Effect of Basic Drive Train Cycle Length on Induction of Ventricular Tachycardia by a Single Extrastimulus

This study determined the effects of a wide range of basic drive cycle lengths on the induction of ventricular tachycardia (VT) by a single extrastimulus (S 2 ). Seventy‐one patients with coronary artery disease and inducible sustained monomorphic VT underwent 121 electrophysiology tests either in the control state or during treatment with an antiarrhythmic drug. Ventricular basic drive trains were eight beats in duration and the intertrain interval was three seconds. Programmed ventricular stimulation was performed with S 2 using the longest possible basic drive cycle length rounded off to the nearest multiple of 100 msec, then using basic drive train cycle lengths that decreased in 100 msec steps to 400 msec, and finally using a basic drive cycle length of 350 msec. At each drive cycle length, an interval of > 50 msec beyond the effective refractory period (ERP) was scanned with S 2 . Monomorphic VT was induced by S 2 in 52/121 studies (43%). The drive cycle length had a significant linear effect on the log odds of inducing VT (P < 0.0001). The highest yield of VT occurred with a drive cycle length of 350 msec (42/121, 34%), and with each increment in drive cycle length, the expected odds of inducing VT decreased by a factor of 1.7. In 88% of cases in which VT was induced at a particular drive cycle length but not at longer drive cycle lengths, the coupling intervals that induced VT exceeded the ERP measured at one or more of the longer basic drive cycle lengths. In conclusion, there is an inverse relationship between the basic drive cycle length and the yield of monomorphic VT induced by S 2 . The use of shorter basic drive cycle lengths often facilitates the induction of VT by some effect other than critical shortening of the S 2 coupling interval.