Papillary Muscle Rupture

Etiology

Papillary muscle rupture most commonly results from myocardial infarction, typically occurring 2 to 7 days after the ischemic event. Rupture occurs more frequently with ST-segment elevation myocardial infarction compared to non–ST-segment elevation infarction. Other documented causes of papillary muscle rupture include trauma, syphilis, periarteritis nodosa, vegetative valvulitis, myocardial abscess, iatrogenic injury, and cocaine use.

Severe acute mitral regurgitation resulting from papillary muscle rupture following acute myocardial infarction is a life-threatening condition if not treated promptly. Although randomized trials are lacking, multiple retrospective studies have consistently shown significantly lower in-hospital mortality rates with timely surgical intervention compared to medical therapy alone.[10] In recent years, single-center studies and national registries have provided comprehensive data on post-acute myocardial infarction papillary muscle rupture, indicating a mean age and male predominance consistent with previous reports. Hypertension, present in over 60% of patients, was the most common cardiovascular risk factor.[11]

Epidemiology

Papillary muscle rupture is a rare complication, estimated to occur in 1% to 5% of patients with acute myocardial infarction. This low incidence is believed to be due to improvements in early identification and early revascularization through percutaneous coronary intervention to limit ischemia. Rupture carries a high mortality rate without surgical intervention, with an estimated 50% mortality within 24 hours in cases of complete rupture. Mortality rates were estimated at 80% to 90% within the first 24 hours before cardiac surgery became a treatment option. A study found that 82% of papillary muscle rupture cases following infarction occurred in patients with their first myocardial infarction.[12][13]

Risk factors for papillary muscle rupture include advanced age, female sex, a history of heart failure, delayed treatment after myocardial infarction, and chronic kidney disease. The mortality rate for papillary muscle rupture can reach up to 75% within the first 24 hours when treated with medical therapy alone and without surgical intervention.

Pathophysiology

Papillary muscle rupture is either partial or complete. A partial rupture, occurring at one of the muscle heads, causes fewer leaflets to flail and results in less valvular regurgitation. Partial ruptures are better tolerated hemodynamically compared to complete ones, which may occur up to 3 months after infarction. Complete rupture of the papillary trunk, typically within a week post-infarction, causes rapid clinical deterioration.

The posteromedial papillary muscle is most often involved due to its single blood supply from the posterior descending artery, the impairment of which can produce inferior wall ischemia. This artery typically originates from the right coronary artery but may also arise from the left circumflex artery. This single blood supply makes rupture of the posteromedial muscle 6 to 12 times more frequent compared to that of the anterolateral muscle, which has a dual blood supply. About 50% of patients have single-vessel disease. Most documented papillary muscle rupture cases demonstrate small areas of ischemia, typically less than 25% of the ventricle, with poor collaterals. In small infarcts, papillary muscle rupture is believed to occur due to preserved ventricular function, which creates high shear forces on the ischemic papillary muscle.

History and Physical

Papillary muscle rupture should be suspected in patients experiencing sudden acute heart failure symptoms within the first week after myocardial infarction, particularly when the inferior wall is involved. Rapid and severe regurgitation from papillary muscle failure leads to atrial dilation due to an abrupt increase in atrial pressure. The combination of a hyperactive precordium and insufficient turbulence of blood flow through the regurgitant valve complicates the clinical diagnosis, often resulting in the absence of an audible regurgitant murmur. This phenomenon occurs because of pressure equalization between the atria and the ventricle, although some patients may exhibit midsystolic, late systolic, or holosystolic murmurs.

Symptoms and physical findings depend on the affected valve, with the posterior-medial papillary muscle of the mitral valve being the most commonly involved. Consequently, symptoms of acute left-sided heart failure, such as rapidly progressive pulmonary edema and hypoxia, are prevalent. Cardiogenic shock, characterized by hypotension, is frequently observed, and some patients may also report chest pain. The rapid onset of cardiogenic shock and the potential for catastrophic complications make prompt identification crucial, as mortality rates increase significantly without emergency surgical intervention.[14]

Evaluation

Papillary muscle rupture and acute valvular insufficiency can be identified using transthoracic echocardiography or transesophageal echocardiography. Transthoracic echocardiography may reveal a flail mitral valve leaflet prolapsing into the atrium during systole, a ruptured papillary muscle head exhibiting erratic movements in the ventricle, or a mobile mass attached to the chordae tendineae. The sensitivity of transthoracic echocardiography for visualizing structural abnormalities ranges from 65% to 85%. Transthoracic echocardiography is recommended when transthoracic echocardiography results are inconclusive, as its sensitivity can reach 92% to 100%  (see Image. Papillary Muscle Rupture on Transesophageal Echocardiography).[15]

Many patients are too hemodynamically unstable to undergo invasive procedures. Thus, transthoracic echocardiography is typically the initial diagnostic method used. Doppler echocardiography and color flow imaging also help determine the severity of the regurgitant jet across the valve. Echocardiography is superior to cardiac catheterization as muscle ruptures may be diagnosed with minimal risk to the patient. Besides acute valvular surgery, coronary revascularization is strongly recommended, as patients undergoing this treatment have demonstrated improved mortality rates.

