Cardiovascular magnetic resonance guided electrophysiology studies

Catheter ablation is a first line treatment for many cardiac arrhythmias and is generally performed under x-ray fluoroscopy guidance. However, current techniques for ablating complex arrhythmias such as atrial fibrillation and ventricular tachycardia are associated with suboptimal success rates and prolonged radiation exposure. Pre-procedure 3D CMR has improved understanding of the anatomic basis of complex arrhythmias and is being used for planning and guidance of ablation procedures. A particular strength of CMR compared to other imaging modalities is the ability to visualize ablation lesions. Post-procedure CMR is now being applied to assess ablation lesion location and permanence with the goal of indentifying factors leading to procedure success and failure. In the future, intra-procedure real-time CMR, together with the ability to image complex 3-D arrhythmogenic anatomy and target additional ablation to regions of incomplete lesion formation, may allow for more successful treatment of even complex arrhythmias without exposure to ionizing radiation. Development of clinical grade CMR compatible electrophysiology devices is required to transition intra-procedure CMR from pre-clinical studies to more routine use in patients

Magnetic Resonance Imaging Assessment of Ventricular Dyssynchrony Current and Emerging Concepts

Despite the numerous documented benefits of cardiac resynchronization therapy (CRT), a significant proportion of patients undergoing CRT do not demonstrate symptomatic or morphologic improvement, triggering the search to improve targeting of this therapy. Many studies now support direct assessment of mechanical dyssynchrony as a method to better identify CRT responders. Among the methods used, echo-Doppler imaging has taken center stage and is covered in other articles in this special issue; however, these methods have several inherent limitations, and other alternatives are also being explored such as magnetic resonance imaging (MRI). This review discusses the concepts and clinical use of MRI methods for quantitative assessment of mechanical dyssynchrony, highlighting newer acquisition and analysis methods and focusing on how the data can be synthesized into robust indexes of dyssynchronous heart failure

Cardiovascular magnetic resonance characterization of peri-infarct zone remodeling following myocardial infarction

<p>Abstract</p> <p>Background</p> <p>Clinical studies implementing late gadolinium-enhanced (LGE) cardiovascular magnetic resonance (CMR) studies suggest that the peri-infarct zone (PIZ) contains a mixture of viable and non-viable myocytes, and is associated with greater susceptibility to ventricular tachycardia induction and adverse cardiac outcomes. However, CMR data assessing the temporal formation and functional remodeling characteristics of this complex region are limited. We intended to characterize early temporal changes in scar morphology and regional function in the PIZ.</p> <p>Methods and results</p> <p>CMR studies were performed at six time points up to 90 days after induction of myocardial infarction (MI) in eight minipigs with reperfused, anterior-septal infarcts. Custom signal density threshold algorithms, based on the remote myocardium, were applied to define the infarct core and PIZ region for each time point. After the initial post-MI edema subsided, the PIZ decreased by 54% from day 10 to day 90 (<it>p </it>= 0.04). The size of infarct scar expanded by 14% and thinned by 56% from day 3 to 12 weeks (<it>p </it>= 0.004 and <it>p </it>< 0.001, respectively). LVEDV increased from 34.7. ± 2.2 ml to 47.8 ± 3.0 ml (day3 and week12, respectively; p < 0.001). At 30 days post-MI, regional circumferential strain was increased between the infarct scar and the PIZ (-2.1 ± 0.6 and -6.8 ± 0.9, respectively;* <it>p </it>< 0.05).</p> <p>Conclusions</p> <p>The PIZ is dynamic and decreases in mass following reperfused MI. Tensile forces in the PIZ undergo changes following MI. Remodeling characteristics of the PIZ may provide mechanistic insights into the development of life-threatening arrhythmias and sudden cardiac death post-MI.</p

Prospective Electrocardiogram-Gated Delayed Enhanced Multidetector Computed Tomography Accurately Quantifies Infarct Size and Reduces Radiation Exposure

