Prevalence, prognosis and characteristics of subjects with short QT interval in an electrocardiogram
1University of Oulu, Faculty of Medicine, Institute of Clinical Medicine, Department of Internal Medicine
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|Persistent link:|| http://urn.fi/urn:isbn:9789514290077
|Publish Date:|| 2009-01-27
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented, with the assent of the Faculty of Medicine of the University of Oulu, for public defence in the Main Auditorium of Päijät-Häme Central Hospital (Keskussairaalankatu 7,
15850 Lahti) on February 6th, 2009, at 12 noon
Docent Markku Mäkijärvi
Docent Vesa Virtanen
Short QT syndrome is an inherited arrhythmia disorder characterized by a short QT interval, typical T-wave and ST-segment morphology and an increased risk of sudden cardiac death. The purpose of this thesis was to study the epidemiology and prognosis of the subjects with short QT intervals. Special attention was paid to the ECG changes that could illustrate the prognosis of subjects with short QT interval.
The first study comprised a group of patients with short QT syndrome. We report clinical presentation, ECG morphology, the prevalence of genetic mutations and the results of therapies in this group of patients.
The second study population consisted of 10 822 randomly selected middle-aged subjects followed up for 29 ± 10 years. QT intervals were measured using three correction methods for the heart rate in order to assess the prevalence and prognosis of those subjects with short QT intervals.
The third population consisted of three patients with short QT syndrome and nine controls. Holter recordings were analyzed to compare transmural dispersion of repolarization between patients and controls and also to study their capability to change repolarization indexes from baseline to maximal values.
In the fourth study ECGs from 10 patients with short QT syndrome were compared with ECGs of 12 asymptomatic subjects with short QT intervals. The aim was to find ECG abnormalities that would predict the outcome of the patients.
We found 62% of patients to be symptomatic, 34% had cardiac arrest. Atrial fibrillation was common. Most of the patients received an ICD or were placed on hydroquinidine.
The prevalence of QTc < 320ms was 0.10% and QTc < 340ms was 0.4%, respectively. Mortality or other serious symptoms did not differ between subjects and controls. We also found that the TPE/QT ratio as an index for abnormal transmural dispersion of repolarization was high compared to controls. Short QT syndrome patients had also lesser capacity to change the QT interval, indicating blunted autonomic response in SQTS.
Ten SQTS patients had significantly shorter Jpoint–Tpeak interval and higher TPE/QT ratio compared to controls.
In conclusion, shorter than normal QT interval might represent a novel short QT syndrome. However, in the general community short QT interval can reflect only the extreme end of the normal Gaussian distribution of QT intervals and these subjects carry a good prognosis. TPE/QT ratio and Jpoint–Tend intervals can be used as risk stratifiers in subjects with short QT intervals.
Acta Universitatis Ouluensis. D, Medica
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