Abnormalities of the QT interval in primary disorders of autonomic failure

Age and Gender Differences in Cardiovascular Autonomic Failure in the Transgenic PLP-syn Mouse, a Model of Multiple System Atrophy

Multiple system atrophy (MSA) is a rare and progressive neurodegenerative disorder. Autonomic failure (AF) is one main clinical feature which has a significant impact on health-related quality of life. The neuropathological hallmark of MSA is the abnormal accumulation of α-synuclein in oligodendrocytes forming glial cytoplasmic inclusions. Only little is known about gender and age differences in AF in MSA. This study was carried out in 6 and 12 months old transgenic PLP-α-syn and WT male and female mice. Heart rate variability (HRV) was assessed both in time, frequential and non-linear domains. Baroreflex sensitivity (BRS) was estimated by the sequence method. Duration of ventricular depolarization and repolarization (QT/QTc intervals) were evaluated from the ECG signals. Three-way ANOVA (genotype x gender x age) with Sidak's method post-hoc was used to analyze data. BRS was significantly changed in PLP-α-syn mice and was age-dependent. QT and QTc intervals were not significantly modified in PLP-α-syn mice. An impaired HRV was observed at 12 months of age in PLP-α-syn female but not in male mice, indicative of cardiovascular AF.

Electrocardiographic signs of autonomic imbalance in medicated patients with first-episode schizophrenia spectrum disorders – relations to first treatment discontinuation and five-year remission status

Purpose

To explore measures in electrocardiograms (ECG) influenced by autonomic balance in early schizophrenia spectrum disorders and to examine their relation to subsequent first antipsychotic pharmacotherapy discontinuation and five-year remission status.

Subjects and methods

Twelve-lead ECGs were recorded at baseline in 58 patients with first-episode schizophrenia spectrum disorders and in 47 healthy controls of similar age. Selected ECG variables included heart rate and measures of repolarization. Pharmacotherapy data were extracted from medical records. At a five-year follow-up the patients were interviewed and assessed with the Positive and Negative Syndrome Scale.

Results

Patients had higher heart rate and a different ST-T pattern than the controls. High T-wave amplitudes in the leads aVF and V5 and ST-elevations in V5 were associated both with higher risk of an earlier discontinuation of first antipsychotic pharmacotherapy and with non-remission five years later.

Discussion and conclusion

In this longitudinal cohort study, simple ECG measures influenced by autonomic balance in the early phase of schizophrenia spectrum disorders contained prognostic information. As this is the first report of this association and is based on a relatively small sample, the results should be interpreted with caution.

Mechanisms of Arrhythmia and Sudden Cardiac Death in Patients With HIV Infection

Long-term survival of HIV-infected patients has significantly improved with the use of antiretroviral therapy (ART). As a consequence, cardiovascular diseases are now emerging as an important clinical problem in this population. Sudden cardiac death is the third leading cause of mortality in HIV patients. Twenty percent of patients with HIV who died of sudden cardiac death had previous cardiac arrhythmias including ventricular tachycardia, atrial fibrillation, and other unspecified rhythm disorders. This review presents a summary of HIV-related arrhythmias, associated risk factors specific to the HIV population, and underlying mechanisms. Compared with the general population, patients with HIV have several cardiac conditions and electrophysiological abnormalities. As a result, they have an increased risk of developing severe arrhythmias, that can lead to sudden cardiac death. Possible explanations may be related to non-ART polypharmacy, electrolyte imbalances, and use of substances observed in HIV-infected patients; many of these conditions are associated with alterations in cardiac electrical activity, increasing the risk of arrhythmia and sudden cardiac death. However, clinical and experimental evidence has also revealed that cardiac arrhythmias occur in HIV-infected patients, even in the absence of drugs. This indicates that HIV itself can change the electrophysiological properties of the heart profoundly and cause cardiac arrhythmias and related sudden cardiac death. The current knowledge of the underlying mechanisms, as well as the emerging role of inflammation in these arrhythmias, are discussed here.

