Sudden Cardiac Death (SCD)

The heart is a vital organ that pumps blood around the body and provides the oxygen that all living tissue in the body requires. Once the heart stops its pumping, there is a sudden loss of oxygen and death of vital organs occurs within minutes. Although there may be subtle warning signs and symptoms before sudden cardiac death occurs, in the majority of victims, the onset of collapse is unexpected.

It is estimated that in Singapore, about 4500 people a year may suffer from SCD. 90% of victims have underlying narrowing of the heart arteries. This occurs due to build up of cholesterol in the wall of arteries. This deposit and narrowing restricts blood supply to the muscle and electrical system of the heart. With reduced oxygen supply to the heart, the electrical activity of the heart becomes erratic and unstable. They may become too fast (medically the heart rhythm is termed ventricular tachycardia or ventricular fibrillation) or too slow (bradycardia). Eventually, after a period of abnormal electrical activity, the electrical activity stops and the heart stops pumping.

One area of common misconception is that SCD is due to a heart attack. Medically, heart attacks occur when the blood supply to the heart muscle becomes so compromised that there is damage to the heart muscle. While, a heart attack can cause SCD, not all SCD is due to heart attacks. Conversely, a person may suffer a heart attack without experiencing SCD.

In many instances, a reduction of blood and oxygen even without causing damage to the heart muscle can cause electrical instability of the heart. In younger people (usually less than 35 years of age), there can be other heart abnormalities that are unrelated to narrowing of the heart arteries. These can generally include electrical system faults, heart muscle abnormalities and other abnormalities relating to the structure of the heart. Some of these may be present since birth.

Exercise and SCD

Vigorous physical activity can precipitate electrical instability in certain individuals. The relative risk of suffering a heart attack can also be increased up to 5 times during physical exercise when compared to periods of more sedentary activity. However, the risk of death during exercise is probably less than 1 per 100000 in younger individuals and about 6 per 100000 in middle aged men.

Importantly, exercise has many favourable effects on reducing risk of a heart attack overall and in general; people who exercise regularly are at lower risk of death than people who are sedentary.

Health Screening and Exercise

Health screening is not needed for all individuals who exercise regularly. However, individual with risk factors that may predispose them to sudden collapse should consider screening. Individuals who should consider screening prior to undertaking regular exercise include those with any one of the conditions or symptoms below.

  1. Persons who experience chest discomfort or severe breathlessness during exercise
  2. Persons who have lost consciousness during or after exercise
  3. Persons who have experienced a dramatic deterioration in their exercise capacity
  4. Persons who have a strong family history of sudden death or heart disease in the family (defined as male relative <55 years of age or female relative <65 years of age) 5. Persons who have diabetes 6. Persons who have been previously diagnosed with heart abnormalities 7. Persons with two or more risk factors for heart artery narrowing. This includes: – High cholesterol. Total serum cholesterol > 200 mg / dl
    • Smoking
    • High blood pressure. Systolic blood pressure greater or equal to 140, or diastolic greater or equal to 90.
    • Obesity with BMI greater or equal to 30 or waist greater than 36 inches
    • Sedentary lifestyle

Persons who do not have the above risks are at low risk of developing heart complications during moderate exercise and generally do not benefit from further screening.

For persons involved in very vigorous exercise such as in marathon runners and other competitive sports, routine screening for all remains controversial but is conducted in certain countries. It would be best to speak to your individual doctor on the appropriateness of screening.

Screening Package Offered at The Novena Heart Center

At the Novena Heart Centre, we offer screening to detect possible abnormalities of the heart that may lead to problems during exercise. This includes

  1. An interview and physical examination by a Cardiologist
  2. Electrocardiogram
  3. Blood investigations including a fasting cholesterol, blood sugar and measurement of hs-CRP (an indicator of future risk of developing coronary artery disease).
  4. Exercise stress echocardiogram. This is a combination of an exercise stress test on a treadmill combined with ultrasound technology to evaluate heart function and structure.

Coronary calcium scoring using ultra-fast CT scanner. This allows us to pick up early cholesterol deposits in the heart arteries. Only severe narrowing of the heart arteries lead to restriction of oxygen to the heart and these are picked up by stress tests. Early narrowing that can still lead to heart problems is undetected by routine stress testing.

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