Characterization of cardiac time intervals in healthy bonnet macaques (Macaca radiata) by using an electronic stethoscope

Abstract

Nonhuman primates are used frequently in cardiovascular research. Cardiac time intervals derived by phonocardiography have long been used to assess left ventricular function. Electronic stethoscopes are simple low-cost systems that display heart sound signals. We assessed the use of an electronic stethoscope to measure cardiac time intervals in 48 healthy bonnet macaques (age, 8±5 y) based on recorded heart sounds. Technically adequate recordings were obtained from all animals and required 1.5±1.3 min. The following cardiac time intervals were determined by simultaneously recording acoustic and single-lead electrocardiographic data: electromechanical activation time (QS1), electromechanical systole (QS2), the time interval between the first and second heart sounds (S1S2), and the time interval between the second and first sounds (S2S1). QS2 was correlated with heart rate, mean arterial pressure, diastolic blood pressure, and left ventricular ejection time determined by using echocardiography. S1S2 correlated with heart rate, mean arterial pressure, diastolic blood pressure, left ventricular ejection time, and age. S2S1 correlated with heart rate, mean arterial pressure, diastolic blood pressure, systolic blood pressure, and left ventricular ejection time. QS1 did not correlate with any anthropometric or echocardiographic parameter. The relation S1S2/S2S1 correlated with systolic blood pressure. On multivariate analyses, heart rate was the only independent predictor of QS2, S1S2, and S2S1. In conclusion, determination of cardiac time intervals is feasible and reproducible by using an electrical stethoscope in nonhuman primates. Heart rate is a major determinant of QS2, S1S2, and S2S1 but not QS1; regression equations for reference values for cardiac time intervals in bonnet macaques are provided.

Figure 1.

Simultaneous recording of electrocardiogram (EKG) and heart sounds used in assessing cardiac time intervals. Q, start of QRS complex; QS1, electromechanical activation time; QS2, electromechanical systole; S1, first heart sound; S2, second heart sound; S1S2, interval between the first and second heart sounds; S2S1, interval between second and first heart sounds.

Figure 2.

Association between various cardiac time intervals and heart rate among the 48 bonnet macaques. All 4 intervals were obtained from all monkeys. QS1, electromechanical activation time; QS2, electromechanical systole; S1, first heart sound; S2, second heart sound; S1S2, interval between the first and second heart sounds; S2S1, interval between second and first heart sounds.