EFFECT OF COUPLING INTERVAL AND PACING CYCLE LENGTH ON MORPHOLOGY OF PACED VENTRICULAR COMPLEXES IMPLICATIONS FOR PACE MAPPING

Background Ventricular pace mapping is performed by comparing the QRS morphology of ventricular paced complexes to that of a template arrhyt hmia, either a premature ventricular depolarization or a QRS complex d uring ventricular tachycardia. The objective of this study was to eval uate tile effect of coupling interval and pacing cycle length on QRS m orphology. Methods and Results The study population consisted of 20 pa tients (mean age, 38+/-16 years) undergoing a clinically indicated ele ctrophysiology procedure. In the first 10 patients, the effect of coup ling interval on the morphology of single paced ventricular complexes was evaluated visually and by signal processing techniques. Visually a pparent differences in QRS morphology occurred in a mean of 4/12 elect rocardiographic leads with a change in coupling interval of greater th an or equal to 100 ms. In the next 10 patients, the QRS complex morpho logy during ventricular overdrive pacing at cycle lengths of 600 and 3 00 ms was found to differ significantly in a mean of 4/12 Leads. The Q RS morphology during overdrive pacing differed significantly from that of a single paced complex whenever the pacing cycle length differed f rom the coupling interval of the single paced complex by >80 ms. Concl usions The morphology of single paced QRS complexes may vary, dependin g on coupling interval, and the QRS morphology during overdrive pacing is affected by the pacing cycle length. During ventricular pace mappi ng, the coupling interval or cycle length of the template arrhythmia s hould be matched during pacing. If not, rate-dependent changes in QRS morphology that are independent of the pacing site may confound the re sults of pace mapping.