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'Prolonged QT Interval' and SIDS

(8/8/00)

Dear Friends,

A number of articles hit the news in June 1998 and July 2000 regarding 'Prolonged QT Interval' and SIDS. The news refers to two Italian studies that appear in the New England Journal of Medicine in the 6/11/98 edition and 7/27/00 edition. More information follows. We have received many e-mail messages asking for more information. The public has been on an information roller coaster, the result of an explosion of medical reports, each heralding a "breakthrough in SIDS research." We need to help people separate myth from fact and risk factor from cause. We will post information as it becomes available to us.

Please keep the following in mind:

- When it comes to media coverage of SIDS, we often feel a sense of frustration in being confronted with misleading headlines, announcements of so-called breakthroughs and statements taken out of context.

- Please read the article, "Mass Media's" Role in SIDS Education, at <http://sids-network.org/media.htm>.

- The Italian study does not claim that 'Prolonged QT Interval' causes SIDS.

We are currently gathering more information about this specific research and will keep you updated.

Thanks!

Chuck Mihalko
Executive Manager
SIDS Network

bullet Correspondence; Prolongation of the QT Interval and the Sudden Infant Death Syndrome, The New England Journal of Medicine -- October 15, 1998 -- Volume 339, Number 16
bullet Editorial; Prolongation of the QT Interval and the Sudden Infant Death Syndrome, The New England Journal of Medicine -- June 11, 1998 -- Volume 338, Number 24
bullet Abstract; Prolongation of the QT Interval and the Sudden Infant Death Syndrome, The New England Journal of Medicine -- June 11, 1998 -- Volume 338, Number 24
bullet Comments; STUDY LINKS ABNORMAL HEART RHYTHM TO SIDS, Mayo Clinic -- June 11, 1998

Media Alert from the SIDS Alliance; Prolonged QT Interval and SIDS Findings Released (6/10/98)

Comments from Henry Krous, M.D.
June 11, 1998

I find this an interesting and provocative study which puts prolonged QTc interval and SIDS risk back on the table for further investigation.

SELECTED STRENGTHS of the study are large size, apparent strength of association, pressure for other investigators to confirm or refute, possible means of screening in early newborn period and possible preventative measures.

SELECTED WEAKNESSES are lack of blinded EKG review, lack of linking QTc results with sleep state, wakefulness, activity level, sleep position, postmortem data, listing of other causes of death, and use of Seattle SIDS definition that does not require scene investigation.

CONCERNS: stampede to have EKGs performed on every baby with highly variable technical and interpretative skills of techs and docs, possible prescription of unwarranted and potentially medications or failure to prescribe medications when actually indicated (this flies in the face of health care reform in the USA with the dumbing down of health care services).

Henry Krous
San Diego

Comments from Joseph DeCristofaro, M.D.
June 11, 1998

I am wondering if QT interval is something that is routinely assessed when an infant is born. I would like to ask my son's pediatrician about this, but if it is not normally "looked for" would it do me any good? I recently received my son's autopsy which showed no abnormalities other than what is stated as "classic SIDS" (petechiae). Any suggestions on what I can do to find out more?

Thank you,

The response from the SIDS Alliance is really quite a good one. The NEJM article also made the point that even with this significant correlation between SIDS and a prolonged QT at birth you would need to treat 100 babies with the long QT to potentially save two lives. This assumes that the treatment would be effective and does not even address the risks involved in the treatment drug(s).

The Schwartz study was certainly a large trial that did find a significant correlation between SIDS and prolonged QT at birth. They found was that 50% of the infants that died of SIDS had a prolonged QTc on the EKG done during the first week of life. However, they did not report the positive predictive value of having a prolonged QTc and subsequent death in the first year of life from SIDS. From their data you would calculate that there were about 850 babies who had a prolonged QTc at birth (= 2.5% of the total infants studied 34,000; about 2 standard deviations from the mean). Of that 850 with prolonged QTc at birth 12 died of SIDS (1.4%) and 838 survived the first year.

In this particular case above, it is not routine to obtain an EKG on all infants in the US. In the Italian study, all infants get an EKG after 2 days of life when there is less variability in the heart rhythm. This is not the case in the US where more than half the infants are home by the third day of life. While there was no history of prolonged QT in the parents in the Italian study of 34,000 births, we do know that sudden unexpected death can occur in adults with prolonged QT. This sudden death by arrhythmia can be prevented with treatment.

I hope this helps.

JDDeCristofaro, MD
Assistant Professor of Pediatrics
Medical Director, Infant Apnea Program
UMC Stony Brook, NY

Comments from Tom Keens, M.D.
June 13, 1996

There have been a number of studies looking for the 'Prolonged QT Interval' in babies who died form SIDS. Most have been done by recording 24-hour ECGs or shorter ECgs in babies before they died, and then analyzing the recordings form children who did die from SIDS, comparing them to normal. Only a few studies suggested a relationship. Most do not show a correlation. I do not know anything about the genetic test, but would be interested in finding out.

