QT dispersion and mortality after myocardial infarction

Possible cardioprotective effect of angiotensin-converting enzyme inhibitors during treatment of American tegumentary leishmaniasis with meglumine antimoniate

We conducted an observational retrospective study to identify factors associated with prolongation of corrected QT (QTc) interval during treatment of American tegumentary leishmaniasis with meglumine antimoniate. A group of 108 patients with normal ECG before treatment were included. Thirty-one patients (29%) developed increase of QTc interval beyond 0.44s in the second ECG performed after an average of (mean+/-S.D.) 12.6+/-4.9 days. After univariate and multivariate analysis, the age was associated with prolonged QTc interval, and the use of angiotensin-converting enzyme (ACE) inhibitors demonstrated a protective factor. These results identify elderly as a risk factor to develop prolonged QTc due to antimonial therapy (odds ratio: 1.1; 95% confidence interval: 1.01-1.12), and suggest that use of ACE inhibitors is a possible cardioprotective agent (odds ratio: 0.3; 95% confidence interval: 0.003-0.34). Further studies using prospective methodology are necessary to define the role of ACE inhibitors as prophylactic agent in high-risk patients.

Increased QT dispersion in sickle cell disease: effect of pulmonary hypertension

BACKGROUND

QT dispersion has been proposed to be a predictor of adverse outcomes in a variety of cardiac disease states. The objective of this study was to examine QT dispersion in patients with sickle cell disease (SCD) and to assess the effect of pulmonary hypertension (PHT) on QT dispersion.

METHODS

We performed Doppler echocardiographic assessments of pulmonary artery systolic pressure in 73 (mean age 18.5 +/- 8.0 years) steady-state SCD patients and 25 (mean age 19.6 +/- 7.2 years) healthy subjects. Resting 12-lead electrocardiogram was recorded and QT dispersion was calculated as the difference between maximum and minimum QT intervals. Bazett's formula was used to obtain a rate-corrected value of the QT interval (QTc).

RESULTS

Maximum QTc, minimum QTc and QTc dispersion were significantly increased in SCD patients compared to the control subjects (p < 0.0001, p < 0.05, p < 0.0001, respectively). Among SCD patients, patients with PHT had higher maximum QTc and QTc dispersion than patients without PHT (p < 0.0001). However, minimum QTc showed no significant differences between the two patient groups.

CONCLUSION

QTc dispersion is significantly increased in SCD patients, especially those with PHT indicating regional inhomogeneity of ventricular repolarization.

Evaluation of serial QT dispersion in patients with first non-Q-wave myocardial infarction: relation to the severity of underlying coronary artery disease

BACKGROUND

Increased QT dispersion (QTD) has been correlated with ventricular arrhythmias. Recent reports suggest that it may serve as a marker of the severity of underlying coronary artery disease (CAD).

HYPOTHESIS

The aim of this study was to examine in-hospital changes of QTD and their possible correlation with the severity of underlying CAD in patients with first non-Q-wave myocardial infarction.

METHODS

In 62 patients we estimated QTD, precordial QTD, as well as their values corrected for heart rate on Days 3 and 7 after admission. The severity of underlying ischemic burden was estimated by means of the number of diseased vessels as well as by the jeopardy score.

RESULTS

On Day 3, patients with jeopardy score > or = 6 exhibited greater QTD, corrected QTD, precordial QTD, and corrected precordial QTD (p = 0.001, p = 0.003, p = 0.02, p = 0.036, respectively); patients with multivessel disease had greater QTD (p = 0.007). On Day 7, patients with jeopardy score > or = 6 and multivessel disease exhibited greater QTD, corrected QTD, precordial QTD, and corrected precordial QTD (p < 0.001 for all). Multiple regression analysis revealed a jeopardy score of > or = 6 as the most significant independent predictor for QTD variables. From Days 3 to 7, only patients with none or one diseased vessel orjeopardy score < 6 had shortened QTD (p = 0.01 and p = 0.015, respectively) and corrected QTD (p < 0.001 for both).

CONCLUSIONS

In patients with first non-Q-wave myocardial infarction, QTD variables and their in-hospital changes reflect the severity of underlying CAD.

Correction for heart rate is not necessary for QT dispersion in individuals without structural heart disease and patients with ventricular tachycardia

BACKGROUND

It remains controversial whether QT dispersion should be corrected for heart rate, especially when the limitations of rate correction formulae are considered. We investigated whether incremental atrial pacing affects QT dispersion and the rate-corrected values according to Bazett's formula in individuals without structural heart disease and in patients with history of sustained ventricular tachycardia.

METHODS

We studied 32 individuals without structural heart disease (group A), and 16 patients with a history of sustained ventricular tachycardia (group B). QT dispersion and corrected for heart rate QT dispersion using Bazett's formula (QTc dispersion) were calculated in sinus rhythm, and during continuous right atrial pacing for one minute at 100 and 120 beats/min.

RESULTS

Interobserver variability was not significant (P > or = 0.10). QT dispersion did not differ at rest between groups A and B and did not change significantly from baseline at any heart rate in both groups. However, QTc dispersion increased significantly with atrial pacing in a similar manner in group A and group B (42 +/- 19 ms at rest vs 53 +/- 23 ms at 120 beats/min, P < 0.001 for group A, 39 +/- 16 ms at rest vs 60 +/- 19 ms at 120 beats/min, P < 0.001 for group B).

CONCLUSIONS

We conclude that QT dispersion remains unchanged during atrial pacing at heart rates up to 120 beats/min in both individuals without structural heart disease and in patients with a history of sustained ventricular tachycardia. Correction by Bazett's formula results in prolongation of QTc dispersion, yielding values which may be misleading.

The immediate and short-term effect of successful percutaneous coronary intervention on repolarization in acute myocardial infarction patients

OBJECTIVES

The primary objective was to assess the immediate and short-term impact of successful percutaneous coronary intervention (PCI) on QT dispersion (QT disp) and corrected QT dispersion (QTc disp). Secondarily, the impact of PCI on QT and QTc disp within different infarct-related arteries and the impact of successful PCI in these different arteries were evaluated.

METHODS

Patients (n = 140, age 61.6 +/- 12.9, 69% male) undergoing direct primary PCI for acute MI were evaluated. Twelve-lead ECGs were obtained before (baseline), immediately after (0 h), 24hours after, and 3 days after PCI. The QT and QTc interval in each of the 12-leads were measured and the shortest interval was subtracted from the longest to derive the QT disp and QTc disp, respectively.

RESULTS

Angiography showed blockages in the left anterior descending, right coronary artery, and circumflex in 37.1, 48.9, and 15.0% of patients, respectively. Overall, 97 patients achieved successful reflow. QT and QTc disp were significantly improved in the group with successful reflow at each follow-up time after PCI versus baseline and corresponding values in the unsuccessful reflow group. QT disp was improved among patients with successful reflow irrespective of which infarct artery was responsible for the acute myocardial infarction.

CONCLUSIONS

Successful reflow with PCI is associated with a rapid reduction in QT disp and QTc disp that is maintained for at least 3 days after the event. Conversely, unsuccessful reflow was not associated with significant reductions in QT or QTc disp.

QT dispersion increases in patients with systemic lupus erythematosus

Although autopsy studies have documented that heart is affected in most of systemic lupus erythematosus (SLE) patients, clinical manifestations occur in less than 10%. QT dispersion, a new parameter that can be used to assess homogeneity of cardiac repolarization and autonomic function, has not been studied in SLE patients. The aim of our study was to evaluate the QT dispersion (QTd) in SLE patients without overt cardiac involvement. Eighty-three patients with a diagnosis of SLE (mean age 41+/-13) and age- and sex-matched 77 healthy control subjects (mean age 43+/-10) were enrolled in the study. All subjects had their complete history taken, laboratory examination, and transthoracic echocardiography (ECG). Patients with cardiac disease, hypertension, diabetes, or taking medications that may effect QTd or any ECG abnormalities were excluded. Resting 12-lead ECG were recorded for measurement of QTd. None of the patients and control subjects had overt cardiac involvement. The mean SLE duration was 86.5+/-15.4 months. QT dispersion was significantly greater in SLE patients than incontrol subjects (55.2+/-24.7 vs 20.7+/-5.3 ms, respectively; p<0.001). There was no correlation between QTd and duration of SLE, SLEDAI-K score, corticosteroid usage, and presence of anti SS-A antibody. QT dispersion is significantly increased in SLE patients without overt cardiac involvement. Our result suggests that prolonged QT dispersion can be a useful noninvasive and simple method for early detection of cardiac involvement in SLE patients.

