Catheter Ablation of Atrial Flutter

Mark Greenberg, MD

Radiofrequency catheter ablation is first-line therapy for atrial flutter, as the most common forms of atrial flutter can be cured with a 90% success rate at very low risk. A recent randomized trial of catheter ablation as first line therapy versus antiarrhythmic drug therapy for atrial flutter (mean follow-up 21 months) reported that 80% of the ablation group was in sinus rhythm off antiarrhythmic drugs versus 36% of those assigned to antiarrhythmics.(1) In the ablation group, atrial flutter recurred in only 6% of patients but de novo atrial fibrillation occurred in a minority of patients post ablation, reducing the overall efficacy rate.

Atrial flutter is recognized electrocardiographically as a rapid atrial tachyarrhythmia, typically at a rate of 240-350 beats per minute, with homogeneous and very regular atrial activity. Most commonly, atrial flutter is due to a large re-entrant circuit in the right atrium proceeding counter-clockwise up the atrial septum and down the lateral wall of the right atrium. Less commonly, the atrial flutter wavefront moves clockwise in the right atrium--down the atrial septum and up the lateral wall. The re-entrant wave front is constrained to an "isthmus" of tissue between the tricuspid valve and the inferior vena cava in the inferior right atrium. Radiofrequency catheter ablation in this area causes a line of conduction block, interrupting the atrial flutter and preventing its recurrence.

The ECG is helpful in selecting patients for radiofrequency catheter ablation. Counter-clockwise isthmus flutter, the most common type of atrial flutter, is recognized by the typical sawtooth pattern in the inferior leads (a prominent negative deflection; see right side of figure below) coupled with upright P waves in V1 and inverted P waves in V6. Clockwise atrial flutter demonstrates the inverse electrocardiographic pattern, namely upright P waves in the inferior leads (see left side of figure below), inverted P waves in V1, and upright P waves in V6. If the P waves in the inferior leads appear sinusoidal, it may be difficult to determine whether the P waves are upright or inverted, but V1 and V6 are generally still interpretable under these circumstances. Catheter ablation in the right atrium has very few complications,(1) though occasionally patients experience pericarditis or deep vein thrombosis. Rarely (less than 1% of the time), catheter perforation of the heart can occur, resulting in cardiac tamponade.

Infrequently, atrial fibrillation can exist as a re-entrant circuit elsewhere in the right atrium or even in the left atrium. These are more challenging tachyarrhythmias to ablate, particularly left atrial flutters. New three-dimensional electrophysiologic mapping techniques may ultimately facilitate ablation of left atrial flutter.

Invasive Therapies for Atrial Fibrillation

A. Radiofrequency catheter ablation of the AV junction for rate control

Radiofrequency catheter ablation of the AV junction is capable of achieving "perfect" rate control and markedly improves symptoms in patients with disabling palpitations or toxicity from high doses of drugs (e.g. beta blockers) needed to slow the AV node . This excellent rate control is achieved at the cost of permanent pacemaker implantation. Nevertheless, randomized controlled trials of radiofrequency catheter ablation versus pharmacologic therapy have demonstrated significant improvement in palpitations and quality of life indicators such as exercise tolerance.(2, 3) Patients may improve their ejection fraction, as many patients with poorly controlled rates in atrial fibrillation have a degree of tachycardia-induced cardiomyopathy ranging from mild to severe. Patients with somewhat slower rates may also benefit from regularization of the R-R intervals, which improves left ventricular filling and cardiac output. However, only a minority of AV junction ablations have been performed in this subset of patients.

B. Invasive methods designed to help maintain sinus rhythm.

Atrial pacing:

Standard anti-bradycardia pacing in the atrium reduces the atrial fibrillation burden compared to single-chamber ventricular pacing, in patients who have a bradycardia indication for pacing.(4) In patients undergoing permanent pacemaker implantation for radiofrequency catheter ablation of the AV junction, in whom bradycardia has not been documented, conventional atrial pacing appears ineffective at reducing the incidence of atrial fibrillation. Bradycardia causes dispersion of atrial refractory periods and increased automaticity of ectopic pacemakers, both of which can lead to atrial fibrillation. New software algorithms are an adjunct to conventional atrial pacing, as they can automatically overdrive the intrinsic atrial rate or help to prevent pauses after atrial premature beats that can lead to atrial fibrillation. Other pacing techniques undergoing evaluation include pacing the high atrial septum in order to more uniformly activate both atria homogeneously, or adding a second atrial lead near the low right atrial septum (near the os of the coronary sinus) to achieve the same end.

The implantable atrial defibrillator:

In the last year, the FDA has approved an implantable defibrillator for patients with refractory episodes of paroxysmal atrial fibrillation. Though this device also offers standard ventricular defibrillation, ventricular tachyarrhythmias are not required for implantation of this device. This device has atrial pacing algorithms that may reduce the atrial fibrillation burden, including atrial pacing to minimize pauses after atrial premature beats, and atrial tachypacing therapies to possibly terminate atrial tachyarrhythmias before they degenerate into atrial fibrillation.(5) In addition, the device allows both automated and patient-activated internal atrial defibrillation for atrial fibrillation. Though these shocks are uncomfortable, some patients prefer this sense of control over their atrial fibrillation, compared to seeking out medical care in an emergency room or physician's office.

