Prevalence

VSD formerly occurred in 1% to 2% of patients after acute MI in the prethrombolytic era (Figs. 1 and 2). The incidence has dramatically decreased with reperfusion therapy.² The GUSTO-I (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) trial has demonstrated an incidence of VSD of approximately 0.2%.^3,4

Figure 1 Ventricular septal defect occurred in 1% to 2% of patients after acute myocardial infarction in the prethrombolytic era.

Figure 2 Ventricular septal defect can be seen on this left ventriculogram (left anterior oblique projection).

VSD can develop as early as 24 hours after MI but was commonly seen 3 to 7 days after MI in the prefibrinolytic era and 2 to 5 days currently. Fibrinolytic therapy is not associated with an increased risk of VSD.^2,5

Pathophysiology

The defect usually occurs at the junction of preserved and infarcted myocardium in the apical septum with anterior MI and in the basal posterior septum with inferior MI. VSD almost always occurs in the setting of a transmural MI and is more often seen in anterolateral MIs. The defect might not always be a single large defect; it can be a meshwork of serpiginous channels that can be identified in 30% to 40% of patients.

Signs and Symptoms

Early in the disease process, patients with VSD may appear relatively comfortable, with no clinically significant cardiopulmonary symptoms. Rapid recurrence of angina, hypotension, shock, or pulmonary edema can develop later in the course.

Diagnosis

Rupture of the ventricular septum is often accompanied by a new harsh holosystolic murmur best heard at the left lower sternal border. The murmur is accompanied by a thrill in 50% of cases. This sign is generally accompanied by a worsening hemodynamic profile and biventricular failure. Therefore, it is important that all patients with MI have a well-documented cardiac examination at presentation and daily thereafter.

An electrocardiogram (ECG) may show atrioventricular (AV) nodal or infranodal conduction delay abnormalities in approximately 40% of patients. Echocardiography with color flow imaging is the best method for diagnosing VSD. There are two types of VSD, which can best be visualized in different echocardiographic planes. A posterobasal VSD is best visualized in the parasternal long axis with medial angulation, apical long axis, and subcostal long axis. An apical-septal VSD is best visualized in the apical four-chamber view. Echocardiography can define LV and RV function—important determinants of mortality—as well as the size of the defect and degree of left-to-right shunt by assessing flow through the pulmonary and aortic valves. In some cases, it may be necessary to use transesophageal echocardiography to assess the VSD.

VSD can also be diagnosed by demonstrating an increase in oxygen saturation in the right ventricle and pulmonary artery (PA) on PA catheterization. The location of the increase is significant, because there have been case reports of peripheral PA increases due to acute MR. Diagnosis involves fluoroscopically guided measurement of oxygen saturation in the superior and inferior vena cava, right atrium, right ventricle, and pulmonary artery. An increase in oxygen saturation of more than 8% occurs between the right atrium and right ventricle and pulmonary artery, with a left-to-right shunt across the ventricular septum. A shunt fraction can be calculated as follows:

Treatment

Early surgical closure is the treatment of choice, even if the patient’s condition is stable. Initial reports have suggested that delaying surgery is likely to result in improved surgical mortality.⁶ These benefits were probably the result of selection bias,⁷ because the mortality rate in patients with VSD treated medically is 24% at 72 hours and 75% at 3 weeks. Therefore, patients should be considered for urgent surgical repair.

A high surgical mortality is associated with cardiogenic shock and multisystem failure. This further supports earlier operation before complications develop.⁸ Mortality is highest in patients with basal septal rupture associated with inferior MI (70%, compared with 30% in patients with anterior infarcts). The mortality rate is higher because of increased technical difficulty and the frequent need for mitral valve repair or replacement in the patients with mitral regurgitation.⁹ Regardless of the location and patient’s hemodynamic condition, surgery should always be considered, because it is associated with a lower mortality rate than conservative management.¹⁰

Intensive medical management should be started to support the patient before surgery. Unless there is significant aortic regurgitation, an IABP should be inserted urgently as a bridge to a surgical procedure. The IABP will decrease the systemic vascular resistance (SVR) and shunt fraction while increasing coronary perfusion and maintaining blood pressure. After the IABP is inserted, vasodilators can be used, with close hemodynamic monitoring. Vasodilators can also reduce left-to-right shunting and increase systemic flow by reducing SVR. Caution should be exercised to avoid a greater decrease in pulmonary vascular resistance than in SVR and a consequent increase in shunting. The vasodilator of choice is intravenous nitroprusside, which is started at 0.5 to 1.0 µg/kg/min and titrated to a mean arterial pressure (MAP) of 60 to 75 mm Hg.

