A promising new technique
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Unlike in the West where atrial fibrillation is often caused due to high blood pressure, rheumatic heart disease causes the condition in Indians.
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LISTENING TO a foetal heart can bring out memories of incessant heavy rain beating on windowpanes. It is not without reason that the foetal heart beats at a rate of 120-150 beats every minute — the small size of the heart necessitates such fast pace to supply blood to the body. It slows down in babies and reaches a rate of 50 to 100 times a minute in a normal adult.
The lub dub of the heart is actually the heart's rhythmic contraction to pump the blood. The rhythmic contraction starts at the sinus node in the upper left chamber (left atrium) and spreads to right atrium before reaching the ventricles.
In a normal adult, the contraction of two ventricles is synchronised with the two upper chambers to pump the blood to the rest of the body.
When the atria quivers
The trouble starts when the contraction is not all that rhythmic — in place of a single smooth wave of contraction spreading through the atria and ventricles, what is seen are multiple simultaneous waves of contraction that spread in a chaotic manner through the upper chambers. The two small upper chambers are then said to be quivering instead of beating rhythmically.
Doctors call the rapid irregular pounding sensation in the chest as `atrial fibrillation.' The quivering of the upper chambers in turn leads to reduced pumping capacity of the heart.
And when the pumping capacity is compromised, stagnation of the blood in parts of the upper chamber cannot be ruled out. In the worst scenario, pooled blood can form clots, which in turn can migrate to the brain to cause stroke.
High blood pressure and coronary artery disease are the most common causes of atrial fibrillation in the developed countries.
"In India it is the rheumatic heart disease which is the most common causal factor," said Dr. Sunil Chandy, Professor of Cardiology at the CMC Hospital, Vellore. Rheumatic fever caused by streptococcus infection is said to `lick the knees and bite the heart.'
The most common manifestation of the infection that goes untreated, as a child is the rheumatic heart disease. The mitral valve gets affected and narrowed down due to rheumatic heart disease. "The narrowing in turn builds up pressure in the left atrium," Prof. Chandy said.
"So the left upper chamber gets enlarged and muscle fibres get stretched and electrical conduction becomes irregular." Opening up the valve does not improve atrial fibrillation.
"So what is common in the aged population in the developed countries is seen in those as young as 40," said Dr. Prashanthan Sanders, Professor of Cardiology at the Royal Adelaide Hospital, Australia.
The prevalence of rheumatic heart disease in India is about 3.2 per cent while the study undertaken by CMC Hospital in the population living in and around Vellore has shown a prevalence rate of 0.69 per cent.
"This could possibly be because the awareness and timely medication for rheumatic fever is good in Tamil Nadu," Dr. Chandy said.
Radiofrequency ablation
While medications are available for atrial fibrillation, they can at best prevent the blood from clotting or provide symptomatic relief; they cannot cure it. "But radiofrequency ablation can provide permanent cure," assured Prof. Sanders.
Radiofrequency ablation kills the cells that cause atrial fibrillation and thus weeds out the problem altogether. This is achieved by ablating the trigger points using 30-50 watts power.
Ablating the four pulmonary veins using radiofrequency ablation is resorted to where the patients from the developed countries have developed atrial fibrillation due to high blood pressure or other reasons.
But with rheumatic heart disease being the causal factor in India, Prof. Sanders and doctors from CMC Hospital Vellore, have to first map the left atrium to know where the atrial fibrillation starts.
Mapping the atria
The doctors would be using electro-anatomical mapping using catheters to accurately pinpoint the origin of the problem. "The first step would be to map the left atrium to locate the trigger points.
Second step would be to do the ablation," Prof. Sanders explained. "Indian patients may also have the trigger points located in the pulmonary veins. Till we do the mapping we cannot be sure," added Dr. Chandy.
Plans are to recruit 48 patients both from India and Australia to map the left atrium. Those with normal hearts without much enlargement of the left atrium but with huge recurrent bouts of atrial fibrillation would be the ideal candidates for mapping.
"Once we map the atrium we can think of the next step," said Prof. Chandy. "Our final goal is to treat patients with atrial fibrillation caused by rheumatic heart disease." A beginning is about to be made.
R. Prasad
in Chennai
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