Question: What type of arrhythmia is known as bidirectional ventricular tachycardia (BDVT)?

Context:
Bidirectional ventricular tachycardia (BVT) is an uncommon type of polymorphic ventricular tachycardia (PVT) with alternating polarity of the QRS complex most commonly described digitalis toxicity. 
Bidirectional ventricular tachycardia (BVT), which is characterized by an alternating beat-to-beat ECG QRS axis, is a rare but intriguing arrhythmia associated with digitalis toxicity, familial catecholaminergic polymorphic ventricular tachycardia (CPVT), and several other conditions that predispose cardiac myocytes to delayed afterdepolarizations (DADs) and triggered activity. Evidence from human and animal studies attributes BVT to alternating ectopic foci originating from the distal His-Purkinje system in the left and/or right ventricle, respectively.
When the heart rate exceeded the threshold for bigeminy at the first site in the His-Purkinje system, ventricular bigeminy developed, causing the heart rate to accelerate and exceed the threshold for bigeminy at the second site. Thus, the triggered beat from the first site induced a triggered beat from the second site. The triggered beat from the second site next reciprocated by inducing a triggered beat from the first site, and so forth. Bigeminy from two sites produced BVT, and that from three or more sites produced polymorphic VT.
This "ping pong" mechanism of reciprocating bigeminy readily produces the characteristic ECG pattern of BVT and its degeneration to polymorphic VT if additional sites develop bigeminy.
The BVT, in this case, was most likely due to myocardial ischema. The ethiology of published BVT cases are most commonly digitalis toxicity and rarely herbal aconitine poisoning, hypokalemic periodic paralysis, cathecolaminergic VT, myocarditis, and Anderson-Tawil syndrome.
Bidirectional ventricular tachycardia (BVT), although a rare arrhythmia in the general population, is frequently observed in patients with Andersen-Tawil syndrome and long QT interval. However, the pharmacologic treatment of this arrhythmia remains unknown.
This report suggests that flecainide can be effective in controlling BVT associated with Andersen-Tawil syndrome and indicates that the left ventricular dysfunction is secondary to the arrhythmia and not due to an associated phenotypic manifestation of the disorder.
Based on similarity of electrocardiographic features, bidirectional ventricular tachycardia has been considered a variant of long QT syndrome.
Double ventricular ectopic rhythms had bizarre abnormal QRS complexes of two different morphologies and were inscribed in opposite directions. Ectopic rhythms in each case had parasystolic characteristics. These observations suggest bifocal automaticity as a mechanism for bidirectional ventricular tachycardia.
Bidirectional ventricular tachycardia, defined as the rapid alternation of the QRS complexes with successive opposing axial deviation, is a rare arrhythmia. In the rare cases which have undergone endocavitary investigations, an infrahisian origin has generally been proved. However, the mechanism of these tachycardias remains poorly understood and is discussed with respect to a new case.
In the light of previously reported cases with documented endocavitary investigation and this new case, it seems possible to talk in terms of true "bidirectional ventricular tachycardia", a tachycardia whose mechanism is obscure but certainly not univocal.
Bidirectional ventricular tachycardia (BVT) is an uncommon type of polymorphic ventricular tachycardia (PVT) with alternating polarity of the QRS complex most commonly described digitalis toxicity.
BACKGROUND: Bidirectional ventricular tachycardia (BVT), which is characterized by an alternating beat-to-beat ECG QRS axis, is a rare but intriguing arrhythmia associated with digitalis toxicity, familial catecholaminergic polymorphic ventricular tachycardia (CPVT), and several other conditions that predispose cardiac myocytes to delayed afterdepolarizations (DADs) and triggered activity.
Bidirectional ventricular tachycardia (BVT) is an uncommon type of polymorphic ventricular tachycardia (PVT) with alternating polarity of the QRS complex most commonly described digitalis toxicity
Bidirectional ventricular tachycardia, defined as the rapid alternation of the QRS complexes with successive opposing axial deviation, is a rare arrhythmia
Bidirectional ventricular tachycardia (BVT) is an uncommon type of polymorphic ventricular tachycardia (PVT) with alternating polarity of the QRS complex most commonly described digitalis toxicity

Answer: Bidirectional ventricular tachycardia (BVT), which is characterized by an alternating beat-to-beat ECG QRS axis, is a rare but intriguing arrhythmia associated with digitalis toxicity, familial catecholaminergic polymorphic ventricular tachycardia (CPVT), and several other conditions that predispose cardiac myocytes to delayed afterdepolarizations (DADs) and triggered activity. Bidirectional ventricular tachycardia (BVT) is an uncommon type of polymorphic ventricular tachycardia (PVT). Based on similarity of electrocardiographic features, bidirectional ventricular tachycardia has been considered a variant of long QT syndrome. Evidence from human and animal studies attributes BVT to alternating ectopic foci originating from the distal His-Purkinje system in the left and/or right ventricle, respectively. This "ping pong" mechanism of reciprocating bigeminy readily produces the characteristic ECG pattern of BVT and its degeneration to polymorphic VT if additional sites develop bigeminy.