A prospective evaluation of the effect of atazanavir on the QTc interval and QTc dispersion in HIV-positive patients

BACKGROUND

Atazanavir (ATV), an HIV protease inhibitor (PI) that may be preferred for the treatment of HIV-infected patients with cardiovascular comorbidities because of its favourable effects on plasma lipids, has been associated with cardiac rhythm disturbances.

OBJECTIVE

To quantify the effect of ATV on corrected QT (QTc) and QTc dispersion (QTd), markers of the potential for cardiac dysrhythmia, in patients switching from other PIs to ATV.

METHODS

In this prospective, single-centre, open-label study, 12-lead electrocardiograms were performed for subjects at baseline, 2 h after the first dose of ATV, and 1 month after initiation of ATV.

RESULTS

Twenty-one patients (19 received ritonavir-boosted ATV) completed the study. There was a trend towards an increase in the QTc at 2 h after the first dose [mean+/-standard deviation 3.19+/-8.0 ms; 95% confidence interval (CI) -0.47 to 6.85 ms; P=0.084]. There was no difference between QTc values at baseline and at 1 month (-1.5+/-8.75 ms; 95% CI -5.50 to 2.46; P=0.43). There was a nonsignificant decrease in the QTd between baseline and 2 h (-5.1+/-15.19 ms; 95% CI -13.22 to 2.96; P=0.197) and between baseline and 1 month (-0.61+/-15.04 ms; 95% CI -8.1 to 6.87; P=0.865). A significant increase in the PR interval (7.4+/-10.7 ms; 95% CI 2.5 to 12.25 ms; P=0.005) was observed at 1 month.

CONCLUSIONS

The use of ATV did not result in increases in the QTc interval or QTd. However, PR interval monitoring may be warranted in patients with underlying heart block or those treated with atrioventricular nodal blocking agents.

Diurnal variation in QT dispersion in patients with chronic heart failure

QT dispersion is defined as the difference in QT interval among the different leads of the standard 12-lead electrocardiogram and reflects inhomogeneity of myocardial repolarization. Dispersion of repolarization is an important electrophysiologic feature that is considered fundamental for the initiation of ventricular fibrillation. However, no data exist regarding the diurnal variation of QT dispersion measured from simultaneous 12-lead recording in chronic heart failure patients. The aim of this study was to identify diurnal variation in QT dispersion in patients with chronic heart failure. QT dispersion was measured in the 12-lead standard electrocardiogram in 11 patients with chronic heart failure. QT dispersion in these patients was increased in the afternoon compared to the morning. It is concluded that QT dispersion has a clear diurnal variation in patients with chronic heart failure. These findings have potentially significant implications for therapy and prevention of sudden cardiac death in patients with chronic heart failure.

The association of QT dispersion and QT dispersion ratio with extent and severity of coronary artery disease

BACKGROUND

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 assessed so far. The effects of extent and severity of stable CAD on rest QT interval were analyzed in this study.

METHODS

Rest 12-lead electrocardiograms (ECG) were recorded in 162 clinically stable subjects undergoing coronary angiography before the angiography for measurement of corrected QT dispersion (cQTd) and the QT dispersion ratio (QTdR) defined as QT dispersion divided by cycle length and expressed as a percentage. Angiographic "vessel score,""diffuse score," and "Gensini score" were used to evaluate the extent and severity of coronary atherosclerosis. Subjects were grouped as follows: those with normal angiogram (Group 1), those with insignificant (<50%) coronary stenosis (Group 2), and those with 1- (Group 3), 2- (Group 4), or 3-vessel disease (Group 5).

RESULTS

cQTd and QTdR were higher in Group 3 compared with Group 1 (P < 0.001 and P = 0.001, respectively), in Group 4 compared with Group 1 (P < 0.001 for both) and Group 2 (P = 0.001 and P = 0.003, respectively), and in Group 5 compared with Group 1 (P < 0.001 for both) and Group 2 (P < 0.001 and P = 0.003, respectively). cQTd and QTdR were positively correlated with the vessel score (r = 0.422, P < 0.001; r = 0.358, P < 0.001, respectively), diffuse score (r = 0.401, P < 0.001; r = 0.357, P < 0.001, respectively) and Gensini score (r = 0.378, P < 0.001; r = 0.373, P < 0.001, respectively). In multiple linear regression analyses, cQTd was found to be independently associated only with diffuse score (beta= 0.325, P = 0.038). Also, QTdR was independently associated with diffuse score (beta= 0.416, P = 0.006) and Gensini score (beta= 0.374, P = 0.011).

CONCLUSIONS

Rest cQTd and QTdR are increased, and related to the extent and severity of coronary atherosclerosis in patients with stable CAD.

QT dispersion increases with aging

BACKGROUND

Age-related changes in cardiovascular system are well-known. Arrhythmias in elderly patients constitute most of the urgencies, consultations, or hospitalizations. QT dispersion (QTd) is a simple noninvasive arrhythmogenic marker to demonstrate the electrical instability of the heart. The aim of this study was to investigate how QTd changes with increasing age by calculating the QTd in the elderly and younger subjects.

METHODS

One hundred and forty-six consecutive subjects (62 males and 84 females; age range: 18-82 years) were enrolled in the study. Sixty-seven of the subjects were 65 years and over (mean age, 70 +/- 4), 79 were younger than 65 (mean age, 37 +/- 11). A 12-lead ECG was recorded. The longest and the shortest QT intervals were measured manually on these ECG recordings. QTd was calculated from the formula, QTd = QTmax - QTmin.

RESULTS

Demographic features were similar between the two groups. QTd of the elderly group was found to be significantly higher than the younger group (35.6 +/- 15.6 in elderly, 24.2 +/- 12.4 in younger group, P < 0.001). A positive relationship was found between QTd and age (r = 0.415, P < 0.001). QTd was greater in female than in male (31.9 +/- 16.7 ms vs 26.0 +/- 11.3 ms, respectively, P = 0.018).

CONCLUSIONS

Our study shows that QTd increases with advancing age. We think that long-term follow-up of these patients would be useful to show if there is any relationship between the clinical outcomes and the increase in QTd.

Pacing-Induced Increase in QT Dispersion Predicts Sudden Cardiac Death Following Cardiac Resynchronization Therapy

OBJECTIVES

This study was designed to determine whether cardiac resynchronization therapy (CRT) by means of biventricular pacing (BiVP) alters the QT interval (QT(c)) and QT dispersion (QTD), and whether such changes relate to the risk of developing major arrhythmic events (MAE).

BACKGROUND

Prolonged QT(c) is associated with MAE. Left ventricular pacing and BiVP alter QT(c).

METHODS

A total of 75 patients with drug-resistant heart failure (New York Heart Association functional class III/IV) and QRS duration > or =120 ms underwent CRT. The QT(c) and QTD were measured before and 48 days after BiVP.

RESULTS

Over 807 days (range 93 to 1,543 days), 11 patients had a MAE. Compared to baseline, at 48 days after CRT, QTD increased in 47% of patients and QT(c) decreased in 53%. The QT(c) at follow-up was higher in MAE patients compared with no-MAE patients (35.9 +/- 14.2 ms vs. 0.52 +/- 6.0 ms; p = 0.0323). Similar differential responses for QTD were observed (46.4 +/- 13.5 ms in MAE vs. -5.1 +/- 4.1 ms in no MAE, p < 0.0001). The MAE occurred in 29% of patients exhibiting an increase in QTD and in 3% of those exhibiting a decrease (p = 0.0017). In multiple regression analyses, change in QTD from baseline (DeltaQTD) strongly predicted MAE, independent of DeltaQT(c), QRS duration, and left ventricular ejection fraction and end-diastolic volume (p < 0.001). Differences in survival curves were observed when patients were dichotomized according to whether QTD increased or decreased in relation to baseline values (p < 0.0001).

CONCLUSIONS

The MAE in patients with BiVP are related to pacing-induced increases in QTD. Measures of ventricular repolarization at the time of pacemaker implantation may guide selection of patients for combined CRT and defibrillator therapy.

QT interval dispersion as a new marker of restenosis after percutaneous transluminal coronary angioplasty of isolated single-vessel coronary artery stenosis

BACKGROUND

There are no reliable non-invasive markers of restenosis after percutaneous transluminal coronary angioplasty (PTCA). The aim of our study was to measure changes in QT interval dispersion after PTCA and to determine whether restenosis subsequently affects QT interval dispersion.

