EFFECTS OF VENTRICULAR PACING-INDUCED TACHYCARDIA ON AORTIC MECHANICSIN MAN

Objective: Effects of pacing-induced tachycardia on left ventricular f unction have been studied extensively. However, little attention has b een focused on aortic elastic properties during heart rate increments. The aim was to determine the effects of right ventricular pacing on t he aortic elastic properties. Methods: We studied 14 normal subjects ( baseline blood pressure, 129/84+/-10/6 mmHg; aortic diameter, 23.5/21. 3+/-2.4/1.9 mm) at rest, during rapid right ventricular pacing (at fiv e stepwise heart rate increases of 20 bpm every 2 min) and after 5 min recovery. Shifts as well as changes in the slope and the stiffness co nstant of the pressure diameter (p-d) relation, derived from simultane ous tip-micromanometer aortic pressure recordings and high-fidelity ul trasonic intravascular aortic diameter recordings, were used as indice s of aortic stiffness. Wave reflection was also studied. Results: Aort ic pulse pressure and strain significantly decreased after pacing-indu ced tachycardia (p<0.0001 and <0.05, respectively). During pacing, the slope of the linear p-d relation as well as the stiffness constant we re decreased, followed by increases at recovery (p<0.0001). The augmen tation index and the aortoventricular coupling ratio were significantl y decreased (p<0.0001). Conclusions: Pacing-induced increases in pulse frequency may result in improved aortic distensibility and aortoventr icular coupling. (C) 1998 Elsevier Science B.V. All rights reserved.