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Atrial flutter

Atrial flutter is a common rhythm disturbance where the atria beat at 250-350 beats per minute. This rate is too fast for them to effectively help fill the bottom the left ventricle, which provides cardiac output to the body. Therefore heart efficiency is diminished somewhat. Fortunately, the AV Node filters the atrial inputs or the pulse would also be at 300 and a cardiac arrest could occur. Usually this results in a pulse of about 150 beats per minute. If the AV Node filters more effectively then the heart rate could be 100, 75, 60 or even slower.

Consequences of atrial flutter

When atrial flutter occurs, the heart does not pump blood as efficiently to the body. This occurs because of several factors. First, when the atrium is no longer coordinated with the ventricle, the stroke volume declines. Compensatory processes occur to support stroke volume via the Frank-Starling mechanism: elevated left atrial and pulmonary pressure augment ventricular filling. However this tends to produce symptoms of breathlessness at rest or with exertion. Secondly, whenever the pulse is rapid and/or irregular, the efficiency declines further. Lastly, when the atria flutter, the walls do not pump as vigorously. After 48 hours, a thrombus can form, usually in the left atrial appendage. If the thrombus dislodges, it has about an 85% chance of being embolized into the carotid arteries causing a stroke. In the other 15% of the time, the clot may embolize into the artery of an organ or into a peripheral artery jeopardizing its viability and requiring emergent vascular surgery or catheter retrieval.

Symptoms of atrial flutter

Some patients do not even know that they are in atrial flutter. However most patients have some symptoms such as palpitations, heart racing, fatigue, shortness of breath and/or chest pain. Light-headedness or syncope is rarer. Sometimes, it is difficult to ascertain the onset of atrial flutter, particularly when the symptoms are not prominent. With other patients, it is fairly easy to tell when atrial flutter started.

Risks of atrial flutter

Atrial flutter is a nuisance and not life threatening, but there is a risk of stroke. Atrial flutter does not cause myocardial infarction, cardiac arrest or death. Therefore it is a nuisance – there are many people who lead decades of their lives in atrial flutter. Therefore it should not be surprising that restoring sinus rhythm and preventing recurrence of atrial flutter does not prolong life. Rather, such treatment with antiarrhythmic medications or procedures always carries some risk. Antiarrhythmic medications may rarely precipitate a cardiac arrest, and curative ablation procedures have rarely been associated with death and other major complications. However the pulse must be controlled or a cardiomyopathy may result.

Patients with atrial flutter

Men are more likely to have atrial flutter than women. Most patients with atrial flutter have hypertension or some form of structural heart disease. These can be identified most easily with an echocardiogram. The echo can show left ventricular hypertrophy, left ventricular dilatation with low ejection fraction, left atrial size, pericardial effusion suggestive of pericarditis as well as valvular heart disease. It may also reveal regional left ventricular wall motion abnormalities from myocardial infarction.

Treatment of atrial flutter

There are only two other reasons to try to get a patient out of atrial flutter into sinus rhythm. The first of these is to alleviate symptoms. Restoring sinus rhythm will relieve the symptoms associated with atrial flutter. However, if the antiarrhythmic medication used has its own side effects, these may in some cases be worse than those from the atrial flutter itself. Nevertheless, most patients feel better in sinus rhythm. The second reason to restore and maintain sinus rhythm is to prevent the rare occurrence of a dilated cardiomyopathy with congestive heart failure that can occur if the pulse remains fast.

Some patients with atrial flutter also have atrial fibrillation, which is usually harder to treat. If only atrial flutter exists, then it makes the job easier. Symptomatic patients should be treated by one of two strategies. With the rate control strategy, no effort is made to restore sinus rhythm. Rather medications (digitalis, calcium or beta blockers) are given to slow ventricular response to atrial flutter and therefore the pulse. Without medications, the pulse is usually about 150 (2:1 response) but this rate is fast enough to lead to congestive heart failure over time. However it usually requires significant doses of a single medication or multiple medications to lower the pulse further. The goal is to reduce the resting pulse ideally to 75 or so and then to be sure that the maximum pulse with exercise does not exceed 150. Because the response of the AV node to atrial flutter occurs in functional levels, the response is much more likely to be multiples of 2:1 (4:1, 6:1) than 3:1 or 5:1. If medications are not effective or cause side effects, then the rhythm control strategy is usually tried rather than AV node ablation and permanent pacing. With the rhythm control strategy the patient is first anticoagulated with oral anticoagulant medications or a transesophageal echo performed to exclude left atrial thrombus. Then cardioversion is performed to restore sinus rhythm. If atrial flutter has been recurrent or if left atrial size is large, antiarrhythmic drugs are usually required to maintain sinus rhythm. Alternatively, intracardiac ablation can be performed to restore and maintain sinus rhythm (see below). Anticoagulation is mandatory for the first month after sinus rhythm is restored no matter which route was used (1).

With regard to antiarrhythmic drugs vs. ablation, there have been two large randomized studies that have both suggested that ablation works better than medications for most patients with atrial flutter (2,3).

Asymptomatic patients may be left in atrial flutter. This strategy works best when the pulse is already slow because the AV Node is sluggish. Such rare patients do not need rate-slowing medications at all. However in these patients, the AV node may become even more sluggish requiring a permanent pacemaker. If this is the case, a ventricular pacemaker can be utilized. However some patients may convert spontaneously back to sinus bradycardia and then be left with pacemaker syndrome requiring upgrade to an AV sequential pacemaker.

