Mechanisms for Absence of Inverse Relationship Between Coupling Intervals of Premature Impulses Initiating Reentrant Ventricular Tachycardia and Intervals Between Premature and First Tachycardia Impulses

Background During initiation of tachycardias by programmed stimulation (PES), an inverse relationship between the coupling interval of the premature impulse (V 1 V 2 ) and the interval between the premature impulse and the first impulse of tachycardia (V 2 T 1 ) has been proposed to be a specific indicator of reentry. However, an inverse relationship has not always been observed during initiation of clinical reentrant ventricular tachycardias (VTs). Methods and Results Reentrant VT was initiated by PES in twelve 4-day-old infarcted dog hearts. The relationship between V 1 V 2 and V 2 T 1 was always direct. Mapping of the epicardial border zone (EBZ) indicated that initiation of VT was secondary to functional orthodromic block of V 2 , propagation of V 2 around the line of block, and antidromic propagation through the original location of the block. In 7 dogs, the line of orthodromic block and the pathway of orthodromic propagation were similar for different V 1 V 2 coupling intervals. Orthodromic conduction time around the line to its distal side was longer at shorter V 1 V 2 intervals, but a shorter antidromic delay in the area of unidirectional block for shorter V 1 V 2 intervals, possibly reflecting small changes in the conduction pathway involving deeper layers of the EBZ, resulted in shorter V 2 T 1 intervals. In the other 5 dogs, the orthodromic conduction pathway of V 2 around the line of block changed markedly, with a shorter pathway for shorter V 1 V 2 intervals resulting in shorter V 2 T 1 intervals. Conclusions An inverse relationship between V 1 V 2 and V 2 T 1 is not a specific indicator of functional reentry.