MRI for Predicting Response to Biventricular Pacing
January 1, 2007 3 minutes read
MRI for Predicting Response to Biventricular Pacing
Abstract & Commentary
by John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Synopsis: The amount of myocardial scar on MRI predicts the clinical response to cardiac resynchronization.
Source: White JA, et al. Delayed Enhancement Magnetic Resonance Imaging Predicts Response to Cardiac Resynchronization Therapy in Patients With Intraventricular Dyssynchrony. J Am Coll Cardiol. 2006;48:1953-60.
Cardiac resynchronization therapy (CRT) by biventricular pacing has shown promising results for improving cardiac function in patients with advanced congestive heart failure and intraventricular conduction defects. However, in all trials, up to 30% of patients may not respond to CRT. In this study, White and his colleagues report on the possible value of magnetic resonance imaging for predicting response.
The authors report on a cohort of 28 consecutive patients who were recruited for the study. All had standard indications for CRT therapy including a QRS duration of greater than 120 m sec and tissue Doppler measured intraventricular dyssynchrony greater than or equal to 60 m sec. Patients underwent delayed enhancement magnetic resonance imaging (DE-MRI) using a 1.5-T magnet with electrocardiographic gating within 48 hours before insertion of the CRT device. Gadolinium contrast was used to allow delayed enhancement imaging. Images were divided into 6 equal wall segments and the amount of myocardium showing delayed enhancement (scar) was determined. The percent scar was determined for each segment by dividing scar area by total wall area and a number for percent total scar was determined. All patients underwent implantation of the CRT device using a coronary sinus lead. Atrioventricular intervals were optimized by echocardiography to maximize the potential benefit from biventricular pacing. Follow-up was performed at 3 months and consisted of an assessment of New York Heart Association functional class, a 6-minute walk test, a left ventricular ejection fraction (LVEF) measurement by radionuclide angiography, and a quality-of-life questionnaire. Patients were determined to be responders if they had either an improvement in ejection fraction greater than or equal to 5% or an improvement in 6-minute walk time plus either improved quality of life or NYHA functional class.
Of the 28 patients initially recruited, 5 patients did not complete the investigation or have a successful device implantation. Among the 23 patients who had complete data, 19 had left bundle branch block and 12 had ischemic heart disease as the cause of heart failure. Thirteen of 23 (57%) had a clinical response to CRT pacing as prospectively defined. Of the 10 nonresponders, 8 had a history of ischemic heart disease. The degree of baseline dyssynchrony was not predictive of response. Percent total scar by DE-MRI was an independent predictor of clinical response. Overall, 74% of the patients had some evidence of scar on DE-MRI imaging. All of the patients with a known previous myocardial infarction and 45% of the nonischemic patients had detectable scar. The mean percent total scar, however, was significantly greater in those with a clinical history of ischemic heart disease (25% vs 8%). Percent total scar was significantly greater in the clinical nonresponder group versus the responder group. Nonresponders could show both transmural injury patterns or dense mid wall scarring. Responders either had subendocardial scarring or just milder mid-wall hyperenhancement. Receiver operating characteristic analysis of total percent scar for the prediction of response showed that a cut-off value of 15% total scar provided a sensitivity of 85% and a specificity of 90% for the prediction of clinical response. Similar relationships were seen between percent total scar in all the outcome measures, including the LVEF, 6-minute walk tests, quality-of-life score, and NYHA functional class.
The authors conclude that the DE-MRI can accurately predict clinical response to CRT and should be considered in patients undergoing a procedure.
Commentary
Cardiac resynchronization therapy has shown impressive results in many patients. However, predicting response in an individual patient may be difficult. The concept that quantification of scar by DE-MRI may help select those patients likely to respond may enable physicians to be more effective when selecting patients for CRT. Other techniques such as radionuclide imaging or contrast echo to quantify scar, or its inverse, tissue viability have also been used for this purpose. DE-MRI has the advantage that it is more quantitative and may have be easier to interpret than the other approaches.
The amount of myocardial scar on MRI predicts the clinical response to cardiac resynchronization.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content