Heart rate-dependence of QTc intervals assessed by different correction methods in patients with normal or prolonged repolarization.
BACKGROUND
There is a continuing debate about the optimal method for QT interval adjustment to heart rate changes. We evaluated the heart rate dependence of QTc intervals derived from five different QT correction methods.


METHODS
Study patients (n = 123, age 68 +/- 11 years) were dual-chamber device recipients with baseline normal or prolonged QT interval who had preserved intrinsic ventricular activation with narrow QRS complexes. Patients were classified to either Normal-QT (n = 69) or Prolonged-QT (n = 54) groups. Serial QT intervals were recorded at baseline (52 +/- 3 beats per minute) and following atrial pacing stages at 60, 80, and 100 beats per minute. The QTc formulae of Bazett, Fridericia, Sagie-Framingham, Hodges, and Karjalainen-Nomogram were applied to assess the effect of heart rate on the derived QTc values by using linear mixed-effects models.


RESULTS
Heart rate had a significant effect on QTc regardless of the formula used (P < 0.05 for all formulae). The Bazett's formula demonstrated the highest QTc variability across heart rate stages (highest F values) in both patient groups (in the total cohort, F = 175.9). In the following rank order, the formulae Hodges, Karjalainen-Nomogram, Sagie-Framingham, and Fridericia showed similar QTc heart rate dependence at both slower and faster heart rates in both patient groups (F = 21.8, 25.6, 28.8, 36.9, in the total cohort, respectively).


CONCLUSIONS
Of the studied QTc formulae, the Bazett appeared the most heart rate dependent. Our results suggest the use of Hodges and the Karjalainen-Nomogram secondly to ensure least heart rate dependence of QTc intervals in patients with either normal or prolonged repolarization.
Chiladakis
John
J
Cardiology Department, Patras University Hospital, Patras, Greece. chil@otenet.gr
Kalogeropoulos
Andreas
A
Arvanitis
Panagiotis
P
Koutsogiannis
Nikolaos
N
Zagli
Fani
F
Alexopoulos
Dimitrios
D
D000368:Aged; D000369:Aged, 80 and over; D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D047548:Defibrillators; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial