Advances in cardiology have made it harder for one to suffer sudden cardiac death. By Michael Lim
MR A, a patient of mine, had come for his regular check-up and was relating to me that within a short span of time, three of his CEO friends had died suddenly. All were physically fit and appeared healthy and had no warning symptoms. He remembered my mantra: With advances in medicine, sudden death from heart attacks is almost always preventable.
Sudden death is most commonly due to an acute heart attack. Those in the 20s and 30s are not spared either – based on recent annual statistics in Singapore, on the average, every five days, a young person falls victim to sudden death. Just this recent Christmas week, a young lady was widowed when her husband slumped across the dinner table at a restaurant and died.
For those younger than 35 years, the commonest cause of sudden death is a life threatening abnormal heart rhythm, ventricular fibrillation, where the heart pumping chamber quivers and stops pumping. Sudden death due to this rhythm in the young is most commonly due to presence of hypertrophic cardiomyopathy. This is a condition where there is abnormal thickening of the heart muscle, and it’s not uncommon, with a reported incidence of one in 500 in the US.
In the large majority of sudden cardiac deaths, there are no warning symptoms and many of the victims exercised actively. Even with a treadmill test, most people will not have symptoms or an abnormal treadmill test unless their heart arteries are more than 70 per cent narrowed. But studies have shown that the large majority of patients who develop a heart attack have no severe narrowing of the heart arteries; two thirds of those with a heart attack have narrowing of 40 to 60 per cent.
Contrary to popular misconception, a heart attack rarely occurs as a result of gradual blockage of the heart artery by cholesterol accumulation in the wall. Better understanding of the basic science of heart disease has helped doctors understand the mechanisms of a heart attack and hence take preventive measures to prevent sudden death.
The heart (coronary) artery is a living structure with three concentric layers of cells that have specific functions. The heart artery is not just a “pipe” that delivers blood to the heart, but it is able to produce chemicals that constrict or dilate the vessel, allows active exchange of cholesterol between the blood and the cells in the wall.
Damage to the inner layer in the lumen of the vessel by high blood pressure, diabetes mellitus or smoking, increases the likelihood of entry of cholesterol or white cells called macrophages through gaps in the inner lining into the wall of the artery.
This accumulation of cholesterol and macrophages (plaque formation) results in narrowing of the artery and weakens the wall of the heart artery and makes the lining vulnerable to tear (plaque rupture) – much like how the skin tears easily when there is a blister on the skin. When there is a tear in the lining, chemicals are released into the blood which triggers the formation of a blood clot. The clot formed can block the entire lumen of the artery and thereby cause a heart attack.
Preventing heart attacks
The key to prevention of a sudden heart attack is to be able to identify those who are at high risk of getting plaque rupture and take preventive measures. Those who have risk factors for heart disease such as high cholesterol, high blood pressure, diabetes mellitus, smoking and a family history should consider assessment even if they are asymptomatic. While treadmill testing is commonly used, its limitations must be understood.
Increasingly, imaging techniques have made prediction more accurate. A commonly used test is the calcium score of the heart arteries. Using a CT scan, the amount of calcium in the heart arteries is measured. The greatest contribution of this test is its negative value; if the test is normal, the likelihood of finding significant disease is extremely low. An abnormal calcium score is associated with an increased likelihood of significant disease of the heart arteries.
My patient, Mr B, who had risk factors, underwent another test called CT angiogram. He did not want to suffer the same fate as his deceased colleague and the test provided a three-dimensional visualisation of his heart arteries, and was able to detect plaques in the heart arteries not detectable by other non-invasive techniques.
The test involved injecting iodine contrast into the arm veins and doing a scan of his heart arteries in less than five seconds. He was found to have a significant narrowing in one of his main heart arteries. Most importantly, he avoided the same fate as his colleague who collapsed while exercising in the gym despite having had a recent normal treadmill test.
Imaging will become one of the key developments in cardiology in the future. Exciting developments in imaging and nanotechnology mean that doctors will, in the near future, be able to determine, by non-invasive means, patients with plaques which have a high likelihood of causing a heart attack and take appropriate preventive measures.
While these imaging tests may be useful for the older people who are at risk of heart attacks, they are generally less useful for those who are at risk of dying suddenly from abnormal rhythms. The basic tests for detecting heart diseases that cause sudden death as a result of abnormal heart rhythms are ultrasound imaging of the heart and a 12 lead ECG (electrocardiogram or electrical pattern of the heart).
In some European countries where screening, using the 12 lead ECG and where necessary an ultrasound of the heart, is compulsory for all young people who take part in competitive sports, the incidence of sudden death has been reduced by more than 90 per cent.
While genetic screening has less practical value when used for prediction of getting a heart attack, it is useful for some of the heart diseases that cause sudden death as a result of abnormal heart rhythms. These include conditions such as long QT syndrome, Brugada syndrome, catecolamine sensitive polymorphic ventricular tachycardia, arrhythmogenic right ventricular dysplasia and hypertrophic cardiomyopathy.
What all these means is that advances in cardiology have made it more difficult for one to get a heart attack or sudden cardiac death. It is not the lack of means, but the lack of will that will make the difference between life or death.
Exciting developments in imaging and nanotechnology mean that doctors will, in the near future, be able to determine, by non-invasive means, patients with plaques which have a high likelihood of causing a heart attack and take appropriate preventive measures.