Cardiogenic shock and the haemodynamic effects of arrhythmias.

Cardiogenic shock or pump failure may be defined as severe circulatory failure resulting from a primary defect in the pumping function of the heart, most commonly from acute myocardial infarction, and less commonly from end-stage congestive cardiomyopathy. It is essential that surgically correctable lesions leading to pump failure are identified and these would include papillary muscle dysfunction with mitral incompetence, rupture of the interventricular septum and pericardial effusion with cardiac tamponade. Pump failure results primarily from impairment of left ventricular function when greater than 40 % of the left ventricle becomes infarcted and is associated usually with triple vessel coronary disease (Harnayaran et al., 1970). A less common but important cause is right ventricular dysfunction secondary to right ventricular infarction (Cohn et al., 1974; Lorell et al., 1979). It is important to recognize this pathology, as treatment is more likely to be successful than when the left ventricle is involved. The haemodynamic consequences of arrhythmias and conduction problems will be discussed later but, clearly, ventricular performance will be further impaired in the presence of both tachyand bradyarrhythmias, particularly when there is asynchrony between atrial and ventricular contraction.