Cardiac Iodine-123 Metaiodobenzylguanidine Imaging Predicts Sudden Cardiac death (SCD) in congestive heart failure patients independent of left ventricular (LV) ejection fraction and other clinical and electrocardiography (ECG) markers of risk?

Disclosure: Employment: Montefiore Medical Center, Albert Einstein College of Medicine; Ownership Interest: Pfizer; Consult/Advisory Board: BG Medicine, theheart.org, MD imaging, Intersocietal Accreditation Council.
Pub Date: Thursday, July 29, 2010
Authors: Mario Garcia, MD 
Article: Cardiac Iodine-123 Metaiodobenzylguanidine Imaging Predicts Sudden Cardiac Death Independently of Left Ventricular Ejection Fraction in Patients with Chronic Heart Failure and Left Ventricular Systolic Dysfunction

Tamaki S, Yamada T, Okuyama Y, Morita T, Sanada S, Tsukamoto Y, Masuda M, Okuda K, Iwasaki Y, Yasui T, Hori M, Fukunami M, ,  Cardiac iodine-123 metaiodobenzylguanidine imaging predicts sudden cardiac death independently of left ventricular ejection fraction in patients with chronic heart failure and left ventricular systolic dysfunction: results from a comparative study with signal-averaged electrocardiogram, heart rate variability, and QT dispersion.,  Journal of the American College of Cardiology,  53 (5) 426-35. View in PubMed

Does cardiac iodine-123 metaiodobenzylguanidine imaging (MIBG) predict sudden cardiac death (SCD) in congestive heart failure patients independent of left ventricular (LV) ejection fraction and other clinical and electrocardiography (ECG) markers of risk?

In this study, Tamaki and colleagues performed cardiac MIBG imaging, SAECG, 24-h Holter monitoring, and standard 12-lead ECG in 106 consecutive stable congestive heart failure (CHF) outpatients with a radionuclide left ventricular ejection fraction (LVEF) <40%. They calculated heart-to-mediastinum (H/M) MIBG activity ratio at 20 and 200 minutes after radioisotope intravenous injection and from the images determined the myocardial washout ratio (WR). They followed the patients for a period of 65 + 31 months, during which 18 patients died suddenly and 12 others died of heart failure. Using univariate and multivariate analysis they determined clinical, electrocardiographic, echocardiographic, and scintigraphic predictors of SCD.

The investigators reported that patients with an abnormal WR (>27%) had a significantly higher risk of SCD (adjusted hazard ratio: 4.79, 95% confidence interval: 1.55 to 14.76). By multivariate Cox analysis WR and LVEF were significantly and independently associated with SCD, whereas the signal-averaged ECG (SAECG), heart rate variability (HRV) parameters, or QT dispersion were not. They also reported that even in those patients with LVEF >35%, SCD was significantly more frequently observed in the patients with than without an abnormal WR (p = 0.02).

A LVEF <35% had a positive predictive value of 19% (15/77) and a negative predictive value of 90% (26/29), compared with 26% (14/53) and 92% (49/53) for MIBG, respectively, for the prediction of SCD.

The authors concluded that cardiac MIBG WR, but not SAECG, HRV, or QT dispersion, is a powerful predictor of SCD in patients with mild-to-moderate CHF, independently of LVEF.

The results of this study demonstrate that the MIBG imaging in heart failure patients adds important prognostic information and that it might be useful in selecting patients at high risk who may benefit from automated internal cardiac defibrillator (AICD) therapy. The absence of additional prognostic benefit obtained from SAECG, HRV, or QT dispersion confirms recent observation from other clinical studies.

The difference in SCD as well as in overall cardiac death in patients with WR >27% versus <27% (value 2 standard deviations above mean of a normal control population) was remarkable, and prompts for conducting larger clinical outcome studies that would investigate the use of this test as a way of refining the selection of patients for AICD therapy.

Nevertheless, the results of this study are too preliminary to recommend adopting this test in routine clinical practice. The population of patients studied was relatively small, and their incidence of SCD may have been higher than expected. The patients enrolled represent a selected cohort at higher risk, because they were not receiving beta blocker therapy at the time of randomization and did not receive AICD therapy during follow-up, which would have been appropriate for most of them according to guidelines.

Because a LVEF <40% was a selection criteria for entering the study, the predictive value of the MIBG WR cannot be compared with this well-established index in this population. Nevertheless, the results of this study clearly support that MIBG is a better predictor than SAECG, HRV, or QT dispersion.

Why shouldn’t the results of this study change our practice? The answer lies in Figure 3 and Table 5. The number of patients (n = 26) and the number of SCD events (n = 3) in patients with LVEF 35 to 45% were too low to advocate yet using MIBG results for identifying patients at risk who currently are above the LVEF threshold of 35% recommended by guidelines, albeit, this appears to be a promising area of investigation. On the other hand, adding a WR >27 as a criteria for limiting AICD implantation in patients with LVEF >35% would lower the sensitivity from 83% (15/18) to 61% (11/18) for SCD event prediction.

Finally, we would like to have more data to support the reproducibility of MIBG studies, not only as it relates to interobserver data analysis but to the potential for day-to-day variability in MIBG uptake.

-- The opinions expressed in this commentary are not necessarily those of the editors or of the American Heart Association. --