with, but not diagnostic of, remote anteroseptal myocardial infarction.

On the second hospital day, an electrocardiogram (Figure 2) was ob- tained during an episode of chest pain. It was remarkable for new S-T segment depression and T wave inversion in leads I, aVL, and precordial leads V4 to Vg. There were R waves in leads II, Ill, and aVF (exceeding or equal to 1 mm in II and aVF) followed by deep S waves, a mean QRS axis of -60 degrees, and terminal R wave in lead aVR, changes consistent with the development of left anterior fascicular block. Evidence of inferior wall infarction was no longer present. The sinus rate was 125 beats/minute.

The ST-T wave changes persisted and a diagnosis of non-Q wave infarction was established on the basis of elevation in total serum MB creatine kinase fraction. Follow-up electrocardiograms remained un- changed.

COMMENTS

Left anterior fascicular block is a common form of intraventricular conduction defect. It results in a delay and alteration of the sequence of electrical activation of the left ventricle [9, lo]. The electrocardiographic manifestations of this conduction disturbance have been well described

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Figure 1. Twelve-lead electrocardiogram showing sinus tachycardia and QS waves in leads 111 and aVF consistent with remote inferior wall myocardial infarction. The mean C?t?S axis is approximately 30 degrees.

[ 1,l l- 131. In addition to the superior deviation of the QRS axis, it can cause other electrocardiographic changes that may result in false-positive or missed electrocardiograph- ic diagnoses. Farnham and Shah [3] described QS waves in precordial leads VI to Vs suggestive of anteroseptal myocardial infarction in a patient with left anterior fascicu- lar block. Results of coronary angiography and left ven-

triculography were normal, thus excluding anteroseptal infarction. Placement of the right precordial electrodes two interspaces below the standard position resulted in normalizatjon of the QRS. They suggested that, as a result of the anterior fascicular block, the orientation of the initial position of the QRS was below the plane of the normal position of these electrodes. Using vectorcardiography, Kulbertus [2] excluded infarction in one of two patients in whom anterior fascicular block and anteroseptal infarc- tion electrocardiographic patterns coexisted.

Masking of right bundle branch block by left anterior fascicular block has also been described [6,7]. The termi- nal R wave in the right precordial leads-the sine qua non of right bundle branch block-is abolished [6]. In three cases described by Rosenbaum et al [!!I], the terminal S waves in leads I and aVL were also abolished. Conceal- ment of right bundle branch block should be suspected whenever left anterior fascicular block is associated with unexplained QRS prolongation equal to or exceeding 0.12 seconds. (A broad terminal R wave in lead aVR should raise the suspicion of concealed right bundle branch block even higher.) Uncovering of the right bundle branch block may occur if precordial lead VI (or V,) is recorded an interspace above its conventional position or if precordial lead VsR is recorded.

Considerable attention has been given to the recogni- tion of coexistent left anterior fascicular block and inferior wall myocardial infarction [ 13-181. In instances in which inferior wall myocardial infarction is associated with supe- rior QRS axis deviation greater than or equal to 30 de grees, the possibility of concomitant left anterior fascicu- lar block exists. If a terminal R wave in lead II is present, left anterior fascicular block is virtually excluded because it characteristically produces a terminal S wave in that lead [ 13,141. A terminal R wave in lead aVR strongly suggests the concomitant presence of left anterior fascic- ular block [ 131. When the infarction is manifested by QRS

Figure 2. Twelve-lead electrocardio- gram one day later. There are R waves in leads II, Ill, and aVF and a terminal R wave in lead a VR, and the axis is now -60 degrees. These changes are com- patible with left anterior fascicular block.

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INFARCTION MASKED BY FASCICULAR BLOCK-BROWN and KING

waves in leads II, Ill, and aVF, a terminal R wave in aVR may provide diagnostic information. A diagnostic chal- lenge occurs when small (less than 1 mm) R waves preceding deep S waves are present in the inferior leads. This QRS pattern may be due to inferior wall infarction and/or left anterior fascicular block. Some of the electro- cardiographic findings proposed to identify infarction in this instance include notching of the tiny R wave [ 191 and notching of the initial portion of the S wave [20].

Left anterior fascicular block may also obscure inferior wall infarction as illustrated in our case, which is similar to cases described by Rosenbaum et al [I]. They postulated that concealment of inferior wall infarction occurred be- cause portions of the inferior wall normally depolarized via the posterior fascicle during the earliest phase of ventricu- lar activation were not infarcted. Hence, these zones of myocardium were able to generate inferiorly directed electrical forces that were unopposed because of the delay in activation of the anterior left ventricular wall due to the left anterior fascicular block. R waves then replaced the Q waves in the inferior leads, masking the infarction. Anatomic confirmation of this hypothesis was subse- quently provided in a case report by Cristal et al [8]. In their patient in whom inferior wall infarction was con- cealed by left anterior fascicular block, the posterior paraseptal zone of the left ventricle-an area activated

1. Rosenbaum MD, Elizari MV, Lazzari JO: The hemiblocks. Oldsmar, Florida. Tampa Tracings, 1970.

2. Kulbertus HE: Electrocardiographic recognition of anterior infarction in left anterior fascicular block. A diagnostic challenge. Chest 1972; 62: 91-93.

