ALTERATIONS OF 1ST DERIVATIVE OF APEXCARDIOGRAM INDEXES DURING INDUCED CHANGES OF HEART-RATE

The aim of this study is to investigate the effects of HR changes, ind uced by a variety of causes, on left ventricular performance as assess ed by the first derivative of apexcardiogram indices. Ten males, mean age 29.6 +/- 8.1 years, without evidence of heart disease, were studie d. In all subjects tachycardia was induced by 1) administration of atr opine (1 mg bolus IV), 2) administration of isoprenaline (0.5-0.25 mug /min IV) and 3) treadmill exercise test according to Bruce protocol. T he blood pressure (BP) was determined before and every 60 sec during e ach test. Drawings of the first derivative of apexcardiogram were obta ined before and at the peak of HR and the indices a/b, ef/ZN and b/ef were determined. Results: the increase of HR was similar (about 30 % f rom baseline) in each test. Exercise test caused more pronounced incre ase of BP compared to the administration of isoprenaline while adminis tration of atropine was not followed by significant changes of BP. Adm inistration of isoprenaline caused similar but more vigorous alteratio ns of the first derivative of apexcardiogram indices (significant incr ease of b/ef and decrease of a/b and ef/ZN indices) compared with the exercise test. Administration Of atropine caused no significant change s of these indices. Conclusions: in this study it was found that the e ffects of various causes of tachycardia on LV performance, as assessed by the indices studied, are not uniform; this may reflect different m echanisms involved in the induction of tachycardia by different causes . These results suggest that the alterations of the indices assessed i n this study can detect dysfunction(s) of the LV; it is also possible that the type of alteration induced, could provide information regardi ng causal relationships of this impairment.