Radiofrequency catheter ablation:

In some instances, atrial fibrillation is precipitated by more common forms of supraventricular tachycardia, such as those tachycardias associated with the Wolff-Parkinson-White syndrome, a concealed accessory pathway, or AV nodal re-entrant tachycardia. Although these cases comprise a minority of patients with atrial fibrillation, ablating the accessory pathway or eliminating the substrate for AV nodal re-entry will cure atrial fibrillation in a high percentage of cases.(6) Some patients who receive anti-arrhythmic drugs for atrial fibrillation will have organization of the rhythm to atrial flutter, which is amenable to catheter ablation (see I. above). In these instances, pharmacologic therapy is often sufficient to control atrial fibrillation after ablating the atrial flutter substrate.

Curative catheter ablation for atrial fibrillation is new, technically difficult, and still evolving. These procedures can target the substrate for atrial fibrillation, or the triggers. Substrate ablations attempt to mimic the surgical MAZE procedure (see below), by making linear radiofrequency lines of block endocardially. This technique is still considered highly investigational. Some dramatic cures of atrial fibrillation have been achieved by targeting the APB's that trigger atrial fibrillation, the majority of which originate from the pulmonary veins.(7) This technique is considered reasonable for patients with minimal structural heart disease who have lifestyle-impairing paroxysmal atrial fibrillation refractory to anti-arrhythmic drug therapy. However, this technique has only a 50-50 long-term success rate, compared to a 90% cure rate for radiofrequency catheter ablation of the common forms of supraventricular tachycardia and atrial flutter. In addition, extensive left atrial ablation in the region of the pulmonary veins appears to carry a larger risk of cerebral embolus than conventional left atrial ablative procedures. The risk of a TIA occurring peri-procedurally is about 2-4%, with a risk of pulmonary vein stenosis of about 1-8%.(8)

MAZE surgery:

The surgical MAZE procedure remains the only nonpharmacologic therapy for atrial fibrillation with a very high cure rate (>95%) in all comers (intermittent atrial fibrillation or persistent atrial fibrillation, with or without heart disease).(9) The MAZE operation compartmentalizes the atria utilizing multiple incisions, including an incision which isolates all four pulmonary vein orifices from the rest of the left atria (and therefore isolating triggers that may initiate atrial fibrillation). Atrial fibrillation is due to several re-entrant wavelets that wander in time and space throughout the atria. Post MAZE surgery, re-entrant circuits which try to form never get started, extinguishing themselves by meeting a line of block at the suture line. Simplified MAZE procedures confined to the left atrium, often performed at the time of mitral valve replacement, can reduce the atrial fibrillation burden but at the present time have a lower cure rate than the established MAZE procedure. Patients who undergo a surgical MAZE procedure have a very low stroke risk off Coumadin, probably due to the fact that the atrial appendages are amputated as part of the procedure. There is hope that a catheter-based procedure will ultimately replicate the excellent results of the MAZE operation. If this is achieved, the procedure will be applicable to a much larger number of patients, given the relatively "non-invasive" nature of a catheter procedure compared to a thoracotomy.

References:

1.Natale A, Newby KH, Pisano E, Leonelli F, Fanelli R, Potenza D, Beheiry S, Tomassoni G. Prospective Randomized Comparison of Antiarrhythmic Therapy Versus First-Line Radiofrequency Ablation in Patients with Atrial Flutter. J Am Coll Cardiol 2000;35:1898-904.
2. Brignole M, Menozzi C, Gianfranchi L, Musso G, Mureddu R, Bottoni N, Lolli G. Assessment of Atrioventricular Junction Ablation and VVIR Pacemaker Versus Pharmacologic Treatment in Patients with Heart Failure and Chronic Atrial Fibrillation. Circulation 1998;98:953-960.
3.Brignole M, Gianfranchi L, Menozzi C, et al. Assessment of Atrioventricular Junction Ablation and DDDR Mode-Switching Pacemaker Versus Pharmacological Treatment in Patients with Severely Symptomatic Paroxysmal Atrial Fibrillation: A Randomized Controlled Study. Circulation 1997;96:2617-24.
4.Connolly SJ, Kerr CR, Gent M, Roberts RS, Yusuf S, Gillis AM, Sami MH, Talajic M, Tang ASL, Klein GJ, Lav C, Newman DM. Effects of Physiologic Pacing Versus Ventricular Pacing on the Risk of Stroke and Death Due to Cardiovascular Causes. N Engl J Med 2000;342:1385-91.
5.Friedman PA, Dijkman B, Warman EN, Xia HA, Mehra R, Stanton MS, Hammill SC. Atrial Therapies Reduce Atrial Arrhythmia Burden in Defibrillator Patients. Circulation 2001;104:1023-28.
6.Haissaguerre M, Fischer B, Labbe T, Lemetayer P, Montserrat P, d'Ivernois C, Dartigues JF, Warin JF. Frequency of Recurrent Atrial Fibrillation After Catheter Ablation of Overt Accessory Pathways. J Am Coll Cardiol 1992;69:493-7.
7.Haissaguerre M, Jais P, Shah DC, Garrigue S, Takahashi A, Lavergne T, Hocini M, Peng JT, Roudaut R, Clementy J. Electrophysiological End Point for Catheter Ablation of Atrial Fibrillation Initiated From Multiple Pulmonary Venous Foci. Circulation 2000;101:1409-17.
8.Asirvatham SJ, Friedman PA. Ablation for Atrial Fibrillation: Is the Cure at Hand? J Cardiovasc Electrophysiol 2001;12:909-11.
9.Cox JL, Boineau JP, Schuessler RB, Jaquiss RDB, Lappas DG. Modification of the MAZE Procedure for Atrial Flutter and Atrial Fibrillation. J Thorac Cardiovasc Surg 1995;110:473-84.

Source: This overview originally accompanied a presentation given by Dr. Greenberg at the 2001 Cardiology Update on December 3, 2001.

back to Arrhythmias