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The corrected QT interval (QTc) can be used to identify individuals who are at a high risk for sudden cardiac death due to life threatening ventricular arrhythmias. Recently, QTc has been suggested as a potential prognostic marker in the setting of coronary artery disease (CAD). In this study, we aimed to evaluate the association between QTc and left ventricule longitudinal, global and circumferential strain using speckle tracking echocardiography (STE) in patients with stable CAD.
This study included 49 patients who were admitted to our clinic between September 2012 and February 2013 with history of stable CAD. Exclusion criteria were prior myocardial infarction, history of by-pass surgery or percutaneous coronary intervention, atrial fibrillation, age<18 years, severe valvular stenosis and regurgitation, concomitant systemic disease, constrictive pericarditis, restrictive or hypertrophic cardiomyopathy, poor imaging quality. Twelve-lead surface electrocardiography was recorded in all patients and QTc was calculated by dividing the QT interval by the square root of the preceeding R - R interval. Patients with QTc duration longer or shorther than 440 msn constituted the group 1 and 2, respectively. 2D STE images were obtained from LV apical 4-chamber (4C), LAX (long axis) and 2-chamber (2C) views. Strain measurements were reported as the peak longitudinal strain (LS) for 4C, LAX, and 2C views, and global strain (GS) was calculated by the average of the three apical views.
The mean age of the study population was 62±13 (F: 29 M: 20). There were no significant differences between groups in terms of age and gender. The mean LVEF calculated by biplane simpson were 59±12 and 60±9, respectively, in Group 1 and 2 (p:0.611). Twenty-four patients had one vessel disease, 14 patients had 2 vessel disease and 11 patients had 3 vessel disease. The patients in group 1 had statistically significantly lower 4C (16.3±4.4 vs. 19.5±3.5, p<0.001), LAX (16.1±3.4 vs. 19±3, p<0.001) and 2C (15.6± 3.5 vs. 18.1± 4.3, p < 0.001) peak longitudinal strain values compared to patients in group 2. GS values were significantly different between the groups (16.4±3.5 vs. 19.1±3, respectively, p:0.010). Basal and apical circumferential strain values were significantly different between the groups (16.8±3.1 vs. 18.8±3.3, p:0.034 and 22.3±5.6 vs. 25.2±3.4, p:0.043, respectively). Moderate correlation was observed between QTc and global longitudinal strain values (r:0.479, p:0.001).
This study shows that prolongation of QTc may be associated with impaired left ventricule longitudinal and circumferential mechanics in patients with stable CAD.