The time course of myocardial uptake of metaiodobenzylguanidine ([123I]MIBG) was studied in 26 patients: seven control subjects (Group 1) and 13 patients with left ventricular hypertrophy secondary to valvular aortic stenosis. Seven of these had received no treatment (Group 2) and six were receiving amiodarone or digoxin (Group 3); six heart transplant recipients were investigated for extra neuronal myocardial uptake of [123I]MIBG (Group 4). The index of myocardial [123I]MIBG uptake was lower in Groups 2 and 3 than in Group 1 (Group 2: 1.42 +/- 0.07, p < 0.001; Group 3: amiodarone, 1.30 +/- 0.10, p < 0.05; digoxin, 1.22 +/- 0.06, p < 0.01; Group I: 1.83 +/- 0.18) and lower in Group 3 than in Group 2. Patients of Group 4 showed a much lower mean index of myocardial [123I]MIBG uptake than the control group (1.07 +/- 0.08, p < 0.001).
In conclusion: 1. Patients with left ventricular hypertrophy secondary to valvular aortic stenosis were found to have lower myocardial [123I]MIBG activity and rapid washout than the control subjects. 2. Amiodarone and digoxin partially inhibited myocardial [123I] MIBG uptake. 3. Extra neuronal myocardial uptake of [123I]MIBG in humans only accounts for 13% of the total cardiac activity.