METHODS AND RESULTS

Fifty-six consecutive patients - 41 men and 15 women (mean age: 56.2 +/-8.3 years) - with isolated stenosis of the left anterior descending artery who underwent successful PTCA were studied. A symptom-limited treadmill exercise test was performed within 7 days after PTCA and then again before repeated angiography. Repeated coronary angiography revealed restenosis in 15 patients (26.8%) and no signs of significant stenosis in 41 patients (73.2%). QT interval dispersion in the group of patients with restenosis measured before exercise increased from baseline 34 +/- 7 to 49 +/- 15 ms after 6 months (p < 0.01) and QT interval dispersion measured immediately after exercise increased from baseline 38 +/- 4 to 68 +/- 21 ms after 6 months (p < 0.001). In contrast, patients without restenosis showed no significant changes in QT interval dispersion measured before (baseline: 34 +/- 9 ms; after 6 months 33 +/- 12 ms; p = NS) and immediately after exercise (baseline: 34 +/- 12 ms; after 6 months: 33 +/- 10; p = NS). When QT interval dispersion > or =60 ms (measured 6 months after PTCA procedure) was considered as a potential marker of restenosis, this indicator had very high sensitivity and specificity when measured immediately after exercise (80 and 95% respectively).

CONCLUSIONS

QT interval dispersion significantly increases in the group of patients with documented restenosis and may be a simple, non-invasive marker of restenosis. However, further studies are needed to confirm this observation.

QT peak dispersion, not QT dispersion, is a more useful diagnostic marker for detecting exercise-induced myocardial ischemia

BACKGROUND

The electrocardiographic indices of QT dispersion (QTd), QT peak dispersion (QTpd), and the principal component analysis ratio (PCAr) are related to the occurrence of fatal arrhythmia and are influenced by physical exercise.

OBJECTIVE

The purpose of this study was to investigate whether or not the QT parameters can be used as markers for exercise-induced myocardial ischemia.

METHODS

We measured these QT parameters at rest and at 3 minutes after exercise using exercise-stress thallium-201 scintigraphy (SPECT), compared with conventional ST segment changes in 161 patients with suspected or known coronary artery disease. The patients were classified into four groups (normal, redistribution, fixed defect, and redistribution with fixed defect) according to SPECT.

RESULTS

At rest, QTd and PCAr were greater in the fixed defect and redistribution with fixed defect groups. PCAr, however, increased after exercise in the redistribution and redistribution with fixed defect groups. Although QTpd at rest was not significantly different among the four groups, it increased in the redistribution and redistribution with fixed defect groups after exercise (QTpd after exercise: normal, 36 +/- 16 ms vs. redistribution, 51 +/- 23 ms, redistribution with fixed defect, 53 +/- 19 ms; P<.05). For myocardial infarction reflected by fixed defect, QTd at rest was the most useful indicator, while QTpd after exercise was the most useful indicator for exercise-induced myocardial ischemia according to multiple logistic regression analysis with receiver operating characteristic curves. In addition, the change in PCAr by exercise was an independent predictor for exercise-induced ischemia.

CONCLUSIONS

QTpd and PCAr could be useful indices for exercise-induced myocardial ischemia. Determining the QTpd of a patient after exercising can improve the diagnostic accuracy of ischemia in a routine clinical setting.

QT dispersion and heart rate variability abnormalities in Alzheimer's disease and in mild cognitive impairment

OBJECTIVES

To investigate the effect of cardiovascular changes (i.e., QT interval, QT dispersion (QTD), heart rate variability (HRV), and other cardiovascular measures) in subjects with Alzheimer's disease (AD) and mild cognitive impairment (MCI).

DESIGN

Each subject underwent clinical and cognitive examination, a structural brain imaging study, echocardioDoppler, electrocardiogram (ECG), HRV analysis using 24-hour ECG monitoring, and 24-hour blood pressure monitoring.

SETTING

Community population-based sample of patients admitted to an AD center for investigation of cognitive disturbances.

PARTICIPANTS

Thirty-three subjects with AD, 39 subjects with MCI, and 29 cognitive healthy subjects (controls) matched for demographic characteristics, hypertensive condition, smoking habits, and laboratory parameters were enrolled consecutively.

MEASUREMENTS

Clinical and cognitive examination, structural brain imaging study, echocardioDoppler, ECG, HRV analysis using 24-hour ECG monitoring, and 24-hour blood pressure monitoring.

RESULTS

QTD and QT corrected dispersion mean values were significantly higher in patients with AD than in patients with MCI and controls and higher in patients with MCI than in controls. HRV time and domain parameters were lower in patients with AD than in patients with MCI and controls. No difference in other cardiovascular measures was found. QTD and HRV were found to be significantly correlated with the degree of cognitive impairment.

CONCLUSION

These findings support the presence of a peculiar neuroanatomic dysfunction in patients with AD and MCI that parallels the disease progression. These noninvasive parameters might prove to be powerful predictive tools in the worsening of cognitive function and mortality risk.

Continuous Administration of Nicorandil Decreases QT Dispersion During the Chronic Phase of Acute Myocardial Infarction

We previously reported that continuous intravenous (IV) administration of nicorandil (NIC) inhibits QT dispersion (QTd). However, no prior study has evaluated the efficacy of NIC when administered orally to acute myocardial infarction (AMI) patients following continuous IV administration. Thirty patients with anteroseptal infarction in whom revascularization was performed successfully within 6 hours of AMI onset were included in the study and assigned to one of 3 groups: group A (continuous IV administration of NIC), group B (continuous IV and oral administration of NIC), and group C (no treatment with NIC). After 24 hours, QTd in groups A and B was significantly decreased compared to QTd in group C (P < 0.01) (group A, 58.1; group B, 58.2; and group C, 81.3). The QTd obtained 3 months later was significantly shorter in group B subjects who were orally administered NIC, and QTd before percutaneous coronary intervention (PCI) was restored in group A, in which no NIC had been administered orally [group A, 66.7; group B, 54.1; and group C, 73.9; P < 0.05 (group A versus group B) and P < 0.01 (group B versus group C)]. The effects were evaluated by comparing different routes of administration. Continuous IV and subsequent oral administration of NIC inhibited prolongation of QTd, suggesting that these effects may prevent the occurrence of cardiac events during both the acute and chronic phases of AMI.

Calcitriol Regresses Cardiac Hypertrophy and QT Dispersion in Secondary Hyperparathyroidism on Hemodialysis

BACKGROUND

Sudden cardiac death is common in patients on hemodialysis (HD), and its rate is as high as 25% of all cardiac deaths associated with left ventricular hypertrophy (LVH) and secondary hyperparathyroidism. A prolonged QT interval on standard electrocardiography is related to an increase in sudden death in various patient groups. It is also well known that LVH has been noted in uremic patients with high parathyroid hormone levels.

METHODS

To evaluate the response of intravenous calcitriol treatment on the QT interval and LVH in HD patients with secondary hyperparathyroidism (intact parathyroid hormone, iPTH, > 450 ng/ml), echocardiographic, electrocardiographic (ECG), and biochemical assessments were performed over a 15-week period in 25 HD patients before and after intravenous calcitriol treatment. We also evaluated 25 age-, sex-, HD duration-, and BMI-matched HD control patients with secondary hyperparathyroidism.

RESULTS

In patients receiving intravenous calcitriol, a significant reduction in iPTH levels (p < 0.05) and alkaline phosphatase levels (p < 0.01) was found without changes in values of serum calcium and ionized Ca2+, phosphorus, Na+, K+, Mg2+, hematocrit, blood pressure, or other hemodynamic changes. Echocardiograms showed significant decreases in the thickness of the interventricular septum (p < 0.05), left posterior wall thickness (p < 0.05), and left ventricle mass index (LVMi, p < 0.01). In addition, sequential ECG measurement in patients with calcitriol treatment showed significant reductions in QTcmax (QTmax interval corrected for heart rates, p < 0.01) and QTc dispersion (QT dispersion corrected for heart rates, p < 0.01). However, in the control patients, biochemical, hemodynamic, and ECG changes, as well as myocardial structural and functional changes were not seen. Multiple regression analysis in all patients indicated that iPTH and LVMi levels were independent predictors of QTcmax while the LVMi level was the only independent predictor of QTc dispersion (p < 0.05).

CONCLUSIONS

Our study showed a significant correlation between LVMi and QT dispersion in HD patients with secondary hyperparathyroidism. Intravenous calcitriol treatment, to be used for the control of secondary hyperparathyroidism, was found to cause regression of myocardial hypertrophy and a reduction in the QTc interval and dispersion, without biochemical and hemodynamic changes. These findings suggest that an active vitamin D metabolite has a cardioprotective action in HD patients.

Surface electrocardiography and histologic rejection following orthotopic heart transplantation

BACKGROUND

Intraventricular conduction delay and QT interval dispersion may be related to electrical instability and the risk of ventricular arrhythmogenesis. The interlead variability of the QT interval on a surface 12-lead electrocardiogram (ECG) has been associated with an increased likelihood of sudden death in patients with long QT syndromes, in patients recovering from myocardial infarction, and dilated cardiomyopathy. We sought to determine the incidence of increased QT(c) dispersion (QT(c-d)) relative to biopsy grade of severity of rejection.

