Haemodynamic alterations of the left ventricle during right atrial pacing

The left ventricular haemodynamic alterations during right atrial pacing were studied in 12 cases. Cardiac index varied little: during maximal rate however, its mean value was slightly lower than the resting one. Stroke index decreased inversely to the heart rate. The course of these indices did not separate the normal from abnormal cases. Ventricular function curves (VFCs) were constructed by relating the changes of left ventricular (LV) end-diastolic pressure (EDP) to those of stroke index (SI). In 4 normal cases the curves were steep, showing a fall of EDP with relatively large decrease of SI; in 3 cases of congestive myocardiopathy they were flat, showing fall of EDP in two and increase in one, with relatively small decrease of SI; in 5 patients with effort angina LVEDP initially decreased. This initial fall of VFCs was steep in two with normal and flattened in three with impaired resting LV function. Increase of EDP, evidently due to development of ischaemia, followed in all; it exceeded resting EDP in two out of three cases developing angina and in one out of two not developing angina. Our findings support the view that the increase of LVEDP is due to decrease of both myocardial contractility and compliance.