# Mechanical Complications of Myocardial Infarction

## Overview

Mechanical complications of acute myocardial infarction are catastrophic events that carry high mortality without surgical intervention. Although their incidence has decreased dramatically in the era of primary PCI, they remain surgical emergencies that every cardiothoracic surgeon must be prepared to manage. The major mechanical complications include post-infarction ventricular septal defect (VSD), papillary muscle rupture, free wall rupture, and left ventricular aneurysm.

## Post-Infarction Ventricular Septal Defect

### Pathophysiology

Post-infarction VSD occurs in approximately 0.2% of acute MI cases (down from 1-2% before reperfusion therapy) and typically develops 3 to 5 days after the infarction, though it can occur anywhere from 24 hours to 2 weeks. The location of the MI determines the type of VSD. Anterior MI (LAD territory) produces an apical VSD with a simple, direct perforation. Inferior MI (RCA/PDA territory) produces a basal or posterior VSD that is often serpiginous and complex, with involvement of the right ventricle. The necrotic septal tissue provides no structural support, making repair technically challenging.

### Clinical Presentation and Diagnosis

Patients present with sudden hemodynamic deterioration and a new harsh holosystolic murmur. Cardiogenic shock with pulmonary edema develops rapidly. A Swan-Ganz catheter reveals a step-up in oxygen saturation from the right atrium to the right ventricle and pulmonary artery. The left-to-right shunt causes RV volume overload and biventricular failure. Echocardiography (TTE or TEE) demonstrates the septal defect, quantifies the shunt (Qp:Qs), and assesses ventricular function. PA catheter findings help differentiate VSD from acute MR due to papillary muscle rupture.

### Surgical Management

Urgent or emergent surgery is required despite high operative mortality (20-50%). Delay allows further tissue necrosis and expansion of the defect. Medical stabilization with IABP, vasodilators, and inotropes is a temporizing measure, not definitive therapy. ECMO can serve as a bridge to surgery in select cases.

The surgical approach is via left ventriculotomy through the infarcted zone. The infarct exclusion technique (David) places a patch on the LV side of the septum, excluding the entire infarcted zone. Sutures are buttressed with Teflon felt strips to avoid tearing through friable necrotic tissue. A prosthetic patch (bovine pericardium or Dacron) is secured to viable myocardium. Concomitant CABG is performed if indicated. Operative mortality ranges from 20 to 50%, with worse outcomes for posterior/inferior VSDs due to more complex anatomy and RV involvement. Percutaneous closure devices have a limited role as a bridge to surgery or in selected late presentations with well-defined defects.

| Feature | VSD | Papillary Muscle Rupture |
|---------|-----|--------------------------|
| Murmur | Holosystolic, thrill at LSB | Holosystolic, radiates to axilla |
| PA catheter | O2 step-up RA to PA | Large V waves |
| Echo | Septal defect with L-to-R shunt | Flail mitral leaflet, severe MR |
| Typical MI location | Anterior (apical VSD), inferior (basal VSD) | Inferior (posteromedial PM) |

<image>Anatomic illustration comparing anterior and inferior post-infarction ventricular septal defects. Left panel shows an apical VSD resulting from LAD territory infarction with a simple, direct perforation through the distal septum. Right panel shows a basal/posterior VSD from RCA territory infarction with a serpiginous, complex path through the basal septum involving the right ventricle. Each panel labels the coronary artery territory involved, the infarcted myocardium (shaded), and the direction of the left-to-right shunt with flow arrows.</image>

## Papillary Muscle Rupture

### Pathophysiology

Posteromedial papillary muscle rupture is far more common than anterolateral because the posteromedial muscle has a single blood supply (from the PDA, usually from the RCA or LCx), while the anterolateral muscle has dual supply (from both the LAD and LCx). Rupture results in acute, severe mitral regurgitation from a flail leaflet. It typically occurs 2 to 7 days post-MI and can involve complete rupture of the papillary muscle head or partial rupture of one or more heads.

