doi: 10.1161/01.CIR.0000164263.19461.AA
(Circulation. 2005;111:e286.)
© 2005 American Heart Association, Inc.
Correspondence |
Letter Regarding Article by Selvanayagam et al, "Value of Delayed-Enhancement Cardiovascular Magnetic Resonance Imaging in Predicting Myocardial Viability After Surgical Revascularization"
Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
With interest we read the study by Selvanayagam et al1 addressing the value of MRI with contrast enhancement to assess myocardial viability and predict subsequent improvement of function after revascularization. In 52 patients, contrast-enhanced MRI was performed early preoperatively (6 days) and late postoperatively (6 months). Clinically most important is the improvement of function at late follow-up because recovery of function may require sufficient time.2 In the article by Selvanayagam et al,1 viability was defined as segments with delayed enhancement on MRI involving <25% in transmurality. Using this cutoff value, the authors reported a positive and negative predictive value of 73% and 69%, respectively, to predict improvement of function. Re-analysis of the data revealed a sensitivity and specificity of 78% and 64%, respectively. The specificity of this approach is somewhat disappointing, as is observed for nuclear imaging techniques as well. This value is even lower when a cutoff value of 50% in transmurality was chosen, resulting in a sensitivity and specificity of 95% and 26%, respectively. These findings are not surprising. In fact, contrast-enhanced MRI is an excellent technique to assess infarcted tissue, but it does not provide information on the viability status of the remaining myocardium. In particular, if the remaining (nonenhanced) myocardium is normal, then no recovery can be anticipated, and the segment can be considered a subendocardial infarct. If the remaining myocardium is ischemically jeopardized (stunned, hibernating, ischemic, or all 3), however, then recovery of function may occur after revascularization. To further discriminate the viability status of the myocardial wall, additional information may be needed, and assessment of contractile reserve may be useful. In a recent study,3 a direct comparison between contrast-enhanced and low-dose dobutamine MRI in 48 patients with chronic left ventricular dysfunction demonstrated that 42% of the segments with an intermediate transmurality of infarction on contrast-enhanced MRI had contractile reserve and 58% did not. Moreover, Wellnhofer et al4 suggested that low-dose dobutamine MRI may be superior for predicting functional recovery. Do the authors believe that a stepwise approach for viability assessment may be considered? In particular, delayed enhancement could be used as an initial test, and in case of subendocardial infarction (25% to 50% transmurality), low-dose dobutamine MRI could be performed to further assess the likelihood of recovery of function.
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1. Selvanayagam JB, Kardos A, Francis JM, Wiesmann F, Petersen SE, Taggart DP, Neubauer S. Value of delayed-enhancement cardiovascular magnetic resonance imaging in predicting myocardial viability after surgical revascularization. Circulation. 2004; 110: 1535–1541.
2. Bax JJ, Visser FC, Poldermans D, Elhendy A, Cornel JH, Boersma E, van Lingen A, Fioretti PM, Visser CA. Time course of functional recovery of stunned and hibernating segments after surgical revascularization. Circulation. 2001; 104: I314–I318.[Medline] [Order article via Infotrieve]
3. Kaandorp TA, Bax JJ, Schuijf JD, Viergever EP, van Der Wall EE, de Roos A, Lamb HJ. Head-to-head comparison between contrast-enhanced magnetic resonance imaging and dobutamine magnetic resonance imaging in men with ischemic cardiomyopathy. Am J Cardiol. 2004; 93: 1461–1464.[CrossRef][Medline] [Order article via Infotrieve]
4. Wellnhofer E, Olariu A, Klein C, Grafe M, Wahl A, Fleck E, Nagel E. Magnetic resonance low-dose dobutamine test is superior to SCAR quantification for the prediction of functional recovery. Circulation. 2004; 109: 2172–2174.
Response
University of Oxford Centre for Clinical Magnetic Resonance Research, Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, UK
Department of Cardiothoracic Surgery, University of Oxford, John Radcliffe Hospital, Oxford, UK
We welcome the interest of Bax et al in our article.1 They state correctly that the improvement of function at late follow-up is clinically important because recovery of regional and global function may take a significant amount of time. Our follow-up window of 6 months after revascularization is as late a follow-up that has been reported in the literature in viability studies with delayed-enhancement magnetic resonance imaging (DE-MRI). The overall specificity of our study matches previous results2 and is only moderate when all hyperenhancement (HE) grades are considered. In our article, we acknowledged that this is particularly so in the intermediate HE segments, and stated that "the addition of low-dose dobutamine stress MR imaging to the DE-MRI protocol may further increase the diagnostic accuracy for viability detection, and future studies are awaited." The study by Kaandorp et al supports this assertion.3 Thus, we agree that a stepwise assessment is the preferred approach.
We do not believe, however, that dobutamine stress MRI (DSMR) is the preferred viability test for all comers. The recent finding by Wellnhofer et al4 that low-dose DSMR is superior to DE-MRI in predicting functional recovery is certainly of interest, but it should be viewed cautiously until larger studies from other centers have confirmed these findings. Furthermore, when considering noninvasive imaging options for viability assessment, many issues need to be considered, including availability, accuracy, safety, ease of use, and local expertise.
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1. Selvanayagam JB, Kardos A, Francis JM, Wiesmann F, Petersen SE, Taggart DP, Neubauer S. Value of delayed-enhancement cardiovascular magnetic resonance imaging in predicting myocardial viability after surgical revascularization. Circulation. 2004; 110: 1535–1541.
2. Kim RJ, Wu E, Rafael A, Chen EL, Parker MA, Simonetti O, Klocke FJ, Bonow RO, Judd RM. The use of contrast-enhanced magnetic resonance imaging to identify reversible myocardial dysfunction. N Engl J Med. 2000; 343: 1445–1453.
3. Kaandorp TA, Bax JJ, Schuijf JD, Viergever EP, van Der Wall EE, de Roos A, Lamb HJ. Head-to-head comparison between contrast-enhanced magnetic resonance imaging and dobutamine magnetic resonance imaging in men with ischemic cardiomyopathy. Am J Cardiol. 2004; 93: 1461–1464.[CrossRef][Medline] [Order article via Infotrieve]
4. Wellnhofer E, Olariu A, Klein C, Grafe M, Wahl A, Fleck E, Nagel E. Magnetic resonance low-dose dobutamine test is superior to SCAR quantification for the prediction of functional recovery. Circulation. 2004; 109: 2172–2174.
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