QT Parameters Research Articles

QTc abnormalities in deliberate self‐poisoning with moclobemide

Several medications have been found to prolong the QT interval in overdose. This can predispose to torsade de pointes-type ventricular tachycardia. To analyse the effects of moclobemide deliberate self-poisoning on the length of both QT and corrected QT (QTc) intervals. Electrocardiograms (ECG) of all patients presenting to a regional toxicology service with moclobemide ingestion were reviewed. Cases where a cardiotoxic agent was coingested were excluded. QT and QTc parameters were compared with a comparison group of patients ingesting paracetamol or benzodiazepines. Of 75 patients where ECG were available, the median ingested dose was 4.5 g (interquartile range (IQR): 2.4-7.5; range: 0.6-18 g) and the median age was 34 years (IQR: 26-44). The mean QT interval was 415 ms (standard deviation (SD): 51 ms) with a mean QTc of 459 ms (SD: 44 ms), and were prolonged compared with the comparison group. Twelve female patients had a QTc > 500 ms and in seven of these causality was established based on a pre- or post-ECG with a QTc < 500 ms. Only 10% of the moclobemide cases had a heart rate (HR) > 100 beats per minute, making overcorrection of HR by Bazett's formula an unlikely cause of the findings. No cardiac arrythmias were observed other than one case of first-degree heart block. Moclobemide prolongs the QT and QTc intervals in overdose and a 12-lead ECG should be done on all moclobemide deliberate self-poisonings. Continuous cardiac monitoring for what is otherwise a relatively benign overdose would appear to be an inappropriate use of resources but can be considered in patients with a QTc > 500 ms or with known risks for QT prolongation.

Patterns of QT Dispersion in Athletic and Hypertensive Left Ventricular Hypertrophy

The objective of this article is to assess whether left ventricular hypertrophy (LVH) due to physical training or of hypertensive patients shows similarities in QT length and QT dispersion. A total of 51 subjects were studied: 17 essential hypertensive patients (27.7 +/- 5.6 years), 17 athletes involved in agonistic activity (canoeing) (24.8 +/- 6.1 years), and 17 normotensive healthy subjects as control group (24.8 +/- 3.6 years). The testing protocol consisted of (1) clinic BP measurement, (2) echocardiography, (3) 12-lead electrocardiographic examination (QT max, QTc max, QT min, QTc min, DeltaQT, DeltaQTc). There were no significant differences between the body surface area, height, and age of the three groups. Clinic blood pressure was higher in hypertensives (146.5 +/- 45.2/93.5 +/- 4.9 mmHg) versus athletes (120.9 +/- 10.8/77.1 +/- 6.0 mmHg) and controls (123.5 +/- 4.8/78.8 +/- 2.9 mmHg) by definition. Indexed left ventricular mass (LVM/BSA) was significantly greater in both athletes (148.9 +/- 21.1 g/m2) and hypertensives (117.1 +/- 15.2 g/m2) versus controls (81.1 +/- 14.5 g/m2; P < 0.01), there being no statistical difference among them. LVH (LVMI > 125 g/m2) was observed in all athletes, while the prevalence in hypertensives was 50%. In spite of this large difference in cardiac structure there were no significant differences in QT parameters between athletes and the control group, while hypertensive patients showed a significant increase in QT dispersion versus the two other groups (DeltaQT 82 +/- 2.1, 48 +/- 1.3, 49 +/- 2.3 ms; P < 0.01; DeltaQTc 88 +/- 2.0, 47 +/- 1.4, 54 +/- 2.7; P < 0.01). LVH induced by physical training activity is not associated with an increase in QT dispersion, whereas pathological increase in LVM secondary to hypertension is accompanied by an increased QT dispersion.

Qt dispersion in soccer players during exercise testing.

