CLINICAL COMMUNICATION TO THE EDITOR

Sudden Cardiac Death: Refining Risk Stratification by Cardiovascular Magnetic Resonance To the Editor: The current guidelines for implantable cardioverter defibrillator (ICD) placement are extremely helpful, but do not include many patients who may benefit from this therapy. Up to 70% of patients suffering from sudden cardiac death have a preserved left ventricular ejection fraction and are not candidates for ICD insertion based on the guidelines.1 We present a patient with aborted sudden cardiac death who had extensive sub-endocardial scarring on cardiovascular magnetic resonance (CMR) imaging suggestive of prior myocardial infarction despite preserved left ventricular ejection fraction. He received an ICD for secondary prevention because he was a survivor of sudden cardiac arrest. We believe the extensive scar noted on CMR was the arrhythmogenic focus for the ventricular fibrillation arrest. Although such a role is not identified in the current guidelines, this case highlights the potential of CMR for detection of myocardial scar and risk stratification in patients evaluated for ICD implantation in ischemic heart disease and preserved ejection fraction.

CLINICAL PRESENTATION A 56-year-old man collapsed while refereeing a soccer game and presented to the hospital after successful resuscitation. He denied any chest pain, dyspnea, palpitations, or dizziness preceding the collapse. His family history is significant for a brother with a sudden cardiac death at 59 years of age who was found to have severe 3-vessel coronary disease on autopsy. Initial electrocardiogram demonstrated no ischemic changes. Cardiac troponins were negative and electrolytes were in normal range. Transthoracic echocardiogram showed mild anterior wall hypokinesis with preserved left ventricular ejection fraction of 55%-60%. Cardiac Funding: None. Conflict of Interest: None. Authorship: All authors had full access to data during design and drafting of this manuscript. IR: Conception and design, drafting of manuscript; TT: Conception and design, drafting of manuscript; RJ: Conception and design, Revision of intellectual content. Requests for reprints should be addressed to Rajesh Janardhanan, MD, MRCP, FACC, FASE, Department of Medicine and Medical imaging, Sarver Heart Center, Box 245037, 1501 N Campbell Avenue, Tucson, AZ 85724. E-mail address: [email protected] 0002-9343/$ -see front matter Ó 2014 Elsevier Inc. All rights reserved.

catheterization revealed chronic total occlusion of the proximal left anterior descending artery with left-to-left collaterals. This was treated successfully with 2 drugeluting stents. Because he had a normal electrocardiogram, undetectable cardiac enzymes, and a chronic total occlusion on arteriography, his ventricular fibrillation arrest was less likely from an acute myocardial infarction. Therefore, CMR was performed to evaluate for any alternate cause for the ventricular fibrillation arrest. This demonstrated overall preserved left ventricular ejection fraction of 58%, but there was extensive sub-endocardial delayed enhancement in the left anterior descending artery territory, involving 50% of the mid-distal septum, anterior wall, and apex (Figure). The etiology for the cardiac arrest was therefore thought to be from a preexistent myocardial scar in the left anterior descending artery territory, and an ICD was placed for secondary prevention.

DISCUSSION Data suggest that the current guidelines for ICD implantation are far from satisfactory1 and do not include the presence or extent of myocardial scar burden. Myocardial scar tissue is known to serve as a substrate for malignant ventricular tachyarrhythmias. Klem et al showed that even in the patients with left ventricular ejection fraction >30%, the presence of significant scarring (>5%) poses the level of risk similar to those patients with left ventricular ejection fraction 30%.2 Delayed enhancement on CMR can reliably identify scar and prognosticate the risk of adverse events. The presence of scar visualized by CMR yields an odds ratio of 5.47 for all-cause mortality and of 8.01 for cardiac mortality, with escalating risk as the scar burden increases.3 In patients where the decision to implant a defibrillator is challenging, such as the case presented, CMR is a useful tool to stratify those who are potentially at a higher risk. Irbaz bin Riaz, MBBS, MMa Tam H. Truong, MDb Rajesh Janardhanan, MDb a

Department of Internal Medicine University of Arizona Tucson b Division of Cardiovascular Diseases Sarver Heart Center University of Arizona Tucson

http://dx.doi.org/10.1016/j.amjmed.2014.06.026

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The American Journal of Medicine, Vol 127, No 10, October 2014

Figure Red arrows pointing to sub-endocardial areas of late-gadolinium enhancement (panels A, B, and C) consistent with extensive myocardial scar.

References 1. Stecker EC, Vickers C, Waltz J, et al. Population-based analysis of sudden cardiac death with and without left ventricular systolic dysfunction: two-year findings from the Oregon Sudden Unexpected Death Study. J Am Coll Cardiol. 2006;47(6):1161-1166. 2. Klem I, Weinsaft JW, Bahnson TD, et al. Assessment of myocardial scarring improves risk stratification in patients evaluated for

cardiac defibrillator implantation. J Am Coll Cardiol. 2012;60(5): 408-420. 3. Bruder O, Wagner A, Jensen CJ, et al. Myocardial scar visualized by cardiovascular magnetic resonance imaging predicts major adverse events in patients with hypertrophic cardiomyopathy. J Am Coll Cardiol. 2010;56(11):875-887.

Sudden cardiac death: refining risk stratification by cardiovascular magnetic resonance.

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