SINGAPORE - A patient who cannot use medicine to regulate his severe irregular heartbeat can now turn to an improved minimally invasive procedure that controls heart rhythm and rate.
The procedure, called catheter ablation, could spare such patients a lifetime of having to take medication. Doctors estimate that about 20 to 30 per cent of patients with significant symptoms of atrial fibrillation would benefit from it. These patients cannot tolerate or do not want to take medicine, or it does not control their symptoms.
This "keyhole" procedure involves the passing of a thin flexible wire through blood vessels in the leg to reach the heart.
Radiofrequency energy is then delivered through the ablation catheter to make a ring of lesions (scars) on the inner wall of the left atrium of the heart. Within the ring are the exits of the four pulmonary veins that drain blood from the lungs into the left atrium of the heart.
Abnormal electrical signals from the pulmonary veins are believed to trigger atrial fibrillation in most patients. As scar tissue is electrically inert, the ring of scars cordoning off the pulmonary veins will block their abnormal electrical signals from reaching the rest of the heart.
Catheter ablation has evolved markedly over the past 10 years. Dr Reginald Liew, senior consultant cardiologist at The Harley Street Clinic at Mount Elizabeth Novena Hospital, said that in the early days of the technique, cardiologists would burn only one or two of the pulmonary veins in which abnormal electrical signals were detected during the procedure.
But they found there was a risk that the pulmonary veins could narrow later due to scar formation at the ablation sites within the pulmonary veins, causing contraction of the blood vessel at a later date. Cardiologists also realised later that the other pulmonary veins which were not targeted might also give off abnormal signals.
The new strategy has made the procedure safer as there is now less chance of a pulmonary vein narrowing after the procedure. It has also significantly improved the outcome of the procedure with a lower chance of atrial fibrillation recurring.
Also, the use of 3-D cardiac equipment allows doctors to combine the anatomy of the heart with the electrical signals and guide the ablation lesions more accurately. Such equipment also helps doctors avoid delivering too much radiofrequency energy to any particular spot, which can cause complications. Catheter ablation and a two- to three-night stay at the Mount Elizabeth Novena Hospital cost $22,000 to $26,000.
Depending on the complexity and patients' medical conditions, the procedure costs between $7,500 and $22,400 for non-subsidised patients at the National University Heart Centre, Singapore (NUHCS). It costs about $10,000 for non-subsidised patients at the National Heart Centre Singapore.
In patients whose atrial fibrillation is intermittent, the procedure has an 80 to 90per cent success rate, compared with the 40 to 50 per cent success rate of medication to regulate heart rhythm, said Dr Liew.
But the atrial fibrillation recurs in 10 to 20per cent of patients with intermittent atrial fibrillation and 30 to 40 per cent of patients with constant atrial fibrillation or with other forms of heart disease such as heart failure.
They will need another procedure to burn away the heart tissue that cause it, said DrLim Toon Wei, a consultant at the cardiac department at the NUHCS.
He added: "Sometimes, to achieve adequate rate control, patients may need the implantation of a pacemaker as well."
Study trials are under way to determine if catheter ablation improves not just symptoms, but also long-term clinical outcomes including stroke prevention.
How medication works
For the majority of patients with atrial fibrillation, however, medication is usually enough. They are given anti-arrhythmic medication to help them either maintain a normal heart rhythm or ensure that the heart rate is not too fast if the rhythm remains irregular.
To lower their risk of stroke, they are also given drugs which "thin the blood". These include aspirin and clopidogrel or anti-coagulants such as warfarin.
The use of these types of drugs is balanced against the risk of stroke of individual patients.
Warfarin is more effective than the other drugs, but patients on it have a higher risk of bleeding as their blood becomes too thin. Warfarin reduces the risk of stroke in patients with atrial fibrillation by about 60 to 80 per cent compared with no drug at all.
Aspirin, used for patients with lower stroke risk, reduces the risk of stroke by about 20 to 40 per cent compared with no drug.
Warfarin is more troublesome to use as it requires frequent blood tests and dose adjustments. Thus, it is used only in higher risk patients as the increased efficacy makes it more worthwhile, said Dr Reginald Liew, a senior consultant cardiologist at The Harley Street Clinic at Mount Elizabeth Novena Hospital.
In the last year or so, two new anti-coagulants, which are at least as effective as warfarin in preventing strokes from atrial fibrillation, have entered the market and may well revolutionise how doctors treat these patients, said Dr Lim Toon Wei, a consultant at the cardiac department at the National University Heart Centre, Singapore.
Dabigatran (pradaxa) and rivaroxaban (xarelto) are more user-friendly and, unlike warfarin, do not require frequent blood tests and adjustments of doses.
However, they cost about 20 to 25times more than warfarin and, hence, are not very widely used yet.
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