Screening for cardiac health should involve relevant parameters or indices that are easy and inexpensive to obtain. Various cardiac adaptation mechanisms develop during regular exercise that are affected by many factors, and these are reflected on a surface electrocardiogram. QT dispersion has been considered a surrogate for heterogeneity of repolarization, leading to ventricular arrhythmias. We compared QT parameters between athletes and sedentary subjects. A total of 225 men were assessed, comprising a group of professional soccer players and sedentaries. Each subject underwent supine 12-lead electrocardiographic examinations and exercise testing by ergospirometry. QT parameters were taken at rest and at peak exercise. Peak oxygen consumption was considerably higher in the athletes than in the controls (59.3 +/- 5.6 vs. 44.3 +/- 2.4 ml/kg/min, mean +/- SD, p < 0.001). QT parameters at rest: There were significant differences in heart-rate-corrected rest maximal QT duration (413.9 +/- 50.5 vs. 445.3 +/- 45.7 ms, p < 0.001) and in heart-rate-corrected rest minimum QT duration (380.5 +/- 51.2 vs. 409.5 +/- 46.7 ms, p < 0.001). QT parameters at peak exercise: maximal QT duration at peak exercise (253.9 +/- 20.8 vs. 261.7 +/- 26.2, p = 0.02), QT dispersion at peak exercise (25.2 +/- 9.1 vs. 29.5 +/- 15.8 ms, p = 0.04), heart-rate-corrected QT dispersion at peak exercise (44.6 +/- 16.4 vs. 52.6 +/- 28.3 ms, p = 0.03) differed significantly between professional soccer players and controls. QT dispersion and corrected QT dispersion at peak exercise are lower in athletes than in controls. Athletes and other subjects identified with a long QT interval should be examined at regular intervals.

Multivariate associates of QT interval parameters in diabetic patients with arterial hypertension: importance of left ventricular mass and geometric patterns.

The aim of the study was to assess the determinants of increased QT interval parameters in diabetic patients with arterial hypertension and, in particular, the strength of their relationships to echocardiographically derived left ventricular mass (LVM) and geometric patterns. In a cross-sectional study with 289 hypertensive type 2 diabetic outpatients, maximal QT and QTc (heart rate-corrected) intervals, and QT, QTc, and number-of-leads-adjusted QT interval dispersions were manually measured from standard baseline 12-lead ECGs. Electrocardiographic criteria for left ventricular hypertrophy (LVH) were either Sokolow-Lyon or Cornell sex-specific voltages. LVM and geometric patterns were determined by 2D echocardiography. Statistical analyses involved bivariate tests (Mann-Whitney, chi2, Spearman's correlation coefficients, ANOVA and receiver-operating-characteristic (ROC) curve analyses) and multivariate tests (multiple linear and logistic regressions). QT dispersion measurements showed significant correlations with echocardiographic LVM (r=0.26-0.27). ROC curves demonstrated a poor isolated predictive performance of all QT parameters for detection of LVH (areas under curve: 0.58-0.59), comparable to that of electrocardiographic voltage criteria. Only patients with concentric hypertrophy had significantly increased QT dispersion (QTd) when compared to those with normal geometries (64.24+/-21.09 vs 53.20+/-15.35, P<0.05). In multivariate analyses, both electrocardiographic and echocardiographic LVH were independent predictors of increased QTd, as well as only QTd and gender were determinants of LVM. In conclusion, increased QT interval dispersion is associated with LVM and concentric hypertrophy geometric pattern in diabetic hypertensive patients, although in isolation neither QTd nor any QT parameter presents enough predictive performance to be recommended as screening procedures for detection of LVH.

Alteration of QT rate dependence reflects cardiac autonomic imbalance in patients with obstructive sleep apnea syndrome.

QT rate dependence is one of the major properties of ventricular repolarization with its circadian and autonomic modulations. The authors postulated that dynamic alterations in QT interval adaptation could help characterize patients with cardiac autonomic alterations, like those with obstructive sleep apnea syndrome (OSAS). To assess ventricular repolarization features in patients with OSAS, QT parameters and their dynamicity along RR intervals were compared from 24-hour ECG data of patients with and without this syndrome, assessing cardiac autonomic nervous system equilibrium by means of time-domain and frequency-domain analyses of heart rate variability (HRV). The study group consisted of 74 consecutive patients referred to the Sleep Laboratory for clinically suspected OSAS. The syndrome was confirmed in 30 (40.5%) patients according to standard polysomnographic criteria. QT length related to heart rate (HR) was found significantly shorter for HR < 70 beats/min in patients with OSAS(-1.32 +/- 0.35)compared with patients without OSAS(-1.99 +/- 0.40; P < 0.01). This flattened relationship was correlated with the severity of the sleep related disorder. Using multiple linear regression analysis, the apnea/hypopnea index and nocturnal normalized high frequencies (HFnu) were the most significant predictors of the QT/RR slope(R = 0.61; P < 0.0001). OSAS is significantly associated with a flattened relationship between QT duration and RR interval at low HRs. The alteration of cardiac parasympathetic tone occurring in severe OSAS patients may explain this altered rate dependent adaptation of myocardial repolarization.

