Mechanical complications of myocardial infarction

Definition

Mechanical complications of myocardial infarction are structural defects of the heart resulting from myocardial necrosis. The classic forms are ventricular septal rupture (post-infarction VSD), papillary muscle rupture with acute mitral regurgitation and rupture of the ventricular free wall. In a broader sense, ventricular aneurysm and pseudoaneurysm (contained rupture) are also included.

This is to be distinguished from functional, ischemic papillary muscle dysfunction, which is usually transient.

Occurrence & epidemiology

Rupture of the ventricular septum or free wall occurs in about 1 % of acute myocardial infarctions, septal rupture alone in about 0.3 %. Women have higher overall rates of mechanical complications; septal rupture is also more common in older people and after delayed reopening of the vessel. Free wall rupture is considered an important cause of out-of-hospital sudden cardiac death; its exact frequency is unknown.

Aetiopathogenesis

In the first days after infarction the necrotic tissue is broken down by macrophages before a stable scar forms; the wall is particularly soft in this phase. Large transmural infarctions are particularly at risk.

• Papillary muscle rupture: most often after inferoposterior infarction due to occlusion of the right coronary or circumflex artery; it affects the posteromedial papillary muscle, which has a single blood supply (the anterolateral one has a dual supply)
• Ventricular aneurysm: localized bulge of the wall, usually anterior or apical, especially after a large transmural anterior infarction; it may develop over days, weeks or months
• Pseudoaneurysm: incomplete rupture of the free wall (often inferior or lateral) contained by the pericardium

Clinical features

• Ventricular septal rupture: sudden loud systolic murmur with a thrill at the left sternal border in the third or fourth intercostal space, accompanied by hypotension with or without signs of left ventricular failure
• Papillary muscle rupture: acute severe mitral regurgitation with a sudden loud apical holosystolic murmur and thrill, usually with pulmonary edema; occasionally the severe regurgitation is silent on auscultation
• Free wall rupture: sudden loss of arterial pressure with momentary persistence of sinus rhythm (pulseless electrical activity), often with signs of cardiac tamponade
• Ventricular aneurysm: rarely ruptures but causes recurrent ventricular arrhythmias, low cardiac output and mural thrombi with systemic embolism
• Pseudoaneurysm: may become large and contribute to heart failure

Diagnosis

• Any abrupt hemodynamic deterioration and any new systolic murmur after an infarction raise suspicion of a mechanical complication.
• Echocardiography: key method to demonstrate a septal defect with shunt flow, a ruptured papillary muscle with severe mitral regurgitation, pericardial effusion and a wall defect
• Right heart catheterization: in septal rupture, a significant increase in oxygen content in the right ventricle compared with the right atrium (left-to-right shunt at ventricular level)
• Ventricular aneurysm: paradoxical precordial movements, persistent ST elevation on ECG and a characteristic bulge of the cardiac silhouette on chest radiograph; confirmation by echocardiography

Keep learning in the app

Further reading (open access)

1. MSD Manual Professional: Complications of Acute Coronary Syndromes
2. StatPearls: Postinfarction Ventricular Septal Rupture
3. StatPearls: Papillary Muscle Rupture

Cross-references