"QT clock" to improve detection of QT prolongation in long QT syndrome patients.
BACKGROUND
The QT interval is a risk marker for cardiac events such as torsades de pointes. However, QT measurements obtained from a 12-lead ECG during clinic hours may not capture the full extent of a patient's daily QT range.


OBJECTIVE
The purpose of this study was to evaluate the utility of 24-hour Holter ECG recording in patients with long QT syndrome (LQTS) to identify dynamic changes in the heart rate-corrected QT interval and to investigate methods of visualizing the resulting datasets.


METHODS
Beat-to-beat QTc (Bazett) intervals were automatically measured across 24-hour Holter recordings from 202 LQTS type 1, 89 type 2, and 14 type 3 genotyped patients and a reference group of 200 healthy individuals. We measured the percentage of beats with QTc greater than the gender-specific threshold (QTc ≥470 ms in women and QTc ≥450 ms in men). The percentage of beats with QTc prolongation was determined across the 24-hour recordings.


RESULTS
Based on the median percentage of heartbeats per patient with QTc prolongation, LQTS type 1 patients showed more frequent QTc prolongation during the day (~3 PM) than they did at night (~3 AM): 97% vs 48%, P ~10(-4) for men, and 68% vs 30%, P ~10(-5) for women. LQTS type 2 patients showed less frequent QTc prolongation during the day compared to nighttime: 87% vs 100%, P ~10(-4) for men, and 62% vs 100%, P ~10(-3) for women.


CONCLUSIONS
In patients with genotype-positive LQTS, significant differences exist in the degree of daytime and nocturnal QTc prolongation. Holter monitoring using the "QT clock" concept may provide an easy, fast, and accurate method for assessing the true personalized burden of QTc prolongation.
Electrical and Computer Engineering Department, University of Rochester, Rochester, New York.
Alex
A
Page
Cardiology Department, University of Rochester Medical Center, Rochester, New York.
Mehmet K
MK
Aktas
Electrical and Computer Engineering Department, University of Rochester, Rochester, New York.
Tolga
T
Soyata
Heart Research Follow Up Program, Rochester, New York.
Wojciech
W
Zareba
Electrical and Computer Engineering Department, University of Rochester, Rochester, New York; Heart Research Follow Up Program, Rochester, New York. Electronic address: Jean-Philippe.Couderc@heart.rochester.edu.
Jean-Philippe
JP
Couderc
D000293:Adolescent; D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use*; D000328:Adult; D002648:Child; D002675:Child, Preschool; D000072237:ERG1 Potassium Channel; D015716:Electrocardiography, Ambulatory / Q000379:methods*; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000235:genetics; D008133:Long QT Syndrome / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics / Q000503:physiopathology; D008297:Male; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D029597:Romano-Ward Syndrome / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics / Q000503:physiopathology; D012737:Sex Factors; D013997:Time Factors
D000319:Adrenergic beta-Antagonists; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human
Cardiac monitoring; Diagnostic; Electrocardiography; Long QT syndrome