Electrical impedance cardiogram in derivation of systolic time intervals.

Abstract

The reliability and use of the differentiated electrical impedance cardiogram (dZ/dt) in calculating systolic time intervals were assessed in 185 subjects under varying conditions. In the first phase, simultaneous recording of carotid pulse, dZ/dt, electrocardiogram and phonocardiogram (PCG) was obtained in 50 normal volunteers under controlled conditions. In the second phase dZ/dt, electro- cardiogram and phonocardiogram were obtained initially, and carotid pulses, electrocardiograms, and phonocardiograms were recorded immediately afterwards. Serial recordings were obtained in 35 subjects at sea-level, and at 3658 m altitude after 1, 2, 3, 4, 5, and 10 days of induction. The subjects returned to sea-level and daily studies were carried out days 2 and 3. It was found that the impedance ventricular ejection time (LVET.) and the ventricular ejection time derived from the carotid pulse (LVETc) were within 10 ms of each other in all recordings and a close correlation was obtained between the two (R = 0.976). The impedance pre-ejection period (PEPZ) obtained by direct measurement (from the onset of the Q wave of the electrocardiogram to the onset of dZ/dt wave form) also had an excellent correlation with carotid pre-ejection period (PEP,) obtained by the formula QS2 -LVETc (R = 0.91), where QS2 represents electromechanical systole.