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“Diseases desperate grown by desperate appliances will be relieved or not at all” (Shakespeare, Hamlet IV 8–10)
The mortality of patients who develop cardiogenic shock following myocardial infarction remains high, despite modern management with medical and interventional treatment.1 Although an invasive approach to revascularisation may have a favourable impact upon mortality in comparison to medical treatment alone, the 30 day mortality of the aggressively treated patients in the SHOCK (should we emergently revascularize occluded coronaries for cardiogenic shock) trial was a discouraging 47%.2 The majority of patients who develop cardiogenic shock have severe left ventricular systolic dysfunction as a consequence of large regions of infarcted or ischaemic myocardium, which underlies a clinical course characterised by progressive haemodynamic deterioration. In contrast, acute haemodynamic deterioration may also result from rupture of the left ventricular free wall, ventricular septum, and papillary muscles. Free wall rupture is by far the most common of all ruptures and usually results in sudden death. Ventricular septal defect and papillary muscle rupture are less frequent but more amenable to intervention; in the SHOCK registry, these two mechanical complications were present in only 8% of all patients presenting with shock.3 Nonetheless, the relative infrequency of these mechanical complications should not belie their importance as a potentially reversible cause of cardiogenic shock.4-8
Often, myocardial rupture occurs in patients with small areas of infarction and well preserved systolic function of the left ventricle.4 5 7 8 The latter results in an increased shear stress in the area of necrosis or at its boundaries leading to the mechanical disruption. The therapeutic implications are obvious and elegantly simple—the correction of the mechanical complication may leave the patient with relatively intact ventricular function, which in turn may be a powerful predictor of a favourable long term outcome. If cardiogenic shock caused by pump failure is a dire example of “paradise lost”, perhaps cardiogenic shock caused by myocardial rupture provides a window of opportunity for “paradise”, or at least a reasonable expectancy of useful life, to be “regained”.5 8 9 In this case, the entire diagnostic and therapeutic focus is to identify expeditiously patients who need surgical correction and for the operation to be performed with minimal delay.
Of all the ruptures that occur following myocardial infarction (for example, free wall rupture, ventricular septal rupture), it is the patient with papillary muscle rupture who has benefited most from this approach.
Anatomy and blood supply of the papillary muscles
The clinical presentation and natural history of papillary muscle rupture is closely linked to the anatomy and blood supply of the anterior and posterior papillary muscles, both of which are an integral part of the mitral valve apparatus.4 5 There are two separate papillary muscles, the anterolateral and the posteromedial papillary muscles. The anterolateral papillary muscle is usually fed by a dual blood supply from the left anterior descending artery and by marginal tributaries from the circumflex artery, whereas the posteromedial papillary muscle usually has a single blood supply from the contributors to the posterior descending artery. Thus, in an acute myocardial infarction, it is the posteromedial papillary muscle that is most vulnerable to infarction, necrosis, and rupture. The posteromedial papillary muscle typically consists of one or two large common trunks and multiple heads, all of which give off chordae to both the anterior and posterior mitral valve leaflets. Acute complete rupture of the large common trunk may occur and this results in torrential mitral regurgitation and severe haemodynamic compromise. There can also be a partial rupture of the large common trunk, which will result in a less severe degree of mitral regurgitation and is better tolerated haemodynamically than acute complete rupture of the large trunk. Complete rupture of one of the multiple heads of the papillary muscle causes less severe deterioration than rupture of the entire trunk. However, in the latter two situations, the potential for additional or more extensive rupture is present which may lead to unpredictable rapid decompensation, even after initial stabilisation.5 7
Clinical presentation and diagnosis
The clinical presentation of a patient with an acute papillary muscle rupture is typically characterised by acute rapid haemodynamic deterioration usually several days following an inferior myocardial infarction.4 5-7 Pulmonary oedema is almost always present and in some patients the severity of mitral regurgitation and other factors, such as left or right ventricular dysfunction, may result in cardiogenic shock. Patients usually have severe dyspnoea with raised venous pressure and rales throughout the lung fields. A murmur of mitral regurgitation may be present but may be inaudible because of the rapid equalisation of left atrial and left ventricular pressures. Acute rupture of the ventricular septum may present in a similar manner but patients may not have the severe dyspnoea and orthopnoea seen in patients with severe mitral regurgitation: a loud systolic murmur and thrill are almost always present.
In some patients, the differentiation of cardiogenic shock due to papillary muscle rupture from that caused by severe left ventricular dysfunction may be difficult, particularly in the face of a relatively unimpressive or absent systolic murmur.4 5 7A heightened index of clinical suspicion is pivotal for prompt recognition and treatment of this syndrome because, from the therapeutic standpoint, “time is of the essence”. The presence of cardiogenic shock or pulmonary oedema in the patient with an acute inferior myocardial infarction, particularly a first infarction, should always raise the possibility of acute mitral regurgitation and papillary muscle rupture.
