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ABSTRACT
Sudden Infant Death Syndrome (SIDS) has been identified as a major cause of death in the neonatal age group. Several studies have hypothesized different etiologies for the above. Long QT interval has been a major cause of debate as a cause of SIDS.
In this study, long QT interval analysis was done on 20 infants/neonates who died presumably due to SIDS. Holter monitoring was performed as a screening tool in the departments of pediatrics at three medical centers in Tehran, Iran and Los Angeles, California.
The holter data of those cases who died due to SIDS was rescanned using a QT analysis software developed by DelMar Medicals. It was found that 43% of the cases had a QT interval greater than 460 ms for more than 20% of the recorded period (24 hrs).
Also it was observed that 65% of the cases had a QT interval of greater than 420 ms for more than 20% of the recorded period. The normal QT interval is less than 360 ms to 420 ms. Authors hypothesize that long QT interval might be a major cause of death
in SIDS. It is therefore recommended that QT interval analysis should be performed as a screening tool in the first week of life
Key Words: Sudden Infant Death Syndrome, Long QT Syndrome, Holter Monitoring
* M H Soltanzadeh , MD professor of pediatrics , Shahid Beheshti University
Tehran , IRAN and head of the Department of Pediatrics at Tehran Resalat Hospital
Introduction
The study of the Electrocardiogram has been a major tool in prognosis and diagnosis of patients with Cardiac, electrolyte and autonomic disorders. With the advent of state-of-the art computer technology, our ability to compute massive amounts of data in a short time span has opened a new window in the study of electrocardiogram.
Since the 1970s when 24 hour EKG monitoring was first used in patients with paroxysmal arrhythmias, several projects have been attempted to further study this in more detailed and segmented fashion. ST segment analysis to study Cardiac Ischemias was one the first tests to utilize the power of computers for segmental data analysis.
In early ‘80s Professor Bazzet studied and published several papers describing QT intervals and its association with cardiac depolarization and repolarization. (1)
Methods
20 subjects were chosen following a chart review of infants/neonates who had died of SIDS from the department of pediatrics of Tehran Resalat Hospital, Teheran, Iran, Olive View Medical Center, Sylmar, California and UCLA Medical Center, Los Angeles, California.
A two year screening approach was chosen where all the siblings of the neonates who had died due to SIDS underwent a Holter test . the EKG data was collected using DelMar Medicals Holter Monitors. The storage means were analogue cassette tapes.
The tapes were analyzed at the Advanced Cardiac Monitoring. Los Angeles. California using DelMar Medicals Holters Scanner 563. The Technologist were all blinded to the studyThe data were analyzed using a QT analyzer Bazzet's formula was used to correct the QT iterval for rate using the formula QTc = QT/ Sqrt RR .
We applied ANOVA (nonparameric repeated measures friedman test ) to determine the changes between different QTc interval groups . A two tailed t test was used to compare the mean values of the variable studied Results were considered significant for p<0.05.
Results:
The following data were collected 90% 0f the patients had an increased QT interval and mean QTc interval . The mean QT interval was 480 ms and the
Mean QTc interval was 500 ms . The percent QTc intervals greater than 450ms and 500 ms were between 12% - 70% and 11% - 98% respectively .
Discussion
The QT interval is a measurement that represents the total time from Ventricular depolarization to complete repolarization.(1) This process begins at the start of the Q wave and extends to the end of the T wave. The QT interval is affected by heart rate (2), autonomic nervous system(3), sympathomimetics, electrolytes (Ca, K)(4), drugs, age, sex and genetics. The QT interval measurement can help to recognize patients who are at risk of life threatening arrhythmias.
Long QTc intervals has been known to cause Torsade de Pointes, a lethal arrhythmia.(5) It appears that all the subjects who were studied suffer from congenital Long QT Interval Syndrome. As long QT interval is treatable in 60 to 80 percent of cases using drugs like beta blockers etc.(6) it is highly recommended that QT interval analysis be used as a screening tool for long QT interval syndrome in new-borns to prevent SIDS and possible lethal arrhythmias later in life
Conclusion
The above values strongly suggest that Long QT Syndrome plays an important role in the occurrence of Sudden Infant Death Syndrome . The patients with Long QT Interval Syndrome are prone to Arrhythmias, Ventricular Tachycardias and rapid Supraventricular Tachycardias. The authors suggest 24-hour Holter Monitoring with QT interval analysis as a screening tool in patients who are in the SIDS high - risk group .
References:
1. Bazzet et al., QT Interval as a measure of cardiac function, JAMA, 1984;213:220-223
2. Smith H., Chakko L., et al., Segmental analysis of Electrocardiogram, Am J Physiol 1988;248:H151-H153.
3. Akselrod S., Gordon D, Ubel FA, Power Spectrum analysis of heart rate, Science 1992;9:371-448
4. Hobson JA, McCarley RW Effects of Drugs on Cardiac Function and Electrolytes, BMJ 1994;122;45-48
5. Mukherjee et al., Lethal Arrhythmias, J of Elctrophysiology, 1988;4;34-44
6. Jacob K, Gordon L, Anti-arrhythmic therapy in teenage arrhythmias, BMJ 1996;176;55-56
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