Mechanical alterations of the left ventricle during right atrial pacing

The effect of increasing heart rate by right atrial pacing on the peak value of the first derivative of left ventricular (LV) pressure(dp/dt) and the maximal velocity of the contractile element (KVmax) was studied in 12 cases. Peak dp/dt was poor as regards its sensitivity in reflecting the changes of contractility, due to its strong dependence on LV end-diastolic (EDP) and systolic pressure. KVmax increased constantly in the 4 normals and in 2 cases of ischaemic heart disease which did not develop angina; the increase exceeded 90 ml sec-1 in the former and one of the latter cases in which resting LV function was normal. In contrast, it decreased during the development of ischaemia in two of the three cases which developed angina; in the third case, in which also resting LV function was seriously impaired, the course of KVmax was almost flat. A similar flat course was observed in the three cases of congestive myocardiopathy. the above alterations of KV max were independent of the EDP and proportional to the basic contractility and its anticipated changes during pacing.