### Clinical Presentation and Diagnosis

Patients develop sudden severe pulmonary edema and cardiogenic shock. A new holosystolic murmur may be present but can be surprisingly soft due to equalization of LA and LV pressures. Flash pulmonary edema on chest X-ray and rapid hemodynamic collapse are typical. TEE reveals a flail mitral leaflet, a severe eccentric MR jet, and often a visible ruptured papillary muscle head attached to chordae. The PA catheter shows giant V waves in the PCWP tracing (V waves above 60-70 mmHg). Mortality without surgery approaches 75% at 24 hours.

### Surgical Management

Emergency mitral valve replacement is the standard treatment. Repair is generally not feasible because the papillary muscle tissue is necrotic. A bioprosthetic valve is preferred to avoid long-term anticoagulation in post-MI patients. The posterior leaflet and subvalvular apparatus should be preserved when possible. Concomitant CABG for the culprit artery and any other significant disease is performed. IABP or Impella serves as a temporizing measure, and VA-ECMO may be needed for refractory shock. Operative mortality is 20-30%, lower than for post-infarction VSD.

## Left Ventricular Free Wall Rupture

### Pathophysiology

Free wall rupture is the most lethal mechanical complication, usually fatal within minutes. It accounts for approximately 10% of in-hospital deaths from acute MI. Risk factors include first MI, anterior MI, female sex, advanced age, and delayed or absent reperfusion. It occurs 1 to 14 days post-MI, with a peak at 3 to 5 days.

### Classification

Acute ("blowout") rupture produces sudden hemopericardium, tamponade, pulseless electrical activity arrest, and death. Subacute rupture is contained by pericardial adhesions or thrombus, forming a pseudoaneurysm. Patients with subacute rupture present with recurrent chest pain, hemodynamic instability, or signs of tamponade, and diagnosis is made by echocardiography or CT showing pericardial effusion and myocardial discontinuity.

### Management

Acute rupture requires emergent surgery if recognized in time (which is rare). Pericardiocentesis temporizes while the patient is brought to the operating room. Repair options include a patch repair with Teflon felt and biologic glue over the rupture site (sutureless technique on necrotic tissue) or direct suture repair buttressed with felt strips. Subacute rupture and pseudoaneurysm warrant semi-urgent surgical repair via left ventriculotomy, debridement of necrotic tissue, and patch closure with pledgeted sutures to viable myocardium, with concomitant CABG as needed.

## Left Ventricular Aneurysm

### Pathophysiology

A true ventricular aneurysm consists of full-thickness scar replacing infarcted myocardium, with paradoxical systolic expansion (dyskinesis). It usually involves the anterior wall and apex (LAD territory) and develops weeks to months after transmural MI. The wall is composed of fibrous scar, and mural thrombus is present in 50% of cases.

### Clinical Consequences

The paradoxical expansion wastes stroke volume, contributing to heart failure. The scar serves as a substrate for re-entrant ventricular arrhythmias. Mural thrombus within the aneurysm creates a risk of thromboembolism. Wall stress is increased, worsening coronary disease symptoms.

### Differentiation: True Aneurysm vs. Pseudoaneurysm

| Feature | True Aneurysm | Pseudoaneurysm |
|---------|---------------|-----------------|
| Wall composition | Fibrous scar (full thickness) | Pericardium and thrombus (no myocardium) |
| Neck | Wide | Narrow |
| Rupture risk | Low | High (requires urgent repair) |
| Location | Anterior/apical | Posterior/inferior (often) |
| Communication with LV | Broad-based | Narrow orifice |

### Surgical Management

Surgery is indicated for symptomatic heart failure, refractory arrhythmias, thromboembolism, or when combined with CABG. The Dor procedure (endoventricular circular patch plasty) involves opening the aneurysm through a left ventriculotomy, placing a circumferential purse-string suture (Fontan stitch) at the junction of viable and scarred myocardium, then suturing an endoventricular patch to exclude the scar and restore LV geometry. This reduces LV volume, eliminates the dyskinetic segment, and improves LVEF and functional status. Linear repair (resecting the aneurysm and closing with buttressed sutures) is an older technique with less geometric restoration. Concomitant procedures may include CABG, mitral valve repair, and cryoablation of arrhythmogenic substrate. The STICH trial found that adding surgical ventricular reconstruction to CABG did not improve outcomes in the overall population, though this remains controversial and may reflect patient selection issues.