Treatment / Management

Patients require careful medical optimization in the early stages of acute mitral regurgitation. Typical measures include:

• Hemodynamic stabilization using vasoactive medications and mechanical circulatory support
• Afterload reduction through the use of an intra-aortic balloon pump
• Management of acute pulmonary edema with intravenous diuretics and ventilatory support
• Treatment of arrhythmias with pharmacologic agents or mechanical cardioversion
• Potential percutaneous intervention for the infarct-related artery
• Monitoring for other possible mechanical complications of myocardial infarction

Once diagnosed, prompt correction of acute mitral regurgitation due to papillary muscle rupture is essential. The treatment approach depends on the patient's comorbidities, the location and extent of the rupture (partial or complete), the anatomy of coronary artery disease, available interventions, and inputs from an interprofessional cardiac team. Treatment options for mitral regurgitation include percutaneous and surgical techniques, though the decision to revascularize during mitral valve intervention may vary by practice.

Surgical intervention remains the gold standard for managing papillary muscle rupture. A treatment controversy exists regarding whether mitral valve repair is more beneficial than valve replacement. Currently, repair is preferred over replacement unless necrotic papillary muscle tissue is present. In addition, concomitant coronary artery bypass has been shown to improve outcomes and should be performed.

Suboptimal outcomes following valve repair have been linked to prolonged cross-clamp times, suturing into friable necrotic tissue, and tissue remodeling after infarction. Surgeons may delay the repair of partial papillary muscle rupture for up to 6 to 8 weeks post-infarction to allow tissue necrosis to resolve. This decision depends on the patient's stability; surgical correction may be required sooner.

Differential Diagnosis

Other complications of myocardial infarction that may present similarly to papillary muscle rupture include cardiogenic shock due to severe left and right ventricular dysfunction, ventricular septal rupture, and free-wall myocardial rupture. These complications are characterized by severe left ventricular dysfunction, which manifests as pulmonary edema and decreased cardiac output, ultimately resulting in organ hypoperfusion. Severe right ventricular dysfunction presents with elevated jugular venous pressure, peripheral edema, hypotension, and clear lung fields. Right ventricular failure may also result in underfilling the left heart chambers, resulting in a low cardiac output state. Ventricular septal rupture has a 5% mortality rate and may be associated with anterior infarction, whereas papillary muscle rupture is infrequently observed in anterior cardiac ischemia.

Septal rupture occurs where necrotic tissue is located, creating a left-to-right shunt and a new pansystolic murmur. Rapid pulmonary edema is typically not observed. Free-wall myocardial rupture, similar to septal and papillary muscle rupture, is often caused by small infarctions and single-vessel disease. The left ventricular wall is the most common rupture site and occurs within 5 days in 50% of patients and 2 weeks in 90% of patients. Survival depends on whether the rupture is complete or subacute, with complete ruptures having a nearly 100% fatality rate due to the abrupt onset of cardiac tamponade.

Prognosis

A study involving 22 patients reported a perioperative mortality rate of 27% and overall survival of 47% at 7 years. Another study involving 55 patients indicated an overall operative mortality rate of 24%. The mortality rate was notably higher in patients who did not undergo coronary revascularization, with a rate of 39% compared to 9% in individuals who received the procedure. In addition, in a study involving 54 patients, the 10-year survival rate was reported to be 35%, and the 10-year heart failure-free rate was 23%.

Several adjusted risk factors have been linked to increased inpatient mortality in patients with ST-elevation myocardial infarction-related papillary muscle or chordae tendineae rupture. For every 5-year increase in age, the risk of in-hospital mortality rose by 9% (aOR: 1.09, 95% CI: 1.07–1.12, p < .001). Female sex (aOR: 1.87, 95% CI: 1.44–2.41, p < .001), Hispanic ethnicity (aOR: 7.05, 95% CI: 3.39–14.64, p < .001), and coagulopathy (aOR: 1.48, 95% CI: 1.06–2.07) were all associated with higher mortality. In addition, comorbid conditions, such as hypertension, smoking, cardiac arrest, and cardiogenic shock, further contributed to an increased risk of in-hospital mortality.

Complications

The early and more assertive use of short-term mechanical circulatory support devices has shown positive outcomes in patients experiencing postcardiotomy cardiogenic shock. Understanding the specific hemodynamic effects of each mechanical circulatory support device is crucial for selecting the most appropriate therapy, particularly in acute severe mitral regurgitation cases. Simulations have provided valuable insights into the hemodynamics of these devices. Although extracorporeal membrane oxygenation is commonly employed for patients with postcardiotomy shock, simulations suggest that this modality may exacerbate severe mitral regurgitation, necessitating additional measures to unload the left ventricle.