CONTINUING DILEMMAS CONCERNING AORTIC-VALVE REPLACEMENT IN PATIENTS WITH ADVANCED LEFT-VENTRICULAR SYSTOLIC DYSFUNCTION

Aortic valve replacement in patients with aortic stenosis or aortic re gurgitation who have severe left ventricular (LV) systolic dysfunction continues to be associated with a high mortality risk despite surgica l, cardiological and anesthetic improvements over time. As a result of earlier surgical referral, however, fewer patients with aortic regurg itation (AR) and advanced LV failure present for operation today. Favo rable operative and long-term results, and data demonstrating recovery of LV systolic function if patients are referred prior to the onset o f systolic dysfunction have largely solved this problem in the context of AR. On the other hand, patients with critical aortic stenosis (AS) and severe LV systolic dysfunction constitute a more heterogeneous an d even more challenging group. On one side of the continuum, patients with truly critical AS and low ejection fraction due to LV 'afterload mismatch' (depressed ejection performance resulting from excessively h igh systolic LV wall stress secondary to a very tight valve) generally respond well to aortic valve replacement, which immediately normalize s LV afterload. Conversely, patients with 'critical' aortic stenosis a nd advanced LV systolic dysfunction who present with a low transvalvul ar gradient and cardiac output constitute a subgroup at high operative risk, which also has a suboptimal prognosis after aortic valve replac ement. This clinical situation has been termed the 'Gorlin Conundrum', and is punctuated by a low mean transvalvular gradient and low flow. The reason for the low transvalvular gradient is not always known, but can be secondary to some type of coexistent cardiomyopathy. Patients with only mild pathologic aortic valve sclerosis/stenosis and markedly depressed LV systolic function are frequently judged to have 'critica l' aortic stenosis (AVA <0.8 cm(2) or AVAI <0.4 cm(2)/m(2)) due to inh erent flaws in the Gorlin equation and limitations of the Doppler cont inuity equation. Although alternative diagnostic techniques have been proposed, e.g. aortic valve resistance, stroke work loss, none has yet proven to be totally reliable. The suboptimal results of aortic valve replacement in low-gradient AS patients underscore our difficulty in currently predicting which patients will benefit from valve replacemen t. Newer diagnostic techniques, including dobutamine echocardiography, and novel new findings regarding the basic molecular mechanisms respo nsible for contractile dysfunction in pressure overload hypertrophy ma y ultimately improve the results of surgical treatment in these patien ts.