METHODS

Records of patients having undergone orthotopic heart transplantation (OHT) were reviewed focusing specifically on surface ECGs performed in temporal proximity to endomyocardial biopsy.

RESULTS

Seventy-five patients were evaluated on 1573 occasions, to include 999 surface ECGs, and 847 endomyocardial biopsies. There were 269 interpretable surface ECGs and endomyocardial biopsies performed within 1.1 +/- 4.6 days. There were no identifiable trends in atrioventricular or intraventricular conduction abnormalities (to include right bundle branch block) when comparing those with and without significant rejection on endomyocardial biopsy. The mean QT(c-d) of those with none (n = 34), mild (n = 194), moderate (n = 39), and severe (n = 2) rejection was 49 +/- 29, 49 +/- 35, 57 +/- 38, 81 +/- 7 ms, respectively (P = 0.28 by ANOVA of means). When comparing those with significant rejection so as to change management there was a trend toward increased dispersion (no to mild rejection, 49 +/- 34 ms vs moderate to severe rejection, 59 +/- 37 ms, P = 0.09).

CONCLUSIONS

In this study investigating noninvasive ventricular depolarization/repolarization and correlation to histologic manifestation of rejection, there was suggestion, but no statistical significance, of QT(c-d) and severity of rejection. QT(c-d) should not be considered a sensitive marker for OHT rejection.

Assessment of QT interval duration and dispersion in athlete's heart

An athlete's heart is characterized by morphological and functional changes occurring as a consequence of regular physical exercise. We sought to determine if these physiological changes lead to ventricular repolarization abnormalities in trained athletes. Forty-four trained athletes and 35 sex- and age-matched healthy sedentary controls were included in the study. A 12-lead surface electrocardiogram (ECG) was obtained from all participants. Maximum QT (QTmax) and minimum QT (QTmin) interval durations, QT dispersion (QTd) and corrected QT dispersion (QTcd) were calculated for each ECG record. Heart rate, systolic and diastolic blood pressure values were found to be identical in both groups. QTmax and QTmin interval durations were not statistically different between the athletic and control groups. Similarly, QTd and QTcd did not differ significantly between the two groups. No association was observed between an athlete's heart and ventricular heterogeneity compared with healthy sedentary controls, despite physiological and structural changes.

Hypertrophic cardiomyopathy: electrical abnormalities detected by the extended-length ECG and their relation to syncope

BACKGROUND

Ventricular repolarization abnormalities can represent a trigger for lethal arrhythmias in hypertrophic cardiomyopathy (HCM). We sought to assess whether multiparametric computerized surface ECG analysis identifies repolarization abnormalities in HCM patients, and whether this approach allows identification of patients with syncope.

METHODS

In 28 HCM patients and 102 healthy subjects (14 and 51 males, mean age 44 +/- 15 and 41 +/- 14 years, respectively), 8-lead ECG (I, II, V1-V6) was recorded for 5 min, acquired in digital format and analyzed. Heart-rate corrected QT (QTc) and T wave complexity index (TWCc), QT dispersion, activation-recovery interval (ARI) and its dispersion, signal duration in the terminal portion of the filtered QRS at 25 Hz (LAS(25 Hz)) were analyzed among other parameters.

RESULTS

Compared to healthy subjects, HCM patients exhibited longer QRS, filtered QRS, QTc and QTd, greater TWCc, minor ARId and LA(25 Hz). QRS duration and maximal septum thickness were linearly correlated (r=0.231 p<0.001). ARId shortening depended on ARI shortening in lead V1 (241 +/- 51 vs. 287 +/- 45, HCM vs. healthy subjects, p<0.0001) and lengthening in V6 (257 +/- 42 vs. 209 +/- 34, HCM vs. healthy subjects, p<0.0001). Significant factors for syncope at Wilks' stepwise discriminant analysis were TWCc, QRSd and LAS(25 Hz) (F=14.394, 10.098 and 9.226, respectively) with 92.3% positive predictive accuracy.

CONCLUSIONS

In HCM, longer QRS and QT intervals are consequences of increased left ventricular mass, while ARI seems to reflect myocardial activation rather than inhomogeneity of recovery. The simultaneous evaluation of TWC, QRSd and LAS(25 Hz), unable by itself to hold a predictive value, yielded high accuracy in predicting cardiogenic syncope.

Comparison of QT interval duration and dispersion in elderly population versus healthy young subjects

We compared QT dispersion (QTd) in 75 elderly and 36 young subjects and found that those over the age of 75 years had higher QTd than those younger than 75. In addition those older than 75 years had higher QTd values compared to the younger subjects. We concluded that QTd increased especially over the age of 75.

Prolonged cardiac repolarisation during spontaneous nocturnal hypoglycaemia in children and adolescents with type 1 diabetes

AIMS/HYPOTHESIS

It has been postulated that hypoglycaemia-related cardiac dysrhythmia and, in particular, prolonged cardiac repolarisation, may contribute to increased mortality rates in children and adolescents with type 1 diabetes.

METHODS

We examined the prevalence of prolonged QT interval on ECG during spontaneous hypoglycaemia in 44 type 1 diabetic subjects (aged 7-18 years), and explored the relationships between serial overnight measurements of QT interval corrected for heart rate (QTc) and serum glucose, potassium and epinephrine levels. Each subject underwent two overnight profiles; blood was sampled every 15 min for glucose measurements and hourly for potassium and epinephrine. Serial ECGs recorded half-hourly between 23.00 and 07.00 hours were available on 74 nights: 29 with spontaneous hypoglycaemia (defined as blood glucose <3.5 mmol/l) and 45 without hypoglycaemia.

RESULTS

Mean overnight QTc was longer in females than in males (412 vs 400 ms, p=0.02), but was not related to age, diabetes duration or HbA(1)c. Prolonged QTc (>440 ms) occurred on 20 out of 74 (27%) nights, with no significant differences between male and female subjects, and was more prevalent on nights with hypoglycaemia (13/29, 44%) than on nights without (7/45, 15%, p=0.0008). Potassium levels were lower on nights when hypoglycaemia occurred (minimum potassium 3.4 vs 3.7 mmol/l, p=0.0003) and were inversely correlated with maximum QTc (r=-0.40, p=0.03). In contrast, epinephrine levels were not higher on nights with hypoglycaemia and were not related to QTc.

CONCLUSIONS/INTERPRETATION

In young type 1 diabetic subjects, prolonged QTc occurred frequently with spontaneous overnight hypoglycaemia and may be related to insulin-induced hypokalaemia.

Are QT measurements on body surface ECG indicative of ventricular refractory patterns?

OBJECTIVE

Increased dispersion (DISP) of refractoriness (ERP) facilitates the induction of malignant ventricular arrhythmias. Accordingly, QT DISP on surface ECG, supposedly reflecting ERP DISP, has been proposed as a noninvasive marker for risk stratification. However, a comparative analysis of local ERPs and QT measurements is not available so far.

METHODS AND RESULTS

In 19 healthy dogs, standard 12 lead surface ECGs were recorded to measure QT and RR intervals. Based on these measurements, corrected QT intervals (QTc, Bazett formula) and DISP (maximum difference) of both QT and QTc intervals (QT-DISP and QTc-DISP, respectively) were calculated. Subsequently, 60 custom-made needle electrodes (12 mm long, 4 bipolar electrodes per needle, interelectrode distance 2.5 mm) were inserted into the left (LV) and right ventricle (RV). At each bipole of 14 randomly selected needle electrodes (8 LV, 6 RV) local ERPs were determined (extrastimulus technique, basic cycle length 1000 ms). Interventricular DISP of ERP (LV-RV-DISP) was defined as the difference between the longest and shortest ERP within both ventricles. Respective values were calculated for each ventricle (LV-DISP; RV-DISP). Scatter plots and correlation analysis did not reveal a significant correlation between QT, QTc, QT-DISP, QTc-DISP and any of the ERP measurements or calculations. Although not statistically significant, the closest correlation was found between QTc and mean ERP and between QTc-DISP and LV-RV-DISP.

CONCLUSION

QT measurements on surface ECG are poorly correlated with local ERPs. If anything, QT- or QTc-DISP might provide a rough estimate of interventricular, that is, global DISP of ERP. Local or even intraventricular DISP of ERP is definitely not reflected by these QT measurements.

Patterns of QT dispersion in athletic and hypertensive left ventricular hypertrophy

OBJECTIVE

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.

METHODS

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).

RESULTS

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).

CONCLUSIONS

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, QT maximum and risk of cardiac death in the Caerphilly Heart Study

BACKGROUND

It has been postulated that increased inter-lead differences in QT interval (QT dispersion) and the maximum QT interval (QTmax), in the standard 12-lead electrocardiogram (ECG), may be associated with an increased risk of cardiac death. The aims of this study were to assess the relationship between QT dispersion and QTmax, corrected and uncorrected for heart rate, and the risk of cardiac death.

