Reproducibility of electrophysiological measurements in cardiac transplant recipients

The clinical usefulness of certain electrophysiological measurements, particularly those of sinus node function, is limited by variation in autonomic tone resulting in poor reproducibility. The denervated transplanted heart is not susceptible to direct autonomic control and, therefore, electrophysiological measurements may be more reproducible in this group. To our knowledge, this hypothesis has not previously been systematically evaluated. Ten adult recipients underwent serial electrophysiological studies between 10-18 days after cardiac transplantation. Five studies were performed at 2-hour intervals during a single day, between 9:00 a.m. and 5:00 p.m. Spontaneous cycle length (SCL) was recorded. Sinus node recovery time (SNRT), sinoatrial conduction time (SACT), and atrioventricular (AV) Wenckebach cycle length were measured using standard techniques. The effective refractory periods of the complete AV conducting system (AVERP), atrium (AERP), and ventricle (VERP) were measured. Corrected maximal SNRT was normal in all subjects. Mean coefficients of variation (Cv) for SCL, corrected maximal SNRT, and SACT were 2.8%, 7.4%, and 3.5%, respectively. AVERP was less than AERP in seven subjects, limiting further analysis. The mean Cv for AV Wenckebach cycle length was 2.1%. The mean coefficients of variation for AERP were 3.6% and 3.7%, and for VERP 3% and 3.3%, at 600- and 400-ms drive cycle lengths, respectively. Previous studies report much greater variation in innervated subjects particularly of indices of sinus node function. Thus, the reproducibility of electrophysiological measurements of sinus and AV node function in the transplanted heart is better than in normal subjects. This may have important implications for the reliability of electrophysiological testing in transplant recipients.