New non-invasive approach to detect cardiac contractility using the first sound of phonocardiogram

During surgery, a non-invasive and easy-to-use method is required for evaluating left ventricular status. The systolic time interval, including pre-ejection period (PEP), of left ventricle has been known to be correlated with cardiac contractility. In this study, we focused on the non-invasive time interval from the Q wave of an electrocardiogram to the third component in the first heart sound (QS₁-3rd) and evaluated the correlation between PEP and peak differentiated left ventricular pressure (LV dp/dt).

Six adult anesthetized pigs were intubated. Mechanical ventilation was started. An electrocardiogram, carotid artery blood pressure, left ventricular pressure, and phonocardiogram on the fourth left intercostal space were monitored using a polygraph system. Cardiac output was measured by the thermodilution method. Data were simultaneously measured at baseline and after the infusion of noradrenaline, nitroprusside, esmolol sulfate, and dobutamine, respectively. Data were analyzed by Spearman's rank correlation coefficient using four-quadrant plot analysis.

A total of 270 points were simultaneously measured. The QS₁-3rd showed a significant correlation with PEP (QS₁-3rd = 7.62 + 0.92 PEP; ρ = 0.91, P < 0.0001). Concordance rate was 92% between PEP and QS₁-3rd (excluded zones were set within ± 5 ms). Both PEP and QS₁-3rd showed a good correlation with LV dp/dt (LV dp/dt = 3861.3-24.4 PEP; ρ = 0.85, P < 0.0001, LV dp/dt = 3763.6-23.5 QS₁-3rd; ρ = 0.82, P < 0.0001).

This non-invasive and easy-to-use hemodynamic parameter (QS₁-3rd) could be helpful for continuous monitoring of left cardiac contraction performance.