Prognostic value of QT interval parameters in type 2 diabetes mellitus: Results of a long-term follow-up prospective study

The prognostic importance of electrocardiographic ventricular repolarization QT parameters (maximum rate-corrected QT interval—QTcmax, QT interval dispersion–QTd, and QTcd), in relation to other risk markers, on cardiovascular and cardiac mortality, and on total fatal or nonfatal cardiovascular events, was evaluated prospectively in 471 type 2 diabetic outpatients. During a median follow-up of 57 months (range: 2–84), 121 (25.7%), patients died, 44 (36.3% of them) from cardiovascular causes and 106 (22.5%) fatal or nonfatal cardiovascular events were observed. In Cox proportional hazards multivariate analysis, both QTd and QTcmax were independent predictors of cardiovascular and cardiac mortality (hazard ratio [HR]: 1.34, 95% confidence interval [95% CI]: 1.12–1.59, for each 10-ms increments in QTd and HR: 1.17, 95% CI: 1.03–1.21 for 10-ms increments in QTcmax, for cardiovascular mortality). They were also predictors of total fatal or nonfatal cardiac and cardiovascular events (HR: 1.18, 95% CI: 1.05–1.33 for QTd and HR: 1.09, 95% CI: 1.04–1.15 for QTcmax). Additional independent prognostic markers for total cardiovascular events were the presence of previous cardiac disease, cerebral or peripheral vascular disease, age, male gender, known diabetes duration, heart rate, and serum triglycerides. Excluding patients with prior cardiac disease did not change significantly the prognostic performance of QTd but decreased that of QTcmax. In conclusion, QT interval parameters give additional prognostic information in patients with type 2 diabetes mellitus, beyond that obtained from traditional risk factors. QT interval dispersion seems a better prognostic marker than maximum QT interval, particularly in patients without previous cardiac diseases.

Day-to-day reproducibility of Holter beat-by-beat analysis of repolarisation

Reproducibility of Holter QT analysis is not well established and has been assessed only in one study.Study design — We evaluated the day-to-day reproducibility of different QT parameters – mean and max (four beats basis) 24h QT and QTc (Bazett formula), QT for heart rate 55-60 [QT60], 75-80 [QT80] and 95-100 [QT100] beats/min and QT/RR slope (calculated in moving window of 3000 beats in 50 beat steps). QT intervals were measured from 48h digital ECG (sampled at 256 Hz) recordings using Del Mar Medical’s QT software in beat-to-beat fashion. The analysed group consisted of 6 women and 24 men – 13 patients with hypertrophic cardiomyopathy, 5 healthy family members of the patients with hypertrophic cardiomyopathy, 7 patients with CAD and 5 with other diseases (hypertension, arrhythmia, aborted sudden death without organic heart disease). Reproducibility was analysed with the methods proposed by Bland and Altman.Results — The overall reproducibility of repolarisation parameters was acceptable. Coefficient of reproducibility for mean 24h QT was 24ms, mean QTc 12ms, max QT 22ms, max QTc 24ms. The best reproducibility was observed for QT60, QT80 and QT100 – 12ms, respectively. The poorest day-to-day reproducibility was recorded for the QT/RR slope parameters, which was related to lower heart rate reproducibility.Conclusions — We can conclude that day-to-day reproducibility of Holter repolarisation analysis is acceptable. QT measurement in narrow heart rate windows has the best reproducibility. Accurate QT analysis requires good quality recording, T wave amplitude above 0.2mV and an interactive QT measurement tool which includes verification, editing abilities.

Temporal repolarization inhomogeneity and reperfusion arrhythmias in patients undergoing successful primary percutaneous coronary intervention for acute ST-segment elevation myocardial infarction: Impact of admission troponin T

