Tuesday, May 17, 2016

The Mystery Of Sudden Cardiac Death

"Three months after he collapsed in a 1993 playoff game against the Hornets, [Reggie] Lewis, one of the most beloved players in Boston Celtics history, crumpled to the court again, this time while just shooting around. He never got up. Reggie Lewis, dead at 27."[1]

This is just one of the tragic examples of sudden cardiac death (SCD). Listening to others describe their experience with SCD paints a terrifying picture of this mysterious disorder:

"The condition we have in our family is called Long QT syndrome and it’s a condition that arises from arrhythmia in the heart. Unfortunately the condition, the very first time you are aware of it is when you collapse and die, which is what happened to our son 9 years ago.”[2]

"Christine remembers fainting for the first time when she was 18. Over the next 25 years, Christine had many other fainting episodes — most of them at night. After each episode, she went to her doctor and went through several tests — all came back negative…Further testing showed that Christine had a condition called Long QT Syndrome (LQTS). This condition is a rare, and sometimes fatal, heart rhythm disorder that may lead to sudden cardiac arrest and death."[3]

"I was a sudden cardiac death survivor, wearing a holter monitor which recorded the entire event. Just 10 days prior, I had been told my heart was in perfect health on every cardiac test imaginable and was in no danger. At the age of 45, I had to die to prove I had a serious problem. The only way I was diagnosed was when the doctors finally saw the holter monitor recording of the unique Torsades signature heart rhythm which only occurred after 7 minutes of fibrillation. The Torsades signature rhythm only appears for less than a minute at the final moment of death. This is the first and only recording of this magnitude."[4]

The incidence of this phenomenon is low in children, with 1-2 cases per 100,000, but higher in adult populations, with 325,000 fatalities in the US every year. These numbers are not always reliable. It is common knowledge that events of SCD often go unreported, both in the literature and in the news. A study published in the medical journal, Circulation, looked at the incidence of SCD among NCAA students. The authors found that SCD was generally uncommon, with one case per 43,770 participants each year. Interestingly, it was determined that the phenomenon of SCD was specific to certain sports. Among male basketball players, not only was the incidence of SCD much higher (1:3,100 per year), but SCD was also responsible for 87% of the cardiac related deaths.[5]

Sudden cardiac death is not a heart attack...so what is it, exactly?
SCD is defined as an unexpected, abrupt death caused by loss of cardiac function. SCD is different than a heart attack. When a heart attack occurs, one or more cardiac arteries are blocked, decreasing oxygen flow to the heart and ultimately the death of the cardiac muscle. When SCD occurs, a disruption in the electrical rhythm of the heart becomes unstable and irregular. The heart may quiver or beat too fast to deliver oxygen to the rest of the body; if medical treatment such as defibrillation and CPR is not provided promptly, it leads to near immediate death.

Risk factors

There are many known risk factors for SCD. Family histories of heart disease, heart rhythm abnormalities, or congenital heart defects are only few common risk factors. Another key feature of individuals who may be predisposed to SCD is called “QT interval prolongation".

QT interval prolongation is a pathophysiological condition that occurs when each cycle of the heart takes longer to get back to its resting stage. It is measured with a simple cardiac test, the electrocardiogram or ECG, which records the electrical activity of the heart. Each time your heart beats, a heart cycle is initiated and brought to an end. This has to happen in a specific time range, otherwise the heart can’t keep up with fulfilling its function.

When the QT interval is prolonged, each cycle is a little bit longer than usual and the heart has difficulties maintaining a regular rhythm. This precarious situation can exacerbate into arrhythmias -potentially fatal disturbances of the heart’s normal rhythm - if any other risk factors that prolong the heart’s cycle are present. The most common arrhythmia is called ventricular tachycardia, a condition characterized by an erratic, disorganized firing of electric impulses from the heart’s lower chamber. When this happens, the heart is unable to pump blood efficiently and, unless treated promptly, can lead to SCD. Torsades De Pointes is an example of a particularly lethal form of ventricular tachycardia. It most often goes undiagnosed because it shows no clinically detectable symptoms other than the fact that it is triggered by a prolonged QT interval.
A prolonged QT interval doesn’t always lead to SCD, but is important to know since it can increase the odds of problems of SCD when other predisposing factors are present. It is therefore essential to raise more awareness about QT interval prolongation. Knowledge about this interval is key for the prevention of a series of potentially lethal cardiac conditions including sudden cardiac death.

In medicine, there is one very simple concept:  if we know the risk factors, we can implement prevention strategies. Knowledge of QT interval prolongation could be life-saving information for someone predisposed to SCD. Such people may need to avoid certain drugs that can prolong the QT interval. In addition, medications are available that can help stabilize the heart’s rhythm.

Contributed by:  Elena Tomaselli
Check out Elena's blog, The International Scientist

5Harmon, Kimberly G., et al. "Incidence of sudden cardiac death in national collegiate athletic association athletes." Circulation 123.15 (2011): 1594-1600.

Straus, Sabine MJM, et al. "Prolonged QTc interval and risk of sudden cardiac death in a population of older adults." Journal of the American College of Cardiology 47.2 (2006): 362-367.
Harmon, K. G., Asif, I. M., Maleszewski, J. J., Owens, D. S., Prutkin, J. M., Salerno, J. C., ... & Drezner, J. A. (2015). Incidence, Cause, and Comparative Frequency of Sudden Cardiac Death in National Collegiate Athletic Association Athletes A Decade in Review. Circulation, 132(1), 10-19.

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