Ablation for atrial flutter

Most atrial flutter results because the heart beat runs in a continuous circle around the right atrium. The flutter pathway requires a certain corridor or isthmus of heart tissue in the low right atrium. The isthmus is between the tricuspid valve and the crista terminalis (a ridge inside the right atrium) or the inferior vena cava. The flutter can go through this isthmus in the clockwise or counterclockwise direction. This is the critical part of the flutter circuit that must be destroyed in the ablation procedure. Other more rare flutters can involve scars within the right or left atrium from previous open heart surgery or the left atrium in patients with atrial fibrillation who have had curative left ablation. The atrial flutter circuits are more complex and are more difficult to cure with ablation.

Before the ablation procedure can occur, the electrophysiologist must do one of two things to be sure that there are no blood clots in the heart. The most common strategy is for the patient to take a blood thinner in pill form for at least a month. The other strategy is for a transesophageal echo or TEE to be performed to ensure that no clot is present in the left atrium is look at the heart. Usually, there is no clot seen and the procedure can be safely performed. If a clot is seen, then the ablation is cancelled, and the patient must undergo more vigorous anticoagulation for at least 1-2 months and the TEE repeated to ensure resolution of the clot.

With the most common right atrial flutter ablation, the tubes or catheters enter through sheathes in the femoral and/or subclavian/internal jugular veins and are passed to the right atrium and the coronary sinus. Special pacing of the heart called entrainment mapping is then performed to prove that the isthmus is required for the flutter to persist. If it is required, then a steerable ablation catheter is placed where the isthmus begins near the tricuspid valve. RF energy is then typically used to create a burn in this portion of the isthmus. After a lesion is made, the catheter is withdrawn a few millimeters and another lesion made. Eventually lesions form a line. When the line finally meets the other border of the isthmus, complete block is produced and the atrial flutter terminates. The line can then be tested for gaps by trying to again induce atrial flutter as well as by special pacing maneuvers. If RF energy is used to burn the isthmus, the heating usually causes some pain for the patient. However if cryoablation is used to make the lesions, the procedure is painless (4).

In general, ablation is successful in preventing conduction through the isthmus (rendering atrial flutter impossible) in about 95% of patients at the end of the procedure. Although isthmus conduction may recover in 30% of patients (5), atrial flutter only recurs in about 5%, and these can usually be cured with a second ablation procedure which identifies the gap in the line and places additional lesion(s) there or creates a whole different isthmus line. Unfortunately, even though AFl may be cured by ablation, atrial fibrillation may occur limiting the number of patients ultimately benefited by ablation ( 6). After the ablation procedure, the patient is started on coumadin/warfarin and usually also on lovenox to bridge the gap until the oral medication takes effect. Anticoagulation is mandatory for about a month to minimize the risk of a stroke. After this period of time, anticoagulation is usually stopped in patients in whom it was started only so the ablation procedure could be performed.

Cryoablation for atrial flutter

Some electrophysiologists prefer cryoablation to RF ablation for atrial flutter. One advantage is that cryoablation does not cause the patient any pain during the procedure like RF ablation usually does. Other potential benefits can be found in the section on the advantages of cryoablation. Several studies have been performed showing that cryoablation works well for atrial flutter (4,5,7,8). There are no large studies directly comparing cryo with RF, so we do not know which is superior. One small study found RF ablation slightly better than cryoablation (9). Preliminary use of microwave energy in atrial flutter ablation suggests it may ultimately also be effective and safe (10).

References

  1. Connolly S, Eikelboom J, O’Donnell M etal. Challenges of establishing new antithrombotic therapies in atrial fibrillation. Circulation 2007; 116:449-455.
  2. DaCosta A, Thevenin J, Roche F etal. Results for the Loire-Ardeche-Drome-Isere-Puy-de-Dome (LADIP) trial on atrial flutter, a multicentric prospective randomized study comparing amiodarone and radiofrequency ablation after the first episode of symptomatic atrial flutter. Circulation. 2006; 114: 1676-1681
  3. Wazni O, Marrouche N, Bharqava M etal. Radiofrequency ablation vs. antiarrhythmic drugs as first-line treatment of symptomatic atrial flutter: a randomized trial. JAMA 2005; 293:2634-2640.
  4. Kurzidim K, Greiss H, etal. Acute success and persistence of bidirectional conduction block in the cavotricuspid isthmus one month post cryocatheter ablation of common atrial flutter. Pacing and Clinical Electrophysiology. 2006; 29: 146-152
  5. Montenero A, Bruno N, Antonelli A, etal. Long-term efficacy of cryocatheter ablation for the treatment of atrial flutter. Journal of the American College of Cardiology. 2005; 45:573-580
  6. Chinitz J, Gerstenfeld E, Marchlinski F etal. Atrial fibrillation is common after ablation of isolated atrial flutter during long-term follow-up. Heart Rhythm 2007; 4: 1029-1033
  7. Montenero A, Bruno N, Zumbo F, etal. Cryothermal ablation treatment of atrial flutter – experience with a new 9 French 8 mm tip catheter. Journal of Interventional Electrophysiology. 2005; 12: 45-54
  8. Montenero A. Bruno N, Antonelli A etal. Comparison between a 7 French 6 mm tip cryothermal catheter and a 9 French 8 mm tip cryothermal catheter for cryoablation treatment of common atrial flutter. Journal of Interventional Cardiac Electrophysiology. 2005; 13:59-69
  9. Kunnis M, Vogtman T, Ventura R etal. Prospective randomized comparison of radiofrequency ablation with cryoablation using a 8 mm tip ablation catheter for the ablation of common atrial flutter (CRYOTIP). Presented at the HRS Meetings 2007 in Denver Colorado
  10. Chan J, Fung J, Yu etal. Preliminary results with percutaneous transcatheter microwave ablation of typical atrial flutter. J Cardiovasc Electrophysiol 2007;18: 286-289