3. Farnham DJ, Shah PM: Left anterior hemiblock simulating anteroseptal myocardial infarction. Am Heart J 1976; 92: 363-367.

4. Brown J, Brudney K, Vanderbush E, Pinckney C: Limited accuracy of the electrocardiogram in predicting left ven- tricular hypertrophy in the presence of left axis deviation (abstr). Clin Res 1984; 32: 152A.

5. Rosenbaum MD, Yeshuron J, Lazzarri JO, Elizari MV: Left anterior hemiblock obscuring the diagnosis of right bun- dle branch block. Circulation 1973; 48: 298-303.

6. Sclarovsky S, Lewin RF, Strasberg B, Agmon J: Left anterior hemiblock obscuring the diagnosis of right bundle branch block in acute myocardial infarction. Circulation 1979; 60: 26-32.

7. Altiere P, Schaol SF: Inferior and anteroseptal myocardial infarction concealed by transient left anterior hemiblock. J Electrocardiol 1973; 6:257-258.

8. Cristal N, Ho W, Gueron M: Left anterior hemiblock masking inferior myocardial infarction. Br Heart J 1975; 37: 543-547.

9. Gallagher JJ, Ticzon AR, Wallace AG, Kassell J: Activation studies following experimental hemiblock in the dog. Circ Res 1974; 35: 752-763.

REFERENCES

QRS forces in left anterior fascicular block. Am Heart J 1977; 94: 407-413.

13. Fisher ML, Mugnon MA, Carliner NH, De Felice GE, Plotnick GD: Left anterior fascicular block: electrocardiographic criteria for its recognition in the presence of inferior myocardial infarction. Am J Cardiol 1979; 44: 645-650.

14. Castellanos A, Chahine RA, Chapunoff E, Gomez J, Portillo 8: Diagnosis of left anterior hemiblock in the presence of inferior wall myocardial infarction. Chest 1971; 60: 543-551.

15. Benchimol A, Desser KB, Schumacher J: Value of the vec- torcardiogram for distinguishing left anterior hemiblock from inferior infarction with left axis deviation. Chest 1972; 61: 74-76.

16. Castellanos A: Diagnosis of left anterior hemiblock and left posterior hemiblock in the presence of inferior wall myo- cardial infarction. Bull NY Acad Med 1971; 47: 923-930.

17. Kulbertus HE, Collignon P, Humblet L, Deleval-Rutten F: Left axis deviation in inferior infarction. Vectorcardiographic recognition of concomitant left anterior hemiblock. Chest 1971; 60: 362-366.

18. Benchimol A, Desser KB, Marsey BJ: Coexisting left anterior hemiblock and inferior wall myocardial infarction: vector- cardiographic features. Am J Cardiol 1972; 29: 7-14.

19. Milliken JA: Isolated and complicated left anterior fascicular block: a review of suggested electrocardiographic crite- ria. J Electrocardiol 1983; 16: 199-212.

20. Recke SH, Knebel R, Recke AS: Vectorcardiographic diag- nosis of inferior myocardial infarction in the presence of rS complex in the orthogonal lead Y. Adv Cardiol 1976; 16: 439-444.

21. Durrer D, van Dam RT, Freud GE, Jange MJ, Meyler FL, Arzbaecher RC: Total excitation of the isolated human heart. Circulation 1970; 41: 899-912.

10. Wyndham CR, Meeran MK, Smith T, Engelman RM, Levitsky S, Rosen KM: Epicardial activation in human left anterior fascicular block. Am J Cardiol 1979: 44: 638-644.

11. Das G: Left axis deviation. A spectrum of intraventricular conduction block. Circulation 1976; 53: 917-919.

12. Jacobson LB, LaFollette L, Cohn K: An appraisal of initial

early via the posterior fascicle, USUally simultaneously with the “opposing” high anterior paraseptal region [21]-and the posterior papillary muscle and subjacent area were not infarcted.

In our patient, once the left anterior fascicular block appeared, there were no electrocardiographic clues of prior inferior wall infarction. The pathologic Q waves in leads Ill and aVF were abolished and a deep S wave appeared in lead II. The R waves in each of these leads equaled or exceeded 1 mm. Vectorcardiographic record- ing was not obtained, but we believe it would have identi- fied the underlying inferior infarction.

Our case illustrates the limitation of scalar electrocardi- ography in identifying inferior wall infarction when perma- nent left anterior fascicular block occurs. The magnitude of the problem of concealment of infarction by left anteri- or fascicular block is unknown. A history consistent with previous myocardial infarction in a patient with left anteri- or fascicular block but without electrocardiographic evi- dence of infarction may warrant additional studies, such as vectorcardiography or nuclear or ultrasound cardiac imaging.

ACKNOWLEDGMENT

We thank Ms. Mariam Heath for her help in the prepara- tion of the manuscript.

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