[Comparison of systolic intervals, cardiac index and systolic index. Changes in frequency induced by a pacemaker]. / Comparación entre intervalos sistólicos, índice cardíaco e índice sistólico. Alteraciones con cambios de frecuencia inducidos por marcapaso.

We have compared the systolic time intervals, cardiac index and stroke index in 15 patients with complete atrio-ventricular block and ventricular rate of less than 50 beats per minute. In all of them we placed a Swan-Ganz thermodilution catheter into the pulmonary trunk and transvenous temporary pacing in right ventricular cavity. In each patient we have simultaneously measured the systolic time intervals and cardiac output with different pacing rates, ranging between 50 and 120 beats per minute. With increasing heart rates we observed the following: PEP did not suffer significative changes; LVET and QS2 always decreased, and the ratio PEP/LVET increased in a constant manner. We could not find any statistical correlation between cardiac index and PEP/LVET; but the individual correlation between stroke index and PEP/LVET was very significant in each patient (r > -0.900). This proves that PLEP/LVET suffer modifications when changes in heat rate occur due to the LVET which reflects the changes of stroke index. This fact must be kept in mind when drugs which change heart rate without inotropic action are used.