162. What alteration in the heart sounds is heard in a patient having an acute coronary syndrome? What is the physiologic mechanism?

An acute coronary syndrome causes an S4 heart sound.

Remember the LV relaxation is an active process which requires ATP (adenosine triphosphate). If ischemia is present, the synthesis of ATP is limited and the LV is not able to relax well. This results in a S4 heart sound.

The fourth heart sound (S4), also known as the "atrial gallop", occurs just before S1 when the atria contract to force blood into the LV.  If the LV is non-compliant and atrial contraction forces blood through the atrioventricular valves (mitral/tricuspid), a S4 is produced by the blood striking the LV. 

S4