QTC Dispersion and P-Wave Dispersion during Migraine Attacks

The aim of this study was to investigate increase of QTc dispersion and P-wave dispersion during migraine attacks. Fifty-five patients (16–65 years of age, 49 women, six men) with migraine were included in our study. Heart rate, QTc interval, maximum and minimum QTc interval, QTc dispersion, maximum and minimum P-wave duration and P-wave dispersion were measured from 12-lead ECG recording during migraine attacks and pain-free periods. ECGs were transferred to a personal computer via a scanner and then used for magnification of x400 by Adobe Photoshop software. Maximum QTc interval (454 ± 24 ms vs. 429 ± 23 ms, P < 0.001), QTc interval (443 ± 26 ms vs. 408 ± 22 ms, P <0.001) and QTc dispersion (63 ± 18 ms vs. 43 ± 14 ms, P <0.001) were found significantly higher during migraine attacks compared with pain-free periods. Maximum P-wave duration (107 ± 11 ms vs. 100 ± 11 ms, P <0.001) and P-wave dispersion (45 ± 13 ms vs. 35 ± 13 ms, P <0.001) were found higher during migraine attacks than pain-free periods. We concluded that migraine attacks are associated with increased QTc and P-wave dispersion compared with pain-free periods.

Central actions of serotonin and fluoxetine on the QT interval of the electrocardiogram in trout

QT interval of the electrocardiogram (ECG) is a measure of the duration of the ventricular depolarization and repolarization. In humans, prolongation of the QT interval is a known clinical risk factor for the development of ventricular arrhythmias including ‘Torsades de Pointes’ and possible sudden cardiac death. After oral administration, fluoxetine (FLX), as well as other selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitors can affect cardiac autonomic control, including the QT interval. However, the action of centrally administered FLX on the QT interval has never been explored. Consequently, using the unanesthetized trout as an animal model, we sought to compare the effects of intracerebroventricular (i.c.v.) injection of FLX (5, 15 or 25 µg) on the QT interval of the ECG with the effects observed following i.c.v. injection of 5-HT (0.05, 0.5 or 5 nmol). The QT interval was corrected for the R–R interval. The highest doses of centrally administered FLX and 5-HT induced a prolongation of the corrected QT (QTc) interval reaching a maximum value of 5–10 min after injection (+8% and +6% respectively, P < 0.05). The intra-arterial (i.a.) injections of 5-HT and FLX were without significant effect on the QTc. The i.a. injection of blockers of the autonomic nervous system indicated that the sympathetic nervous system modulated the QTc interval. In conclusion, our data demonstrate that for the first time in any animal species, cardiac electrophysiology is sensitive to central 5-HT and that FLX within the brain may disrupt the autonomic control of ventricular repolarization.

Myalgic Encephalomyelitis: Symptoms and Biomarkers

Myalgic Encephalomyelitis (ME) continues to cause significant morbidity worldwide with an estimated one million cases in the United States. Hurdles to establishing consensus to achieve accurate evaluation of patients with ME continue, fueled by poor agreement about case definitions, slow progress in development of standardized diagnostic approaches, and issues surrounding research priorities. Because there are other medical problems, such as early MS and Parkinson's Disease, which have some similar clinical presentations, it is critical to accurately diagnose ME to make a differential diagnosis. In this article, we explore and summarize advances in the physiological and neurological approaches to understanding, diagnosing, and treating ME. We identify key areas and approaches to elucidate the core and secondary symptom clusters in ME so as to provide some practical suggestions in evaluation of ME for clinicians and researchers. This review, therefore, represents a synthesis of key discussions in the literature, and has important implications for a better understanding of ME, its biological markers, and diagnostic criteria. There is a clear need for more longitudinal studies in this area with larger data sets, which correct for multiple testing.

Associations between changes in city and address specific temperature and QT interval--the VA Normative Aging Study

BACKGROUND

The underlying mechanisms of the association between ambient temperature and cardiovascular morbidity and mortality are not well understood, particularly for daily temperature variability. We evaluated if daily mean temperature and standard deviation of temperature was associated with heart rate-corrected QT interval (QTc) duration, a marker of ventricular repolarization in a prospective cohort of older men.

METHODS

This longitudinal analysis included 487 older men participating in the VA Normative Aging Study with up to three visits between 2000-2008 (n = 743). We analyzed associations between QTc and moving averages (1-7, 14, 21, and 28 days) of the 24-hour mean and standard deviation of temperature as measured from a local weather monitor, and the 24-hour mean temperature estimated from a spatiotemporal prediction model, in time-varying linear mixed-effect regression. Effect modification by season, diabetes, coronary heart disease, obesity, and age was also evaluated.

