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 functio n is sinus node recovery time (SNRT), which requires right heart cathe terization. On the other hand SNRT has high specificity but only moder ate sensitivity in the diagnosis of sick sinus syndrome (SSS). The aut hors 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 co rrected sinus node recovery time (SNRTc) and sinus cycle length (SCL) before and after dipyridamole administration. SCL was slightly decreas ed from a mean basal value of 1025 +/- 323 to 913 +/- 213 msec after d ipyridamole administration (mean -10%), but this was not statistically significant. SNRTc was increased from a mean basal value of 344 +/- 9 1 to 606 +/- 156 msec after dipyridamole administration (+ 76% P less than or equal to 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 pat ients with suspected SSS and normal SNRT.