SYMPOSIA CT of the Pulmonary Veins Joan M. Lacomis, MD,* Orly Goitein, MD,w Christopher Deible, MD, PhD,* and David Schwartzman, MDz component of stroke volume (‘‘atrial kick’’), combined Abstract: Atrial fibrillation (AF) is a common cardiac rhythm with heart rates that are either too fast or too slow to disturbance and its incidence is increasing. Radiofrequency maintain an adequate cardiac output, leads to hemody- catheter ablation (RFCA) is a highly successful therapy for namic compromise, poor left ventricular function, and treating AF, and its use is becoming more widespread; however, heart failure.3 The left atrial appendage (LAA) has been with its increasing use and evolving technique, known complica- documented as the source of thrombi in 90% to 100% of tions are better understood and new complications are emer- nonrheumatic AF.3–6 Not only do up to 20% of all ging. Computed tomography (CT) of the pulmonary veins, or ischemic strokes occur in AF patients, but AF patients more correctly, the posterior left atrium (LA), has an established also have an 18 times higher rate of systemic arterial role in precisely defining the complex anatomy of the LA and emboli than the general population.3–6 pulmonary veins preablation and has an expanding role in Normally, the sinoatrial node fires by self-excitation identifying the myriad of possible complications postablation. eliciting a single electrical impulse. This impulse rapidly The purposes of this article are: to review AF and RFCA; to spreads across the right atrium (RA) along defined discuss CT evaluation of the LA and pulmonary veins electrical pathways and to the left atrium (LA) via preablation; and to review the complications of RFCA focusing Bachman’s Bundle.7 Synchronous atrial contraction on the role of CT postablation. forces blood into the ventricles. The speed of the electrical Key Words: atrial fibrillation, pulmonary veins, left atrium, impulse is slowed by the atrioventricular (AV) node radiofrequency catheter ablation, CT before the impulse continues to the Bundle of His and is propagated through the interventricular septum via the (J Thorac Imaging 2007;22:63–76) right and left bundle branches causing synchronous ventricular contraction (Fig. 1).7 AF occurs when multiple ectopic electrical foci fire independently sending the AV node as many as 300 discharges per minute.7 The irregular ventricular response ATRIAL FIBRILLATION depends on the refractoriness of the AV node, vagal and The most common of the sustained cardiac rhythm sympathetic tone, and the presence of accessory pathways disturbances, atrial fibrillation (AF) is a supraventricular resulting in heart rates ranging from 30 to over 300 beats tachyarrhythmia that has an overall prevalence of 0.4%, per minute.4,8 Although regular R-R intervals are but increases in incidence with age.1,2 Although rare in possible, on an electrocardiogram (ECG), AF is char- children, in adults, the incidence nearly doubles every 10 acterized by a lack of P waves which are replaced by years affecting approximately 5% of the population over fibrillatory waves of varying morphology and frequency, 65 years.3 It is estimated that approximately 2.2 to 2.5 with an irregularly irregular, often rapid, ventricular million people in the United States are affected by AF rhythm.4 which has significant clinical and economic consequences, Terminology describing AF can be confusing. Lone accounting for as many as one-third of yearly cardiac AF, accounting for 45% of AF cases, is defined as AF dysrhythmia hospitalizations.4 occurring in patients under 60 years of age without AF is an important overall marker for cardiovas- underlying cardiopulmonary disease.9,10 Paroxysmal AF cular risk and a major risk factor for stroke related to its (PAF) lasts less than 7 days and terminates sponta- 2 main complications: hemodynamic compromise and neously; whereas, persistent AF lasts at least 7 days and formation of thromboemboli.3 The loss of the atrial lasts indefinitely unless cardioverted. Both PAF and persistent AF can be recurrent, occurring more than once.4 With increasing age, recurrent episodes of PAF z tend to become persistent as the LA undergoes electrical From the *Department of Radiology; Cardiovascular Institute, 4 University of Pittsburgh Medical Center, Pittsburgh, PA; and and structural remodeling. Permanent AF lasts longer wDepartment of Radiology, Sheba Medical Center, Tel Hashomer, than a year and sinus rhythm is not possible.4 Isolated AF Israel. is defined as AF occurring without associated atrial Reprints: Joan M. Lacomis, MD, UPMC Presbyterian, Suite E-177, 200 4 Lothrop St, Pittsburgh, PA 15213-2582 (e-mail: lacomisjm@ tachycardia or aflutter. upmc.edu). Acute causes of AF include: recent surgery espe- Copyright r 2007 