There was a time when the treatment of an irregular heartbeat, or atrial fibrillation, was straightforward. Digoxin, a long-established medication derived from the foxglove plant, is still used to reduce the fast heart rate associated with fibrillation. It brings relief of symptoms in some patients, but does not really address the root cause of the problem.
Atrial fibrillation is a rhythm disturbance of the heart. "Atrial" refers to the upper chambers of the heart and "fibrillation" means that, rather than contracting slowly and rhythmically, the atrium moves chaotically and out of sequence with the lower chambers.
Jim, an 89-year-old retired farmer, came to the surgery complaining of palpitations, shortness of breath and tiredness. A cardiograph confirmed the clinical findings of atrial fibrillation and he was referred to a cardiologist for further investigation. In Jim's case, no underlying heart problems were detected. He did not have coronary artery disease, hypertension or a problem with the valves in his heart. He had already been assessed to see if his thyroid gland was over-active, which is a common cause of atrial fibrillation.
Jim returned to the surgery on anti-arrhythmic medication and his fibrillation had been well controlled. Most importantly, his symptoms had settled.
However, Jim was a little upset because the cardiologist had also prescribed warfarin, the anti-coagulant tablet. He did not want the trouble of having to attend weekly anti-coagulation clinics to monitor the effects of the blood thinner. And he was a little afraid that the warfarin could cause a haemorrhage. "Anyway, am I not too old for warfarin? Can't I take an aspirin instead?" he asked.
In fact, Jim was in one of the categories of patients at increased risk of developing a stroke caused by a blood-clot from the fibrillating heart (see panel).
Several studies have shown that the risk of a stroke is reduced from 5 per cent to 2 per cent in atrial fibrillation patients whose blood is properly thinned by warfarin. Thus, Jim was advised to continue with the medication. However, he was adamant that, despite the risks, he did not wish to continue. He agreed to take aspirin instead, even though it does not offer the same protective benefits.
Another group of patients who may be offered anti-coagulants on a short-term basis are those who are suitable for a procedure called cardioversion. This involves giving the heart a minor electric shock to "kickstart" a normal rhythm again. But because the procedure carries a 7 per cent risk of releasing a clot to the brain, it is usual to thin out the blood for a minimum of three weeks before cardioversion and four weeks after.
Atrial fibrillation is one of a number of conditions which can arise from problems with the heart's natural pacemaker. The sinoatrial (SA) node sets the pace or rhythm of the heart and transmits this information down an electrical system to the arteriovenous (AV) node at the junction of the upper and lower chambers. It then spreads out in bundles to the right and left of the heart.
As well as using cardioversion to influence this electrical system, surgical approaches to the problem have also been attempted. The "corridor" operation is designed to isolate the SA and AV nodes and the corridor of connecting tissue between them from the rest of the fibrillating upper chamber. While this can be reasonably successful in the short term, a significant number of patients subsequently require the insertion of a pacemaker.
The ultimate treatment, which cardiologists believe will be developed in the next three to seven years, would be a non-invasive procedure to ablate (burn) the faulty currents in the heart.
Using a catheter threaded into the heart via a small incision in the groin, micro-catheters could be used to ablate the faulty tissue in the conducting system so that a normal rhythm could re-establish itself.
Whether such a technique will ever replace current treatments using anti-arrhythmic medication, or whether it will be an option of last resort, remains to be seen. In the meantime, the majority of people with atrial fibrillation will get relief from one of the many drugs which have been developed since digoxin was first discovered in the early 1900s.
Dr Muiris Houston, Medical Correspondent, can be contacted at mhouston@irish-times.ie or messages can be left on tel: 01- 6707711, ext 8511. Dr Houston regrets he cannot reply to individual medical problems.