Background The presence of admission cardiac troponin-T (cTnT) is a means of identifying a high-risk subgroup in patients with acute ST-segment elevation myocardial infarction (AMI). Because a substantial number of these patients has malignant ventricular arrhythmias, we hypothesized that there is a relation between cTnT status on admission and inhomogeneity of ventricular repolarization, and we tested this assumption in the setting of primary percutaneous coronary intervention (PCI). Methods Temporal fluctuations of ventricular repolarization were studied during and after primary PCI (Thrombolysis In Myocardial Infarction [TIMI] 2 and 3) in 94 consecutive patients with a first AMI by continuous beat-to-beat QT-interval measurement, performed with Holter monitoring initiated on admission. Troponin-T levels on admission were >0.1 ng/mL in 53 patients (cTnT+) and <0.1 ng/mL in 41 patients (cTnT−). There were no significant differences in baseline clinical characteristics between the groups. Results The incidence of severe reperfusion arrhythmias (RAs) was significantly higher in patients in the cTnT+ group within the first 2 hours after recanalization. The course of the QT interval revealed a significant decline ( P < .001) after recanalization of the infarcted vessel within 10 hours in both groups; however, hourly values were significantly lower and normalization of the QT parameters was more rapid in patients in the cTnT− group than patients in the cTnT+ in this period (QTc, 438.5 ± 28.3 ms vs 449.3 ± 35.3 ms [hour 1, P < .01]; 413.6 ± 35.8 ms vs 420.1 ± 39.2 ms [hour 10, P < .05]). QT-interval variability also significantly declined within 4 hours after PCI ( P < .001), and likewise, patients in the cTnT− group exhibited lower values in this period (QTSD, 29.7 ± 6.8 ms vs 33.5 ± 10.5 ms [hour 1, P < .01]; 23.0 ± 6.1 ms vs 25.9 ± 7.5 ms [hour 4, P < .01]). Conclusions Positivity of cTnT on admission is associated with a significantly higher temporal inhomogeneity of ventricular repolarization and a higher incidence of malignant RAs, which suggests more advanced microvascular injury. Early successful primary PCI ultimately results in a significant recovery of parameters of QT interval and mean RR interval in all patients, although it was significantly delayed in patients in the cTnT+ group. (Am Heart J 2003;145:484-92.)

Sildenafil citrate does not affect QT intervals and QT dispersion: an important observation for drug safety.

Sildenafil is an effective and widely used therapeutic agent for erectile dysfunction. Deaths have been reported due to sildenafil use and most of them are attributed to concurrent use of nitrates. However, the effects of sildenafil on QT intervals, QT dispersion, and the possible risk of ventricular arrhythmia have not been studied before. Our aim in this study was to evaluate the effect of sildenafil citrate on QT intervals and QT dispersion. Thirty-six patients with erectile dysfunction were included in this study. Twenty-one patients had coronary artery disease whereas 12 of them also had accompanying diabetes mellitus. Standard 12-lead electrocardiograms (ECG) were recorded three times: before, and at the first and fourth hours of 50 mg sildenafil citrate ingestion. All QT parameters were corrected for heart rate. Mean age of the patients was 54 +/- 12 years. The mean heart rate did not differ significantly between the three ECG examinations. The corrected and uncorrected maximum and minimum QT intervals were not significantly different between the three ECG examinations. The QT dispersion and corrected QT dispersion before and 1 hour and 4 hours after sildenafil ingestion were 31 +/- 9 ms, 36 +/- 10 ms; 32 +/- 11 ms, 37 +/- 14 ms; 27 +/- 8 ms, 32 +/- 9 ms, respectively (P > 0.05). Sildenafil does not prolong QT intervals or increase QT dispersion in patients with erectile dysfunction. Our results suggest that the risk of ventricular arrhythmia does not increase with ingestion of 50 mg sildenafil.

Effects of Long-Term Hormone Replacement Therapy on QT and Corrected QT Dispersion during Resting and Peak Exercise Electrocardiography in Post-Menopausal Women.

It is known that the QT interval is longer in women than men. Estrogen is reported to account for the QT interval prolongation in several studies conducted with hormone replacement therapy (HRT) in postmenopausal women. Along with this, there are conflicting data as regards the effects of HRT on QT interval and dispersion. Moreover, there is no evidence about the effect of HRT on exercise QT parameters. We compared QT parameters obtained from surface electrocardiograms during resting and peak exercise before and after 6 months of HRT consisting of estrogen plus progesterone in healthy postmenopausal women. Twenty-four healthy postmenopausal women were given 0.625 mg/day conjugated estrogens and 2.5 mg/day medroxyprogesterone acetate for 6 months. Exercise stress testing using the Bruce protocol was performed before and after HRT. QT maximum, minimum, dispersion and corrected QT maximum, minimum and dispersion were calculated during resting and peak exercise. HRT resulted in a significant increase in estradiol plasma levels from 24+/-10 pg/mL to 117+/-66 pg/mL (P<0.001). There was no significant difference in resting QT parameters after HRT, whereas QT dispersion and corrected QT dispersion were significantly increased during peak exercise (20+/-7 versus 25+/-10 ms; P<0.05, 33+/-12 versus 41+/-16 ms; P<0.05, respectively). Nonetheless, the other exercise QT parameters were unchanged. The resting QT parameters are not affected by long term HRT consisting of estrogen plus progesterone, which leads to an increase in QT dispersion and corrected QT dispersion during peak exercise.