Prolonged QT interval is a condition where the time between contraction of the heart muscle (Q wave) and 'repolarization' of the heart muscle cells (T wave) is increased. Repolarization means that the muscle cell resets itself so it can contract again. Measured on an ECG, the time between the Q wave and the T wave is prolonged in this condition. The problem is that the heart is more vulnerable during this time. If the next heart beat begins before the end of repolarization, an arrhythmia or irregular heart beat could occur, such as ventricular fibrillation, which could be fatal. This is a rare condition, and is diagnosed on an ECG. It is unclear whether or not it is related to SIDS, though I believe most of the studies do not indicate a strong relationship. That is, it is not generally thought to be an important cause of SIDS. However, those children who have Prolonged QT Interval, usually require some treatment for it.

You are correct that sleeping on the back has not completely eliminated or prevented SIDS. Babies who sleep on their backs still die from SIDS. Most babies who slept on their stomachs did not die from SIDS. There is still much work for SIDS researchers to do to find the cause.

Prolonged QT interval syndrome is when the heart takes a longer time to 'repolarize' the heart cells after a contraction than normal. When the heart beats, the cells 'transmit' the impulse, which causes the muscle cells to contract, to other cells in a way similar to nerve cell transmission. That is, the electrical charge on the surface of the cell changes. In order to prepare for the next heartbeat, the cell has to restore that charge (repolarize). Because this occurs a fraction of a second later than normal in prolonged QT interval babies, there is a possibility that the next heartbeat could reach this cell before it is finished recharging. This may cause a serious irregularity of the heartbeat, such as ventricular fibrillation. This could cause death.

Obviously, there is a lot of variation in the normal time it takes to recharge the heart (QT interval). Therefore 'prolonged' QT interval is defined based on statistics. For any individual baby, it is best to consult a pediatric cardiologist to find out the significance (or lack of significance) of any finding about your baby's QT interval. If it is felt to be significant, there are medications which can be given to treat it.

Some has suggested that prolonged QT interval may be a cause of SIDS. However, most investigators do not currently believe this is an important cause of SIDS.

I hope this is helpful. Thank you.

Tom Keens
Children's Hospital Los Angeles

Comments from Carl Hunt, M.D.
February 8, 1997

When I spoke at length with our pediatrician that truthfully says he knows very little about SIDS, he said that one thing that has occurred to him is that very often the event happens at a time of a big developmental phase such as learning a new skill. He said that maybe during these periods of rapid growth, the brain just sends the wrong message down at the wrong time. He said that his theory is that for some unknown reason the brain instructs the heart to beat twice, simultaneously, which of course is instant death.

I had heard the part about the event happening during a developmental spurt, as it did with my Rachel. The theory about two heartbeat instructions is a new one on me. Can the doctors comment on this: has the theory been advanced before? Does it make sense? Has there been any study on the topic?

Except for 1 rare heart conduction problem (Prolonged Q-T Interval), numerous studies appear to have excluded any heart rhythm disorder as a cause of SIDS. Such problems are very important causes of death, however, in adults with prior histories of a heart attack. Two beats occurring very close together can be part of the irritability of the heart muscle in such situations, but it is not related to the brain stem control of heart rate and does not appear to have anything to do with SIDS.

From an entirely different context, we do know that some of the heart rate recordings of infants later succumbing to SIDS do show somewhat higher heart rates in general, with less variability in the rate compared to other infants (but with lots of overlap between the SIDS and the non-SIDS infants). This IS related to the brain stem control of heart rate (and respiratory rate). The few recordings of heart rate and breathing in terminal situations often show slower heart rates, due either to brain stem regulation problems and/or to obstructive apnea that cannot otherwise be detected with the standard home monitors.

This response is perhaps more technical than anticipated, but heart rate issues and the inter-relationships to breathing pattern (apnea, etc.) are certainly a very important focus for current research efforts, including our CHIME project.

Hope this is helpful.

Dr. Carl Hunt
Washington, DC/Toledo

I am curious whether my daughter actually may have died from what is being called "Long QT". Since no EKG was run on her, we never will know for sure. However, we would like somebody to review some of our EKG's, that were taken during some routine physical exams in the past. If a positive result were detected, we might test the DNA in a strand of our daughter's hair.

My question is: is a Family Practice physician qualified to diagnose and (if warranted) treat this? If it warrants a specialist, should "any" cardiologist be sufficiently qualified? If none of the above, how do I find somebody who truly as the qualifications?

Despite the recent emphasis, we still consider prolonged QT interval to be a rare cause of SIDS. For this reason, SIDS experts are not recommending routine electrocardiogram (ECG) screening of infants. Even if a prolonged QT interval were found on routine screening, the risk of SIDS is probably very low, and it is not clear that any medication would be of more benefit than potential harm.

ECG's are routinely interpreted by a cardiologist, and evaluation of the QT interval is a routine part of the interpretation. There are some problems, however, with consistency of interpretation in borderline instances. In the absence of a family history of sudden death in older children and adults (sometimes associated with deafness), routine screening of adults with an ECG is not likely to yield positive results. However, any cardiologist could perform an ECG, or review an existing ECG, if you want to do this.

Hope this is helpful.
Dr. Carl Hunt
chunt@MCO.EDU
 

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