[Echo-Doppler evaluation of hemodynamic response during exercise in patients with rate-responsive...

The aim of this study was the 2D-echocardiographic and Doppler evaluation of the hemodynamic behaviour under stress in a group of 7 patients bearing Biotec BioRate RDP 3 and MB1 rate-responsive respiration-dependent pacemakers, programmed with the same heart rate/respiratory frequency correlation curve. The following parameters were monitored in basal conditions and during each level of the stress test at the horizontal cycloergometer: cardiac output (CO), cardiac index (CI), stroke volume (SV) and pacing rate (HR). All the 7 patients presented a progressive increase in CO and CI, but with a marked range of SV and HR increase. Two types of hemodynamic response under stress were consequently found: the first was characterized by a conspicuous increase in SV during the initial and middle levels of the stress, concomitant with scarce HR increase. The second, instead, was characterized by scarce or no SV increase during the same levels, concomitant with marked HR increase. At the highest stress levels, the CO increase was, in both types, almost exclusively due to HR increase. By analyzing the clinical features and the basal echocardiographic aspects of the patients studied, the first type was found to represent normal contractility features, while the second type was characterized by compromised contractility with reduced ejection fraction. It was thus demonstrated that there are 2 ways of increasing the CO under stress: by means of predominant increase of either the SV or the HR. This hemodynamic behaviour, very similar to the spontaneous behaviour of the heart, occurred in a group of constantly paced patients, thanks to the highly physiological guide parameter of their pacemakers: respiratory activity, which is bound to O2 consumption by a linear relationship.