QT intervals and QT dispersion as measures of left ventricular hypertrophy in an unselected hypertensive population

Electrocardiographic (ECG) QT intervals and dispersion correlate with echocardiographic left ventricular mass index (LVMI) in groups of selected essential hypertensives. We tested the strength of this relationship in a large group of unselected hypertensives to assess whether QT measurements may be a simple screening test for LVH in clinical practice. In a cross-sectional study of 386 unselected hypertensive subjects, maximal QT intervals (QT max), QT dispersion (QT disp), and ECG voltages (Sokolow-Lyon and Cornell sex-specific voltages) were measured from 12-lead ECG. The LVMI correlated most strongly with Cornell voltage (linear regression r = 0.44, P < .001). The strongest relationship between LVMI and QT parameters was with QT max, (r = 0.25, P < .001). This relationship weakened using heart rate-corrected QT max. Correlations between LVMI and QT disp were weak, whether or not they were corrected for heart rate. Sokolow-Lyon voltages, Cornell voltage and QT max, but not QT disp, were independently predictive of LVMI after adjustment for age, sex, race, and the other ECG parameters. Receiver operating characteristic (ROC) curve analyses demonstrated that no QT parameter performed better than simple ECG voltage criteria in the detection of LVH. In conclusion, QT max, the QT parameter most strongly associated with LVMI, was independently associated with LVMI after adjustment for standard ECG voltage criteria. However, as an isolated measure it was no better than simple ECG voltage criteria as a screening test for LVH in clinical practice.

Qt Dispersion and Signal-Averaged Electrocardiogram in Hemodialysis and Capd Patients

The aim of this study was to compare QT dispersion (QTd) and signal-averaged electrocardiogram (SA-ECG) parameters that may predict risk of malignant arrhythmias in patients on hemodialysis (HD), on continuous ambulatory peritoneal dialysis (CAPD), and in controls. Controlled cross-sectional study in a tertiary-care setting. 28 HD (M/F 18/10; mean age 32 +/- 9 years), 29 CAPD (M/F 17/12; mean age 34 +/- 10 years), and 29 healthy controls (M/F 17/12; mean age 32 +/- 8 years) were included. On ECG, minimum (QTmin) and maximum (QTmax) QT duration and their difference (QTd) were measured. In SA-ECG, duration of filtered QRS, HFLA signals less than 40 microV, and RMS voltage (40 ms) were also measured. Higher serum Ca2+ and lower K+ levels were found in CAPD compared to HD. All QT parameters were increased in HD and CAPD compared to controls. QT dispersion was significantly prolonged in HD compared to CAPD. In HD, QTd was correlated with left ventricular (LV) mass index (r = 0.53, p = 0.004), but not in CAPD (r = -0.09, p = 0.63). QT dispersion was significantly prolonged in patients with LV hypertrophy compared to patients without hypertrophy on HD (68 +/- 18 ms vs 49 +/- 18 ms, p = 0.008). In the analysis of SA-ECG, 3 of the 28 (11%) HD and 2 of the 29 (7%) CAPD patients had abnormal late potentials. Patients on HD and CAPD had significantly higher filtered-QRS duration compared to controls (105 +/- 15 ms and 104 +/- 12 ms vs 95 +/- 5 ms, respectively, p = 0.04). Patients with LV hypertrophy had higher filtered-QRS duration compared to patients without hypertrophy (109 +/- 12 ms vs 95 +/- 8 ms, p < 0.001). Dialysis patients had prolonged QTd and increased filtered-QRS duration in SA-ECG compared to controls. Patients on HD had longer QTd than patients on CAPD. QTd has been correlated to LV mass index in HD, but not in CAPD. This difference might be due to the effect of different dialysis modalities on electrolytes, especially the higher serum Ca2+ levels.

Reproducibility of QT parameters derived from 24-hour ambulatory ECG recordings in healthy subjects.

