Session S64.6

Relative Prolongation of the Terminal Part of the QT Segment Is Associated with Sudden Death in the Elderly

DW Lee*, PK Stein, EP Lundequam, N Sotoodehnia

Washington University
St. Louis, MO, USA

Background: Prolonged QT on Holters is linked to sudden cardiac death (SCD). Prolongation of the terminal segment of the QT may be more strongly associated with SCD than overall QT prolongation.
Methods: Holter-based QT parameters were measured in 40 participants (age 73.03±4.51, 24 M, 8 F), 20 w/SCD and 20 controls matched by age, gender, beta-blocker use, history of MI, and use of hypoglycemic medications. Recordings were from the Cardiovascular Health Study. Time to SCD was 6.5±2.8 (range 0.4-9.7) yrs. Digitized ECGs were integrated with beat-to-beat files obtained from Holter scanning using ecgpuwave (www.physionet.org). This program detected the start, peak and end of the R- and the T-wave. A customized MATLAB program was overread beat detection and excluded misdetected beats. It was run separately on the two ECG channels and the better one used for the analysis. Data from the first 2-min segment of each hour with at least 80% correctly detected beats were used. QTonset, QTpeak, and QTend times were measured for each beat/2-min segment and were used to determine the duration of the average initial and terminal portions of the T-wave which were then averaged/hr. Also, the % of the QT in the pre- and post-peak portions was determined/hr. Values were compared between groups using t-tests.
Results: N=4 cases and N=4 controls did not have sufficient usable QT data but there was no difference by SCD status by matching parameters. QT interval was significantly longer among cases (445 ± 88 vs. 405 ± 45 ms, p<0.001). Correcting the QT for heart rate did not affect this relationship. However, % QT in the pre-peak interval was significantly shorter in SCD (23.7 ± 3.1% vs. 24.2 ± 3.7%, p=0.002) whereas the percent QT in the post-peak interval was significantly longer in SCD (23.4 ± 3.9% vs. 22.0± 2.5%, p<0.001). N= 24 were analyzed on ch1 and N= 8 on ch2. Results did not differ by the channel examined.
Conclusion: Results are consistent with a prolonged Holter-based QT in older adults who suffered SCD. In addition, results suggest a further alteration in the relative proportion of the initial and terminal portions of the QT, with a relative prolongation of the terminal QT, in SCD cases.

(Abstract Control Number: 7)