What will be the role of I-123 MIBG in improving the outcome of medically treated heart failure patients?

Abstract

Heart failure (HF) remains the most common cause for hospital admissions in the Medicare age population. In recent decades, major advances in medical treatment of HF patients have resulted in longer survival and improved quality of life. Randomized clinical trials have documented that beta-adrenergic blockers (b-blockers), angiotensin-converting enzyme inhibitors (ACE-inhibitors), angiotensin receptor blockers (ARBs), and aldosterone inhibitors have provided improved outcomes for HF patients. Although widely used, these medications have frequently not been used in the doses validated in large clinical trials. This likely reflects concerns about using the full doses of b-blockers in patients with baseline bradycardia and/or using increasing doses of b-blockers, ACE-inhibitors, or ARBs in patients with low baseline systolic blood pressure. Maximum benefit of pharmacologic therapy is limited by inadequate data for drug selection for individual HF patients and inadequate data documenting the optimal therapeutic target for blood pressure and heart rate. Excessive activity of the sympathetic nervous system is a major contributor to HF progression, by increasing cardiac work, promoting myocardial fibrosis, and causing down-regulation of post-synaptic adrenergic receptors. The impact of the sympathetic nervous system in HF patients can be assessed non-invasively by imaging cardiac neuronal uptake and retention of the norepinephrine congener, I-123 metaiodobenzylguanidine (I-123 MIBG). A growing literature addresses the potential role of I-123 MIBG for identifying HF patients at high risk for sudden cardiac death, in whom implantation of a cardioverter-defibrillator may be life-saving. Relatively little attention has been focused on the potential role of I-123 MIBG in guiding medical therapy of HF and avoidance of HF progression. Therefore, this review focuses on the question of whether sympathetic cardiac neural imaging with I-123 MIBG has the potential to guide medical therapy of properly selected patients with advanced HF, thereby improving symptoms and outcome.