Clinical Scenario: Jessica is a 23-year-old university student who presents to hospital with anorexia and symptoms of a lower respiratory tract infection. She is otherwise healthy and is on no medications.The remainder of her history is unremarkable except for a family history of sudden, unexplained death in a maternal aunt.Baseline blood work shows mild hypokalemia and a left lower lobe infiltrate on her chest xray.She is admitted to hospital for correction of her electrolytes and is given clarithromycin for her pneumonia. The following day, she suffers a cardiac arrest. Polymorphic wide QRS complex tachycardia is seen on the monitor. A post-resuscitation ECG demonstrates striking QT findings (Figure 1).

Exploration of the interlead QT variation (QT dispersion) introduced cardiologists to some new concepts including the need to define a standard for lead selection in the measurement of QT interval and the reason or factors contributing to QT dispersion. However, still there dose not exist a generally acceptable standard for lead selection and the reason for the QT dispersion has not been given the importance it deserves. Only a few hypotheses have been suggested, none of which have been seriously experimented. Finding important factors causing QT dispersion can lead to a better understanding of its basics and more accurate usage of QT dispersion as an index in clinical practice. This paper examines the “Vector cancellation theory” on the basis that if “Vector cancellation” affects the QT interval duration in different leads, the nearest lead to the mean QRS axis must have the longest QT interval and vice versa. This was tested on the electrocardiograms taken from 34 people without cardiovascular problems. We came across a statistically significant inverse correlation between the QT interval in each limb lead and its angle to the ECG’s mean QRS axis. Thus this study gives weight to the vector cancellation theory. And as the nearest lead to the mean QRS Axis is likely to have the longest QT interval and given its practicality, it can be suggested as the standard lead for measuring QT interval in an electrocardiograph.

Ramadan fasting is one of the most important religious duties of Muslims, that its effect on the heart has not been determined yet. Our objective was to evaluate the effect of Ramadan fasting on ventricular repolarization as assessed by QT interval, corrected QT interval, QT dispersion or corrected QT dispersion. Sixthy healthy subjects aged 20 to 35 years were dispersion included in this study. QT interval, corrected QT interval (QTc) QT dispersion QTc dispersion, RR interval and QRS axis were measured in 12-lead surface electrocardiogram, once during fasting (10 to 11. 5 hours of absolute fasting from food and liquid) and another time, 15 to 60 minutes after eating food at sunset. All of the subjects had been fasting 11 to 12 hours each day at least for 25 days during Ramadan. The study was performed at Anvr Alam hospital in the year 2000. Maximal QT interval, mean QT interval and RR-interval, were longer during fasting (P<0.05), and both QT dispersion and QTc dispersion were increased (p<0.05). (QT dispersion: meant SD- 57.2± 20.1 ms during fasting Vs 41.6 ± 15.1 ms after meal, QTc dispersion =75.4±24.6 ms during fasting Vs 64.1 ± 22.8 ms after meal). But mean QTc interval, maximal QTc interval and QRS axis showed no significant difference. Prolongation of QT interval and RR interval during fasting, instead of no significant changes in corrected QT interval may primarily suggest that prolongation of RR-interval causes QTc interval not to have significant difference. But increases of QT dispersion and corrected QT dispersion (QTc dispersion) during fasting-that are more reliable indicators of ventricular repolarization-support the idea that ventricular repolarization may be changed during Ramadan fasting. QT dispersion in cardiac patients is showed to increase from normal values of 30-40 to 67-138 ms, but in our study their increases did not reach critical value.

Background: Cardiovascular mortality and morbidity are high in chronic renal failure (CRF) patients. Increased dispersion of QT intervals is known to predispose to ventricular arrhythmias and sudden cardiac death. This study was conducted to assess the effect of hemodialysis (HD) on corrected QT (QTc) intervals and their dispersions (QTd) in chronic hemodialyzed patients.Methods: Fifty-eight patients (mean age 54.2±15.8 years) with chronic renal disease on chronic hemodialysis (HD) were assessed by standard examination including blood pressure, body weight, heart rate, 12–lead electrocardiography and laboratory tests like electrolytes (Na+, K+, Ca++, phosphate), urea, and creatinine 30 minutes before and after HD. The QT intervals and QTc QTc=QT √R-R/ (in milli seconds [ms]) for each lead were measured manually by one observer using calipers. The difference between the maximum and the minimum of QT interval was noted as QT dispersion (QT d).Results: The mean of pre and post dialysis R-R intervals was 859.22±96.85 ms and 870.43±91.45 ms, respectively (p>0.05). The mean of corrected QT cmax intervals increased significantly from 423.45±24.10 to 454.41±30.25 ms (p<0.05). The mean of QT dispersions and the corrected QT interval dispersions changed from 51.56±12.45 to 63.21±14.43 ms (p<0.05) from 59.40±13.58 to 68.33±14.55 ms (p<0.05), respectively. The changes in serum potassium and calcium levels were related with QT interval prolongation.Conclusion: QT and QTc interval and dispersion increase in HD patients. Prolonged QT interval indices had relation with K+ and Ca++ions before but not after HD.