To estimate the reproducibility of QT parameters derived from 24-hour ambulatory ECG recordings. Ten healthy volunteers aged 25 to 41 years participated. In two 24-hour ambulatory ECG recordings obtained 1 day apart, the QT interval was measured manually at stable heart rates in approximately 16 periods during daytime and 6 periods during nighttime. The association between the QT and RR interval was described by linear regression for day and nighttime separately and the following QT parameters were calculated: the QT interval at heart rate 60 beats/min during daytime (QT(60)day), slope(day), slope(night), and the difference in QT(60) between day and nighttime (DeltaQT(60)). The QT parameters were assessed four times for each participant to discriminate method inaccuracy from day to day variation. The reproducibility was estimated as the coefficient of repeatability, the relative error, and the ratio between within-subject variability and between-subject variability. The coefficient of repeatability, the relative error and the ratio, respectively, were 19 ms, 1.8% and 0.5 for QT(60)day, 0.076, 21% and 0.68 for slope(day), 0.116, 43% and 1.37 for slope(night), and 37 ms, 325% and 1.19 for DeltaQT(60) when estimating the overall day to day reproducibility. Inaccuracy of QT measurement accounted for approximately 40% of this variation, whereas the error caused by selecting segments was small. QT(60)day has a high reproducibility and may with advantage replace the conventional QT interval measured on a resting ECG. To assess QT dynamics, the slope of the regression line during daytime is suitable and the short term reproducibility acceptable for clinical trials. Regarding slope(night) and DeltaQT(60), the variation is high and the parameters should be used with caution.

Cardiovascular Safety of Cocaine Anaesthesia in the Presence of Adrenaline during Septal Surgery

The purpose of this study was to investigate the possible cardiovascular side effects of 4% cocaine solution in the presence of adrenaline during septal surgery. Sixty adult patients undergoing elective septal surgery with local anaesthesia were included in the study. Noses were packed with 5-mL 4% cocaine (200-mg) solution on cotton pledgets, which were left in the nose for 15 minutes. Then, 10 mL of local anaesthetic (lidocaine 2% and adrenaline 1:100,000) were infiltrated in septal mucosa, and 15 minutes later, the surgical procedure was initiated. At the beginning of the operation, intervals from 12-lead surface electrocardiograms and vital signs including blood pressures and heart rate were recorded as a baseline. All measurements were repeated just before local anaesthetic infiltration, just before the beginning of the surgical procedure, and, finally, at the end of the operation. All four measurements and electrocardiographic tracings were examined. Systolic and diastolic blood pressures and QT parameters, RR intervals, and heart rates obtained from electrocardiogram were compared statistically with repeated-measures analysis of variance. No statistically significant difference was found among all four staged measurements. None of the patients developed tachycardia, hypertension, hypotension, or any chest pain. In electrocardiogram tracings, no sinus tachycardia depression, elevation, or bundle branch block was noted. This study shows that concomitant use of cocaine and adrenaline in the proper concentration and volume and in a carefully screened patient group was safe for the cardiovascular system.

Is There A Relationship Between Baroreflex Sensitivity, Cardiac Autonomic Function And Cardiac Repolarisation In Type 1 Patients?

Established diabetic autonomic neuropathy (DAN) carries a poor prognosis, with an increased risk of sudden death. Recently, baroreflex sensitivity (BRS) has been proposed as a sensitive marker of autonomic function in diabetes (DM). An association between DAN and abnormal cardiac repolarisation, manifest by increases in QT interval and/or QT dispersion on the ECG, has also been described. The aim of this study was to investigate the relationship between BRS and QT parameters. We have studied 28 Type 1 DM subjects (age 39 ± 10yrs (mean ± SD), DM duration 14 ± 11yrs, HbA1c 8.5 ± 1.3%) with normal cardiac autonomic function tests (DAN–) and 8 subjects (age 49 ± 13yrs, duration 22 ± 9yrs, HbA1c 9.5 ± 1.1%) with abnormal tests using standard criteria (DAN+). We measured supine BRS using sequence analysis of systolic blood pressure and pulse interval. Rate‐corrected QT (QTc) interval was measured using a high‐resolution ECG system, and QT dispersion from a 12‐lead ECG recorded at 50mm/s. Results are summarised below.Regression analysis revealed no correlation between BRS and QTc interval or QT. In summary, DAN+ patients had significantly lower BRS (p &lt; 0.001) and increased QT dispersion (p &lt; 0.01) compared to DAN− subjects, but no difference in QTc. In contrast to BRS, changes in QTc and QT dispersion may occur relatively late in the disease. BRS ms/mmHg QTc interval QT dispersion DAN− 12.7 ± 6.6 (n=28) 411 ± 22 ms (n=28) 38 ± 12 ms (n=28) DAN+ 3.9 ± 1.9 (n=8) 409 ± 22 ms (n=8) 54 ± 12 ms (n=6)

QT intervals and heart rate variability in hypertensive patients.