DESIGN

Nested case-control study within the Caerphilly prospective cohort study.

METHODS

We studied 2512 men who participated in phase 1 of the Caerphilly study between 1979 and 1983. After a mean follow up of 7.1 years, 218 men had died from coronary heart disease and these men were compared with 218 age-matched controls.

RESULTS

Data are presented on 422 patients with ECG suitable for analysis, 207 cases and 215 controls. Four trained observers measured the QT intervals and the reliability of each observer was estimated using repeat measurements on a randomly chosen sub-sample of ECGs. Median corrected QT dispersion and corrected QTmax were significantly higher in cases than in controls (51.9 versus 47.7 ms [P=0.01] and 430 versus 421 ms [P<0.001] respectively). In univariate analyses by quartiles of corrected QT dispersion and corrected QTmax, increased risk was largely confined to the upper quartile of the distribution with these subjects having twice the risk of those in the lower quartile [odds ratio (OR) 2.14, 95% confidence interval (CI) 1.2-3.7 and 2.56 (95% CI 1.5-4.5) respectively]. In logistic regression analysis, adjusted for age, smoking, body mass index, hypertension, history of myocardial infarction and ECG Minnesota code, we observed an increased risk in the upper quartile of the corrected QT dispersion relative to the other three quartiles combined [adjusted OR=1.74 (P=0.03)]. The magnitude of this association was increased in analyses based on the data from the most reliable observers. The association between corrected QTmax and cardiac death was attenuated in multivariate analysis. The findings in relation to both uncorrected QT dispersion and uncorrected QTmax were similar, i.e., consistent with a significant independent effect of QT dispersion but not QTmax for cardiac death in multivariate analysis.

CONCLUSION

The data suggest that QT dispersion is an independent predictor of cardiac death provided it can be measured with sufficient reliability. The association is non-linear with increased risk largely confined to the upper quartile of the distribution. The QT maximum is not an independent predictor of cardiac death.

T vector and loop characteristics in coronary artery disease and during acute ischemia

OBJECTIVE

Three-dimensional characterization of the ventricular repolarization by the T vector and T vector loop morphology in coronary artery disease (CAD), and their response to short-term (no flow) ischemia induced by coronary occlusion during a percutaneous intervention (PCI).

BACKGROUND

The risk for sudden cardiac death is increased in conditions of acute or permanently heterogeneous ventricular repolarization, for which ischemia is a risk factor.

METHODS

Fifty-six CAD patients without visible collateral circulation were studied during an elective single-vessel PCI, and 10 healthy controls twice at rest. T vector parameters (Televation, Tazimuth, and QRS-T angle), and T loop parameters (Tarea, Tavplan, and Teigenv) were measured by vectorcardiography. ST vector magnitude (ST-VM) and its change (STC-VM) were used for reference.

RESULTS

At rest, T vector loop morphology (Tarea, Teigenv) was significantly different in CAD patients and controls, while T vector angles did not separate the groups. Ischemia induced significant changes in T loop parameters in the entire CAD group, whereas in the LAD subgroup significant changes were seen also in T vector angle. The T loop morphology was significantly different at baseline and a more pronounced response to ischemia (Tarea) was seen in patients with, than in those without, a history of hypertension.

CONCLUSION

T loop morphology, rather than the T vector angle, separated CAD patients from healthy controls. Coronary occlusion had significant impact on ventricular repolarization, as assessed by T vector and morphology analysis, and most prominently in the LAD group. Hypertensive patients appeared especially vulnerable to ischemia.

Exercise-induced changes in QT interval duration and dispersion in patients with isolated myocardial bridging

BACKGROUND

Isolated myocardial bridging (MB) often is considered to be an unimportant angiographic finding; however, its association with cardiovascular event has been shown. In this study we aimed to assess exercise-induced electrocardiographic (ECG) changes and susceptibility to arrhythmia in patients with MB.

METHOD

21 consecutive patients who had angiographically proven MB (group I) and 25 subjects (group II) who had normal coronary arteries underwent exercise test using Bruce protocol. Before and after the exercise test the changes in QT interval duration and dispersion were compared.

RESULTS

Baseline characteristics of both groups were similar. Heart rate significantly increased after exercise test in both groups. In group I, after exercise mean QT(max) and QT(min) durations did not change significantly compared to baseline values, respectively. (QT(max): 411+/-20 vs. 421+/-18 ms, p>0.05 and QT(min): 380+/-12 vs. 378+/-10 ms, p>0.05). However, following exercise test QT dispersion (QT(d)) and corrected QT dispersion (QT(cd)) significantly increased when compared to baseline values, respectively. (34+/-13 vs. 66+/-14 ms, p<0.05 and 37+/-14 vs. 69+/-17 ms, p<0.05) On the other hand, in control group QT(max) and QT(min) durations, QT(c) and QT(cd) did not change significantly compared to baseline values, respectively. (QT(max): 408+/-18 vs. 412+/-17 ms, p>0.05 and QT(min): 390+/-11 vs. 387+/-10 ms, p>0.05; QT(d): 25+/-14 vs. 31+/-16 ms, p>0.05; QT(cd): 27+/-15 vs. 33+/-17 ms, p>0.05).

CONCLUSION

Treadmill exercise test significantly increased QT dispersion in patients with MB. This increase may result from exercise-induced ischemia at the area perfused by bridged artery.

Left ventricular hypertrophy and QT interval in obesity and in hypertension: effects of weight loss and of normalisation of blood pressure

BACKGROUND

Left ventricular hypertrophy (LVH) and prolonged QT interval at ECG (QTc) are common in both obesity and arterial hypertension (AH), and are risk factors for cardiovascular disease and sudden death.

METHODS

We compared the frequencies of LVH (ECG criteria) and QTc in obese-AH (n=41), in normotensive obese (n=75), in lean-AH (n=30), and in lean controls (n=68) comparable for age and sex; in obese patients, LVH and QTc were evaluated under basal conditions and 1 y later, that is, after a significant weight loss induced by bariatric surgery.

RESULTS

LVH was more frequent, and QTc was longer, in obese-AH, in normotensive obese, and in lean-AH than in lean controls; after weight loss, frequency of LVH decreased in obese subjects becoming normotensive (n=87), not in obese subjects remaining hypertensive (n=29), while QTc decreased in all obese subjects.

CONCLUSION

Weight loss can effectively reduce QTc; when concomitant AH disappears, weight loss can also reduce the prevalence of LVH. In obese patients remaining hypertensive, aggressive pharmacological treatment is therefore indicated to correct LVH.

Excessive Increase in QT Interval and Dispersion of Repolarization Predict Recurrent Ventricular Tachyarrhythmia after Amiodarone

Although chronic amiodarone has been proven to be effective to suppress ventricular tachycardia (VT) and ventricular fibrillation (VF), how we predict the recurrence of VT/VF after chronic amiodarone remains unknown. This study evaluated the predictive value of the QT interval, spatial, and transmural dispersions of repolarization (SDR and TDR) for further arrhythmic events after chronic amiodarone. Eighty-seven leads body surface ECGs were recorded before (pre) and one month after (post) chronic oral amiodarone in 50 patients with sustained monomorphic VT associated with organic heart disease. The Q-Tend (QTe), the Q-Tpeak (QTp), and the interval between Tpeak and Tend (Tp-e) as an index of TDR were measured automatically from 87-lead ECG, corrected Bazett's method (QTce, QTcp, Tcp-e), and averaged among all 87 leads. As an index of SDR, the maximum (max) minus minimum (min) QTce (max-min QTce) and standard deviation of QTce (SD-QTce) was obtained among 87 leads. All patients were prospectively followed (15 +/- 10 months) after starting amiodarone, and 20 patients had arrhythmic events. The univariate analysis revealed that post max QTce, post SD-QTce, post max-min QTce, and post mean Tcp-e from 87-lead but not from 12-lead ECG were the significant predictors for further arrhythmic events. ROC analysis indicated the post max-min QTce > or = 106 ms as the best predictor of events (hazard ratio = 10.4, 95%, CI 2.7 to 40.5, P = 0.0008). Excessive QT prolongation associated with increased spatial and transmural dispersions of repolarization predict the recurrence of VT/VF after amiodarone treatment.

Corrected QT Dispersion and Cardiac Sympathetic Function in Patients With Obstructive Sleep Apnea-Hypopnea Syndrome

STUDY OBJECTIVES

Hypoxemia increases corrected QT dispersion (QTcD), which is the difference between the maximum and minimum QT intervals and is a strong risk factor for cardiovascular mortality. The aim of this study was to investigate the QTcD in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS), and the relationship between the QTcD and (123)I-metaiodobenzylguanidine (MIBG) cardiac imaging, which reflects cardiac sympathetic activity.

