Significance of sustained monomorphic ventricular tachycardia induced with short coupling intervals in patients with ischemic cardiomyopathy.

P ventricular stimulation has emerged as an important tool for identifying patients at risk for sudden cardiac death, especially in those with coronary artery disease, left ventricular dysfunction, and nonsustained ventricular tachycardia (VT). Most induction protocols include programmed stimulation with up to triple ventricular extrastimuli at 2 cycle lengths from 2 right ventricular sites. Because of concerns regarding specificity, many electrophysiology laboratories and multicenter trials like the Multicenter Automatic Defibrillator Implantation Trial (MADIT) preclude stimulation at coupling intervals 200 to 180 ms. To determine the specificity of a protocol that permitted the introduction of ventricular extrastimuli at coupling intervals 200 ms, we evaluated patients with coronary artery disease and left ventricular dysfunction undergoing electrophysiologic study for nonsustained VT, and compared the annualized event rates (sustained VT or ventricular fibrillation [VF] requiring implantable cardioverterdefibrillator [ICD] therapy) in patients in whom sustained monomorphic VT or VF was induced with coupling intervals 200 ms with those in whom at least 1 coupling interval was 200 ms. A similar analysis was also performed comparing coupling intervals 180 ms or 180 ms. • • • The study population was derived from 298 consecutive patients with ischemic cardiomyopathy (ejection fraction 40%) and nonsustained VT (lasting for 3 beats and 30 seconds at a rate 100 beats/min) who were evaluated for inducibility of sustained ventricular tachyarrhythmias. After giving written informed consent, patients underwent electrophysiologic study after an overnight fast. Quadripolar catheters were advanced under fluoroscopic guidance to the high right atrium, His bundle position, and right ventricular apex, and to the right ventricular outflow tract if VT was not induced from the right ventricular apex. Bipolar intracardiac electrograms were filtered at 30 to 500 Hz and recorded on optical disk. Ventricular stimulation was performed at 4 times diastolic threshold using a pulse width of 2 ms, and extrastimuli were introduced until refractoriness was reached. Electrophysiologic study included the introduction of up to 3 extrastimuli at 2 right ventricular sites delivered during 2 drive cycle lengths. Extrastimuli were delivered using an iterative protocol. For example, during delivery of triple ventricular extrastimuli, a second extrastimulus (S3) was routinely decremented after the third extrastimulus (S4) failed to capture. When both extrastimuli subsequently captured the ventricles, S4 was once again decremented. This iterative process was repeated until S3 achieved refractoriness. This sequence was then duplicated using all 3 extrastimuli and was completed when the first extrastimulus reached absolute refractoriness. If sustained monomorphic VT was not inducible with up to triple ventricular extrastimuli from 2 right ventricular sites, isoproterenol was infused (in contrast to MADIT and the Multicenter Unsustained Tachycardia Trial [MUSTT]). The isoproterenol dose was titrated to increase the baseline heart rate by 20% to 25%, and programmed stimulation was repeated from the right ventricular outflow tract. Positive end points for induction included sustained monomorphic VT regardless of cycle length or polymorphic VT/VF (induced with single or double extrastimuli). All inducible patients received an ICD. Appropriate device therapy (antitachycardia therapy or shock) was confirmed during ICD interrogation at 3to 6-month intervals or immediately after a defibrillator discharge. Comparison of group means was performed using the paired t test or Mann-Whitney test as appropriate (SPSS for Windows, 9.0, SPSS Inc., Chicago, Illinois). In addition, Kaplan-Meier survival analysis was performed to ascertain differences in time to first arrhythmic event requiring device therapy (antitachycardia therapy or shock). For all comparisons, a p value 0.05 was required to reject the null hypothesis. One hundred seven patients received an ICD for either sustained monomorphic VT (101 patients) or polymorphic VT/VF induced with single or double ventricular extrastimuli (6 patients). Two patients died due to nonarrhythmic causes within the first 3 months of ICD implant and 3 patients were lost to follow-up. The mean age was 67 11 years and 86 patients (84%) were men. Seventy-three patients (72%) required triple ventricular extrastimuli for induction. From the Department of Medicine, Division of Cardiology, New York Hospital-Cornell University Medical Center, New York, New York. This work was supported in part by Grant RO1 HL-56139 from the National Institutes of Health, Bethesda, Maryland, and grants from the American Heart Association Grand-in-Aid, New York Affiliate, the Maurice and Corinne Greenberg Arrhythmia Research Grant, and the Raymond and Beverly Sackler Foundation, New York, New York. Dr. Lerman’s address is: Division of Cardiology, The New York HospitalCornell Medical Center, 525 East 68th Street, Starr 409, New York, New York 10021. E-mail: blerman@med.cornell.edu. Manuscript received August 13, 2001; revised manuscript received and accepted January 7, 2002.