Acute electrophysiological effects of dipyridamole on sinus node function in patients with sick sinus syndrome.

One of the most widely used tests for evaluation of sinus node function is sinus node recovery time (SNRT), which requires right heart catheterization. On the other hand SNRT has high specificity but only moderate sensitivity in the diagnosis of sick sinus syndrome (SSS). The authors studied acute electrophysiologic effects of dipyridamole (0.40 mg/kg IV) in 16 patients with clinical SSS. All of them had normal SNRT and had undergone permanent DDD pacemaker implantation. By the aid of temporary pacing inhibition, the authors noninvasively measured the corrected sinus node recovery time (SNRTc) and sinus cycle length (SCL) before and after dipyridamole administration. SCL was slightly decreased from a mean basal value of 1025 +/-323 to 913+/-213 msec after dipyridamole administration (mean -10%), but this was not statistically significant. SNRTc was increased from a mean basal value of 344+/-91 to 606+/-156 msec after dipyridamole administration (+76% P< or =0.004). These results suggest that dipyridamole must be used cautiously in patients with SSS. Intravenous dipyridamole may be a useful test to assess sinus node function. SNRT measurement after intravenous dipyridamole may increase sensitivity of this test in patients with suspected SSS and normal SNRT.