Low heart rate variability and increased QT dispersion are risk factors for cardiac mortality in various patient populations. We studied dispersion of QT interval, i.e. an index of inhomogeneity of repolarization, and heart rate variability (HRV) i.e., a measure of cardiac autonomic modulation in 76 essential hypertension cases (45 women, 53.0 +/- 11.1 years, body mass index: 25.1 +/- 1.4 kg/m2) and 70 healthy cases (42 women, 54.0 +/- 10.2 years, body mass index: 25.5 +/- 1.6 kg/m2, p > 0.05). QT-corrected QT intervals and their dispersions were significantly higher in the hypertensive group (p < 0.0001), all showing a direct relation with the level of systolic and diastolic blood pressures, ventricular mass index and high Lown grade ventricular rhythm problems. Time domain measures like standard deviation of RR intervals, standard deviation of the means of all corrected RR intervals calculated at 5 min intervals (p < 0.0001), proportion of adjacent RR intervals differing by > 50 msec (p = 0.005), HRV triangular index (p = 0.007), the square root of the mean squared differences of successive RR intervals (p = 0.011), and the high frequency (HF, 0.16-0.40 Hz, p < 0.0001) part of the frequency domain measure of HRV were all decreased, whereas the low frequency (LF, 0.04-0.15 Hz, p = 0.013) part of the frequency domain measures and LF / HF ratio (p < 0.0001) were increased in hypertensive cases. Time domain and the HF part of frequency domain measures of heart rate variability showed an inverse relation with the increased levels of both systolic and diastolic blood pressures and Lown grading system of ventricular rhythm problems, whereas LF and LF / HF showed direct relations with high levels of systolic and diastolic blood pressures and high Lown grade ventricular rhythm problems. The measures of heart rate variability apart from LF and LF / HF were inversely related with the QT intervals and dispersions, whereas LF / HF was directly related with them. Therefore, we conclude that the levels of both systolic and diastolic blood pressures are related to the generation of ventricular rhythm problems either via increasing left ventricular mass which results in an increase in QT parameter measurements, or by altering heart rate variability measures indicating a disturbance in cardiac autonomic balance in essential hypertension.

The relationship between QT intervals and mortality in ambulant patients with chronic heart failure. The united kingdom heart failure evaluation and assessment of risk trial (UK-HEART)

Mortality in patients with heart failure remains high and is difficult to predict. QT interval parameters on a 12-lead ECG have been shown to predict arrhythmic events in patients with a variety of myocardial diseases. There is some, but not consistent, evidence that QT interval parameters may act as predictors of mortality, in particular sudden death, in patients with heart failure. In an adequately powered prospective study we have studied QT interval parameters in patients with stable chronic heart failure in order to determine whether they are predictive of all-cause mortality or mode of death. Five hundred and fifty-four ambulant outpatients with chronic heart failure were recruited. A 12-lead ECG, chest radiograph, echocardiogram, 24 h ambulatory electrocardiogram and serum for biochemical analysis were obtained at baseline. Patients were followed for 471+/-168 days. QT intervals were measured in all leads blinded to patient's characteristics and outcome, were corrected for heart rate, and the maximum QT intervals, and QT dispersion (range of QT intervals) were determined. The same parameters were determined for JT intervals. The primary end-point was all-cause mortality, secondary end-points were sudden cardiac death and death due to progressive heart failure. Multivariate analysis with the Cox's proportional hazards model was used to determine which variables were independently related to outcome. Four hundred and ninety-five patients had analysable ECGs at study entry and of these 71 died during follow-up. The heart rate corrected QT dispersion and maximum QT interval were significant univariate predictors of all-cause mortality (P=0.026 and <0.0001 respectively), and also of sudden death and progressive heart failure death, but were not related to outcome in the multivariate analysis. The independent predictors of all-cause mortality were cardiothoracic ratio (P=0.0003), creatinine (P=0.0009), heart rate (P=0.007), echocardiographically derived left ventricular end-diastolic dimension (P=0.007) and ventricular couplets on 24 h electrocardiographic monitoring (P=0.015). In an adequately powered prospective study none of the QT or JT parameters were shown to be independent predictors of outcome in patients with mild to moderate congestive heart failure. These variables do not therefore add to the prognostic information which can be gained from simple radiographic, biochemical, echocardiographic and Holter data in this group of patients.

