Preventing sudden cardiac death

IT IS not uncommon to read about people who were apparently in the pink of health who passed away suddenly in their sleep. This is almost always due to sudden cardiac arrest (SCA), a condition in which the heart stops pumping effectively as a result of a life-threatening heart rhythm. Death due to a cardiovascular cause that occurs within an hour of the onset of the cardiovascular event is termed sudden cardiac death (SCD).

The annual incidence of SCA based on data from the United States and European studies ranges from 0.04 per cent to 0.1 per cent of the population. In the US, the median age of SCA is between 66 and 68 years, and males are more likely than females to develop SCA.

For a long time, it has been thought that the main mechanism of SCA was a life threatening arrhythmia such as ventricular fibrillation (VF) or ventricular tachycardia (VT). Both sustained VT or VF are abnormal heart rhythms originating from lower heart chambers that prevent the transmission of electrical signals from the “generator” or pacemaker sited in the upper right heart chamber.

Data from the United States National Registry of Cardiopulmonary Resuscitation found only about 24 per cent of SCA patients had an initial rhythm of VT or VF, whereas the remaining 37 per cent and 39 per cent had pulseless electrical activity (PEA) or absence of electrical activity as the initial rhythm (asystole), respectively. Similar trends have been reported for out‐of‐hospital arrests. PEA is a condition in which there is spontaneous organised cardiac electrical activity without sufficient blood flow to maintain organ perfusion and consciousness. The survival rate for VT/VF averages 20 per cent, and the survival rate for PEA/asystole is substantially lower, averaging 5 per cent.

These abnormal heart rhythms result in ineffective pumping of the heart muscle and a severe drop in blood pressure. The subsequent significant decrease in blood flow to the brain results in loss of unconsciousness. As a result, the person becomes unresponsive within seconds or minutes, has no normal breathing and the pulse is not palpable. If the condition is not treated immediately or does not revert spontaneously to a normal heart rhythm, the person can die.

Warning symptoms

As many SCA patients do not survive to provide any information on preceding symptoms, it has been difficult to get data on this. A 10-year community-based study of 839 patients with SCA published in the Annals of Internal Medicine in January 2016 provided some data on “warning” symptoms preceding SCA. Such symptoms were gleaned from the surviving patient, from family members, witnesses at the scene of the event, or medical records from the 4 weeks preceding the event. In this study, 51 per cent had “warning” symptoms within 4 weeks preceding SCA, 34 per cent had symptoms more than 24 hours before SCA and 80 per cent had symptoms at least 1 hour before SCA. The most common symptoms were chest pain (almost half) and shortness of breath (almost one fifth).

Risk factors for SCA

Understanding the risk factors for SCA will enable one to take precautionary measures. Smoking and a daily number of cigarettes increase the risk of SCA in those with underlying heart disease. In the Nurses’ Health Study which followed more than 100,000 women over 30 years, active smokers had more than double the risk of SCD than non-smokers. This risk declined with smoking cessation, and after stopping smoking for 20 years, the risk was the same as those who never smoked.

For middle-aged or older people with risk factors for heart disease who lead sedentary lives and are about to embark on an active exercise programme, it is wise to consult a doctor prior to starting vigorous exercise. There is evidence that the risk of SCA is increased during vigorous exercise and this risk extends up to 30 minutes post-exercise. In absolute terms, the risk is still low, occurring 1 per 1.51 million episodes of vigorous exercise.

For young people embarking on competitive sports, the presence of unrecognised underlying inherited heart disease is an important cause of SCA. While SCD is rare in the young, it is nevertheless the leading cause of non-traumatic death among young athletes. Sports-related SCD varies from 0.5 to 2.1 per 100,000 yearly in the US and is higher in elite athletes, with an incidence of 1:8,253 a year according to the National Collegiate Athletic Association (NCAA).

SEE ALSO

Listen to your heart: Separating myth from fact

There are differing views about pre-participatory screening for young people engaged in competitive sports, with the European Society of Cardiology advocating examination and routine 12-lead electrocardiogram (ECG) and the American Heart Association recommending only questionnaire and examination (from a national economic perspective and cost considerations). In the American Heart Association guidelines, those found to have an abnormal examination findings or those with a positive personal or family history may be referred for cardiac testing including ECG and echocardiogram (ultrasound of the heart).

Not unexpectedly, excessive alcohol consumption (6 or more drinks a day) or binge drinking increases the risk for SCD. While many may intuitively think that caffeinated beverages increase the risk of SCA, the current data does not show any significant link between caffeine intake and SCD.

Preventing sudden cardiac arrest

Taking appropriate precautionary measures can help reduce the likelihood of SCA.

If you are a sedentary middle-aged or older person with risk factors for heart disease who want to commence on a vigorous exercise programme, you should first consult your doctor.

If you have new onset of chest pain or shortness of breath that is aggravated by exertion, you should consider an early evaluation of your heart condition for any underlying blockage of heart arteries.

If you have underlying heart disease, you should stop smoking and avoid excessive alcohol consumption to reduce your risk of SCA.

If you have significantly impaired heart pump function and had a previous heart attack, you are at high risk of abnormal heart rhythms such as VT or VF, and you should discuss with your cardiologist on the need and usefulness of an implantable pacemaker with a defibrillator function that can convert the VT or VF into a normal heart rhythm.

Finally, for those with a strong family history of sudden death or heart attacks, you should consider getting your heart evaluated, especially if you have multiple risk factors for heart disease.

Dr Michael Lim

Medical Director

Royal Healthcare Heart Stroke & Cancer Centre

MBBS ( NUS) , MRCP (UK), M Med (Int Med, NUS), FAMS (Cardiology), FRCP (Edin), Dip Sports Medicine (NTU)