<image>Surgical illustration of the Dor procedure (endoventricular circular patch plasty) for left ventricular aneurysm repair. Sequential panels show: (A) the opened LV aneurysm through a left ventriculotomy with visible thinned scar and mural thrombus being evacuated, (B) a circumferential purse-string suture (Fontan stitch) placed at the junction of viable and scarred myocardium to define the new LV cavity, (C) an endoventricular patch being sutured to the Fontan stitch to exclude the scarred region, and (D) the final closure of the ventriculotomy over the patch with buttressed sutures restoring a more elliptical LV geometry.</image>

## Timing of Surgery: The Central Dilemma

### Early Surgery

Early surgery is required for hemodynamically unstable patients (VSD, papillary muscle rupture, free wall rupture). Tissue quality is poor in the acute phase, with sutures tearing through necrotic myocardium, resulting in higher operative mortality. However, there is no viable alternative for unstable patients.

### Delayed Surgery

When delay is feasible, tissue quality improves at 3 to 4 weeks as fibrosis and scarring provide holding strength for sutures, and operative mortality drops. This is only possible in hemodynamically stable patients with adequate mechanical circulatory support. ECMO or Impella can serve as a bridge to allow tissue maturation in select cases.

## Clinical Pearls

Mechanical complications of MI are rare but uniformly lethal without surgery — every CT surgeon must be able to recognize and manage them emergently. The posteromedial papillary muscle ruptures far more often than the anterolateral because of its single blood supply, a high-yield anatomy fact. Post-infarction VSD should be repaired with the infarct exclusion (David) technique rather than simple patch closure through necrotic tissue. A "quiet" murmur in a patient with acute MI and cardiogenic shock does not rule out papillary muscle rupture — pressure equalization between the LV and LA can render the murmur barely audible. Pseudoaneurysms have a narrow neck and high rupture risk and require urgent surgery regardless of symptoms. The STICH trial showed no benefit to adding SVR to CABG in the overall population, but careful patient selection (large akinetic/dyskinetic segments, LVESVI above 60 mL/m2) may still identify those who benefit. ECMO as a bridge to surgery is increasingly used for post-infarction VSD and papillary muscle rupture, allowing partial tissue maturation and hemodynamic stabilization.

## References

- **David TE, Dale L, Sun Z.** Postinfarction ventricular septal rupture: repair by endocardial patch with infarct exclusion. *J Thorac Cardiovasc Surg.* 1995;110(5):1315-1322.
- **Arnaoutakis GJ, Zhao Y, George TJ, et al.** Surgical repair of ventricular septal defect after myocardial infarction: outcomes from the Society of Thoracic Surgeons National Database. *Ann Thorac Surg.* 2012;94(2):436-444.
- **Jones BM, Kapadia SR, Smedira NG, et al.** Ventricular septal rupture complicating acute myocardial infarction: a contemporary review. *Eur Heart J.* 2014;35(31):2060-2068.
- **Dor V, Sabatier M, Montiglio F, et al.** Endoventricular patch plasty for LV aneurysm: results of a prospective series. *J Thorac Cardiovasc Surg.* 1999;118(4):643-650.
- **Velazquez EJ, Lee KL, O'Brien SM, et al.** STICH Hypothesis 2: CABG with or without surgical ventricular reconstruction. *N Engl J Med.* 2009;360(17):1705-1717.