[Left ventricular performance during exercise in patients with constant heart rate].

In order to evaluate the response of left ventricular (LV) performance in pacemaker implanted patients (PMI pts) with constant heart rate during exercise, supine bicycle ergometer exercise was performed simultaneously in 21 PMI pts and 4 age-matched normal subjects. PMI pts were classified into two groups; Group I consisted of 16 pts with relatively good physical work capacity (maximal load: male; 80 watt or more, female; 60 watt or more), and Group II consisted of 14 pts with depressed physical work capacity (maximal load: male; 60 watt or less, female; 40 watt or less). During dynamic exercise LV end-diastolic dimension (EDD), stroke excursion (SE), percent fractional shortening (%FS) and posterior wall velocity (PWV) showed a significant increase and LV end-systolic dimension (ESD) showed a significant decrease in Group I in contrast with Group II and normal subjects. Systolic blood pressure (sBP) and sBP/ESD ratio significantly increased in Group I and normal subjects than in Group II. Furthermore, resting cardiac parameters were more impaired in Group II than Group I. Thus, it was suggested that Group I adapted to exercise according to Frank-Starling mechanism (increased EDD) and contractility due to probably increasing circulatory catecholamine (increased PWV and decreased ESD). On the other hand, Group II did not adapt sufficiently to exercise because of the limitation of preload-reserve and contractility-reserve on exercise and also at rest.