SUDDEN LOSS OF CONSCIOUSNESS (SYNCOPE) AND SUDDEN DEATH IN CHILDREN - The Emerging Importance of the Long QT Syndrome
Sudden and unexpected cardiac death in young persons is being recognised with increasing frequency. The sudden death of a young athlete is the most obvious and reported example, but death during non-competitive physical activity, during emotional upsets, or even during sleep are being recognised with progressively greater frequency. These events are usually due to a disturbance of the heart's electrical system, causing an abnormality of the heart beating or rhythm, called an arrhythmia. Fortunately many of these deaths are preventable if the underlying condition is correctly recognised and properly treated. Unfortunately, many times the condition is unsuspected and, therefore, not treated, with a tragic sudden death the outcome. Particularly, a condition known as The Long QT Syndrome (LQTS) is being recognised as a common cause of these loss of consciousness and sudden death episodes, it is often not recognised prior to a sudden death.
WHAT CAUSES SUDDEN LOSS OF CONSCIOUSNESS?
The arrhythmia's cause loss of consciousness by interfering with the blood pumping function of the heart with the consequence that the blood flow to the vital organs, particularly the brain, is diminished or absent. When the brain is deprived of blood flow for more than a few seconds, loss of consciousness occurs. This form of loss of consciousness is referred to as syncope. Syncope can also occur when the blood pressure falls dramatically, again resulting in lack of blood flow to the brain. The common faint, known medically as a vasovagal event, is primarily due to a fall in blood pressure, usually accompanied by a slowing of the heart rate. Another common cause of loss of consciousness is a seizure. In seizure disorders, the blood flow to the brain and other organs is normal, but loss of consciousness occurs because of abnormal electrical discharges in the brain.
WHAT ARE THE COMMON CAUSES OF ARRHYTHMIAS AND CARDIAC SYNCOPE IN CHILDREN?
Almost any heart disease can cause arrhythmia's and syncope. Structural (anatomic) heart disease such as congenital (present at birth) disorders, like a narrowed or leaking heart valve, a hole in the heart (septal defects), or more severe malformations, or rheumatic heart disease which affects the heart valves and muscle, are well known examples. Most of the time these conditions are not manifest by sudden loss of consciousness, but by shortness of breath or fatigue, or by physical exam findings detected by the physician.
Of more concern are inherited diseases which principally affect the heart electrical system, such as LQTS, and the heart muscle, such as hypertrophic cardiomyopathy. The LQTS is particularly of concern because there are no physical abnormalities to detect, only a subtle electrical disturbance.
WHEN SHOULD A LIFE THREATENING CARDIAC PROBLEM BE SUSPECTED?
Fainting (vasovagal) episodes and seizures must be separated from cardiac arrhythmia's, for while they are important they do not commonly lead to sudden cardiac death. A vasovagal event is most often precipitated by obvious factors such as pain, nausea, seeing blood, or other unpleasant stimuli.
The individual becomes dizzy, warm and sweaty, has blurred vision, and usually has time to sitor lie down which might lessen the symptoms or prevent the loss of consciousness. Seizures, on the other hand, usually have no obvious precipitating factors, have no preceding symptoms other than occasionally a strange feeling of various types and are associated with movement of the extremities such as stiffening of the muscles and/or body then shaking, and often with tongue biting and loss of urine or bowel control. The event may last around a few seconds to a minute or more, and the person is confused, disoriented and often lethargic for some time after the event.
In contrast the syncope of life threatening cardiac arrhythmia's is sudden, usually without warning, often occurs during exercise, and is accompanied by gasping or absence of breathing, the absence of a pulse, and in some cases by cyanosis or turning blue. Usually the loss of consciousness lasts from one to several minutes and in some cases requires resuscitation (CPR). The difference in presentation usually allow the conditions to be correctly separated, although some cases are confusing.
FAMILY HISTORY
Because these cardiac conditions are often inherited, a family history of syncope in relatives or unexplained sudden cardiac death in young persons may be present, and should be inquired about. The absence of family history of these events, however, does not exclude these diseases.
DIAGNOSIS OF THE LONG QT SYNDROME
When a cardiac condition is suspected medical evaluation is of utmost importance to prevent sudden cardiac death. A careful history and physical examination will eliminate many of other causes of syncope. The principle test required is the electrocardiogram (ecg), and specific observations for a prolonged QT interval and certain T-wave abnormalities. Importantly, 10-40% of LQTS patients have a normal QT interval on initial evaluation, so a normal QT interval does not exclude the condition. The diagnosis in these patients can be clarified by an ecg during exercise and often by examining ecg's on parents and siblings. One parent will also be a gene carrier, and 50% of siblings would be at risk from inheriting the condition. Therefore, it is likely that a parent or other siblings will have the condition as well. Once a person is diagnosed with LQTS it is extremely important that members of the extended family be screened by history and electrocardiograms, to identify others who are at risk of sudden cardiac death.
TREATMENT
Most of the cardiac conditions associated with unexpected sudden cardiac death are treatable, and events can be prevented or diminished. This is particularly for the Long QT Syndrome, as treatment is very effective, in most instances just by administration of a medication.
Original text submitted to the Utah School Health News by G. Michael Vincent, M.D., President SADS Foundation, Professor and Association Chairman, Dept. of Internal Medicine, University of Utah School of Medicine Chairman, Department of Internal Medicine, LDS Hospital, Salt Lake City, Utah - Website: www.sads.org