QT dispersion is not related to infarct size or inducibility in patients with coronary artery disease and life threatening ventricular arrhythmias

OBJECTIVETo relate QT parameters to infarct size and inducibility during electrophysiological studies.DESIGNAnalysis of a prospective register.SETTINGUniversity hospital.PATIENTS64 patients with coronary artery disease and documented life threatening ventricular arrhythmias.INTERVENTIONSMeasurements of QT-max,...

QT dispersion in athletic left ventricular hypertrophy

Objective To assess whether physiologic left ventricular hypertrophy as a result of physical training is associated with an increased QT length or dispersion. Methods Thirty-three subjects were assessed. These consisted of a group of international endurance athletes (including 8 rowers, 2 cyclists, and 1 triathlete), a group of 12 professional soccer players, and a further group of 10 control subjects. Each underwent 2-dimensional echocardiography and 12-lead electrocardiographic examination. Results Left ventricular mass index was considerably greater in both the endurance athlete (163.3 ± 14.4 g/m 2; P < .01) and soccer player groups (144.2 ± 5.5 g/m 2; P < .05) compared with the controls (109.2 ± 6.3 g/m 2). In spite of these large differences in cardiac structure there were no significant differences in QT parameters between the groups (QT dispersion 56.9 ± 5.5, 68.5 ± 9.5, and 67.2 ± 12.6 ms; QTc dispersion 61.4 ± 9.2, 69.4 ± 13.3, and 54.2 ± 6.5 ms; maximum QT 402 ± 10.3, 404 ± 9.6, and 392 ± 14.0 ms; and maximum QTc 404 ± 7.0, 413 ± 9.3, and 399 ± 9.9 ms among endurance athletes, soccer players, and controls, respectively). Conclusion Left ventricular hypertrophy occurring as a consequence of athletic training does not appear to be associated with a major increase in QT length or QT dispersion. (Am Heart J 1999;137:678-81.)

QT dispersion and autonomic nervous system function in patients with type 1 diabetes

Cardiac arrhythmias and markedly increased mortality rate have been demonstrated in patients with diabetic autonomic neuropathy. Abnormal prolonged QT dispersion interval (QTd) is associated with a higher risk of ventricular arrhythmias. The aim of this study was to evaluate the relationship between autonomic dysfunction, QT and JT interval dispersion parameters and ventricular arrhythmias. Twenty-six patients with type 1 diabetes mellitus and 20 healthy subjects as controls were enrolled in the study. Resting 12-lead electrocardiograms were recorded for measurement of QTd, corrected QTd (QTcd), JT dispersion (JTd) and corrected JT dispersion (JTcd). After taking ECG, all patients underwent autonomic function tests. Patients and control group were also evaluated by 24-h Holter monitoring. Fourteen patients were identified who had autonomic dysfunction. QTd, QTcd, JTd, and JTcd values were significantly higher in patients with autonomic dysfunction than both patients without autonomic dysfunction and the control group (QTd: 78±16 vs. 51±13 ms, P=0.002; 78±16 vs. 48±9 ms, P<0.001; QTcd: 91±14 vs. 66±12 ms, P=0.001; 91±14 vs. 61±11 ms, P<0.001; JTd: 81±12 vs. 58±13 ms, P=0.001; 81±12 vs. 49±7, P<0.001; JTcd: 96±15 vs. 73±11 ms, P<0.001; 96±15 vs. 67±8 ms, P=0.001). There was no significant difference between the dispersion parameters in diabetic patients without autonomic dysfunction and the control subjects ( P>0.05). Also, patients with autonomic dysfunction had higher Lown classes of ventricular arrhythmias and patients with higher Lown classes of ventricular arrhythmias had more prolonged QTd and QTcd values. The data suggest that diabetic patients with autonomic dysfunction have increased dispersion of ventricular refractoriness, which may be one of the factors contributing to the increased incidence of arrhythmias and sudden death observed in these patients.