Prevalence

Mitral regurgitation (MR) after acute MI predicts poor prognosis, as demonstrated in the GUSTO-I trial. MR of mild to moderate severity is found in 13% to 45% patients following acute MI.^11–14 Whereas most MR is transient in duration and asymptomatic, MR caused by papillary muscle rupture (Fig. 3) is a life-threatening complication of acute MI. Fibrinolytic agents decrease the incidence of rupture; however, when present, rupture can occur earlier in the post-MI period than in the absence of reperfusion. Although papillary muscle rupture was reported to occur between days 2 and 7 in the prefibrinolytic era, the SHOCK (SHould we emergently revascularize Occluded Coronaries in cardiogenic shocK?) Trial Registry demonstrated a median time to papillary muscle rupture of 13 hours.¹⁵ Papillary muscle rupture is found in 7% of patients in cardiogenic shock and contributes to 5% of the mortality after acute MI.^16,17

Figure 3 Most mitral regurgitation is transient in duration and asymptomatic. However, mitral regurgitation caused by papillary muscle rupture is a life-threatening complication of acute myocardial infarction.

Pathophysiology

Mitral regurgitation can occur as a result of a number of mechanisms, including mitral valve annular dilatation secondary to LV dilatation, papillary muscle dysfunction with associated ischemic regional wall motion abnormality in close proximity to the insertion of the posterior papillary muscle, and partial or complete rupture of the chordae or papillary muscle.¹⁶

Papillary muscle rupture is most common with an inferior MI. The posteromedial papillary muscle is most often involved because of its single blood supply through the posterior descending coronary artery.¹⁸ The anterolateral papillary muscle has a dual blood supply, being perfused by the left anterior descending (LAD) and left circumflex coronary arteries. In 50% of patients with papillary muscle rupture, the infarct is relatively small.

Signs and Symptoms

Complete transection of the papillary muscles is rare and usually results in immediate pulmonary edema, cardiogenic shock, and death. Physical examination demonstrates a new pansystolic murmur, which is audible at the cardiac apex and radiates to the axilla or the base of the heart. If there is a posterior papillary muscle rupture, the murmur radiates to the left sternal border and may be confused with the murmur of VSD or aortic stenosis (intensity of the murmur does not always predict the severity of MR). In patients with severe heart failure, poor cardiac output, or elevated left atrial pressures, the murmur may be soft or absent.

Diagnostic Testing

The ECG usually shows evidence of a recent inferior or posterior MI. The chest radiograph shows evidence of pulmonary edema. Focal pulmonary edema can occur in the right upper lobe when flow is directed at the right pulmonary veins.

The diagnostic test of choice is two-dimensional echocardiography with Doppler and color flow imaging. In severe MR, the mitral valve leaflet is usually flail. Color flow imaging can be useful in distinguishing papillary muscle rupture with severe MR from VSD. Transthoracic echocardiography might not fully appreciate the amount of MR in some patients with posteriorly directed jets. In these patients, transesophageal echocardiography (TEE) may be particularly useful.

Hemodynamic monitoring with a PA catheter can reveal large (>50 mm Hg) V waves in the pulmonary capillary wedge pressure (PCWP). Patients with VSD can also have large V waves as a result of augmented pulmonary venous return in a left atrium of normal size and decreased compliance. Further complicating the diagnostic picture, patients with severe MR and reflected V waves in the PA tracing may have an increase in oxygen saturation in the PA.¹⁹ Mitral regurgitation can be distinguished from VSD with a Swan-Ganz catheter by two characteristics. First, prominent V waves in the PCWP tracing preceding the incisura on the PA tracing are almost always secondary to severe MR. Second, blood for oximetry should be obtained with fluoroscopic control from the central PA rather than from more distal branches to identify a significant increase in oxygen content associated with VSD.

