Pseudo–severe AS where dobutamine induces a >20 % increase in SV with an associated increase in AVA and no change in ∆P_mean (Fig. 8.2, Table 8.2), and

Indeterminate AS without contractile reserve where dobutamine infusion fails to increase SV (Fig. 8.3, Table 8.3)

Whether dobutamine truly distinguishes between different types of LF/LG AS with depressed LV EF or merely assesses flow-related changes to the effective orifice area (EOA) has come to question. Nevertheless, dobutamine infusion remains routine in clinical practice to help evaluate individual surgical risk and prognosis [2]. Previous studies have shown that patients with a ∆P_mean >30 mmHg at baseline or following dobutamine infusion likely have true or fixed AS with a better prognosis and improved LV function following AVR [5, 11, 14]. In general, AS patients with depressed LVEF have worse outcomes following surgery than those with preserved LVEF. However, regardless of the subtype as determined by dobutamine, all patients with low flow/low gradient with depressed ejection fraction and severe AS have a higher mortality in the absence of surgery [5, 12].

As there may be significant patient-to-patient variability in the peak trans-valvular flow rates achieved with dobutamine infusion, other parameters have been studied to improve the diagnostic accuracy of this test in the evaluation of LF/LG AS [15]. The projected AVA (AVA _proj ) defined as the expected AVA at a standardized flow rate of 250 mL/s is derived from the regression slope of AVA versus flow during dobutamine infusion and accounts for individual variations in flow augmentation in response to dobutamine [5, 11, 15] (Fig. 8.4, Table 8.4). An AVA_proj ≥1.2 cm², together with a peak dobutamine EF >35 %, and high Duke activity status index, denote a good prognosis [5, 11, 15].