Enhanced cardiac MR indicates dilated myopathy risk, identifies salvageable LV walls

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Not enough data for wide-spread adoption

Although these two imaging studies add to our knowledge of how supplemental noninvasive imaging studies can help cardiovascular specialists, "the clinical challenge remains in deciding which patients to evaluate with CMR and LGE and what to do with the findings," wrote Dr. Deepak Gupta, Dr. Raymond Kwong, and Dr. Marc Pfeffer.

The dilated cardiomyopathy (DCM) study, they note, did not take into consideration "proven and readily available" risk markers, such as recent hospitalization, renal function, and medication use. In addition, the study "was not powered nor designed to investigate the additional benefit of CMR beyond current class I indications for cardioverter-defibrillator therapy in DCM patients." Therefore, the data are "not sufficiently robust" to support the authors’ suggestion that LGE-CMR "may refine" the sudden cardiac death risk estimate ... [and] could guide [cardioverter defibrillator] implantation."

Regarding the thinned left ventricular wall study, the investigators failed to make clear whether all of the thinned segments assessed in this analysis were also akinetic, "which is generally considered as part of the criteria for nonviable myocardium. Furthermore, and perhaps most important, in the context of the results from [a recent] trial addressing the value of viability assessments in guiding revascularization decisions (N. Engl. J. Med. 2011;364:1617-25), the clinician is still left trying to decide what to do with a finding of viable myocardium.

Together, the two studies "provide a consistent message that detailed assessments of tissue composition, in particular fibrosis by LGE, may provide superior information than morphologic parameters, in both ischemic and nonischemic cardiomyopathies. CMR with LGE imaging adds to the practitioner’s armamentarium for assessment of cardiac structure and function and augments diagnostic and prognostic capabilities."

Dr. Gupta, Dr. Kwong, and Dr. Pfeffer, of the Division of Cardiovascular Medicine at Brigham and Women’s Hospital in Boston, made these comments in an editorial accompanying the two imaging studies (JAMA. 2013;309:929-30). They reported no disclosures.



By identifying cardiac fibrosis, cardiovascular magnetic resonance imaging with late gadolinium enhancement proved to be a useful cardiac assessment tool in two studies published in the March 6 edition of JAMA.

In the first, British researchers from London’s Royal Brompton Hospital and elsewhere used cardiovascular magnetic resonance imaging with late gadolinium enhancement [LGE-CMR] to detect and quantify midwall fibrosis in patients with dilated cardiomyopathy. They found that doing so "provided independent prognostic information beyond LVEF" – left ventricular ejection fraction, the basis of current risk stratification schemes –in patients with nonischemic dilated cardiomyopathy.

Separately, American investigators used the same technology in coronary artery disease patients to assess the extent of scarring in their thinned left ventricular walls. They found that "myocardial regions with severe wall thinning do not necessarily consist entirely of scar tissue but instead may have minimal or no scarring," which is inconsistent with current assumptions that thinned regions are made of permanent scar tissue and have no residual viability.

The British group, led by Dr. Ankur Gulati of Royal Brompton Hospital in London, followed 472 patients with dilated cardiomyopathy, assessed at baseline for midwall fibrosis, for a median of 5.3 years.

Thirty-eight of the 142 patients (27%) found to have midwall fibrosis – but only 35 of 330 (11%) without it – died during the trial. Adjusted for LVEF and other conventional prognostic factors, both fibrosis presence (hazard ratio 2.43) and extent (HR, 1.11) were independently and incrementally associated with all-cause mortality. Midwall fibrosis increased by more than five times the likelihood of sudden or aborted cardiac death (JAMA 2013;309:896-908).

LGE-CMR also appeared to "facilitate identification of high-risk patients with milder degrees of left ventricular dysfunction who are currently overlooked by assessment of global left ventricular function alone, Dr. Gulati and colleagues wrote, noting that use of the technology could help guide patient selection for implantable cardioverter defibrillators. Addition of fibrosis to LVEF also significantly improved risk reclassification, they said.

The Duke team, led by Dr. Dipan J. Shah of the Duke Cardiovascular Magnetic Resonance Center in Durham, N.C., followed 201 ischemic heart disease patients with LV wall thinning spanning a mean of 34% of LV surface area; thinning was defined as a diastolic wall thickness at or below 5.5 mm. Thirty seven patients (18%) had had limited or no scar burden, defined as no more than 50% involvement.

Seventy-two of the 201 patients underwent revascularization, including revascularization of the coronary artery supplying the thinned region. Among the 14 limited-scar-burden patients who had repeat CMR-LGE afterward, diastolic wall thickness increased significantly, from 4.4 mm to 7.5 mm; their LV walls were no longer thin. A multivariate analysis showed that the extent of scarring was the strongest predictor of improvement. (JAMA 2013;309:909-18).

The function of the thin walls was also related scar burden. Limited scar burden was "strongly associated with contractile improvement and reversal of wall thinning after revascularization." The results, taken together, showed that as long there is limited scarring, the myocardial wall may thin and revert back to full thickness. Thus, myocardial thinning should not be considered permanent, they concluded.

Most of the 201 patients had significant LV dysfunction and multivessel coronary artery disease. Neither age, sex, cardiac risk factors, angina, heart failure symptoms, nor Q wave presence predicted the amount of scarring.

"The findings suggest that these clinical characteristics should not be used to assess viability in a region of thinning." They also indicate that "the end-stage of remodeling is better determined by tissue composition (i.e., scarring) rather than any set level of morphological changes to the LV cavity or LV wall," the Duke team concluded.

Members of the British team disclosed grants, consulting arrangements, and other commercial relationships with Biotronik, Boston Scientific, Roche, Servier, Celladon, AstraZeneca, GlaxoSmithKline, GE Healthcare, Bayer, ResMed, Roche Diagnostics, Pfizer, Boehringer, Novartis, Medtronic, Siemens, ApoPharma, AMAG, and Cardiovascular Imaging Solutions.

Two authors on the Duke and Northwestern team are named inventors on a Northwestern University patent for delayed-enhancement cardiovascular magnetic resonance imaging. Another reported speaker fees, consulting deals, or pending grants from Astellas, Siemens, AstraZeneca, Lantheus Medical Imaging, and Takeda.

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