الفهرس 
Qt interval and qtcOnly 14 pages are availabe for public view
 |  | from | 171 |  |  |
| | | from | 171 | | |
Abstract
Almost a century after Einthoven’s invention of the string galvanometer, the surface electrocardiograph retains its central place in cardiological diagnosis. In seeking to extract yet more information from the standard 12 lead ECG; much attention has been given in recent years to the measurement of QT dispersion (Wellen et al., 2004).
The QT interval reflects the duration of depolarization and repolarization of the ventricular myocardium. Abnormal prolongation of the QT interval (congenital or acquired) predisposes to ventricular
tachycardia of ‘torsade de pointes’ morphology. Abnormal QT dispersion (measured as the difference between the longest and the shortest QT duration in the 12 ECG leads) reflects inhomogeneous repolarization of ventricular muscle which may provide a substrate for serious ventricular arrhythmias (Gur et al., 2007).
In the context of ischaemic heart disease, researchers have explored the measurement of QT dispersion as a potential marker of arrhythmic risk, of myocardial ischaemia and of myocardial viability. In none of these applications has the technique so far established a place in routine clinical practice, though some progress has been made in our understanding of the measurement and significance of QT dispersion (Jimenez-Candil, et al., 2008).
In population studies, QT dispersion has been reported to be an independent predictor of long-term cardiovascular mortality in subjects with known cardiovascular disease.
Although prolongation of the QT intervals in acute ischemic conditions, such as acute myocardial infarction, intracoronary balloon inflation, and exercise induced ischemia has been shown, association of rest QT intervals with extent and severity of stable coronary artery disease (CAD) has not been extensively assessed so far. So, the aim of this study was to explore a possible relationship between QT dispersion and the number of affected coronary vessels at rest.
The current study included 120 subjects admitted for elective coronary angiography at Benha Catheterization laboratory from February 2011 to February 2012. The cases were divided, according to the number of the affected coronary vessels, into four groups [normal, single vessel disease (SVD), double vessel disease (DVD) and three vessel disease (TVD)] with 30 patients in each group.
The suitable candidates were subjected to the following:
Detailed medical history.
Clinical examination including local cardiac examination and body mass index (BMI).
High quality resting 12 lead ECG which was analyzed regarding the rhythm, rate, QRS complex and ST-T changes. We paid special interest to the QT intervals and dispersion as well as corrected QT measurements.
Transthoracic echocardiography (TTE) including M-mode,
two-dimensional (2D), doppler and tissue Doppler parameters.
Selective left and right coronary arteriography using the standard technique and the angiographic data were analyzed.
All these data were analyzed and correlated to each other. The age of the study population ranged from 32 to 80 years with the mean age 54 ± 9.43 years and BMI ranged from 19 to 33 with a mean value of 25.66 ± 2.67. The study included 60 males (50%) (Table 4).
Diabetics were found to be more in the DVD and TVD groups in relation to the normal and SVD groups (p=0.002). Moreover, TVD patients were more likely hypertensive versus other groups (p=0.001), while smokers were found to be more in the SVD group (p=0.009) (Table 7 & fig.14, 15, 16)).
It was found that QT max was greater in patients with DVD and TVD, while QT min was shorter in these groups. The values of QTD were 33±6, 49.6±6, 79.2±8 and 119.8±12 msec for the normal, SVD, DVD and TVD groups respectively (p=0.001). QTD was corrected for heart rate (QTcD) and the values were found to be 35.9±6, 53.7±7, 86.9±8 and 131±10 msec for the normal, SVD, DVD and TVD respectively. Statistically, these differences were found to be highly significant (p value = 0.001) (Table 9 & fig. 25, 28).
Regarding the echocardiographic findings of this study, the mean ejection fraction in the whole study was 57% ranging from 27 to 73%. The E/Ea ratio was found to be greater in patients with DVD and TVD (15.87±5.0 and 18.0±4.34 respectively, p=0.001) (Table 8 & fig. 20). This can be explained by that myocardial ischemia slows ventricular relaxation and can impair ventricular distensibility resulting in diastolic dysfunction.
We concluded that QTD and QTcD measurement at rest increases in patients with stable coronary artery disease in relation to normal. More important, there was also a strong relation between QTD and QTcD in one hand and the extent of CAD represented by the number of diseased coronary arteries on the other hand. The more the number of diseased coronary vessels, the longer QTD and QTcD. The sensitivity of both increases with the increase in number of stenosed coronary arteries.