The diagnosis of papillary muscle rupture previously required right heart catheterisation, which was invasive and had limitations. The presence of a large “V” wave on the pulmonary artery wedge pressure tracing was the criteria used for diagnosis but this could also be present in patients with severe left ventricular dysfunction and decreased chamber compliance.10 The diagnosis of a ventricular septal defect could be made by a high saturation in the pulmonary artery wedge pressure, but a “step up” in saturation has also been documented in the patient with papillary muscle rupture caused by transmission of oxygenated blood retrograde across the pulmonary circulation. Today, the diagnosis of papillary muscle rupture is made rapidly and non-invasively by echocardiography.11 A transthoracic echocardiogram can visualise directly a flail mitral valve leaflet or “swinging” papillary muscle in many instances. In those patients in whom the mitral valve apparatus cannot be directly visualised, the diagnosis is suspected by the presence of haemodynamic compromise concomitant with preserved systolic function, in which case transoesophageal echocardiography can be performed for further delineation. There is no longer a need for right heart catheterisation or left ventriculography, although coronary angiography may be performed if the patient is stable from the haemodynamic standpoint.
The prognosis of acute papillary muscle rupture associated with myocardial infarction before surgical intervention was poor, with 33% of patients dying immediately, 50% dying within 24 hours, and only 6% surviving longer than two months.6 7The management of the patient with an acute papillary muscle rupture consisted of medical stabilisation with afterload reduction, inotropic support, and intra-aortic balloon pumping. Surgical intervention was felt to be the definitive treatment but the timing of surgery has been controversial. In the 1970s and early 1980s, patients with acute mitral regurgitation had a reported 35–50% mortality when surgery was performed within 30 days after myocardial infarction.12-15 If surgery was delayed for more than three months after myocardial infarction, the reported operative mortality was “lowered” to 15–25%. These observations combined with the work of Mallory and colleagues,16 who described a 3–6 month interval for healing of myocardium after an infarct, led to the recommendation that operation be delayed as long as possible to achieve this lower surgical mortality.
This delay in surgical intervention resulted in a selection process whereas patients with relatively preserved ventricular function and less severe mitral regurgitation would be the candidates for mitral valve operation, a manifestation of “survival of the fittest”. Although this strategy might be expected to improve the outcome of those patients treated surgically, we and others have noted the labile course with rapid clinical deterioration in patients with acute papillary muscle rupture, even after apparent stabilisation with medical treatment, including intra-aortic balloon pumping.4 5 7 The limited extent of myocardial damage caused by necrosis and the distribution of coronary disease in patients with papillary muscle rupture provide a strong theoretical rationale for current approaches to treatment. Overall systolic function remains preserved in the majority of patients, and postmortem examinations showed that in many patients the extent of necrosis was limited and confined to the subendocardium in some. The extent of coronary artery disease in these patients is usually not extensive, with almost half of patients having either single vessel disease or a thrombus located at the site of minimal underlying coronary disease. Both the relatively minimal involvement of the myocardium and the modest extent of coronary disease are powerful predictors of a favourable long term outlook in the event that the acute haemodynamic abnormality is surgically corrected. Other factors favouring a surgical approach in these patients include the preservation of the integrity of the mitral annulus and avoidance of surgery in the area of necrosis.
Strategy of prompt recognition and early surgical intervention
Before the 1980s, the overall mortality of papillary muscle rupture approached 60%, as patients were stabilised for weeks before surgery. In the recent era, many clinicians have adopted a strategy of early surgery for all patients presenting with the diagnosis of papillary muscle rupture.8 9 In stable patients, deterioration may be sudden and unpredictable and a delay in timing of the operation would be risky. In patients presenting in shock, mortality with medical treatment is inevitable. Thus an approach of early surgery for all patients has been recommended, irrespective of whether stabilisation could be achieved by medical treatment. Although early surgery might be accompanied by an initial high mortality, it was thought that the overall rate of patient salvage would be increased. In the past decade, using this approach of rapid diagnosis and surgical intervention, the mortality of all patients presenting with acute papillary muscle rupture has been less than 30%.8 9Improved surgical methods, especially management of myocardial protection, have further improved the overall survival to over 80% of all patients presenting with papillary muscle rupture. In addition, repair of a ruptured papillary muscle is possible in some patients, thus avoiding the late sequelae of a prosthetic valve. The long term outlook for survivors is excellent.9
There will continue to be a high mortality for patients presenting with cardiogenic shock after myocardial infarction. However, prompt recognition and early surgical intervention for one of the less common causes of shock—that is, papillary muscle rupture—can be immensely rewarding. The pathophysiologic and natural history studies of papillary muscle rupture at our institution and others have led to a direct change in our attitude towards early surgical repair over the last 15 years. The universal mortality with medical treatment in patients presenting with cardiogenic shock, in conjunction with the unpredictable but frequent deterioration in other patients after initially stabilising on medical treatment, has caused us to adopt an approach of early emergency surgery in all patients once the diagnosis has been confirmed. In the past decade, our goal has been to have a patient diagnosed and within the operating room within hours of the presentation. With this approach, a substantial number of these desperately ill patients will not only survive surgery but also enjoy an excellent and fulfilling life in the years to come.