by Lippincott Williams & Wilkins cially cardiothoracic surgery, acute myocardial infarction, J Thorac Imaging Volume 22, Number 1, February 2007 63 Lacomis et al J Thorac Imaging Volume 22, Number 1, February 2007 RADIOFREQUENCY CATHETER ABLATION Although treatments for AF include direct electrical cardioversion or chemical cardioversion with antiarrhyth- mic agents, these are of limited success, with AF often refractory to or recurrent after the treatment.4 In addition, these require the use of long-term anticoagula- tion therapy. Newer therapies such as the surgical Cox-Maze procedure, cryoablation and radiofrequency catheter ablation (RFCA) are aimed at causing anatomic scars to disrupt electrical communication between the ectopic foci of the pulmonary veins and the LA body.14,15 If successful, long-term anticoagulation is unnecessary. RFCA, which is predominantly used for PAF, less often for persistent AF, is still under investigation and is a rapidly evolving therapy. As originally described by Haissaguerre et al in 1994, point ablation of site- specific arrhythmogenic foci within the walls of the distal pulmonary veins has subsequently proven to have a success rate of approximately 47%, often requiring repeat procedures and multiple veins, and has been associated with a high risk of pulmonary 12,14,16–20 FIGURE 1. ‘‘Conduction system’’: graphic representation of vein stenosis. The trend since then has been the basic components of the cardiac conduction system away from identifying the specific site of origin or superimposed on a volume rendered whole heart model with trigger point of AF, and to increase the number of an anterior cut away. AV indicates atrio-ventricular node; HIS, ablation lesions, thus increasing the volume of ablated bundle of HIS; LA, left atrium; LBB, left bundle branch; LV, left or electrically isolated substrate for the AF, the left ventricle; RA, right atrium; RBB, right bundle branch; RV, right atrial myocardium. Circumferential, also known as ventricle; SA, sino-atrial node. segmental, ablation of the extraostial region of the pulmonary vein(s) increased the success rate to 67%.18,19,21–23 To minimize the potential of recurrence of AF and the need for repeat ablation procedures, more myocarditis, pulmonary embolism or other acute pul- recent advances involve posterior left atrial ablation monary disease, hyperthyroidism, electrocution, stimu- which is circumferential ablation of the pulmonary lants such as caffeine or alcohol or increased sympathetic venous inflow vestibules bilaterally. Success rates in or parasympathetic tone.4 Treatment of the underlying patients without underlying structural heart disease have conditions can resolve the AF. However, AF is also increased to 88%, resulting in the more widespread associated with underlying structural heart disease, clinical use of RFCA for AF (Fig. 2).17–25 The 2005 particularly mitral valvular disease, hypertension, and worldwide RF catheter compilation reported that the coronary artery disease.4 Other independent risk factors numbers of AF ablations have increased every year since include: male sex, white race, age, diabetes, smoking, and 1995 when 18 patients underwent the procedure to a total obesity. With the increasing incidence of obesity, parti- of 8745 patients in 181 centers.23 Circumferential extra- cularly childhood obesity, the incidence of AF is expected ostial ablation and posterior left atrial ablation for to significantly increase.11 segmental isolation of the pulmonary veins are the Ectopic foci responsible for the initiation of AF current most widely used techniques; point ablation have been identified in the walls of the superior vena cava within the distal pulmonary veins has been aban- (SVC), both atria, the crista terminalis, ostium of the doned.19,26 coronary sinus, interatrial septum, and the muscular Technically, RFCA has several procedural varia- sleeves of the distal pulmonary veins.4,8,12 The importance tions, understanding the common features and challenges of the pulmonary veins in the initiation of AF is now well are important for both pre-RFCA and post-RFCA established. The myocardium of the LA extends a computed tomography (CT) evaluation. The procedure variable length into the distal pulmonary veins with the time is long, typically lasting several hours, and is myocardial sleeves of the superior and left pulmonary performed with the patient under general anesthesia. This veins longer than those of the inferior and right requires endotracheal or oro-tracheal intubation and the pulmonary veins.12,13 Over 90% of ectopic beats initiating use of high frequency ventilation to minimize respiratory AF arise from the pulmonary veins, 50% from the left motion.15–20,22 Transesophageal echocardiography (TEE) superior