Heart failure
Prognostic Value of Iodine-123-Metaiodobenzylguanidine Myocardial Uptake and Heart Rate Variability in Chronic Congestive Heart Failure Secondary to Ischemic or Idiopathic Dilated Cardiomyopathy

https://doi.org/10.1016/j.amjcard.2005.03.093Get rights and content

Autonomic nervous system dysfunction is common in congestive heart failure (CHF) and is believed to predispose patients to an increased risk of death. This study aimed to assess the prognostic significance of heart rate variability (HRV) measurements in conjunction with scintigraphic imaging using metaiodobenzylguanidine (MIBG) labeled with iodine-123 (I-123-MIBG), which detects abnormalities in autonomic nervous activity, in patients with stable CHF during optimal medical treatment. The study population included 52 patients (56 ± 12 years of age) with a mean left ventricular ejection fraction of 31 ± 12%. All underwent I-123-MIBG scanning and 24-hour ambulatory electrocardiographic monitoring for the analysis of HRV on entrance into the study. The heart/mediastinum MIBG uptake ratio was calculated. HRV analysis included the assessment of time- and frequency-domain variables. During the 2-year follow-up, 14 patients (27%) died. MIBG uptake at 1 hour was less (1.39 ± 0.10) in nonsurvivors than in survivors (1.50 ± 0.16; p = 0.013). In univariate Cox regression analysis, MIBG uptake was a significant prognostic factor (p = 0.038, hazard ratio [HR] 0.017, 95% confidence interval [CI] 0.00 to 0.79). Time- and frequency-domain variables were similar in survivors and nonsurvivors. However, high-frequency power was associated with an increased risk for sudden death (HR 0.310, 95% CI 0.101 to 0.954, p = 0.041) but not with all-cause mortality. In conclusion, cardiac I-123-MIBG imaging identifies patients with CHF at high risk of dying and may be a more reliable predictor of overall mortality than HRV.

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Patient population

The study population consisted of 52 consecutive patients with stable, chronic CHF, with left ventricular ejection fractions <40% by radionuclide ventriculography. Patients with atrial fibrillation or paced rhythms were excluded. The follow-up period was 2 years. With an expected mortality of 30% at 2 years, it was estimated that an adequate number of events would be available at the completion of the follow-up to allow prognostic assessments, at least univariately. At enrollment into the

Results

During a follow-up of 2 years, 14 patients (27%) died, 4 suddenly. The baseline characteristics, MIBG uptake, and HRV parameters measured in the overall patient population are listed in Table 1. The mean values of these same parameters in survivors versus nonsurvivors are compared in Table 2. There was a significant difference in the left ventricular ejection fraction and I-123-MIBG uptake at 1 hour between the 2 groups and a trend toward a significant difference at the 4-hour uptake. Of the

Discussion

I-123-MIBG uptake and HRV have been validated to assess the effects of the autonomic nervous system on cardiac function. MIBG is a noradrenaline analog taken up by cardiac sympathetic nerve endings, reflecting local sympathetic activity. A strong correlation between MIBG myocardial uptake and noradrenaline content in endomyocardial biopsy samples has been reported.9 In ischemic and dilated cardiomyopathy, regions of myocardial necrosis and fibrosis have reduced sympathetic innervation, which is

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