The selective bradycardic effects of zatebradine (UL-FS 49) do not adversely affect left ventricular function in conscious pigs with chronic coronary artery occlusion

Summary
This study was designed to test whether the selective bradycardic effects of zatebradine (UL-FS 49) were altered in the setting of chronic mild left ventricular dysfunction secondary to a myocardial infarction. We therefore administered four doses of UL-FS 49 at 15-min intervals (cumulative doses of 10, 30, 100, and 300 μg/kg) to eight normal conscious pigs and to seven pigs in which the left circumflex coronary artery was occluded 3 weeks previously. Left ventricular dysfunction in this second group of animals was manifested by an increase in left ventricular end-diastolic pressure (LVEDP 11±2 mmHg vs. 7±1 mmHg, respectively; p<0.05) and a decrease in LVdP/dtmax (3020±210 mmHg vs. 3720±210 mmHg, respectively; p<0.05). The results showed that UL-FS 49 was equally effective in reducing heart rate in both groups of animals [from 126±4 to 95±2 beats/min and from 140±5 to 98±6 beats/min for the normal animals and for the animals with a chronic myocardial infarction (MI), respectively]. The duration of left ventricular systole was not affected, but the duration of diastole was prolonged from 290±10 msec to 420±20 msec in the normal animals and from 250±10 msec to 430±30 msec in the animals with MI (both p<0.05). Up to 100 μg/kg UL-FS 49 did not affect arterial blood pressure, whereas LVdP/dtmax and cardiac output decreased by less than 10% in either group. With the highest dose there were decreases in cardiac output (20%) and LVdP/dtmax (15%) and a 5–6 mmHg increase in left ventricular end-diastolic pressure in both groups. The data suggest that UL-FS 49 in doses up to 100 μg/kg may also, in the setting of chronic mild left ventricular dysfunction, be an attractive agent when heart rate has to be reduced selectively.