Masquerading bundle branch block: an often missed electrophysiological event

Abstract

Masquerading bundle branch block is an easily overlooked pattern on the ECG that indicates severe disease of the atrioventricular nodal conduction pathway. It is often caused by coronary artery disease, infiltrative diseases of the heart and idiopathic degeneration of the atrioventricular nodal conduction pathways. The diagnosis is easily missed as it needs a detailed interpretation of the ECG in addition to the clinical presentation of the patient. The presence of this specific bundle branch block pattern on the ECG indicates severe degeneration of the conduction system requiring intervention. Given its rarity, this clinical entity risks misdiagnosis and inappropriate management. This case highlights two diagnostic challenges for clinicians: the rarely described masquerading bundle branch block and the art of clinically differentiating between epilepsy and convulsive syncope.

Keywords: Arrhythmias; Medical education; Pacing and electrophysiology.

Figure 1

Initial ECG at presentation: ventricular rate, 25 beats per minute; PR interval, * ms; QRS duration, 124 ms; QT/QTc, 676/436 ms; P-R-T axes, *, −78, 20. Idioventricular rhythm present, right bundle branch block and left anterior fascicular block (bifascicular block).

Figure 2

Baseline ECG: ventricular rate, 81 beats per minute; PR interval, 206 ms; QRS duration, 100 ms; QT/QTc, 394/457 ms; and P-R-T axes, 79, –59, 122. Normal sinus rhythm. Incomplete right bundle branch block and left anterior fascicular block.

Figure 3

Persistent ECG on admission depicting an MBBB pattern: ventricular rate of 49 beats per minute; PR interval, 240 ms; QRS duration, 122 ms; QT/QTc, 516/466 ms; P-R-T axes of 77, 74, 68. Sinus bradycardia with first-degree AV block, right bundle branch block and left anterior fascicular block (trifascicular block).

Figure 4

Non-contrast head CT scan revealed moderate chronic small vessel disease with chronic lacunar infarcts of the right caudate nucleus, right cerebellum and generalised parenchymal volume loss but no acute intracranial abnormalities.

Figure 5

Non-contrast head CT scan showing moderate chronic small vessel disease with chronic lacunar infarcts of the right caudate nucleus, right cerebellum and generalised parenchymal volume loss but no acute intracranial abnormalities.