RESULTS

Higher mean temperature as measured from the local monitor, and estimated from the prediction model, was associated with longer QTc at moving averages of 21 and 28 days. Increased 24-hr standard deviation of temperature was associated with longer QTc at moving averages from 4 and up to 28 days; a 1.9°C interquartile range increase in 4-day moving average standard deviation of temperature was associated with a 2.8 msec (95%CI: 0.4, 5.2) longer QTc. Associations between 24-hr standard deviation of temperature and QTc were stronger in colder months, and in participants with diabetes and coronary heart disease.

CONCLUSION/SIGNIFICANCE

In this sample of older men, elevated mean temperature was associated with longer QTc, and increased variability of temperature was associated with longer QTc, particularly during colder months and among individuals with diabetes and coronary heart disease. These findings may offer insight of an important underlying mechanism of temperature-related cardiovascular morbidity and mortality in an older population.

Utility of corrected QT interval in orthostatic intolerance

We performed this study to determine whether electrocardiographic corrected QT (QTc) interval predicts alterations in sympathovagal balance during orthostatic intolerance (OI). We reviewed 1,368 patients presenting with symptoms suggestive of OI who underwent electrocardiography and composite autonomic function tests (AFTs). Patients with a positive response to the head-up tilt test were classified into orthostatic hypotension (OH), neurocardiogenic syncope (NCS), or postural orthostatic tachycardia syndrome (POTS) groups. A total of 275 patients (159 OH, 54 NCS, and 62 POTS) were included in the final analysis. Between-group comparisons of OI symptom grade, QTc interval, QTc dispersion, and each AFT measure were performed. QTc interval and dispersion were correlated with AFT measures. OH Patients had the most severe OI symptom grade and NCS patients the mildest. Patients with OH showed the longest QTc interval (448.8±33.6 msec), QTc dispersion (59.5±30.3 msec) and the lowest values in heart rate response to deep breathing (HRDB) (10.3±6.0 beats/min) and Valsalva ratio (1.3±0.2). Patients with POTS showed the shortest QTc interval (421.7±28.6 msec), the highest HRDB values (24.5±9.2 beats/min), Valsalva ratio (1.8±0.3), and proximal and distal leg sweat volumes in the quantitative sudomotor axon reflex test. QTc interval correlated negatively with HRDB (r = −0.443, p<0.001) and Valsalva ratio (r = −0.425, p<0.001). We found negative correlations between QTc interval and AFT values representing cardiovagal function in patients with OI. Our findings suggest that prolonged QTc interval may be considered to be a biomarker for detecting alterations in sympathovagal balance, especially cardiovagal dysfunction in OH.

Relation between QT interval variability and cardiac sympathetic activity in hypertension

Elevated QT interval variability is a predictor of malignant ventricular arrhythmia, but the underlying mechanisms are incompletely understood. A recent study in dogs with pacing-induced heart failure suggests that QT variability is linked to cardiac sympathetic nerve activity. The aim of this study was to determine whether increased cardiac sympathetic activity is associated with increased beat-to-beat QT interval variability in patients with essential hypertension. We recorded resting norepinephrine (NE) spillover into the coronary sinus and single-lead, short-term, high-resolution, body-surface ECG in 23 patients with essential hypertension and 9 normotensive control subjects. To assess beat-to-beat QT interval variability, we calculated the overall QT variability (QTVN) as well as the QT variability index (QTVi). Cardiac NE spillover (12.2 ± 6.5 vs. 20.7 ± 14.7, P = 0.03) and QTVi (-1.75 ± 0.36 vs. -1.42 ± 0.50, P = 0.05) were significantly increased in hypertensive patients compared with normotensive subjects. QTVN was significantly correlated with cardiac NE spillover (r(2) = 0.31, P = 0.001), with RR variability (r(2) = 0.20, P = 0.008), and with systolic blood pressure (r(2) = 0.16, P = 0.02). Linear regression analysis identified the former two as independent predictors of QTVN. In conclusion, elevated repolarization lability is directly associated with sympathetic cardiac activation in patients with essential hypertension.

Electrocardiographic QT interval and cardiovascular reactivity in fibromyalgia differ from chronic fatigue syndrome

BACKGROUND

Fibromyalgia (FM) and chronic fatigue syndrome (CFS) frequently overlap clinically and have been considered variants of one common disorder. We have recently shown that CFS is associated with a short corrected electrocardiographic QT interval (QTc). In the present study, we evaluated whether FM and CFS can be distinguished by QTc.

