Abstract
The diagnosis of myocardial infarction with left bundle branch block is difficult. We report a case of 56‐year‐old man with old extensive anterior myocardial infarction and left bundle branch block (masked each other). The recurrent myocardial infarction indicated right bundle branch block and first‐degree atrioventricular block, making a clear diagnosis of complicated and interesting ECG.
Keywords: atrioventricular block, ECG, left bundle branch block, myocardial infarction, right bundle branch block
1. INTRODUCTION
Left bundle branch block (LBBB) can change the ventricular depolarization (affect the initial vector). Therefore, infarct area of myocardial infarction (MI) cannot be localized by abnormal Q wave. At the same time, MI can affect the performance of LBBB, which brings confusion to the diagnosis. Here, we report a case of 56‐year‐old man with old extensive anterior MI and LBBB (masked each other). The recurrent MI indicated right bundle branch block (RBBB) and first‐degree atrioventricular block, making a clear diagnosis of complicated and interesting ECG.
2. CASE REPORT
A 56‐year‐old man with a history of old extensive anterior MI was admitted to the hospital for heart failure. The ECG on admission recording in Figure 1 demonstrated sinus rhythm. The PR interval was 0.17 s, the QRS duration was 0.12 s and the mean frontal QRS axis was −60°. Narrow R wave was in lead I. The QRS complex was in qR pattern in lead aVL, rS pattern in leads II, III, aVF, and V1−6, poor R wave progression ,consistent with a diagnosis of left anterior fascicular block with nonspecific intraventricular block (Surawicz, Childers, Deal, & Gettes, 2009), but the combination of history suggests extensive anterior wall myocardial infarction with LBBB (MI affect the performance of LBBB, LBBB mask the performance of necrotic) (Schamroth, 1975). On next day of hospitalization, the patient was having chest pain and shortness of breath. The ECG (Figure 2) showed that the PR interval was 0.23 s, the QRS complex was in RBBB pattern, obvious pathological Q waves are seen at the initial part of QRS complex in leads V1−5. ST‐segment changed into horizontal type and T wave changed into symmetrical inversion in leads V1−3. ST‐segment changed into slightly convex on the elevation in leads V5−6. Combined with significantly higher troponin, these were consistent with a diagnosis of recurrent extensive anterior wall MI, first‐degree atrioventricular block and RBBB.
Figure 1.
The ECG on admission. The PR interval was 0.17 s, the QRS duration was 0.12 s. The QRS complex was in rS pattern in leads II, III, aVF, and V1−6
Figure 2.
The patient was having chest pain and shortness of breath. The ECG revealed extensive anterior wall myocardial infarction, first‐degree AV block, and RBBB
3. DISCUSSION
Figure 2 noted obvious pathological Q waves at the initial part of QRS complex in leads V1−5,which further confirmed old extensive anterior MI in Figure 1. But why doesn't pathological Q wave appear in leads V1−5 in Figure 1, LBBB can change the ventricular depolarization (affect the initial vector),masked the performance of MI (Schamroth, 1975). Combined with ventricular depolarization sequence changes in LBBB (Figure 3a), we note that anterior wall MI may manifest as q wave in leads aVL; anterior MI may manifest as the reduction in the first part of the blunt in RV5−6; lateral wall MI may manifest as S wave in leads V5−6 (Figure 3b).
Figure 3.
LBBB ECG changes and the mechanisms of affect myocardial infarction ECG findings. (a) Patient with LBBB,the relationship between the depolarization of each part of the ventricular vector and the various parts of QRS. (b) Patient with anterior wall myocardial infarction and LBBB, the depolarization vector disappeared,the QRS complex was in RS pattern in leads V5−6
Figure 2 further confirmed old extensive anterior MI. In Figure 1, it was the typical performance of MI affecting the LBBB. Figure 1 was LBBB. Why can LBB in Figure 2 conduct to ventricular? Due to the occurence of RBBB (significantly heavier than LBBB). When there are different degrees of block in left and right bundle branch, the QRS conduct to ventricular represents the heavier side branch block. PR interval represent the time of the lighter side bundle branch conducted to ventricular. Figure 2 shows RBBB, the prolongation of PR interval (0.17 s change to 0.23 s) is the manifestation of first‐degree LBB block. These findings confirmed that Figure 2 was the recurrent extensive anterior MI with complete RBBB and first‐degree LBB block.
4. CONFLICT OF INTEREST
None.
ACKNOWLEDGMENTS
We thank all the people who participated in the study.
Jiang H, Chang Q, Zhang Y, Liu R. Recurrent extensive anterior myocardial infarction with left and right bundle branch block. Ann Noninvasive Electrocardiol. 2018;23:e12506 10.1111/anec.12506
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