Dynamic QT/RR relationship in post-myocardial infarction patients with and without cardiac arrest.
OBJECTIVE
Changes in QT interval dynamicity may be associated with susceptibility to ventricular fibrillation (VF) after myocardial infarction (MI). We tested the hypothesis that dynamic QT/RR relationship might differ between post-MI patients with and without a history of VF. We also evaluated the influence of negative T-waves on the assessment of QT/RR relationship.


METHODS
We reviewed Holter recordings from 37 post-MI patients resuscitated from VF not associated with new MI (VF group) and 30 patients after MI without known sustained ventricular arrhythmias (control group). With an automated computerized program, we measured QT interval dynamicity as the mean QT/RR slope and as the maximal QT/RR slope determined at stable heart rates.


RESULTS
The mean QT/RR slope was 0.20 ± 0.08 in control group and 0.15 ± 0.09 in VF group (p=0.01) whereas corresponding maximal QT/RR slope values were 0.42 ± 0.20 and 0.33 ± 0.18 (p=0.01), respectively. Thirteen control patients (43%) and 22 VF patients (59%) showed only negative or both positive and negative T-waves (p=0.45). Mean QT/RR slope values were similar irrespective of T-wave polarity whereas maximal QT/RR slopes were steeper in cases with both positive and negative T-waves. Cases showing T-waves of both positive and negative polarity exhibited greatest intersubject variability of both QT/RR slope values.


CONCLUSIONS
Lower mean QT/RR slope may be associated with a risk of VF after MI. A detailed assessment and definition of differing T-wave polarities is essential in evaluating the QT/RR relation in post-MI patients.
Department of Cardiology, Helsinki University Central Hospital, Helsinki, Finland. jere.jarvenpaa@hus.fi
Jere
J
Järvenpää
Lasse
L
Oikarinen
Petri
P
Korhonen
Heikki
H
Väänänen
Lauri
L
Toivonen
Matti
M
Viitasalo
D000328:Adult; D000368:Aged; D004562:Electrocardiography; D015716:Electrocardiography, Ambulatory; D005260:Female; D006323:Heart Arrest / Q000473:pathology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000473:pathology*; D012189:Retrospective Studies; D012307:Risk Factors; D012984:Software; D013223:Statistics as Topic; D018709:Statistics, Nonparametric; D013318:Stroke Volume; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000473:pathology*; D016277:Ventricular Function, Left