Atrial flutter is an atrial arrhythmia characterized by uniform morphology and a rate that is regular and greater than 240 BPM. It is often accompanied by a fixed 2:1 ventricular response, and it is this rapid ventricular response that results in the majority of symptoms. It may be observed transiently following cardiac surgery, or may persist for months to years. Atrial flutter is generally classified into three types: common, uncommon, and atypical (impure or type 2) atrial flutter. Common atrial flutter (also called typical counterclockwise flutter) is characterized by negative flutter waves in II, III, and aVF and an atrial rate of 250-320 BPM (Fig. 7). Uncommon atrial flutter (also called typical clockwise flutter) is characterized by upright flutter waves in II, III, and aVF and an atrial rate of 250-320 BPM. Atypical atrial flutter demonstrates morphologic features intermediate between AF and atrial flutter with atrial rates greater than 320 BPM.
Catheter Ablation for Atrial Flutter
The common and uncommon forms of atrial flutter are macroreentrant tachycardias confiend to the right atrium, and can potentially be cured with catheter ablation. In the common form of atrial flutter, the reentrant wavefront travels caudo-cranially along the interatrial septum and around the right atrium in a counterclockwise direction through a critical zone of slow conduction in the inferior right atrium between the triscupid annulus, the inferior vena cava (IVC), and the ostium of the CS. Conversely, the wavefront in uncommon atrial flutter travels in the reverse direction, proceeding cranio-caudally down the interatrial septum and around the right atrium in a clockwise direction. In contrast, atypical atrial flutter does not rely on an anatomically defined circuit, and thus is currently not amenable to catheter ablation.
Indications. Ablation of atrial flutter is indicated for patients with atrial flutter that is drug-resistant, or when the patient is drug-intolerant or does not desire long-term drug therapy (9).
Techniques. Catheter ablation of atrial flutter was first reported in 1986, and was performed by employing cryosurgery in the region of the CS ostium (61). Subsequently, success rates of approx 50% were reported for catheter ablation of atrial flutter using DC shock energy delivered in the low posteroseptal right atrium (62). Direct current energy has subsequently been abandoned in favor of radiofrequency energy (63-67).
Catheter ablation of atrial flutter is performed using an anatomic approach (63-65). A series of radiofrequency lesions are delivered along a line connecting the tricuspid annulus and the IVC or connecting the tricuspid annulus, the coronary sinus ostium, and the IVC. Radiofrequency energy (25-50 W) are delivered for 30-60 s at each ablation site either in sinus rhythm or during atrial flutter. The end point for catheter ablation of atrial flutter is the creation of bidirectional block along the ablation line
(68). Since restoration of sinus rhythm may transiently increase a patient's chance for embolic events, anticoagulation with warfarin is recommended for at least 1 mo prior to and following the procedure.
Outcomes and Complications. Although follow-up times are limited, the reported acute efficacy for radiofrequency catheter ablation of atrial flutter exceeds 85% in most series (64-69). Recurrences of atrial flutter or AF following a successful ablation procedure occur in approx 10% of patients using current techniques (27). Techniques to create larger radiofrequency lesions, such as ablation catheters with larger or saline-irrigated electrodes, have recently been shown to be useful in patients who fail ablation with standard radiofrequency catheters (12-15). No significant complications have been reported.
Theoretically, catheter ablation of the AV junction can eliminate any type of supraventricular arrhythmias that utilize the AV node as part of the reentrant circuit and can slow the ventricular response to supraventricular arrhythmias confined to the atrium.
Indications. In practice, catheter ablation of the AV junction is reserved for atrial arrhythmias that cannot be controlled with pharmacologic therapy, and which result in a rapid ventricular response.
Techniques. The procedure is performed by positioning a steerable ablation catheter across the tricuspid annulus to record a His bundle electrogram associated with a large atrial electrogram. A second electrode catheter is placed at the apex of the right ventricle for temporary pacing. Once an appropriate target site is identified, radiofrequency energy is delivered for 30-60 s. If AV conduction remains unchanged, the catheter is repositioned and a repeat attempt is made. If unsuccessful, a left-sided approach can be used (54). The ablation catheter is passed retrogradely across the aortic valve into the left ventricle and positioned immediately below the aortic valve to record a His bundle electrogram. Radiofrequency energy is then delivered in a standard fashion.
Outcomes and Complications. The overall efficacy of catheter ablation of the AV junction using these two approaches is nearly 100% (27,70-72). The recurrence rate is approx 2% (Fig. 3A) (27). In one recent series, the 1-yr survival following catheter ablation of the AV junction was 86% (27) (Fig. 4). Prior to or following ablation of the AV junction, a permanent rate-responsive pacemaker is inserted. For patients with drug-refractory AF, AV junction ablation with implantation of a DDDR pacemaker has been shown to be superior to drug therapy in controlling symptoms and improving quality of life (73). Complication rates are generally less than 2%, with an estimated incidence of procedure-related death of 0.2% (2,27). Late, sudden death has been reported following both DC or radiofrequency ablation of the AV junction (27,74). Because many of these patients have severe underlying heart disease, it is difficult to attribute these late, sudden deaths directly to the ablation procedure (27).
Recent studies have demonstrated the feasibility of slowing the ventricular response during AF by delivering radiofrequency energy along the posteroseptal portion of the tricuspid annulus, using a technique similar to the posterior approach to ablation of AVNRT (75,76). Although the initial results appear promising, the long-term safety and efficacy of this procedure remain uncertain and await the results of larger studies. This procedure has not gained widespread acceptance.
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