Cases Of Right Bundle Branch Block Research Articles

Masquerading bundle branch block

We here describe a surface 12-lead electrocardiogram (ECG) of a 72-year-old female with a prior history of breast cancer and chemotherapy-induced cardiomyopathy. An echocardiogram revealed left ventricular dysfunction, ejection fraction of 23%, with mild enlarged left ventricle. The 12-lead ECG showed atrial fibrillation with a mean heart rate of about 100 bpm, QRS duration 160 ms, QT interval 400 ms, right bundle branch block (RBBB) and left anterior fascicular block (LAFB). The combination of RBBB features in the precordial leads and LAFB features in the limb leads is known as ''masquerading bundle branch block''. In most cases of RBBB and LAFB, the QRS axis deviation is located between - 80 to -120 degrees. Rarely, when predominant left ventricular forces are present, the QRS axis deviation is near about -90 degrees, turning the pattern into an atypical form. In a situation of RBBB associated with LAFB, the S wave can be absent or very small in lead I. Such a situation is the result of not only purely LAFB but also with left ventricular hypertrophy and/or focal block due to scar (extensive anterior myocardial infarction) or fibrosis (cardiomyopathy). Sometimes, this specific ECG pattern is mistaken for LBBB. RBBB with LAFB may imitate LBBB either in the limb leads (known as 'standard masquerading' - absence of S wave in lead I), or in the precordial leads (called 'precordial masquerading' - absence of S wave in leads V₅ and V₆). Our ECG showed both these types of masquerading bundle branch block - absence of S wave in lead I and in leads V₅ and V₆.

An unusual bundle-branch block

We report a case of right bundle-branch block (RBBB) showing a QRS configuration typical for left bundle-branch block (LBBB) in leads V 5 and V 6. The QRS axis was at +90°, and the QRS duration was 0.14 second. There were wide S waves in leads I and aVL, suggesting at first glance an RBBB, but the QRS morphology in the inferior leads (monophasic R wave with secondary ST-T changes) was more consistent with an LBBB. Lead V 1 suggested an RBBB, whereas leads V 5 and V 6 showed a monophasic R wave as in LBBB; moreover, a negative T wave, typical of LBBB, was present in lead V 5. Placement of the electrodes of leads V 4, V 5, and V 6 2 intercostal spaces above restored in these leads a QRS configuration suggestive of RBBB. The diagnostic problem was mainly caused by the inferior direction of the QRS axis. Because the electrode of V 6 is normally placed below the electrical center of the heart, namely, on a plane that is not orthogonal to the sagittal plane, a vector directed mainly inferiorly and slightly to the right does not project on the negative part but on the positive of the lead line. For this reason, the S waves normally observed in the left precordial leads with RBBB disappear. The superior displacement of the electrodes “normalizes” the plane upon which the lead lines lie, thereby restoring the expected QRS configuration.

The Natural History of Right Bundle Branch Block and Frontal Plane QRS Axis in Apparently Healthy Men

We examined the characteristics, long-term follow-up, and prognosis of right bundle branch block (RBBB) detected on a routine ECG in men with no apparent heart disease. During the 29-year period, 59 cases of RBBB were observed in men with a mean age of 44.4 +/- 1.9 years. Because marked right or left axis deviation may identify cases with concomitant involvement of the left bundle branch system, subsets of frontal plane QRS (A QRS) were examined. Comparisons were made with groups of similar ages who were free of RBBB. Cases with RBBB were observed for 936 person-years (mean 15.9 +/- 1.6 years per case), showing no excess ischemic heart disease incidence, no cases of progression to advanced AV block (second- or third-degree), or sudden death. Right bundle branch block was associated with a greater proportion of both right axis (greater than or equal to +90 degrees) and marked left axis (-45 degrees to -90 degrees) deviation compared with those of the same age without this conduction disturbance. In apparently healthy men, RBBB had no adverse long-term prognosis regardless of frontal plane QRS axis.