¹²³I-MIBG myocardial scintigraphy predicts abnormalities of myocardial functional reserve in response to β-adrenergic stimulation in idiopathic dilated cardiomyopathy patients

Objectives We examined whether ¹²³I-MIBG myocardial scintigraphy predicts abnormalities of myocardial functional reserve in response to β-adrenergic stimulation in idiopathic dilated cardiomyopathy patients (IDCM).

Methods 40 IDCM patients (NYHA class I to II, age 52±13 years, LVEF 39±11%) underwent myocardial ¹²³I-MIBG scintigraphy and cardiac catheterization. ¹²³I-MIBG findings were expressed as early heart-mediadtinum ratio (H/M), delayed H/M, and washout rate(WR). LV dP/dt_max and T_1/2 were determined from left ventricular pressure curve during dobutamine infusion (15μg kg^-1 min^-1). Patients were classified as follows: group A comprised 20 patients showing a delayed H/M of ≤1.8; group B comprised 20 patients showing the ratio >1.8.

Results The percent change in heart rate (%HR), LV dP/dt_max(%LV dP/dt_max) andT_1/2 (%T_1/2) from baseline to dobutamine stress were significantly reduced in the group A than those in group B (39±20% vs 58±24%, p<0.01; 102±46% vs 161±70%, p<0.01; 40±15% vs 50±12%, p<0.05, respectively). Significant correlations were found between delayed H/M and %HR (r=0.35, p<0.05), %LV dP/dt_max (r=0.45, p<0.01) and %T_1/2(r=0.34, p<0.05). Significant correlations were also found between WR and %HR (r=0.37, p<0.05), %LV dP/dt_max(r=0.60, p<0.01) and %T_1/2 (r=0.34, p<0.05).

Conclusions Reduced ¹²³I-MIBG uptake and increased washout were related to an impairment in adrenergic myocardial chronotropic (increase in HR), inotropic (increase in LV dP/dt_max), and lusitropic(shortening of T_1/2) functional reserve. Myocardial ¹²³I-MIBG scintigraphy may noninvasively predict functional reserve in response to β-adrenergic stimulation in mild to moderate IDCM patients