Does the presence of hibernating myocardium in patients with impaired left ventricular contraction affect QT dispersion?
BACKGROUND
Hibernating myocardium is associated with increased cardiovascular events. Increased QT dispersion on the surface electrocardiogram is a marker for serious ventricular arrhythmias. In this study, we determine whether hibernating myocardium is associated with increased QT dispersion in patients with coronary artery disease and impaired left ventricular contraction.


METHODS
Positron emission tomography with (13)N-ammonia and (18)F-fluorodeoxyglucose determined the presence of metabolic-perfusion mismatch defect. QT dispersion was measured by means of a digitizing tablet with validated software. QT intervals were measured on two separate occasions by two investigators blinded to the result of the positron emission tomography scans.


RESULTS
Forty-two patients with impaired left ventricular contraction were studied. They were divided into two groups: group A was made up of patients with mismatch defects (n = 26) and group B was made up of patients with no mismatch defects (n = 16). The mean (SD) QT dispersion measurements were 61.7 +/- 29.8 ms and 70 +/- 24.6 ms for groups A and B, respectively (not significant). When the patients were divided according to the dominant viability status of the impaired myocardial segment, a similar result was found. The patients whose impaired myocardium was dominantly hibernating (n = 19) had a mean QT dispersion of 66.4 +/- 31.9 ms compared with 63.6 +/- 24.8 ms in the patients whose impaired myocardium was mainly scarred (not significant).


CONCLUSIONS
QT dispersion is not affected by the presence of hibernating myocardium and is therefore not clinically useful in identifying patients with this phenomenon. This is in contrast with recent reports by other groups and calls for further investigation of this dichotomy.
Al Mohammad
A
A
Department of Cardiology, Aberdeen Royal Infirmary, Grampian University Hospitals NHS Trust, Foresterhill. aammay@hotmail.com
Mahy
I R
IR
Buckley
A
A
Cargill
R I
RI
Norton
M Y
MY
Welch
A E
AE
Walton
S
S
D000641:Ammonia / Q000378:metabolism; D001145:Arrhythmias, Cardiac; D004562:Electrocardiography; D005260:Female; D005462:Fluorine Radioisotopes; D005947:Glucose / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000503:physiopathology*; D009206:Myocardium / Q000378:metabolism*; D009590:Nitrogen Radioisotopes; D011446:Prospective Studies; D014055:Tomography, Emission-Computed; D018487:Ventricular Dysfunction, Left
D005462:Fluorine Radioisotopes; D009590:Nitrogen Radioisotopes; D000641:Ammonia; D005947:Glucose