Sunday, May 20, 2012
Singapore - The beat that your heart skipped
Madam T has been having recurrent strokes every year for the last four years. In the past six months alone, she was incapacitated by the development of two new strokes. Her latest stroke occurred about two months ago and left her with slurred speech and partial weakness.
She first turned up in my clinic soon after the latest stroke. Although she had mild weakness, she managed to walk into my clinic without any assistance, but she was particularly frustrated with her slurred speech and inability to express herself. What was obvious was that she had a fast and irregular heart rhythm, atrial fibrillation (AF), which explained why she had recurrent strokes.
In AF, electrical impulses are being generated in the atria (upper chambers) in a chaotic manner at a rate of about 400 per minute. The impact of this is that the atria are effectively just "quivering". The inflowing blood will slow down considerably when entering the left upper heart chamber (LA).
In the LA, there is a blind pouch called the atrial appendage (LAA). The blood entering into this area may slow down so significantly that it may stagnate and result in the formation of blood clots. Blood clots in the LAA may occasionally be dislodged by incoming blood flow and the dislodged blood clot may traverse into the main artery, the aorta, and thereafter into the neck arteries leading to the brain, resulting in a stroke.
While an occasional skipped heart beat may not mean much, one must not be too hasty to dismiss the presence of an irregular pulse which does not seem to have any particular rhythmic pattern. The accompanying symptoms of AF are not specific and may include palpitations, dizzy spells, breathlessness and near fainting. If these symptoms are present in association with an irregular heart rhythm, the presence of AF can easily be confirmed with an electrocardiogram (ECG) which is a recording of the electrical pattern of the heart.
Dangers of irregular heart rhythm
The presence of AF is not to be taken lightly as it is associated with a higher risk of stroke, heart failure and death. Fortunately, AF prevalence is relatively low, being present in about one per cent of the population, and mainly in those above the age of 60. The prevalence increases with age, increasing to 8 per cent in those above 80. Once AF becomes a recurring event, the incidence of stroke averages about 5 per cent annually. If "silent" strokes detected by brain scans are included, the rate of stroke associated with AF exceeds 7 per cent annually. Furthermore, strokes resulting from blood clots that arise from the heart as a result of AF are usually severely disabling and associated with a high risk of death.
The age-old adage "prevention is better than cure" is especially true for AF. Common medical conditions such as high blood pressure, diabetes mellitus, obstructive sleep apnoea and excessive thyroid hormones, as well as obesity and lifestyle choices such as alcohol consumption and endurance exercise training increase the likelihood of developing AF. Lifestyle changes may potentially reduce these risks in some cases.
Medication or invasive procedure?
Drugs are currently the recommended first line of therapy. Using drugs to keep the heart rhythm "normal", or in the case of persistent AF, using drugs to prevent the heart rate from being high appears to result in similar outcomes with no difference in mortality or stroke rate.
In addition, blood thinning agents are often used to decrease the likelihood of blood clot formation in the LA. For those who fail to respond to drugs and remain significantly symptomatic, an invasive technique, catheter ablation, where special electrodes are inserted through veins and manipulated into the heart to map out the source of AF, and to electrically isolate the source or burn away the source of the AF, is an alternative option.
A difficult question facing doctors is whether patients with AF should be sent for catheter ablation, given that there are potential benefits if the source of AF can be "burnt" away. In the 2012 expert consensus statements on catheter ablation of AF published in the Europace journal, the authors caution that while there are several hypothetical reasons to perform AF ablation procedures, including potential improvement in quality of life, reduced stroke risk, reduced heart failure risk and improved survival, these reasons "have not been systematically evaluated as part of a large randomised clinical trial and are therefore unproven". It is important to recognise that the primary justification for an AF ablation procedure at this time is the presence of symptomatic AF after failure to respond to drugs.
Reasons for this cautionary approach include a high reported complication rate of 6 per cent (based on a first worldwide voluntary survey) and the high incidence of recurrence after ablation. Complications include death, life-threatening heart complications and strokes.
The complication rate is higher if new silent strokes seen on Magnetic Resonance Imaging brain scans after AF ablation procedures are included (a range of 7 to 38 per cent; mean 17 per cent). An important but less obvious potential complication is the delayed effect of the radiation received by the patients, including skin injury, cancer and genetic abnormalities.
Catheter ablation of AF is a complex procedure requiring a long X-ray imaging time (usually more than 60 minutes ) and is often preceded and followed by Computed Tomography X-ray scans which contribute further to the radiation exposure.
The other major challenge is to improve the technology to prevent recurrences. In a five-year follow-up study after AF ablation published in the Journal of the American College of Cardiology in 2011, 40 per cent were free of abnormal heart rhythms after one year, and at five years only 29 per cent remained free of abnormal rhythms. The high complication rate, high radiation dose and high AF recurrence rate mean that further developments are needed to address these issues.
Madam T came for her review a few days ago and her strength and speech had improved significantly. Most importantly, her heart rhythm was normal and her stroke risk had diminished considerably. Perhaps, if she had paid more attention to her palpitations years ago, she would not have had multiple strokes. Nevertheless, it was not too late for her to start paying attention to her palpitations.
Dr Michael Lim is medical director at the Singapore Heart, Stroke & Cancer Centre. He is also editor-in-chief, Heart Asia; British Medical Journals Publishing Group, chairman; Scientific Advisory Board, Asia Pacific Heart Association honorary professor and senior medical adviser, Peking University Heart Centre.
This series is brought to you by the Heart, Stroke and Cancer Centre.
Dr Michael Lim
The Business Times