REGIONAL EFFECTS OF MYOCARDIAL-ISCHEMIA ON EPICARDIALLY RECORDED CANINE FIRST HEART SOUNDS

To determine whether focal changes in myocardial material properties a re important in determining the response of first heart sound accelera tion amplitude and frequency to myocardial ischemia, cardiac vibration s were simultaneously recorded from ischemic and nonischemic regions o f canine epicardium by use of ultra-light acceleration transducers. Ca rdiac acceleration and hemodynamics were recorded before and 5 min, 15 min, 1 h, and 2 h after left circumflex coronary artery occlusion. Pe ak-to-peak amplitude declined transiently in the nonischemic zone duri ng early occlusion (P < 0.05) but was not decreased at any time in the ischemic myocardium. The median frequency of first heart sound vibrat ions in the ischemic region increased 31% within 5 min after occlusion (P < 0.01) and remained elevated for 2 h (P < 0.05). Nonischemic zone frequency was not statistically different from baseline at any time p oint. The disparate regional response of first heart sound vibrational frequency to myocardial ischemia suggests that propagating mechanical transients and myocardial contractile acceleration, rather than reson ant vibrations, produce the first heart sound.