Bidirectional Ventricular Tachycardia
Definition
Bidirectional ventricular tachycardia (BVT) is a subtype of polymorphic VT characterized by a 180-degree beat-to-beat rotation of the QRS complex axis on ECG. It is the hallmark arrhythmia of catecholaminergic polymorphic ventricular tachycardia (CPVT) and is typically triggered by physical exertion or emotional stress.
Key Concepts
- BVT in CPVT arises from delayed afterdepolarizations caused by excessive Ca²⁺ release from the sarcoplasmic reticulum via mutant RYR2 channels, producing triggered activity particularly during adrenergic stimulation. (sources/channelopathies-jaha-2025)
- The ectopic initiation site is typically the RV outflow tract, suggested by a left bundle branch block pattern with an inferior axis — the most sensitive and specific ECG feature distinguishing CPVT-related PVCs from normal ones. (sources/channelopathies-jaha-2025)
- BVT may self-terminate or degenerate into VF (in ~1/3 of cases), causing SCD. (sources/channelopathies-jaha-2025)
- During exercise stress testing, CPVT PVCs progress from bigeminy/trigeminy at increasing workloads into BVT — a characteristic escalation pattern. (sources/channelopathies-jaha-2025)
- BVT must be distinguished from polymorphic VT seen in other channelopathies; the bidirectional alternating morphology is specific to CPVT. (sources/channelopathies-jaha-2025)
Contradictions / Open Questions
- BVT in ATS vs. CPVT — distinct mechanisms, similar ECG: Both Andersen-Tawil Syndrome (KCNJ2 LOF) and CPVT (RYR2 GOF) produce bidirectional VT on ECG. In CPVT, BVT is triggered by adrenergic stimulation and DADs during exercise; in ATS, it arises from impaired terminal repolarization and is often spontaneous or associated with periodic paralysis. The shared ECG pattern can lead to misdiagnosis; ATS is frequently labelled as CPVT, and vice versa. Distinguishing features (exercise trigger, extracardiac features, QU interval morphology) must be assessed systematically. (sources/channelopathies-jaha-2025, sources/VA-SCD-ESC-2022)
- Prognostic weight in ATS: BVT in CPVT is an arrhythmic emergency that can degenerate into VF. In ATS, BVT is frequently well-tolerated and SCD is less common than expected from the arrhythmia burden — the prognosis is paradoxically more benign. The same ECG morphology therefore carries very different risk implications depending on the underlying diagnosis. (sources/VA-SCD-ESC-2022)
Connections
- Related to concepts/Sudden-Cardiac-Death
- Related to concepts/Cardiac-Action-Potential
- Related to entities/CPVT
- Related to entities/RYR2