Background

Bundle branch reentrant ventricular tachycardia (BBRVT) is a unique type of ventricular tachycardia (VT) that employs both bundles and the ventricular septum as integral components of a re-entrant circuit. It is a life-threatening arrhythmia and accounts for 6–8% of all inducible sustained VTs [1].

Its incidence is still underreported in the literature, and its recognition is important because of the inefficiency of pharmacological therapy.

Case report

We report the case of a 67 years man with a history of Fabry disease with renal impairment under Migalastat, and atrial fibrillation ablation, without any coronary disease, admitted to our department for a wide QRS tachycardia at 150 bpm, with left bundle branch block (LBB) well tolerated (Fig. 1).

Fig. 1
figure 1

EKG at admission showing wide QRS tachycardia

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Transthoracic echocardiography showed hypertrophic left and right ventricles, a preserved left ventricular function, and an altered right ventricle function.

At the intensive care unit, pharmacological cardioversion and adenosine failed to stop and slow the arrhythmia, atrioventricular reentrant tachycardia was excluded. An urgent electrophysiological study (EPS) showed an atrioventricular (VA) dissociation and a His-ventricular (HV) sequence at 50 ms, excluding supra-ventricular tachycardia (Figs. 2, 3, 4).

Fig. 2
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EPS showing an AV dissociation

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Fig. 3
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EPS showing the HV sequence. A The His in sinus rhythm. B Fluoroscopic image of multipolar catheter position. C HV sequence measurement

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Fig. 4
figure 4

EPS showing HV sequence in BBRVT. A HV sequence measurement. B The His in BBRVT

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In addition to the similar morphology between VT and sinus rhythm, a left BBRVT (type A) diagnosis was done. An overdrive stopped the arrhythmia (Fig. 5).

Fig. 5
figure 5

An overdrive at the EPS that stopped the arrhythmia

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A few hours later, the same arrhythmia reappeared, not well tolerated, with loss of consciousness. External electrical cardioversion restored it to a sinus rhythm.

We decided to implant a cardiac defibrillator for secondary prevention and to ablate the right bundle branch. No inducible arrhythmia was detected after the ablation, and the final EKG showed a sinus rhythm with a LBBB (Fig. 6).

Fig. 6
figure 6

EKG after right bundle branch ablation

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Discussion

BBRVT is a unique arrhythmia because its circuit depends exclusively on the specialized conduction system and is suspected in the presence of typical QRS morphology on the surface electrocardiogram (EKG) during normal sinus rhythm and VT. It is a different entity than interfascicular re-entrant tachycardia that utilizes ramifications of the LBB.

BBRVT arrhythmia is usually observed in patients with acquired structured heart disease, frequently in dilated cardiomyopathy, and rarely in hypertrophic cardiomyopathy [2], and also occurs in patients with valvular heart disease, aortic or mitral valve surgery, and in patients with myotonic myocardial dystrophy, or with idiopathic isolated conduction system disease [3, 4]. The presence of BBRVT in Fabry disease is unusual.

An etiological work-up is required to determine the structural heart disease, by using echocardiography, coronary arteriography and MRI, and other examinations if needed.

The most commonly reported VT morphology is the LBBB-like pattern (type A) [5] described as counterclockwise activation, and explained by the activation and propagation of the wavefront from the LB to the His’s-Bundle (HB), and then down to the right bundle (RB). In the RBBB pattern, the mechanism is reversed. Type B involves reentry within the fascicles of the LBB (fascicular VT). Type C is described as clockwise activation, with a RBBB-like VT morphology.

Intracardiac recordings confirm the diagnosis of BBRVT. HB recordings are essential and AV dissociation is typically present. The method used to induce BBR with an LBBB pattern is ventricular stimulation (VES) from the right ventricle apex. In some patients, it can be inducible with atrial pacing, in others; procainamide and isoproterenol can favor its induction.

In the majority of patients with BBRVT, the HV interval is prolonged in sinus rhythm [6], and may be in normal limits, however in these patients functional His-Purkinje system impairment is manifesting as H-V interval prolongation or split His-bundle potentials and becomes commonly evident during atrial programmed stimulation or burst pacing.

The use of pharmacological therapy in BBRVT is usually inefficient. If sustained BBR VT is inducible during programmed stimulation, catheter ablation of the bundle branch is the first-line therapy [7] but can result in an excessive prolonged HV interval or complete atrioventricular block in 30% of cases. An implantable cardioverter defibrillator is recommended for secondary prevention and can provide backup pacing [1].

Conclusion

BBRVT is a rare entity that is underreported.

The recognition of this tachycardia is important because of the inefficiency of pharmacological therapy.