BACKGROUNDShen song Yang xin (SSYX) is a compound of Chinese medicine with the effect of increasing heart rate (HR). This study aimed to evaluate its electrophysiological properties at heart and cellular levels.

METHODSThe Chinese miniature swines were randomly assigned to two groups, administered with SSYX or placebo for 4 weeks (n = 8 per group). Cardiac electrophysiological study (EPS) was performed before and after drug administration. The guinea pig ventricular myocytes were enzymatically isolated and whole cell voltage-clamp technique was used to evaluate the effect of SSYX on cardiac action potential (AP).

RESULTSSSYX treatment accelerated the HR from (141.8 +/- 36.0) beats per minute to (163.0 +/- 38.0) beats per minute (P = 0.013) without changing the other parameters in surface electrocardiogram. After blockage of the autonomic nervous system with metoprolol and atropin, SSYX had no effect on intrinsic HR (IHR), but decreased corrected sinus node recovery time (CSNRT) and sinus atrium conducting time (SACT). Intra cardiac EPS showed that SSYX significantly decreased the A-H and A-V intervals as well as shortened the atrial (A), atrioventricular node (AVN) and ventricular (V) effective refractory period (ERP). In isolated guinea pig ventricular myocytes, the most obvious effect of SSYX on action potential was a shortening of the action potential duration (APD) without change in shape of action potential. The shortening rates of APD(30), APD(50) and APD(90) were 19.5%, 17.8% and 15.3%, respectively. The resting potential (Em) and the interval between the end of APD(30) and APD(90) did not significantly change.

CONCLUSIONSThe present study demonstrates that SSYX increases the HR and enhances the conducting capacity of the heart in the condition of the intact autonomic nervous system. SSYX homogenously decreases the ERP of the heart and shortens the APD of the myocytes, suggesting its antiarrhythmic effect without proarrhythmia.