Will Imaging Assist in the Selection of Patients With Heart Failure for an ICD?

Abstract

Sudden cardiac death remains the leading cause of death in the U.S. A left ventricular ejection fraction (LVEF)<30% to 35% identifies a population of patients at increased risk for sudden cardiac death. Once identified, an implantable cardioverter-defibrillator (ICD) is effective in reducing the occurrence of sudden cardiac death. Yet in a substantial proportion of patients who receive an ICD based on reduced LVEF, the device never delivers therapy. Furthermore, the majority of patients who die suddenly do not qualify for ICD placement under current LVEF-based criteria in the guidelines. This review considers the potential role of cardiac imaging in improving the selection of patients most likely to benefit from an ICD. The presence of myocardial scar and/or unrevascularized myocardial ischemia provides an important substrate for the occurrence of potentially fatal ventricular arrhythmias. The presence of clinical heart failure further increases the risk of ventricular arrhythmia. The sympathetic nervous system provides an important trigger for major arrhythmic events, both through global overactivity and through regional heterogeneity of sympathetic activity. A mismatch of myocardial perfusion and innervation may pose a particularly great risk. Imaging modalities provide unique opportunities to investigate the anatomic and pathophysiologic substrates, as well as the triggering effects of cardiac sympathetic innervation. Combining imaging and electrophysiologic modalities offers promise for improved accuracy in future selection of patients with heart failure for ICD placement.

Cardiac autonomic imaging with SPECT tracers

“…117 Autonomic imaging depicts cardiac pathophysiology closer to the underlying mechanisms of arrhythmias, 100,118 and there is much evidence that 123 I-mIBG imaging can effectively indicate which patients are likely to benefit from an ICD. 119 Arora et al, 120 in a small study of 17 patients with advanced HF and an ICD, found that an H/M \ 1.54 was associated with increased incidence of ICD discharges, and that on tomographic imaging patients who had ICD discharges had more extensive 123 I-mIBG defects and more extensive autonomic/perfusion mismatches, shown in Figure 7. An example of a SPECT images in a patient…”

Nuclear Cardiology: 2014 Innovations and Developments

“…24 In addition to its established prognostic ability, there are preliminary data pointing to a potential role of cardiac MIBG imaging in guiding AICD implantation for prevention of sudden cardiac death and in guiding medical therapy with beta blockers. [25][26][27] Cardiac MIBG is currently FDA approved for assessing prognosis in patients with class II-III congestive heart failure who have an LVEF ≤ 35%.…”

It’s not all in the numbers

“…Theoretically, identification of regional defects, especially in areas of preserved perfusion, should identify patients at risk of electrical instability and thus lethal arrhythmias. [45][46][47] The need for tomographic imaging is suggested by a recent analysis reporting that planar HMR, although a strong predictor of all-cause mortality, cardiac mortality, and eventual need for heart transplant, likely does not provide enough contrast and 3D detail for highly accurate prediction of arrhythmic events. 48 Small cohort studies using semiquantitative visual scoring techniques suggest clinical utility for SPECT 123 I-mIBG in assessing arrhythmic risk, [49][50][51][52][53][54][55][56][57] but utility in a large trial has not been established.…”