Heart rhythm disorders that circulate in the atria are called atrial flutter. The arrhythmia may be noticed as a fast and regular heartbeat, but not everyone notices it. It is not uncommonly discovered at a routine check-up with the GP or occupational health doctor. Most people can nevertheless confirm that their fitness has been poorer recently.
Typical atrial flutter
The most common type comes from the right atrium and depends on an area between the tricuspid valve and the inferior vena cava, called the cavotricuspid isthmus. When the electrical impulses enter this area, they are conducted slowly across to the other side. There they meet “rested” heart muscle cells that are able to conduct the impulses onward, and the circuit is maintained.
The circuit typically goes around 250–350 times a minute. Most commonly it runs counterclockwise, but clockwise flutter also occurs. If all the impulses passed freely down to the ventricles, they could cause severe heart failure within a short time. Fortunately they are slowed in the AV node, which acts as a filter and protects the ventricles from overload.
Cardioversion and blood thinners
Atrial flutter can be stopped with an electric shock through the chest while the patient is under brief general anaesthesia. This is called electrical cardioversion. The arrhythmia can also be stopped with potent antiarrhythmic drugs given intravenously, or by pacing the atria with a pacemaker lead. The latter is mainly relevant for patients who already have a pacemaker or defibrillator (ICD), and requires experience in programming such devices.
Before cardioversion it is important that the risk of blood clots is as low as possible. In atrial fibrillation and atrial flutter the atria have lost their pumping force, and blood clots can form that at worst are carried with the blood to the brain. This is one of the most common causes of stroke. Before cardioversion you must usually either have taken appropriate blood-thinning treatment for at least three weeks, or it must be certain that the arrhythmia has not lasted more than 48 hours.
As in atrial fibrillation, the treating doctor and the patient must decide together whether blood-thinning treatment should continue after cardioversion. Put simply, the risk of blood clots is weighed against the risk of bleeding.
Treatment
There are medicines that reduce the chance of recurrence, and medicines that slow the heart when the arrhythmia occurs. They can be effective, but experience shows that atrial flutter is difficult to treat with medication.
Many with typical atrial flutter are therefore referred to a regional hospital for ablation. The aim is to burn a line across the critical area between the tricuspid valve and the inferior vena cava. The line must completely block signals in both directions (bidirectional block). We achieve this in more than 90 per cent.
Even so, not everyone is relieved of their symptoms. Many people with typical atrial flutter also have atrial fibrillation or atypical atrial flutter, or develop it later. These arrhythmias do not depend on the cavotricuspid isthmus and therefore do not disappear, even when the line is complete.
The procedure starts with local anaesthesia around the large blood vessels in the right groin. Catheters are passed through the veins up to the heart. One is used to burn the line, the others to check that the line is complete. There are many nerve fibres in this area, so we give painkillers and sedatives before and during the treatment. Complications such as bleeding from the puncture site or into the pericardium can occur, but are relatively rare with this procedure. The threshold for doing it is therefore fairly low.
Atypical atrial flutter
Atypical atrial flutters are all the other flutters – those that do not depend on the area between the tricuspid valve and the inferior vena cava. They can be located in both the right and the left atrium. We most often find them in patients who have had previous heart surgery, have congenital heart disease or have undergone extensive ablation in the atria, for example atrial fibrillation ablation.
Ablation lines in the left atrium can become “leaky” and start conducting electrical signals again. Just as in the cavotricuspid isthmus, this can create slowly conducting areas and flutter circuits. If a valve or ring has previously been implanted between the left atrium and ventricle, the atrial wall has usually been both cut and sutured. Suture lines behave like leaky ablation lines and can also cause atypical flutter circuits.
These arrhythmias can often be treated with ablation, but experience shows that the procedures are long and extensive, with corresponding risk. Bleeding can occur wherever we have equipment. When we work in the left side of the heart, we must give a blood thinner (heparin) directly into the bloodstream, because both the equipment and the wound surfaces increase the tendency to form clots. Blood vessels lead directly from the left side of the heart to the brain, so we must be extra careful with anticoagulation. This increases the risk of bleeding, but reduces the chance of stroke. The risk of one of these serious complications is usually 1–2 per cent for ablation of atypical atrial flutter or atrial fibrillation, and lower for typical atrial flutter.
When deciding whether a procedure should be done, the chance of improving the patient’s situation must be weighed against the risk. The patient must be well informed about why we do the procedure, what we want to achieve, the chance of success and, not least, possible complications.