Systolic anterior motion of the mitral valve leaflet leading to haemodynamic compromise

Abstract

We report a case of systolic anterior motion of the mitral valve leaflet during a coronary artery bypass graft surgery causing ST-T changes and hypotension. Anaesthetic induction and cardiopulmonary bypass were uncomplicated with minimal inotropic support. The elderly patient received 1000 ml of colloid and 700 ml of pump blood. While the heart rate was 80 min−1 with a mean arterial pressure of 70 mmHg, ST segment changes were noted with the surgical closure of chest. More colloids were infused and the systolic blood pressure remained around 90–100 mmHg. The chest was reopened, the heart continued to contract well, the surgeon was confident of the integrity of the grafts but the ST segment progressed to −2.0 mm. Dopamine was increased to 10 μg.kg.min−1 and the ST dipped to −3.5 mm. At this point, the blood pressure started dropping and the heart rate increased to 100 min−1. An intra-aortic balloon was inserted, noradrenaline was started; subsequently transoesophageal echocardiography was performed. The left ventricle was empty and contracting vigorously without any wall motion changes. Significant anterior motion of the mitral valve leaflet during systole was observed causing obstruction of the outflow tract (2, 3). More fluids were infused and inotropic support was stopped. The ST depression reverted back to normal, with good control of heart rate and blood pressure. Transoesophageal echo showing systolic anterior motion. Diagrammatic representation of long axis transoesophageal echo in Fig. 2 showing systolic anterior motion. Systolic anterior motion is an important feature of idiopathic hypertrophic subaortic stenosis [1]. It can be an associated finding in patients without any organic heart disease [2] and can be fatally symptomatic in extreme hypovolaemia [3]. Systolic anterior motion appears to be a non-specific motion of mitral valve leaflets occurring in vigorously contracting volume depleted, completely obliterated systolic cavities. Death from systolic anterior motion has been reported in severely ill patients without pre-existing cardiac disease [3]. The extent of hypovolaemia caused by vasodilatation from most anaesthetic drugs and regional anaesthesia is often underestimated, leading to inadequate fluid replacement and inappropriate infusion of inotropes. Judicious infusion of fluids did not improve the situation in our case, probably because the vasodilatation of general anaesthesia and cardiopulmonary bypass were underestimated. Echocardiography allowed visualisation of the anterior motion of the leaflets, hypercontractile ventricles and acute mitral regurgitation. Although transoesophageal echocardiography is superior to transthoracic echo-cardiography [4], in unexplained hypotension, transthoracic echo-cardiography could be used if the anterior chest wall can be exposed [5]. Though rare, severe systolic anterior motion in acute hypotensive episodes can go unrecognised causing severe cardiovascular compromise. The treatment of severe systolic anterior motion should be mainly fluids, vasopressor drugs and control of tachycardia. Echocardiography is useful not only in diagnosing systolic anterior motion, but to visualise empty hyperdynamic ventricles and in preventing further complications.