To Investigate the Relationship Between Prolonged QT Interval

and Maternal Smoking

Research Done by: Bindu Punnoose

Mentor: Dr. Michael Myers, Ph.D.

Columbia Presbyterian Medical Center

Review of Literature

• Moss AJ, Schwartz PJ: Delayed Repolarization (QT or QT-U prolongation) and Malignant Ventricular Arrhythmias. Mod. Concepts Cardiovascular Dis 1982

• Schwartz PJ, Montemerio M, et al: The QT Interval Throughout the First Six Months of Life Circulation 1982

• Malloy MH, Kleinman JC, Land GH, et al: The Association of Maternal Smoking With Age and Cause of Infant Death Am. J. of Epid. 1988

Review of Literature (..cont’d)

• Milerad J, Sundell H: Nicotine Exposure and Risk of SIDS Acta. Paediatr. Suppl. 1993

• Schwartz PJ, et al: Prolongation of the QT Interval and the Sudden Infant Death Syndrome The New England Journal of Medicine 1998

Hypothesis

• A relationship exists between prolonged QT interval in infants and maternal smoking

Materials and Methods• Electrocardiograms of 24 infants (12 males

12 females) all 2 months old analyzed

• 17 babies from rural Native American population

• 7 babies from urban population in New York City

• All infants healthy at birth with apgar scores greater than 8

• Smoking habits of mothers obtained via questionnaire given at beginning of study

Materials and Methods (..cont’d)• Babies selected by means of availability,

good health, and no other risk factor (maternal alcohol consumption, low birth weight, difficult pregnancy)

• ECG’s taken during baseline period of previous study were amplified and collected onto VCR tapes

• Data from tapes digitized at 500 samples/sec and transformed into plottable wave forms

Materials and Methods (..cont’d)

• ECG’s of each baby marked at Q, R1, R2, and T segments using special purpose software programs for 25 intervals per baby

• Intervals measured in milliseconds, times recorded into SYSTAT

• QT adjusted for heartrate using Bazette’s formula: QTc= (Q-T)/ (R2-R1)

• Average QTc’s were found

Materials and Methods (..cont’d)

• QTc’s analyzed using SYSTAT

• Statistical analyses performed: t test for paired and unpaired observations

• Relationships looked for between QTc interval and maternal smoking

• Factors such as birth weight, sex, and maternal age also tested

Results• The mean QTc for all cases was 399+/- 26

msec

• Smoking during pregnancy did not affect QTc interval

• Sex and birthweight did not affect QTc interval

• Maternal age affected QTc interval

– Infants divided into 2 groups:

– “old” mothers >25 years of age– “young” mothers <25 years of age

Results (..cont’d)

• Infants with mothers classified as “young” had significantly longer QTc’s than infants with “old” mothers (t(23)=2.11, p<.05)

Discussion• As further supported by this study, QT

interval of infants should be researched more thoroughly

• Since prolonged QT interval is mostly thought to be genetically based and the extreme of a normal distribution, risk may be quantitatively related to length; factors affecting length could alter risk

Discussion (..cont’d)• Environmental contributions such as maternal

age could give infants at risk the extra push needed for prolonged QT interval to occur

• Perhaps young mothers have sub-optimal in-utero environments, making their infants prone to such a syndrome

• Controversy exists as to whether ECG’s should be done on all infants. This would be costly and can have clinical implications