Atrial Fibrillation Ablation: Do We Really Need Preprocedural Imaging?

Complications of catheter-based ablation

To consider the relative merits of any imaging modality, the focus should first be on the potential procedural complications that may be encountered during or after the procedure and on how these may be affected by imaging studies. Major complications during AF ablation include pulmonary vein (PV) stenosis, thromboembolism, atrioesophageal fistula, and phrenic nerve paralysis.¹³

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  PV stenosis. Initial ablation approaches targeted ectopy within the PVs and was associated with an unacceptably high

Preprocedural transesophageal echocardiography

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  Detection of intracardiac thrombi. Transesophageal echocardiography (TEE) provides high-quality images of cardiac structure²⁵ and function.²⁶ It is the most sensitive and specific technique to detect sources and potential mechanisms for cardiogenic embolism,²⁷ surpassing transthoracic echocardiography.²⁸ TEE features associated with thromboembolism in patients with nonvalvular AF include LA/left atrial appendage (LAA) thrombus, LA/LAA spontaneous echo contrast (SEC), reduced LAA flow velocity,

Current guidelines

The Heart Rhythm Society Consensus Statement on catheter ablation of AF recommends preablation TEE to exclude LA thrombus in patients with persistent AF; no specific recommendation is made for patients with paroxysmal AF.³⁰ However, the use of TEE to assess atrial thrombus before AF ablation is variable. Recent data suggest that preablation TEE is routinely used in up to 72% of centers performing catheter ablation of AF.¹³ However, TEE requires moderate sedation and, at times, esophageal

Incidence and predictors of periprocedural CVA in patients undergoing catheter ablation of AF

Although a successful AF ablation procedure may reduce the occurrence of future stroke, periprocedural stroke, and transient ischemic attack, CVAs remain among the most serious complications of catheter ablation of AF. The incidence and predictors of left atrial thrombus in patients undergoing AF ablation have been reported in several studies. McCready and colleagues³⁷ assessed a cohort of 635 patients who underwent TEE before AF ablation. All patients were on warfarin for a minimum of 4 weeks

Assessing intracardiac thrombus using CT

Although 64-slice CT scanning has been used to identify LA thrombus, TEE remains the gold standard. Patients referred for RF PV antral isolation often undergo contrast-enhanced multidetector CT (MDCT) to assess PV and left atrial anatomy as well as TEE to detect intra-atrial thrombus. A study by Kim and colleagues⁴³ sought to determine the accuracy of MDCT to qualitatively and quantitatively detect severe SEC or thrombus by TEE in the LAA and, in addition, to determine the ability of MDCT to

Assessing intracardiac thrombus using MRI

The data assessing MRI detection of LA and LAA thrombi are sparse. Abstract data on 110 patients undergoing two-dimensional (2D) and three-dimensional (3D) contrast and noncontrast MRI and TEE before PVI have been reported.⁴⁹ There was 100% concordance between MRI and TEE results (only 2 cases positive for thrombus). The 2D cardiac MRI (CMR) images were indeterminate in 9 cases in which 3D contrast images were most helpful in the final ruling out of LAA. They concluded that CMR offered a

CT and MRI of cardiac anatomy

Understanding the morphologic characteristics of the LA in detail not only helps achieve a more efficient and successful ablation but may also prevent procedure-related complications. CT/MRI may facilitate AF ablation procedures by³⁰ (1) imaging the anatomic features of the PVs and LA before procedures, (2) assessing the anatomic relationship between the LA, esophagus, and adjacent vascular structures, (3) providing an understanding of the degree of morphologic remodeling of the PVs and LA, and

Radiation exposure during AF ablation

Catheter ablation of AF is often a complex and long procedure requiring long fluoroscopy exposure time and often preceded and followed by CT scans. An important, less easily recognized, and rarely considered potential complication of AF ablation is the delayed effect of the radiation received by the patients, including acute and subacute skin injury,53, 54 malignancy, and genetic abnormalities.⁵³ Radiation exposure during AF ablation has been evaluated by Lickfett and colleagues.⁵⁵ They

Is preprocedural TEE mandatory?

In several studies, the incidence of thrombi in patients undergoing PVI is low, ranging from 0.6% to 2.9%. Clinical risk factors associated with the presence of thrombus in these studies were diverse: hypertension, advanced age and cardiomyopathy,³⁷ CHADS₂ score greater than or equal to 2, and LA dilatation, but not the type of AF and rhythm at the time of TEE,³⁸ increased LA diameter, female sex, persistent AF and structural heart disease,⁴⁰ impaired left ventricular function and a history of

Can thrombi be accurately identified by CT/MRI?

Although not the gold standard, intracardiac thrombi can be effectively identified using modalities other than TEE. MDCT has been shown to be highly sensitive and has a high NPV in the detection of severe LAA SEC and thrombus compared with TEE.43, 46, 47 MDCT has the potential ability to effectively exclude LAA filling defects. In addition, LAA/AscAo HU ratios greater than 0.75 show 100% NPV for exclusion of LAA thrombus or dense SEC⁴⁶ so, in patients undergoing PVI, MDCT examinations that show

Summary

Indications for preprocedural imaging vary and include assessing the presence of a thrombus before cannulation of the LA and delineating LA and PV anatomy either to facilitate the procedure or as a reference point to help to determine whether there are postprocedural complications. Because of the potential for various complications, it is important that these procedures are made as safe and effective as possible by combining safe procedural planning with effective therapy delivery. Predictors