SETTING

A university hospital.

PATIENTS

Forty-eight OSAHS patients without cardiac diseases (mean [+/- SD] age, 45.9 +/- 10.8 years; apnea-hypopnea index [AHI] 51.9 +/- 18.5 events per hour) who underwent polysomnography before treatment and on the first night of nasal continuous positive airway pressure (nCPAP) treatment.

METHODS

Before and after nCPAP treatment was started, we measured the QTcD with computer software, before, during, and after sleep, as well as the washout rate of the MIBG administered for cardiac imaging. As a control, QTcD was also measured in the morning from 26 healthy subjects.

RESULTS

Before treatment, the mean QTcD during sleep (65.0 +/- 14.6 ms) was greater than that before sleep (57.0 +/- 13.5 ms; p < 0.0001). Meanwhile, after 1 night of nCPAP therapy, the QTcD during sleep (50.6 +/- 11.4 ms) decreased from that before treatment (p < 0.0001) and was smaller than the QTcD before sleep (56.2 +/- 13.3 ms; p = 0.003). Before treatment, the QTcD during sleep correlated with the AHI (r = 0.38; p = 0.009) and the percentage of time that SaO(2) was < 90% (SaO(2) < 90% time) [r = 0.34; p = 0.018]. The QTcD did not correlate with the body mass index or the washout rate of MIBG. However, the washout rate of MIBG correlated with the AHI and the SaO(2) < 90% time.

CONCLUSIONS

Nocturnal QTcD is increased in OSAHS patients but is decreased by nCPAP therapy independently of cardiac sympathetic function.

QT dispersion correlates with systolic rather than diastolic parameters in patients receiving anthracycline treatment

OBJECTIVE

The aim of this study was to investigate the relation of QT dispersion to left ventricular (LV) systolic and diastolic function in patients undergoing anthracycline therapy.

METHODS

We used echocardiography to evaluate LV systolic and diastolic function and electrocardiography to evaluate QT dispersion and corrected QT dispersion (QTcD) in patients with hematological diseases, who received anthracycline therapy.

PATIENTS

Seventy-two patients with hematological diseases who were receiving anthracycline treatment were enrolled in the present study.

RESULTS

LV end-diastolic diameter or LV end-systolic diameter had a significant positive correlation to QTcD (r = 0.35, p < 0.01, r = 0.43, p < 0.01). Also left ventricular ejection fraction of (LVEF) or fractional shortening had a significant negative correlation to QTcD (r = -0.46, p < 0.001, r = -0.27, p = 0.02). The highest QTcD group had a significantly larger LV end-diastolic diameter or LV end-systolic diameter than the lowest QTcD [48.5 +/- 5.7 vs. 44.4 +/- 4.5 (mm), p < 0.001, 34.1 +/- 6.4 vs. 28.8 +/- 4.3 (mm), p < 0.001] and the highest QTcD group had a significantly lower LVEF than the lowest QTcD [57.5 +/- 8.0 vs. 65.5 +/- 6.4 (%), p < 0.001]. On the other hand, none of the diastolic function markers were significantly correlated with QTcD.

CONCLUSION

We concluded that increased QTcD is correlated with LV dilation and systolic dysfunction induced by anthracycline therapy, and does not reflect a dispersion of ventricular repolarization or asynchronous motion.

QT dispersion and myocardial viability in patients after acute myocardial infarction

BACKGROUND

In recent years QT dispersion (QTd) in post-infarct patients was estimated in many studies, but still little is known about its association with the presence of dysfunctional but viable myocardium.

AIM

We investigated the relation between dispersion of QT interval and myocardial viability in patients after acute myocardial infarction (AMI).

MATERIAL AND METHODS

In 52 patients (mean age 67.2+/-11.7) treated thrombolytically because of AMI 12-lead ECG and low dose-high dose dobutamine echocardiography was performed on 14th day after treatment. QTd and regional myocardial contractility were estimated three times: at baseline, low dose dobutamine (LDD) (10-15 microg/kg per min) and high dose dobutamine (HDD) infusion (up to 40 microg/kg per min).

RESULTS

Patients with viable myocardium had lower baseline QTd than patients with only necrosis in infarct zone. Significant increase in QTd was shown during LDD and HDD both in patients with and without myocardial viability. During infusion of HDD QTd was significantly higher in patients with myocardial ischemia. The greatest percentage increase of QTd at HDD was shown in patients with biphasic response to dobutamine infusion i.e. with myocardial viability evidenced at LDD and myocardial ischemia at HDD.

CONCLUSION

Patients with preserved myocardial viability had lower QTd values compared to those with similar left ventricular dysfunction but caused only by post-infarction necrosis. Ischemia evoked on 14th day after AMI was accompanied by greater increase in QTd in patients with myocardial viability in infarct region than in patients without. It may be one of the reasons of greater risk of serious ventricular arrhythmias in such patients during myocardial ischemia.

QT interval, cardiovascular risk factors and risk of death in diabetes

A prolonged QT interval is considered an indicator of increased risk of malignant ventricular arrhythmias and/or sudden death. It has been proposed that autonomic neuropathy in diabetes is related to QT interval prolongation and increased mortality rates. Several studies in Type 1 and Type 2 diabetic patients have confirmed the independent relation between prolonged QT interval duration or increased QT interval dispersion and chronic ischemic heart disease. It has been consistently shown that autonomic neuropathy is related to QT interval duration while more controversies exist on the association with QT interval dispersion. In recent years, studies have confirmed the value of QT interval as a predictor of total mortality in both diabetic and non-diabetic subjects. Moreover, several studies have shown a significant relation between QT interval prolongation and cardiovascular disease risk factors. QT interval could be used to stratify the cardiovascular risk in diabetic patients. We still do not know why QT interval is prolonged and how this abnormality leads to death. Nevertheless, QT interval is a simple, low-cost measure, easily obtainable without the need of the patient's compliance and which could help to select patients who need second level diagnostic procedures and strict observation.

Relation between QT dispersion and myocardial viability in ischemic cardiomyopathy

The aim of this study was to evaluate the relation between QT dispersion and myocardial viability as assessed by single-photon emission computed tomography. The study population included 97 consecutive patients with severely impaired left ventricular function secondary to chronic coronary artery disease. Patients with a low QT dispersion had a substantial amount of viable myocardium, whereas patients with a high QT dispersion had predominantly nonviable scar tissue.

Prediction of sudden cardiac death after myocardial infarction in the beta-blocking era

OBJECTIVES

This study assessed the predictive power of arrhythmia risk markers after an acute myocardial infarction (AMI).

BACKGROUND

Several risk variables have been suggested to predict the occurrence of sudden cardiac death (SCD), but the utility of these variables has not been well established among patients using medical therapy according to contemporary guidelines.

METHODS

A consecutive series of 700 patients with AMI was studied. The end points were total mortality, SCD, and nonsudden cardiac death (non-SCD). Nonsustained ventricular tachycardia (nsVT), ejection fraction (EF), heart rate variability, baroreflex sensitivity, signal-averaged electrocardiogram (SAECG), QT dispersion, and QRS duration were analyzed (n = 675). Beta-blocking therapy was used by 97% of the patients at discharge and by 95% at one and two years after AMI.

RESULTS

During a mean (+/-SD) follow-up of 43 +/- 15 months, 37 non-SCDs (5.5%) and 22 SCDs (3.2%) occurred. All arrhythmia risk variables differed between the survivors and those with non-SCD (e.g., the standard deviation of N-N intervals was 98 +/- 32 vs. 74 +/- 21 ms [p < 0.001] and the QRS duration was 103 +/- 22 vs.89 +/- 16 ms [p < 0.001]). Sudden cardiac death was weakly predicted only by reduced EF (<0.40; p < 0.05), nsVT (p < 0.05), and abnormal SAECG (p < 0.05), but not by autonomic markers or standard ECG variables. The positive predictive accuracy of EF, nsVT, and abnormal SAECG as predictors of SCD was relatively low (8%, 12%, and 13%, respectively).

CONCLUSIONS

The common arrhythmia risk variables, particularly the autonomic and standard ECG markers, have limited predictive power in identifying patients at risk of SCD after AMI in the beta-blocking era.

