Sudden cardiac death occurs in 1/3 to half of patients with chronic heart failure (HF); As shown by multicentre studies such as COMPANION and DEFINITE, the cardioverter-defibrillators (ICD) have an important impact in reducing both mortality and hospitalization rate in patients with symptomatic HF, irrespective of the nature of cardiomyopathy. Of course, if all the patients with HF and potential arrhythmias would have placed an ICD, the costs for every health care system would be extremely high. I-123 meta-iodo-benzylguanidine (MIBG), a radiolabeled norepinephrine analogue, is able to image the bio-distribution of the function of the autonomic nervous system. Failure in nervous afference to viable myocardium is an important factor in triggering and sustaining a variety of malignant ventricular arrhythmias. Thus scintigraphy with MIBG can take on an important role in selecting patients who would benefit from ICD by identifying those at increased risk for potentially fatal arrhythmias. In this study we evaluated if integration between perfusion, viability and adrenergic innervation imaging in patients with ICD could help in identifying arrhythmogenic foci and in selecting candidates for ICD placement.
After having studied 3 patients scheduled for 18F-DFG-PET and 99mTc-Sestamibi (MIBI) studies for non cardiac reasons, we enrolled 10 patients in whom Parkinson disease was excluded, with left ventricular dysfunction, EF <35%, and previously implanted ICD for primary or secondary prevention. All patients underwent rest planar scan and early-late single photon emission tomography (SPECT) with 123I-MIBG plus rest GATED SPECT imaging with 99mTc MIBI and PET/CT imaging with the viability tracer flourodeoxyglucose (18F-DFG). Patients were followed up for at least six months.
Normal patients did not show mismatches. The EF measured by gated SPECT was 25.6, SD 3.6. Two patients showed a non valuable MIBG SPECT due to scarce uptake by the entire heart. Mismatch between MIBI and MIBG SPECT occurred in 6 patients, considering that the two pts with non valuable MIBG SPECT had to be classified as mismatch bearing. All the patients who showed mismatch between MIBG and MIBI showed also mismatch between MIBG SPECT and DFG PET. Two patients did not show MIBI-MIBG mismatch but showed mismatch between MIBG and DFG. The patients who showed mismatches experienced ICD discharges during the follow-up, whereas the 2 patients without mismatch did not.
The analysis of mismatch zones between MIBG SPECT and MIBI SPECT and/or DFG PET is an accurate non invasive method to discover arrhythmogenic myocardium. DFG PET is more expensive but also more sensitive to this end.