Pump Dysfunction: Infarct Size, Location, and Mechanical Complications | AI Learning Guide

How sick a patient gets after a heart attack depends on two things: how much muscle died and where. Size sets the ceiling — lose forty percent of the left ventricle and the remaining muscle cannot maintain blood pressure, which is cardiogenic shock. Location changes the pattern. An inferior infarct often takes out the right ventricle, so the problem is preload, and the patient may respond to fluids. An anterior infarct reduces forward flow directly. Then there are mechanical complications: the wall or its supports give way. Papillary muscle rupture causes sudden mitral regurgitation, septal rupture creates a shunt, and free wall rupture causes tamponade. These cluster in the granulation phase, days three to fourteen, when the wall is weakest.

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Size and location both determine outcome

Infarct size sets the ceiling on pump function: the larger the necrotic mass, the lower the ejection fraction. Location determines which pump function is lost first. Inferior infarcts threaten right ventricular output and preload; anterior infarcts reduce left ventricular forward flow. The two dimensions together predict whether the patient develops heart failure, shock, or neither.

Mechanical complications and their signatures

Papillary muscle rupture: acute mitral regurgitation, new murmur, pulmonary edema; most common after inferior infarct.
Ventricular septal rupture: left-to-right shunt, harsh holosystolic murmur, right heart failure.
Free wall rupture: hemopericardium and tamponade, sudden collapse; highest risk in the granulation phase.

Timing of mechanical complications

These complications cluster in the granulation phase, roughly days 3–14, when necrotic tissue has been cleared but collagen has not yet matured. This is the same window identified in the previous chapter as the period of greatest mechanical vulnerability.