ObjectivesThis study sought to determine whether low-dose, prospective electrocardiogram (ECG)-gated delayed contrast-enhanced multidetector computed tomography (DCE-MDCT) can accurately delineate the extent of myocardial infarction (MI) compared with retrospective ECG-gated DCE-MDCT.BackgroundFor defining the location and extent of MI, DCE-MDCT compares well with delayed enhanced cardiac magnetic resonance. However, the addition of a delayed scan requires additional radiation exposure to patients. MDCT protocols using prospective ECG gating can substantially reduce effective radiation dose exposure, but these protocols have not yet been applied to infarct imaging.MethodsTen porcine models of acute MI were imaged 10 days after MI using prospective and retrospective ECG-gated DCE-MDCT (64-slice) 10 min after a 90-ml contrast bolus. The MDCT images were analyzed using a semiautomated computed tomography density (CTD) threshold technique. Infarct size, signal-to-noise (SNR) ratios, contrast-to-noise (CNR) ratios, and image quality metrics were compared between the 2 ECG-gating techniques.ResultsInfarct volume measurements obtained by both methods were strongly correlated (R = 0.93, p < 0.001) and in good agreement (mean difference: −0.46 ml ± 4.00%). Compared with retrospective ECG gating, estimated radiation dosages were markedly reduced with prospective ECG gating (930.1 ± 62.2 mGy×cm vs. 42.4 ± 2.3 mGy×cm, p < 0.001). The SNR and CNR of infarcted myocardium were somewhat lower for prospective gated images (22.0 ± 11.0 vs. 16.3 ± 7.8 and 8.8 ± 5.3 vs. 7.0 ± 3.9, respectively; p < 0.001). However, all examinations using prospective gating protocol achieved sufficient diagnostic image quality for the assessment of MI.ConclusionsProspective ECG-gated DCE-MDCT accurately assesses infarct size compared with retrospective ECG-gated DCE-MDCT imaging. Although infarct SNR and CNR were significantly higher for the retrospective gated protocol, prospective ECG-gated DCE-MDCT provides high-resolution imaging of MI, while substantially lowering the radiation dose

Diminished Left Ventricular Dyssynchrony and Impact of Resynchronization in Failing Hearts With Right Versus Left Bundle Branch Block

ObjectivesWe compared mechanical dyssynchrony and the impact of cardiac resynchronization therapy (CRT) in failing hearts with a pure right (RBBB) versus left bundle branch block (LBBB).BackgroundCardiac resynchronization therapy is effective for treating failing hearts with conduction delay and discoordinate contraction. Most data pertain to LBBB delays. With RBBB, the lateral wall contracts early so that biventricular (BiV) pre-excitation may not be needed. Furthermore, the magnitude of dyssynchrony and impact of CRT in pure RBBB versus LBBB remains largely unknown.MethodsDogs with tachypacing-induced heart failure combined with right or left bundle branch radiofrequency ablation were studied. Basal dyssynchrony and effects of single and BiV CRT on left ventricular (LV) function were assessed by pressure-volume catheter and tagged magnetic resonance imaging, respectively.ResultsLeft bundle branch block and RBBB induced similar QRS widening, and LV function (ejection fraction, maximum time derivative of LV pressure [dP/dtmax]) was similarly depressed in failing hearts with both conduction delays. Despite this, mechanical dyssynchrony was less in RBBB (circumferential uniformity ratio estimate [CURE] index: 0.80 ± 0.03 vs. 0.58 ± 0.09 for LBBB, p < 0.04; CURE 0→1 is dyssynchronous→synchronous). Cardiac resynchronization therapy had correspondingly less effect on hearts with RBBB than those with LBBB (i.e., 5.5 ± 1.1% vs. 29.5 ± 5.0% increase in dP/dtmax, p < 0.005), despite similar baselines. Furthermore, right ventricular-only pacing enhanced function and synchrony in RBBB as well or better than did BiV, whereas LV-only pacing worsened function.ConclusionsLess mechanical dyssynchrony is induced by RBBB than LBBB in failing hearts, and the corresponding impact of CRT on the former is reduced. Right ventricular-only pacing may be equally efficacious as BiV CRT in hearts with pure right bundle branch conduction delay