Bidirectional tachycardia, an uncommon type of arrhythmia mostly occurs as a result of digital intoxication. Although it has been reported to occur in other conditions including fulminant myocarditis, covid-19 infection, sarcoidosis, catecholaminergic polymorphic ventricular tachycardia(CPVT), and Andersen-Tawil syndrome, cardiac surgeries, acute ischemia, ischemic cardiomyopathies, coronary allograft vasculopathy, familial hypokalemic periodic paralysis,  cardiac tumors, drug overdose (caffeine, aconitine), and cases of familial channelopathies, the use of digitalis in 40% of cases [1,2]. Although atrioventricular dissociation and bigeminy extrasystoles are frequently encountered in digital intoxication (5% and 21%), bidirectional tachycardia is a rare arrhythmia (less than 0.5%) [1,3-6]. The mechanism for bidirectional ventricular tachycardia (BiVT) is not as well known as other forms of ventricular tachycardia but appears to include typical mechanisms including triggered activity from afterdepolarizations, abnormal automaticity, or reentry [1-3]. Evidence from human studies and optical mapping experiments in a genetic CVPT mouse model attribute BiVT to alternating ectopic foci originating from the distal His-Purkinje system in the left and/or right ventricles, respectively.

It was interesting that in our case, besides bidirectional tachycardia, other rhythm disorders due to digital intoxication were detected together.

Bidirectional tachycardia has certain criteria. It is a fast regular rhythm, the ventricular rate is 140-180/minute. QRS complexes appear as consecutive complexes of opposite directions. The QRS frontal plane electrical axis is -60⁰, -80⁰ in one of the opposite complexes, and +120⁰ in the other [1-6].

In our case, *His Bundle* recordings could not be made, which could clearly explain the origin of bidirectional tachycardia. * A-type* ectopic beats may be beats that come out of the left ventricle and are transmitted to the left ventricle and then to the right ventricle through the left anterior division, or they are supraventricular beats that are transmitted from the anterior division of the left branch to the left ventricle due to aberrant conduction in the right branch and posterior division of the left branch. Likewise, *B-type* ectopic beats originating from the left ventricle, and they may be transmitted to the left ventricle through the left posterior division and then to the right ventricle, or there may be aberrantly conducted supraventricular beats in the right branch and anterior division of the left branch. As it can be understood from the electrocardiograms of the case, the presence of nodal and ectopic beats as well as compound (fusion) beats are observed. It has been reported that the appearance of fusion beats on the surface electrocardiogram is one of the important findings supporting the ventricular origin of the ectopic focus [6]. Based on this finding alone, we can say that at least one of type A and B ectopic beats is of ventricular origin.

Another important criterion in differentiating between aberrantly conducted supraventricular beats and ventricular beats is the QRS morphology in V1. It has been reported that the QRS pattern showing an initial q wave in V1 and in biphasic form is typical for ventricular ectopic beats, while the beats showing the initial r wave, triphasic form and transmitted to the initial QRS vector in the same direction as the initial QRS vector are supraventricular beats showing phase aberrant ventricular conduction [6]. When we examine the beats in V1 during bidirectional tachycardia in our case from this point of view, it is understood that *A-type ectopic beats are of ventricular origin,* B-type* beats are aberrantly conducted supraventricular beats. As a matter of fact, one of the most important findings that support the ventricular origin of *A-type* ectopic beats is that the bigeminy ventricular extrasystoles seen in the electrocardiogram taken after bidirectional tachycardia disappeared in our case were the same as *A*type* ectopic beats seen during tachycardia. These bigeminy extrasystoles show the character of bigeminal extrasystoles of ventricular origin with all their features.

Some authors, who determined that one of the ectopic beats disappeared by performing sinus carotid massage during bidirectional tachycardia, also suggested the presence of two ectopic foci, one ventricular and the other supraventricular [7].

In the classification of Scherf and Kisch  II; It has been reported that acceptance of the presence of two ectopic foci, one supraventricular and the other ventricular, may be the most appropriate explanation in cases of bidirectional ventricular tachycardia [5]. In our case, the relationship between ectopic beats corresponds to type II bidirectional tachycardia in the Scherf and Kisch classification (the AA interval and BB interval are equal, AB interval is not equal to the BA interval) (Scheme 1).