Role of MRI in patient selection for CRT

Cardiac Magnetic Resonance as a Tool to Assess Dyssynchrony

Cardiac resynchronization therapy (CRT) improves cardiac mechanics and quality of life in many patients with evidence of electromechanical cardiac dyssynchrony. However, up to 30% of patients receiving CRT do not respond to therapy. The mediator for poor response likely varies among patients; however, careful evaluation of mechanical dyssynchrony may inform management strategies. In this article, some of the methods and supporting evidence for dyssynchrony assessment with MRI as a predictor for CRT response are presented. The case is made for pre-implant assessment with MRI because of its ability to characterize scar, coronary venous distribution, and regional strain patterns.

Twelve-Lead ECG Optimization of Cardiac Resynchronization Therapy in Patients With and Without Delayed Enhancement on Cardiac Magnetic Resonance Imaging

Background

Delayed enhancement (DE) on magnetic resonance imaging is associated with ventricular arrhythmias, adverse events, and worse left ventricular mechanics. We investigated the impact of DE on cardiac resynchronization therapy (CRT) outcomes and the effect of CRT optimization.

Methods and Results

We studied 130 patients with ejection fraction (EF) ≤40% and QRS ≥120 ms, contrast cardiac magnetic resonance imaging, and both pre‐ and 1‐year post‐CRT echocardiograms. Sixty‐three (48%) patients did not have routine optimization of CRT. The remaining patients were optimized for wavefront fusion by 12‐lead ECG. The primary end point in this study was change in EF following CRT. To investigate the association between electrical dyssynchrony and EF outcomes, the standard deviation of activation times from body‐surface mapping was calculated during native conduction and selected device settings in 52 of the optimized patients. Patients had no DE (n=45), midwall septal stripe (n=30), or scar (n=55). Patients without DE had better ∆EF (13±10 versus 4±10 units; P<0.01). Optimized patients had greater ∆EF in midwall stripe (2±9 versus 12±12 units; P=0.01) and scar (0±7 versus 5±10; P=0.04) groups, but not in the no‐DE group. Patients without DE had greater native standard deviation of activation times (P=0.03) and greater ∆standard deviation of activation times with standard programming (P=0.01). Device optimization reduced standard deviation of activation times only in patients with DE (P<0.01).

Conclusions

DE on magnetic resonance imaging is associated with worse EF outcomes following CRT. Device optimization is associated with improved EF and reduced electrical dyssynchrony in patients with DE.

A practical approach to imaging dyssynchrony for cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is believed to benefit patients by primarily correcting heterogeneity in regional ventricular mechanical contraction, known as dyssynchrony. Although many symptomatic heart failure patients with depressed left ventricular ejection fraction and widened electrocardiographic QRS complexes have clinical improvement from CRT, a significant subset of approximately one-third do not seem to respond. Because the degree of mechanical dyssynchrony may be widely variable, interest has remained high to attempt to improve patient selection for CRT using cardiac imaging as a means to quantify dyssynchrony. This article will review the principal echocardiographic methods of dyssynchrony analysis by tissue Doppler imaging, (opposing wall delay, 12-site standard deviation or Yu index, and longitudinal strain), routine pulsed-Doppler (interventricular mechanical delay, pre-ejection delay and filling time ratio), and speckle tracking (including radial, circumferential, and longitudinal strain). In addition, dyssynchrony analysis by cardiac magnetic resonance imaging is introduced as a potential alternative technique. The technical features, strengths and limitations, and clinical evidence for these methods are discussed, including a practical clinical approach.

Assessment of the coronary venous system in heart failure patients by blood pool agent enhanced whole-heart MRI

OBJECTIVE

To investigate the feasibility of MRI for non-invasive assessment of the coronary sinus (CS) and the number and course of its major tributaries in heart failure patients.

METHODS

Fourteen non-ischaemic heart failure patients scheduled for cardiac resynchronisation therapy (CRT) underwent additional whole-heart coronary venography. MRI was performed 1 day before device implantation. The visibility, location and dimensions of the CS and its major tributaries were assessed and the number of potential implantation sites identified. The MRI results were validated by X-ray venography conventionally acquired during the device implantation procedure.

RESULTS

The right atrium (RA), CS and mid-cardiac vein (MCV) could be visualised in all patients. 36% of the identified candidate branches were located posterolaterally, 48% laterally and 16% anterolaterally. The average diameter of the CS was quantified as 9.8 mm, the posterior interventricular vein (PIV) 4.6 mm, posterolateral segments 3.3 mm, lateral 2.9 mm and anterolateral 2.9 mm. Concordance with X-ray in terms of number and location of candidate branches was given in most cases.

CONCLUSION

Contrast-enhanced MRI venography appears feasible for non-invasive pre-interventional assessment of the course of the CS and its major tributaries.

Role of cardiac MRI and nuclear imaging in cardiac resynchronization therapy

Cardiac resynchronization has emerged as a highly effective therapy for heart failure. However, up to 40% of patients do not benefit from this treatment. In this Review, we discuss the potential role of MRI and nuclear molecular imaging in providing additional insights into the response to cardiac resynchronization therapy. Variables with potential prognostic and therapeutic values include the evaluation of cardiac dyssynchrony, scar, cardiac sympathetic function, myocardial blood flow, myocardial glucose and oxidative metabolism. Other molecular targets to characterize apoptosis, fatty acid metabolism, angiogenesis and angiotensin-converting enzyme activity will also be described. The potential use of these techniques in identifying and measuring responses to cardiac resynchronization therapy and future areas of research will be explored.