Imaging Before and After Electrophysiology Procedures

Imaging Before and After Electrophysiology Procedures

Introduction

Pre- or intraprocedural imaging has become integral to electrophysiologists to minimize the risks of invasive and technically difficult electrophysiology (EP) procedures. Postprocedural imaging is also imperative to detect complications. CT and MR are emerging as valuable noninvasive imaging modalities to provide this information, including establishing the etiology, identifying the substrate, prognosis/risk stratification, preprocedural evaluation/mapping, guidance during intervention, and postprocedural assessment.

Transthoracic echocardiography is a 1st-line means to image the heart, given that it is relatively inexpensive, available, and trusted. However, this modality is limited by variability in user skill and acoustic windows in individual patients. Though transesophageal echocardiography (TEE) may increase sensitivity for other cardiac findings, it is more expensive and obviously more invasive than its transthoracic counterpart.

Establishing Etiology

MR can help in establishing the etiology of an arrhythmia, with cine SSFP imaging demonstrating the morphology and quantifying functional parameters, whereas T1, T2, perfusion, and late gadolinium enhancement (LGE) sequences help with tissue characterization. The etiology of an arrhythmia (different cardiomyopathies) can be established based on the pattern of LGE. Parametric mapping techniques (T1, T2, T2*, ECV) also help in tissue characterization.

Identifying Substrate

Scarring or fibrosis identified with LGE MR likely contains the focus or substrate for an arrhythmia. Scar border-zone is critical in the perpetuation of an arrhythmia. MR is generally better in identifying substrates in the ventricles than the thin-walled atria. Using MR, myocardial disease is identified in 74% of patients, compared to 51% using non-MR techniques and 50% that are reassigned as a new or alternative diagnosis.

Prognosis/Risk Stratification

Several MR biomarkers are prognostic indicators of future adverse cardiovascular events. Scar burden (scar percentage, transmurality), total scar size, scar core size, scar heterogeneity, and peri-infarct gray zone are predictors of an arrhythmia. MR is a risk stratification tool for implantable cardioverter defibrillator (ICD) selection, based on the extent of the scar and ventricular function. Fibrosis also predicts appropriate device therapy in patients with an ICD.

Preprocedural Evaluation and Mapping

Atrial Fibrillation/Flutter Ablation

For atrial fibrillation (AF) ablation, CT and MR provide knowledge on the anatomy and variations of the pulmonary veins, which is essential to ensure that all the ectopic foci are ablated. Variations can be seen in the number, branching pattern, and length. Accessory ostium (1.6-19%) and common ostium (2.4-25%) are the common variations. Knowledge of ostial orientation and distances of the branches from the ostia is essential to avoid branch vessel stenosis. Pulmonary vein stenosis and thrombus are contraindications for the procedure. The location of the esophagus relative to the pulmonary vein ostia has the potential to minimize iatrogenic esophageal injury.

MR can also evaluate left atrial (LA) volume and function, which indicate persistent AF. The extent of LGE is a predictor of the type of AF (paroxysmal vs. persistent) and the recurrence of AF. Postcontrast T1 MR has also been used for the same purpose.

Left Atrial Appendage Closure

For patients being considered for left arterial appendage (LAA) closure devices, CT is useful in identifying contraindications, accurate sizing, and minimizing manipulation. Contraindications include LAA thrombus and pericardial abnormalities. For accurate sizing of the device, consider LAA parameters, such as LAA ostial diameter, LAA length from the landing zone, and the shape of the LAA. Atrial septal anatomy, pulmonary vein anatomy, LA size, and accessory LAA/diverticula morphology can also be assessed.

Ventricular Arrhythmia Ablation

For ventricular fibrillation (VF) ablation, the scar information from MR is fused with electroanatomic mapping (EAM) systems, allowing the electrophysiologist to focus on that area for ablation. Similar to AF, thrombus is a contraindication for the procedure.

Cardiac Resynchronization Therapy/Implantable Cardioverter Defibrillator

CT or MR provide knowledge about coronary venous anatomy and variations prior to cardiac resynchronization therapy (CRT), which is essential for venous access and to minimize fluoroscopy time. CRT is not possible if there are no coronary sinus tributaries, either as a normal variation or due to thrombosis. Intraprocedural venography is limited by its 2D nature. The presence of an extensive scar in LGE MR, especially in the lateral left ventricular wall, indicates that CRT will not be successful. Dyssynchrony mapping can also be performed using MR. The presence of septal-lateral delay in strain imaging, such as velocity-encoded or feature tracking MR, is a predictor of good CRT response.

Procedural Guidance

Procedural guidance is typically performed using fluoroscopy or a transesophageal echocardiograph (TEE). CT or MR data is loaded on to electroanatomic mapping systems. Interventional MR-guided EP procedures offer the potential for enhanced arrhythmia substrate assessment, improved procedural guidance, and real-time assessment of ablation formation.

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Tags: CT and MR in Cardiology

Apr 6, 2020 | Posted by admin in CARDIOVASCULAR IMAGING | Comments Off

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