Abstract 12271: A New 24-Hour Holter Index to Measure Instantaneous Response of QT to RR Changes and Its Association With Cardiac Events in the LQT-1 Syndrome
Background: The long QT syndrome type 1 (LQT1) has been associated with cardiac events triggered by high adrenergic stimulus. The QT intervals are expected to shorten following heart rate (HR) acceleration, and increased cardiac risk for LQT1 patients is thought to be due to abnormal QT response to high β-adrenergic stimuli. We hypothesize that instantaneous changes in QT in response to changes in HR, measured from Holter ECGs, can help identifying LQT1 patients with an increased risk for cardiac events (CE).
Method: We designed a method to quantify the instantaneous response of QT to RR changes, based on 24-hour Holter recordings, using a fully computerized beat-to-beat QT and RR measurements. We quantified the percentage of beats that responded appropriately, with QT shortening preceded by RR shortening (QTacc), and that shows QT increase preceded by RR lengthening (QTdec). We defined an index that measures the balance between instantaneous responses of QT: QTbal=QTacc/QTdec. We applied the method to 195 Holter ECGs from controls, and 66 ECGs from genotyped adult LQT1 patients off beta-blockers. CE were defined as syncope, appropriate ICD shocks and sudden cardiac death.
Results: Average RR, QT, and QTbal values from controls (97[[female symbol]], 39±15yrs) were 803±100ms, 431±22ms, and 1.00±0.24, respectively. The values for the groups with and without cardiac events for all patients, and for patients wit QTc≤500 msec are in the table:* p=0.008 and ψ p≤0.05 when comparing groups with and without event. Binary logistic model showed that QTbal was associated with 37% increased risk for CE for each 0.1 increment (OR: 1.37, 95%CI:1-1.9, p=0.04) after adjustment for age, gender, QTc, and HRV parameters.
Conclusion: There is a significant association between QTbal increase and CE in LQT1 patients. Therefore, 24-hour Holter analysis in LQTS patients may represent an alternative to current protocols designed to unmask concealed form of the LQTS and assess their level of risk for CE.
- © 2013 by American Heart Association, Inc.