An elderly woman woke from sleep with acute breathlessness and wheeze. She had been treated for late-onset asthma by her GP. She had no other previous medical history and was exceptionally active. In the emergency department she received standard treatment for acute severe asthma . A systolic murmur was noted and an echocardiogram requested. After 24 hours of relative stability she experienced a sudden deterioration in her breathing and despite increased therapy for her asthma she had a respiratory arrest.
Following resuscitation and emergency tracheal intubation she was transferred to the ICU. On examination she was peripherally cool. Chest auscultation revealed extensive wheeze and crackles. Investigations revealed a raised troponin I (0.92 ug/L) and raised BNP (530 pmol/L). Her CXR revealed pulmonary oedema and her ECG showed sinus rhythm without overt evidence of ischaemia.
Initial problems included poor oxygenation, oliguria and a low cardiac output state (LiDCO revealed cardiac index of 2.1 l/min/m2). She received norepinephrine (up to 0.6 mcg/kg/min) and dobutamine (up to 40 mcg/kg/min). Levosimendan was introduced to augment her cardiac function as her CI had not achieved to 2.5l/min/m2. Norepinephrine was increased to maintain a MAP over 65mmHg. After levosimendan her urine output, acid-base status and CI were not substantially improved. The dobutamine had been stopped and she remained on norepinephrine.
An echocardiogram revealed hyperdynamic LV and RV and mitral regurgitation, which was initially assessed as being moderate in severity. Cardiac surgical opinion was that the risk of mitral valve surgery was unacceptably high.
Over the following few days she had problems with recurrent compromising atrial fibrillation and was treated with varying degrees of success with a variety of measures including DC cardioversion, amiodarone, metoprolol, digoxin and verapamil. Diuresis was obtained with a frusemide infusion and ramipril was introduced. Her CXR appearances improved and ventilation became easier.
On the 3rd day a trans-oesphageal echocardiogram confirmed severe mitral regurgitation (MR) with prolapse of the posterior mitral valve (MV) leaflet due to a ruptured chordae tendinae. There was resultant left atrial enlargement and pulmonary hypertension with an estimated PA systolic pressure of 60-70mmHg. Within a week she was weaned from ventilatory support and recovered sufficiently to mobilise independently prior to discharge home.
What are the clinical features of acute mitral valve failure?
The commonest causes of acute MR are acute myocardial ischaemia or infarction, endocarditis, and chest trauma. The valve may fail due to disease of the leaflets, chordae tendinae or the papillary muscle. Approximately 10% of acute myocardial infarctions are complicated by a degree of MR and it is associated with a significant increase in the risk of subsequent cardiac death.
Pathophysiology of acute mitral valve failure
During ventricular systole the volume of blood in the LV flows both out the LV outflow tract through the aorta into the systemic circulation but also back through the failing MV into the lower pressure left atrium. This increases pressure in the left atrium (LA) and therefore increases LV preload. The regurgitation decreases the LV afterload. The LV becomes volume overloaded and hyperdynamic and the ejection fraction may appear to be maintained. In acute severe MR, physical examination and auscultation may be misleading, in particular, with a murmur of low intensity, and colour Doppler flow may underestimate the severity of the lesion.
The clinical impact of MR is modulated largely by the compliance of the left atrium and the pulmonary vasculature. In a normal left atrium with a relatively low compliance, acute mitral regurgitation results in high LA pressure, which can lead rapidly to pulmonary oedema. In contrast, in patients with chronic mitral regurgitation, in whom compensatory changes over time increase LA and pulmonary venous compliance, symptoms of pulmonary congestion may not occur for many years. In acute MR effective flow of blood from the LV through the aortic valve and to the systemic circulation becomes diminished and despite a hyperdynamic LV and a compensatory increase in heart rate there is effectively low cardiac output. A detrimental neurohormonal response to this exacerbates the situation: increased sympathetic drive causes systemic vasoconstriction and increases LV afterload.
Clinical features are of acute pulmonary oedema, hypotension, and signs and symptoms of cardiogenic shock. Atrial dysrhythmias are common. Acute right-sided heart failure may result from the pulmonary hypertension.
Management of acute MR
International guidelines recommend early surgical intervention in severe symptomatic mitral regurgitation,. Medical management is recommended primarily to stabilise the patient prior to surgery. Mortality and morbidity both with and without surgery is high. Age is highly predictive of operative mortality in cardiac surgery and is therefore not always appropriate. Valve repairs rather than replacements are becoming increasingly common for MR.
Even in non-acute but severe and symptomatic MR surgery is commonly (49% in a recent European survey) withheld despite consensus guidelines encouraging surgical intervention. The characteristics independently associated with a decision not to operate were lower LVEF, non-ischaemic aetiology, older age, higher Charlson comorbidity index, and grade 3 MR.
Sodium nitroprusside (SNP) may increase aortic flow and partially restore MV competence as LV size diminishes. SNP dilates the arterial side of the circulation in addition to the venous, nitrates (such as GTN) are said to preferentially affect the venous side. Both SNP and GTN have disadvantages – SNP produces cyanide toxicity (particularly when there is concurrent renal or hepatic impairment) and GTN demonstrates marked tachyphylaxis.
In the context of hypotension, vasopressors and/or inotropes may also be needed. Filling pressures may also be reduced by reduction of intravascular volume with diuretics and vasodilatation with nitrates. There is a fine balance to be sought as excessive systemic vasoconstriction will increase afterload and worsen MR, conversely a low MAP will threaten systemic tissue perfusion. Similarly excessive inotropy and chronotropy may be detrimental through increased MR.
Maintenance of sinus rhythm is very difficult in severe MR and the effect of cardioversion is likely to be short-lived. Rate control is a more realistic aim and should be achieved using standard agents.
Intra-aortic balloon pumping reduces aortic impedance and regurgitant fraction without adverse effects on LV function and is recommended in acute MR.
Levosimendan is a novel agent that is both a Ca++ channel sensitizer and K+ channel activator. It acts as an intrope, a lusitrope and produces vasodilatation. It is indicated in patients with symptomatic low cardiac output heart failure secondary to cardiac systolic dysfunction without severe hypotension. There is no literature relating to its role in acute MR but its use in this context has a physiological rationale.
It is always appropriate to question previously given diagnoses (asthma). The presentation of acute MR can be difficult as physical signs may be subtle and echocardiography may not initially be diagnostic and can be falsely reassuring. Early echocardiography has an important role in establishing aetiology of cardiorespiratory failure.
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