Revascularization Can Reverse Some Myocardial Damage, CMR Imaging Suggests

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Key Points:
  • CMR imaging contradicts idea of thinned myocardium as nonviable scar tissue
  • Thinned segments with less than 50% scarring improved after revascularization
  • But finding of `viable` myocardium still leaves revascularization decision unsettled, editorial says

By L.A. McKeown
Tuesday, March 05, 2013

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A large imaging study of patients with coronary artery disease (CAD) refutes the assumption that myocardial wall thinning is evidence of chronic myocardial damage. The study, published in the March 6, 2012, issue of the Journal of the American Medical Association, found that regional wall thinning with limited scar burden is associated with improved contractility after revascularization, indicating the potential for reversibility.

For the 3-center study, Raymond J. Kim, MD, of Duke University Medical Center (Durham, NC), and colleagues used delayed-enhancement cardiac magnetic resonance (CMR) imaging to examine regional myocardial wall thinning and scar burden in 1,055 CAD patients from August 2000 through January 2008.

Contractile Improvement, Reverse Remodeling Seen

Overall, 201 patients (19%) showed myocardial wall thinning, which encompassed a mean 34% of the left ventricular surface area. The vast majority (98.5%) of patients with wall thinning had scarring within the thinned region. Of these, 18% had limited scarring involving less than 50% of the thinned region. In multivariable analysis, compared with patients with extensive scarring in myocardial segments, those with limited scarring had:

  • Lower Selvester score (OR 0.87; P = 0.01)
  • Greater severity of stenosis in the coronary vessel supplying the thinned region (OR 1.03; P < 0.03)
  • Higher end-diastolic wall thickness (OR 1.86; P = 0.02)

Seventy-two patients underwent surgical or percutaneous revascularization including the coronary artery supplying the thinned region. Of these, 42 were followed for a mean of 116 days. Within the thinned region, the extent of scarring varied inversely with regional (r = -0.72; P < 0.001) and global (r = -0.53; P < 0.001) contractile improvement. After grouping patients into limited (≤ 50%) vs. extensive scar burden (> 50%), only those with limited scar burden showed contractile improvement in the thinned region, with a mean increase of 2.3 mm (P < 0.001) in absolute systolic wall thickening.

On multivariable analysis, scar extent had the strongest association with contractile improvement and reversal of thinning (both P < 0.001).

A Case for Reversibility

“Because the lack of scarring was associated with significant contractile improvement and reverse remodeling with resolution of wall thinning following revascularization, we believe the data indicate that myocardial thinning is potentially reversible and therefore should not be considered a permanent state,” Dr. Kim and colleagues write.

Furthermore, they say the similarity between patients with extensive and limited scarring suggests “that common clinical characteristics will not be useful in predicting whether thinned regions have limited scar tissue.” The findings “highlight that the pathophysiology of hibernating myocardium is still incompletely understood and that there is much to improve regarding the assessment of viability,” they write.

Future studies should focus on reversible ischemic injury and whether CMR guidance for coronary revascularization decisions results in improvements in outcome, the authors conclude.

Little Help in Guiding Revascularization Decision

However, in an editorial accompanying the study, Marc A. Pfeffer, MD, PhD, and colleagues, of Brigham and Women's Hospital (Boston, MA), urge caution in interpreting the results since it is unclear if “all of the thinned segments assessed in this analysis were also akinetic, which is generally considered as part of the criteria for nonviable myocardium.” Additionally, they say the study suffers from referral and selection bias with regard to which patients underwent CMR and which underwent revascularization and repeat CMR imaging.

“Furthermore, and perhaps most important, in the context of the results from the [Surgical Treatment for Ischemic Heart Failure (STICH)] trial addressing the value of viability assessments in guiding revascularization decisions, the clinician is still left trying to decide what to do with a finding of viable myocardium,” they conclude.

In the STICH trial, the presence of viable myocardium was associated with a greater likelihood of survival in patients with CAD and left ventricular dysfunction, but the relationship was not significant after adjustment for multiple baseline variables.

For now, Dr. Gupta and colleagues say, the incremental information gained from imaging “is not yet sufficient to alter clinical practice guidelines.”

Study Details

Patients with myocardial thinning were predominantly men (79%), had CAD risk factors (mean, 2.3), and significant left ventricular dysfunction (LVEF 32.6%). Most also had history of MI (71%) and Q waves on ECG (67%).

 


Sources:
1. Shah DJ, Kim HW, James O, et al. Prevalence of regional myocardial thinning and relationship with myocardial scarring in patients with coronary artery disease. JAMA. 2013;309:909-918.

2. Gupta DK, Kwong RY, Pfeffer MA. Cardiovascular imaging in clinical practice: What does late gadolinium enhance? JAMA. 2013;309:929-930.

 

Disclosures:

  • Dr. Kim reports being an inventor named on a US patent owned by Northwestern University for delayed enhancement cardiovascular MRI.
  • Dr. Gupta reports no relevant conflicts of interest.

 

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