Introduction: Prolongation of QT interval might result in dangerous cardiac arrhythmias, including Torsades de Pointes (TdP), consequently leading to syncope or death. A limited number of studies carried out in this respect to date have shown that QT interval might increase during pregnancy. On the other hand, it has been shown that each pregnancy might result in an increase in the risk of cardiac accidents in patients with long QT interval. Therefore, the present study was undertaken to compare QT intervals in pregnant and non-pregnant women.Methods: Pregnant women group consisted of 40 women in the second and third trimesters of pregnancy and the non-pregnant control group consisted of healthy women 18-35 years of age. All the patients underwent standard 12-lead electrocardiogram (ECG). The QT interval was measured for each patient at lead II. The mean corrected QT interval (QTc) and QT dispersions (QTd) were compared between the two groups.Results: Mean heart rates in the pregnant and non-pregnant groups were 98.55±14.09 and 72.53±13.17 beats/minutes (P<0.001). QTd and QTc means were in the normal range in both groups; however, these variables were 49.50±12.80 and 43.03±18.47 milliseconds in the pregnant group and 39.5±9.59 and 40.38±17.20 milliseconds in the control group, respectively (P<0.001). Conclusion: The QT interval was longer in pregnant women compared to non-pregnant women; however, it was in the normal range in both groups. Therefore, it is important to monitor and manage risk factors involved in prolongation of QT interval and prevent concurrence of these factors with pregnancy.

Introduction: Methadone is used for the treatment of opioid dependency. Methadone causes QTc prolongation & occasionally torsade de pointes. Because the wide availability of methadone in methadone maintenance treatment (MMT) centers, dose-related effects of methadone on QT interval were evaluated.Methods: The study was clinical trial. Ninety patients who were under Methadone maintenance treatment in the MMT center of Noor Hospital and Ghaedi Clinic were evaluated. According to methadone doses patients divided into three groups (0-59 mg, 60-109 mg, 110-150 mg). Twelve-lead electrocardiograms (ECGs) were performed in patients at both baseline and after the maximum daily doses of methadone therapy. The ECGs were manually interpreted. The QTc intervals were calculated for each patient. In different groups, comparison of mean differences of QTc interval between baseline and follow up were analyzed by ANOVA.Results: There were significant differences between means of QTC interval before and after treatment with methadone in all groups. Methadone modestly increased QTc interval.Conclusion: Although QTc interval prolongation may occur after methadone treatment, the risks for torsade depoint arrhythmia is low.

Background: The prevalence of gestational diabetes mellitus is rising. Myocardial hypertrophy is the most common cardiac disorder in the infants of diabetic mothers, which hypothetically can cause fatal arrhythmias. This study investigated prolonged QT in the newborns of diabetic mothers in Afzalipour Hospital in Kerman City, in 2015. Methods: This case-control study was conducted on 49 neonates of diabetic mothers and 30 babies of healthy mothers. Routine echocardiograms and Tissue Doppler Imaging (TDI) were performed for all the newborns. QTc values were computed from randomly selected beats on ECG. Results: Twenty-nine (59%) newborns in case group had septal hypertrophy which was higher than control group (P < 0. 05). There was no difference between case and control groups in QTc values (P > 0. 05), and there was no relationship between septal hypertrophy and QT prolongation. Twenty-one percent of the infants in control group, had septal hypertrophy. Although parameters of M-Mode Echocardiography were similar, TDI showed differences between the two groups. (TDI) is applicable for the measurement of both systolic and diastolic functions. Conclusion: Findings revealed that the screening and treatment of diabetes during pregnancy need a revision in our context. In addition, there is a paucity of studies concerning the evaluation of TDI in the newborns of diabetic mothers. We recommend conducting studies to compare the routine echocardiograms with TDI in these high risk infants.