STEADY-STATE AND DYNAMIC BEHAVIOR OF VENTRICULAR REPOLARIZATION AND REFRACTORINESS IN THE DOG - THE EFFECT OF MULTIPLE CYCLE LENGTH CHANGESAND D-SOTALOL ADMINISTRATION

In anesthetized dogs with chronic, complete Air block we studied the c haracteristics of ventricular repolarization and refractoriness. There fore, we determined: (1) steady-state values of ventricular effective refractory period (VERP), action potential duration (APD), and stimulu s T interval (STI) before and after d-sotalol treatment at various pac ing cycle lengths (PCLs); and (2) the dynamics of VERP, APD, and STI b efore and after d-sotalol treatment after the abrupt PCL decreases. VE RP, APD, and STI showed a normal frequency dependency. All three param eters increased significantly after d-sotalol administration. During s teady-state and dynamic measurements, STI was always longer than APD a nd APD was always longer than VERP in an individual animal, irrespecti ve of PCL and conditions. Standard deviations of steady-state and dyna mic Values indicated a considerable interindividual variation. However , the dynamics of VERP, APD, and STI after an abrupt decrease in PCL w ere highly correlated (linear regression analysis: r(2) greater than o r equal to 0.93). The best mathematical model to describe these dynami cs was a bi-exponential model (r(2) greater than or equal to 0.98) wit h a very short first and a much longer second time constant. We found that there was a very consistent relation between VERP, APD, and STI; not only during steady-state but also in the dynamic situation after v arious abrupt PCL decreases. This relation does not change after the a dministration of d-sotalol. Therefore, STI could be used to predict st eady-state and dynamic values of VERP and APD. Since STI can be made a vailable online in implantable pacing systems this could lead to the d evelopment of new features in these devices.