Limited predictive value of inducible sustained ventricular tachycardia for future occurrence of spontaneous ventricular tachycardia in patients with coronary artery disease and relatively preserved cardiac function

To evaluate the significance of inducible sustained ventricular tachycardia (VT) in patients with coronary artery disease and relatively preserved cardiac function, 33 patients who met the following criteria were studied; documented nonsustained VT but no history of life-threatening arrhythmia, inducible sustained VT at electrophysiologic study, and implantation of a cardioverter-defibrillator. Eighteen patients developed clinical sustained VT within 2 years. By univariate analysis, left ventricular ejection fraction (EF) and the cycle length of induced VT were associated with clinical VT occurrence. By multivariate analysis, however, EF was the only independent predictor. Among 23 patients with EF <or=40%, 16 patients developed clinical sustained VT compared to 2 of 10 patients with EF >40% (P <.01). In coronary artery disease patients with relatively preserved EF, the incidence of clinical VT is considerably low even though sustained VT is inducible. Inducible VT is therefore not appropriate for risk stratification in this patient population.

Long-term improvement of QT dispersion is unaffected by short-term changes in blood pressure during treatment of systemic hypertension with enalapril

BACKGROUND

We report the reduction of QT and QTc dispersion in patients treated for 7 years with enalapril for systemic hypertension with left ventricular (LV) hypertrophy. We assess the correlation between QT dispersion and LV mass during this period and at the end of an 8-week period of suspension of enalapril treatment after 5 years.

METHODS

Twenty-four previously untreated patients with this condition took enalapril (20 mg twice daily) for 7 years, except during an 8-week period following 5-year follow-up. Cardiovascular parameters were determined by two-dimensional guided M-mode echocardiography, and QT interval was measured, in a pretreatment placebo phase, 8 weeks and 1, 3, 5, and 7 years after the start of the therapy, at the end of the 8-week suspension effected after 5 years, and 8 weeks after the end of the suspension.

RESULTS

Therapy rapidly reduced blood pressure (BP) from 156/105 mmHg to normal values: 134/84 mmHg after 8 weeks' treatment, 130-84 mmHg at 7-year follow-up (P < 0.001 with respect to the placebo phase). LV mass index decreased progressively until at 5-year follow-up the reduction had reached 39% (P < 0.001), after which neither LV mass nor any other structural parameter underwent any further significant change. During this time, QT dispersion (DeltaQT) and the dispersion of "corrected" QT (DeltaQTc) decreased significantly: DeltaQT (from 61 +/- 21 to 37 +/- 13 ms) and DeltaQTc (from 67 +/- 27 to 41 +/- 16 ms). After suspension of treatment for 8 weeks following 5-year follow-up, DeltaQT was 40 +/- 14 ms and DeltaQTc was 44 +/- 17 ms; there were no significant changes either in DeltaQT and DeltaQTc or LV hypertrophy although BP had returned to pretreatment values (BP: 150 +/- 16; 101 +/- 10 mmHg).

CONCLUSIONS

Long-term enalapril treatment of hypertensive patients with LV hypertrophy induces marked regression of LV mass and improvement of QT dispersion. These improvements occur on a longer timescale than improvement in BP, and are not affected by transient changes in BP values.

QT dynamicity and sudden death after myocardial infarction: results of a long-term follow-up study

INTRODUCTION

The aim of this study was to determine whether impaired adaptation of the QT interval to changes in heart rate predicts sudden death after an acute myocardial infarction.

METHODS AND RESULTS

The Groupe d'Etude du Pronostic de l'Infarctus du Myocarde (GREPI) trial was a prospective multicenter study designed to evaluate the long-term outcome of myocardial infarction. QT dynamicity was evaluated in 265 patients by analyzing 24-hour Holter recordings obtained 9 to 14 days after myocardial infarction. The linear regression slope of QT intervals measured to the apex and to the end of the T wave (QTe) plotted against RR intervals was calculated using a dedicated Holter algorithm. The value of QT/RR in predicting sudden death and total mortality was compared with those of ejection fraction, heart rate variability, and late potentials. Mean follow-up was 81 +/- 27 months. There were 73 deaths, of which 23 were sudden. Of all the parameters, an increased diurnal QTe/RR slope (>0.18) was the strongest independent predictor of sudden death (relative risk 6.07, confidence interval 1.48-24.95, P = 0.01).

CONCLUSION

Increased diurnal QTe dynamicity is independently predictive of sudden death among patients with myocardial infarction. This simple parameter may help to stratify risk and select patients who may benefit from antiarrhythmic prophylaxis.

Effects of ischemia on repolarization in patients with single and multivessel coronary disease

To evaluate if QT dispersion (QTd) may be affected by the number of obstructed coronary arteries (CAs) in patients with acute myocardial infarction (MI) and undergoing angioplasty, and to evaluate if QTd may be affected by ejection function of the heart. The infarct related CA was identified by coronary angiography in 141 patients (97 men, mean age 61.6 +/- 12.9 years) with acute MI undergoing percutaneous angioplasty. Successful reperfusion was defined as TIMI III flow with < 20% residual stenosis. QTd, calculated by subtracting the shortest from the longest QT interval on 12-lead electrocardiograms, was examined immediately before and after angioplasty, at 24 hours, and 3 days after angioplasty. Successful reperfusion was achieved in 98 (69.5%) patients. Prolonged QTd at baseline was found in all patients with ischemia. A trend toward a decrease in QTd was observed immediately after angioplasty and at 24 hours, and a significant decrease at 3 days in patients with successful reperfusion regardless of the number of occluded CAs. There was no change in QTd found in patients with no reperfusion. An increase in QTd was observed in patients with acute ischemia due to single or multivessel disease.

Effect of thrombolytic therapy on QT dispersion in elderly versus younger patients with acute myocardial infarction

The objective of this study was to assess the degree of QT dispersion and effect of thrombolytic therapy on QT dispersion in elderly (age > or =65 years) versus younger (age <65 years) patients with acute myocardial infarction. The QT dispersion was measured manually in 10 +/- 2 leads of 12-lead electrocardiograms on admission, at completion of thrombolytic therapy, and at day 2 after thrombolytic therapy in 36 elderly (73 +/- 5.7 years) and 36 younger (59.9 +/- 7.7 years) patients with acute myocardial infarction. Before initiation of thrombolytic therapy, elderly patients had higher absolute and corrected QT dispersion than younger patients (absolute QT dispersion: 76.3 +/- 7.3 versus 69.6 +/- 7.5 milliseconds, respectively, P < 0.0001; corrected QT dispersion: 77.9 +/- 7.6 versus 70.8 +/- 7.4 milliseconds, respectively, P < 0.001). The difference in QT dispersion between elderly and younger patients persisted at the completion of thrombolytic therapy (absolute QT dispersion: 75.1 +/- 7.2 versus 69.1 +/- 8.4 milliseconds, respectively, P = 0.001; corrected QT dispersion: 77.2 +/- 7.2 versus 70.7 +/- 8.0 milliseconds, respectively, P = 0.001) and at day 2 after thrombolytic therapy (absolute QT dispersion: 74.1 +/- 8.2 versus 69 +/- 9.1 milliseconds, respectively, P = 0.01; corrected QT dispersion: 76.0 +/- 7.9 versus 70.5 +/- 8.8 milliseconds, respectively, P = 0.006). Compared with the prethrombolytic values, there was no significant change in absolute and corrected QT dispersion at the completion of thrombolytic therapy or at day 2 after thrombolytic therapy in elderly or younger patients. Elderly patients with acute myocardial infarction have higher QT dispersion than younger patients with acute myocardial infarction, and QT dispersion does not change early after thrombolytic therapy in elderly or younger patients.

Chemoreflex sensitivity as a predictor of arrhythmia relapse in ICD recipients

BACKGROUND

The chemoreflex sensitivity as a marker of a disturbed vagal reflex activity has proved to be a parameter of increased risk for ventricular tachyarrhythmias or sudden cardiac death. The sensitivity of patients with prior myocardial infarction concerning ventricular tachyarrhythmias amounted to about 70%. This prospective study should evaluate the positive predictive accuracy of this new method in patients at risk for ventricular arrhythmias.

METHODS

42 patients were enrolled into this study. All had a prior myocardial infarction at least 6 months previously; 35 patients were resuscitated from sudden cardiac death, and seven patients had documented monomorphic ventricular tachycardias. All patients were recipients of an ICD. The chemoreflex sensitivity was measured by determination of the venous partial pressure of oxygen and the heart rate before and after inhalation of pure oxygen. The difference in the RR-intervals before and after inhalation divided by the difference in the oxygen pressures were calculated as the chemoreflex sensitivity [ms/mmHg]. Furthermore, in all patients additional risk stratifiers used in this study were the presence of ventricular late potentials (LP), the short-term heart rate variability (HRV), the baroreflex sensitivity (BRS) and a decreased left ventricular function (ejection fraction<40%, EF).

