Moderate Hypothermia Attenuates Pro-Arrhythmic Electromechanical Relations in the Left Ventricle – A Clinical Study

BackgroundTargeted temperature management is recommended after cardiac arrest, but the beneficial effects are controversial. The recently published TTM2 study reports that arrhythmias causing hemodynamic compromise are more common during moderate hypothermia. The causation is not explored. Experimentally, moderate hypothermia attenuates electromechanical relations with pro-arrhythmic impact. Mechanical systole outlasts the electrical systole to a greater extent giving increased electromechanical window positivity, and dispersion of electrical and mechanical activity are unaltered. In this prospective clinical study, we explored the effect of moderate hypothermia on electromechanical relations in un-insulted left ventricles. We hypothesized that during moderate hypothermia, prolongation of systolic duration would exceed electrical duration without dispersed electrical- or mechanical activity. Methods20 patients with normal left ventricular function, undergoing surgery on the ascending aorta and connected to cardiopulmonary bypass, were included. Measurements were obtained at 36 °C and 32 °C prior to aortic-repair, and at 36 °C after repair at spontaneous and paced heart rate 90 bpm. Comparable loading conditions were ensured and cardiopulmonary bypass was reduced to 20% of estimated maximum during the measurements. Global cardiac function was measured invasively and with echocardiography. Electromechanical window, dispersion of repolarization by ECG and mechanical dispersion by echocardiography, were calculated. ResultsAt moderate hypothermia (32°C), mechanical systolic prolongation exceeded electrical prolongation so that electromechanical window increased (29 ± 30 to 86 ± 50 ms, p <0.001). Dispersion of repolarization and mechanical dispersion remained unchanged. Myocardial function was preserved with maintained strain, fractional shortening and stroke volume. Similar electromechanical relations were present also at comparable increased heart rate during moderate hypothermia. After rewarming to 36°C, electromechanical alterations were reversed. ConclusionModerate hypothermia increased electromechanical window positivity. Dispersion of repolarisation, mechanical dispersion, and myocardial function were unchanged. Moderate hypothermia did not induce adverse electromechanical changes in the left ventricle during standardized conditions, but rather an attenuation of pro-arrhythmic electromechanical relations.