Myocardial ischemia leads to depressed ventricular contractility or systolic dysfunction. Cardiac output and blood pressure are depressed, while ventricular filling pressures frequently rise. As well as impairing systolic function, myocardial ischemia depresses ventricular compliance (i.e. diastolic dysfunction). This limits ventricular filling, thereby preventing full use of the heart's Starling mechanism to support cardiac output and function. Coronary perfusion may also be affected. Paradoxically, circulatory compensation, particularly elevated systemic resistance and tachycardia, may elevate heart work and myocardial O 2 needs at the very time that supply is threatened. Tachycardia may also impair diastolic coronary perfusion. Therefore autoregulatory compensation of cardiogenic hypotension may worsen myocardial O2 balance, exacerbating myocardial ischemia.
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