RESULTS

The chemoreflex sensitivity in the patient group as a whole amounted to 2.59+/-2.06 ms/mmHg. During follow-up, out of the 42 patients enrolled, 20 had a documented arrhythmic event (AE: sustained ventricular tachycardia or ventricular fibrillation). Patients with and without AE showed significantly different values of chemoreflex sensitivity (1.58+/-1.09 vs. 3.51+/-2.31 ms/mmHg, P<0.01) and EF (33.3+/-15.6 vs. 47.9+/-17.9%, P<0.05), but not of LP, HRV or BRS. The relative risk of reduced chemoreflex sensitivity concerning an AE amounted to 2.83 (95% CI 0.99-8.01).

CONCLUSIONS

The chemoreflex sensitivity as a marker of increased risk for ventricular tachyarrhythmias shows a high positive predictive power in patients with prior myocardial infarction and who previously survived ventricular tachyarrhythmias. These results should be confirmed by studies in broad populations and without survived arrhythmic event.

Differential effect of glyburide (glibenclamide) and metformin on QT dispersion: a potential adenosine triphosphate sensitive K+ channel effect

Glyburide (glibenclamide) is a specific blocker of the adenosine triphosphate (ATP) sensitive potassium (K+) channel. It has been reported to result in prolongation of the QT interval. QT interval dispersion (QTd) is a potentially sensitive marker for increased risk of arrhythmia and sudden cardiac death. The aim of the present study was to evaluate the effect of glyburide on QTd and compare it with that of metformin, a hypoglycemic agent that does not block the adenosine triphosphate sensitive K+ channel. Thirty patients with type 2 diabetes were randomized to glyburide and metformin groups. A 12-lead electrocardiogram was obtained before and at 2 months after being on glyburide or metformin. Therapy with QT and QTd were measured and QT corrected for rate (QTc). There was no significant difference between the glyburide and metformin groups in age (62 +/- 9 vs 59 +/- 10 years), baseline RR interval (819 +/- 86 vs 753 +/- 100 ms), QT (387 +/- 28 vs 383 +/- 27 ms), and QTc (433 +/- 25 vs 444 +/- 15 ms). Glyburide was associated with a significant increase in QTc (433 +/- 24 to 467 +/- 24 ms, p <0.001), QTd (24 +/- 16 to 60 +/- 22 ms, p <0.001), and QTc dispersion (QTcd) (35 +/- 18 to 68 +/- 21 ms, p <0.001). In contrast, metformin was associated with a decrease in QTc (444 +/- 15 to 432 +/- 15 ms, p <0.01) and did not affect QTd (14 +/- 5 to 12 +/- 6 ms, p = NS) and QTcd (23 +/- 9 to 22 +/- 10 ms, p = NS). Glyburide, unlike metformin, causes an increase in QT dispersion. Increased dispersion may be a factor underlying an increased risk of arrhythmias and sudden cardiac death.

Spinal muscular atrophy: recent advances and future prospects

Spinal muscular atrophies (SMA) are characterized by degeneration of lower motor neurons associated with muscle paralysis and atrophy. Childhood SMA is a frequent recessive autosomal disorder and represents one of the most common genetic causes of death in childhood. Mutations of the SMN1 gene are responsible for SMA. The knowledge of the genetic basis of SMA, a better understanding of SMN function, and the recent generation of SMA mouse models represent major advances in the field of SMA. These are starting points towards understanding the pathophysiology of SMA and developing therapeutic strategies for this devastating neurodegenerative disease, for which no curative treatment is known so far.

Prevalence of increased QT interval duration and dispersion in type 2 diabetic patients and its relationship with coronary heart disease: a population-based cohort

OBJECTIVE

To evaluate the prevalence of prolonged QT interval and dispersion in a population-based cohort of type 2 diabetic patients and their relationship with clinical and metabolic variables.

DESIGN

Cross-sectional population-based cohort.

SETTING

Diabetes clinics and general practitioners in Casale Monferrato (Northern Italy).

SUBJECTS

A total of 1357 patients with known type 2 diabetes (70% of the cohort).

MAIN OUTCOMES MEASURES

Albumin excretion rate and coronary heart disease (CHD); a standard supine 12-lead electrocardiogram (ECG) was recorded and coded according to the Minnesota code criteria. QT interval corrected for heart rate (QTc) > 0.44 s and QTc dispersion > 0.080 s were considered abnormally prolonged.

RESULTS

Prevalence of increased QTc duration and QTc dispersion were 25.8% (95% CI 23.5-28.3) and 33.1% (95% CI 30.6-35.7), with no sex differences. No metabolic differences were found, apart from fibrinogen and creatinine levels, which were higher in patients with increased QTc dispersion. Patients with CHD had higher mean adjusted values of QTc and QTc dispersion, whereas no association was found with albumin excretion rate (AER) and diabetes treatment. QTc duration and QTc dispersion were significantly correlated (0.17, P < 0.001). In multiple regression analysis, only CHD was independently associated with QTc, after adjustment for age and sex (beta=0.010, P < 0.001, R2=2.5%); as regards QTc dispersion, a similar association with CHD was found (beta=0.20, P < 0.001, R2=4.8%).

CONCLUSIONS

This population-based study shows a considerably high prevalence of increased QTc and QTc dispersion in type 2 diabetic patients and their association with CHD. These findings have both epidemiological and clinical relevance, as they might be implicated in the excess mortality risk of type 2 diabetic patients.

QT interval dispersion in young women with anorexia nervosa

OBJECTIVES

To evaluate the degree of QT dispersion in a group of young women in the starvation phase of anorexia nervosa (AN) and its relation to left ventricular (LV) mass.

STUDY DESIGN

Sixteen patients with self-induced starvation were matched with 16 women of normal weight and 16 constitutionally thin women (body mass index <20 kg/m2). Starving patients and control patients underwent an electrocardiogram and echocardiogram. QT intervals were measured from surface electrocardiograms and QT dispersion was defined as the difference between maximum QT and minimum QT occurring in any of the 12 leads.

RESULTS

LV-chamber mass was significantly less in women with AN than in thin and normal-weight women. QT dispersion was significantly greater in AN than in the thin and control groups (QT dispersion: 50 +/- 14 vs 34 +/- 9 and 37 +/- 11 ms, P <.001; QT interval dispersion corrected for heart rate: 49+12 vs 34 +/- 9 and 36 +/- 7 ms, P <.01, respectively). A significant relation between QT dispersion and LV-mass index (r = -0.726, P <.01), and between QTc dispersion and LV mass index (r = -0.693, P < 0.01) were found only in the patients with AN.

CONCLUSION

Starving patients show an increased QT dispersion related to reduced LV mass. This result could represent a useful indicator of arrhythmic risk and sudden death in AN.

Is gender a risk factor for adverse drug reactions? The example of drug-induced long QT syndrome

Drug-induced torsade de pointes is a rare life-threatening adverse drug reaction (ADR) which is strongly influenced by gender. Drugs that prolong cardiac repolarisation include antiarrhythmics, gastrokinetics, antipsychotics, antihistamines and antibacterials. Such drugs share the potential to block cardiac voltage-gated potassium channels, particularly the rapid component (I(Kr)) of the delayed rectifier potassium current (I(K)). By doing so, such drugs usually, but not always, prolong the QT interval. Even if the electrocardiographic signs are subdued, the underlying blockade of I(Kr) current may precipitate the occurrence of arrhythmia. Women are perceived to be more prone to ADRs than men. Such a propensity may result from gender-associated differences in drug exposure, in the number of drugs prescribed (polypharmacy), in drug pharmacology, as well as from possible differences in the way the adverse event is perceived. A prolonged QT interval on the electrocardiogram (time that elapses from the onset of the cardiac ventricular depolarisation to the completion of its repolarisation) is associated with the occurrence of torsade de pointes and related ventricular arrhythmias. The QT interval is influenced by heart rate, autonomic nervous system, electrolyte disturbances and above all, drugs that block potassium channels. Two-thirds of the cases of drug-induced torsade de pointes occur in women. Therefore, this adverse effect represents a perfect example of gender differences impairing women's health. Clinical and experimental studies show that female gender is associated with a longer corrected QT interval at baseline and a greater response to drugs that block I(Kr), both of which facilitate the emergence of arrhythmia. This results most likely from a specific regulation of ionic channel expression (potassium, calcium, etc) by sex steroids, even though nongenomic effects may play a role as well. Estrogens facilitate bradycardia-induced prolongation of the QT interval and the emergence of arrhythmia whereas androgens shorten the QT interval and blunt the QT response to drugs. Hence, underlying genetic defects of potassium channels that may be asymptomatic in normal conditions, may precipitate drug-induced arrhythmia in women more frequently than in men. Even in the presence of a drug that mildly blocks I(Kr) and seldom prolongs the QT interval, women are still more prone to drug-induced torsade de pointes, due to their reduced cardiac 'repolarisation reserve'. This is an important aspect of I(Kr) blockade to be aware of during the development of new drugs.