Treatment

Patients with papillary muscle rupture should be rapidly identified and receive aggressive medical treatment while being considered for surgery. Medical therapy includes vasodilator therapy. Nitroprusside is useful in the treatment of patients with acute MR. Nitroprusside directly decreases SVR, thereby reducing the regurgitant fraction and increasing the forward stroke volume and cardiac output. Nitroprusside can be started at 0.5 to 1.0 µg/kg/min and titrated to a MAP of 60 to 75 mm Hg. An IABP should be inserted to decrease LV afterload, improve coronary perfusion, and increase forward cardiac output. Patients with hypotension might tolerate vasodilators after an IABP is inserted.

Patients with papillary muscle rupture should be considered for emergency surgery, because the prognosis is dismal in medically treated patients. Coronary angiography should be performed before surgical repair, because revascularization during MVR is associated with improved short-term and long-term mortality.^17,20 Additional surgical candidates include patients with moderate MR who do not improve with afterload reduction.

Prevalence

Free wall rupture occurs in 3% of MI patients and accounts for approximately 10% of mortality after MI (Fig. 4). The timing of cardiac rupture is within 5 days in 50% of patients and within 2 weeks of MI in 90% of patients. Free wall rupture occurs only among patients with transmural MI. Risk factors include advanced age, female gender, hypertension, first MI, and poor coronary collateral vessels.

Figure 4 Free wall rupture occurs in 3% of myocardial infarction (MI) patients and accounts for approximately 10% of mortality after MI.

Pathophysiology

Free wall rupture accounts for part of the early hazard in patients treated with fibrinolytic agents. The overall incidence of free wall rupture is not higher in patients treated with fibrinolytics, however.^21–23 Although any wall can be involved, cardiac rupture most commonly occurs at the lateral wall.

Free wall rupture occurs at three distinct intervals, with three distinct pathologic subsets. Type I increases with the use of fibrinolytics. It occurs early (within the first 24 hours) and is a full-thickness rupture. Type II rupture occurs 1 to 3 days after MI and is a result of erosion of the myocardium at the site of infarction. Type III rupture occurs late and is located at the border zone of the infarction and normal myocardium.

The reduction in type III ruptures as a result of the advent of fibrinolytics has resulted in no change in the overall free wall rupture rate. It has been postulated that type III ruptures can occur as a result of dynamic LVOT obstruction and the resultant increased wall stress.²⁴

Signs and Symptoms

Sudden onset of chest pain with straining or coughing can suggest the onset of myocardial rupture. Acute rupture patients often have electromechanical dissociation and sudden death. Other patients may have a more subacute course as a result of a contained rupture, or pseudoaneurysm. They might complain of pain consistent with pericarditis, nausea, and hypotension. In a study evaluating 1457 patients with acute MI, 6.2% of patients had free wall rupture. Approximately one third of these patients presented with a subacute course.²²

Jugular venous distention, pulsus paradoxus, diminished heart sounds, and a pericardial rub suggest subacute rupture. New to-and-fro murmurs may be heard in patients with subacute rupture or pseudoaneurysm. A junctional or idioventricular rhythm, low-voltage complexes, and tall precordial T waves may be evident on the ECG. Additionally, a large number of patients have transient bradycardia just before rupture, as well as other manifestations of increased vagal tone.

Diagnostic Testing

Although there is generally insufficient time for thorough diagnostic testing in the management of patients with acute rupture, transthoracic echocardiography is the urgent test of choice. Echocardiography demonstrates a pericardial effusion with findings of cardiac tamponade. These findings include right atrial (RA) and RV diastolic collapse, dilated inferior vena cava, and marked respiratory variations in mitral and tricuspid inflow. Additionally, a Swan-Ganz pulmonary artery catheter may reveal hemodynamic signs of tamponade, with equalization of the RA, RV diastolic, and pulmonary capillary wedge pressures.

Treatment

The goal of therapy is to diagnose the problem and perform early emergency open heart surgery to correct the rupture. Emergency pericardiocentesis may be performed immediately on patients with tamponade and severe hemodynamic compromise while arrangements are being made for transport to the hospital. The procedure may be dangerous because of reopening of communication with the pericardium as the intrapericardial pressure is relieved. Medical management has no role in the treatment of these patients, except for the use of vasopressors to maintain blood pressure temporarily as the patient is rushed to the operating room.

Pathophysiology

Pseudoaneurysm is caused by contained rupture of the LV free wall. The aneurysm may remain small or undergo progressive enlargement. The outer wall is formed by the pericardium and mural thrombus. The pseudoaneurysm communicates with the body of the left ventricle through a narrow neck whose diameter is by definition less than 50% of the diameter of the fundus.