Calculate the corrected QT interval of your patient !!
Some interesting facts about QT intervals
Normal QT interval = 392+ 27 msec.(Bazzet HC; An Analysis of the time relations of electrocardiograms. Heart 1920; 7:353-67)
QT dispertion is the difference between maximum and minimum QT interval in any 2 leads in a 12 lead Electrocardiogram
Normal QT dispertion is 49 + 20 millisec.
QT dispertion >80 ms indicates loss of synchronisation of repolarisation favouring arrythmogenic re-entrant mechanisms.
QTc > 440 ms is associated with 8 times increased risk of CVS mortality.
QT dispertion >80 ms is associated with 3.5 times increased risk of CVS mortality.
QTc & QT dispertion have limited prognostic value in normal subjects without any cardiovascular disease.
Prolonged QTc & QTd indicate shift of sympathetico-vagal balance
towards sympathetic predominance and reduced vagal modulation, this produces increased dispertion of ventricular repolarisation.
It could be associated with increased resting heart rate and decreased heart rate variability.These features are suggestive of autonomic modulation of the sinus node due to conditions like Hypertension, Acute myocardial infarction or congestive heart failure.
Epidemiological studies suggest that QT interval calculated by the Bazzet's formula has only limited correcting effect for the heart rate.
It has been observed that QTc changes significantly with changing heart rates and doesn't make QT interval independent from the heart rate.
If normal resting QT interval is increases after exercise could indicate underlying coronary artery disease.
(The QT interval and QT Dispertion"the smaller, the better." F. Lambardi. European H Journal Sept 1998 ;19; 1279-1281)
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