METHODS

The study groups were comprised of women with FM (n=30) and with CFS (n=28). The patients were evaluated with a 10 min supine-30 min head-up tilt test. The electrocardiographic QT interval was corrected for heart rate (HR) according to Fridericia's equation (QTc). In addition, cardiovascular reactivity was assessed based on blood pressure and HR changes and was expressed as the 'hemodynamic instability score' (HIS).

RESULTS

The average supine QTc in FM was 417 ms (SD 25) versus 372 ms (SD 22) in CFS (p<0.0001); the supine QTc cut-off <385.7 ms was 79% sensitive and 87% specific for CFS vs. FM. The average QTc at the 10th minute of tilt was 409 ms (SD 18) in FM versus 367 ms (SD 21) in CFS (p<0.0001); the tilt QTc cut-off <383.3 ms was 71% sensitive and 91% specific for CFS vs. FM. The average HIS in FM patients was -3.52 (SD 1.96) versus +3.21 (SD 2.43) in CFS (p<0.0001).

CONCLUSION

A relatively short QTc and positive HIS characterize CFS patients and distinguish them from FM patients. These data may support the contention that FM and CFS are separate disorders.

Sympathetic disturbances increase risk of sudden cardiac arrest in sporadic ALS

BACKGROUND

ALS exclusively involves motor neurons, however, accumulating evidence suggests involvement of sympathetic neurons, as in other diseases including Parkinson's disease and multiple system atrophy. In these diseases increased risk of sudden cardiac arrest is established, while that in ALS remains uncertain.

METHODS

The authors retrospectively studied 12 pathologically confirmed sporadic ALS patients who received no assisted ventilation. Among them, two patients died of sudden cardiac arrest. Changes in QTc interval and dispersion, indices of sympathetic activities obtainable by routine electrocardiograms, were evaluated at the early stage and the terminal stage. Pathologically, intermediolateral nucleus (IML) sympathetic neurons in the upper thoracic cord were examined.

RESULTS

The QTc intervals and dispersion were significantly increased at the terminal stage compared with that at the early stage (p<0.01). The numbers of IML neurons were significantly lower in ALS patients than in controls (p=0.017), and had linear inverse correlation with the rate of increases in maximum QTc interval and QTc dispersion (p=0.01, r=-0.915 and p=0.02, r=-0.884). Notably, two patients with sudden cardiac arrest showed longer QTc interval, larger QTc dispersion, and lower number of IML neurons than most of others.

CONCLUSIONS

Patients with ALS had reduced sympathetic activities at the terminal stage of disease, presumably due to neuronal loss in IML, which may increase risk of sudden cardiac arrest. Thus, prolonged QTc intervals and increased QTc dispersion may suggest an increased risk of sudden death in ALS, as in other neurodegenerative diseases.

Shortened QT interval: a distinctive feature of the dysautonomia of chronic fatigue syndrome

PURPOSE

Because autonomic nervous functioning is frequently abnormal in chronic fatigue syndrome (CFS), we examined whether the corrected QT interval (QTc) in CFS differs from QTc in other populations.

METHODS

The QTc was calculated at the end of 10 minutes of recumbence and the end of 10 minutes of head-up tilt. In a pilot study, groups of 15 subjects, CFS, and controls, matched for age and sex, were investigated. In a second phase of the study, the QTc was measured in larger groups of CFS (n = 30) and control patients (n = 96) not matched for demographic features.

RESULTS

In the pilot study, the average supine QTc in CFS was 0.371 +/- 0.02 seconds and QTc on tilt, 0.385 +/- 0.02 seconds, significantly shorter than in controls (P = .0002 and .0003, respectively). Results of phase II confirmed this data.

CONCLUSIONS

Relative short QTc intervals are features of the CFS-related dysautonomia. The significance of this finding is discussed.

Stability of Ventricular Repolarization in Conscious Dogs with Chronic Atrioventricular Dissociation and His-Bundle Pacing

Following AVN ablation, eight dogs were surgically instrumented for chronic (continuous) HIS-bundle pacing. For data collection, implanted pacemakers were transiently programmed to pace in stepwise ascending ramps at rates from 50 to 200 beats/min in 30-beat/min steps. Each rate was held for 60 seconds. At each rate, ECG signals were collected from conscious dogs for measurements of QT intervals during the last 10 seconds of each paced rate to construct a QT-HR ramp. This QT-HR ramp was repeated twice on each day of study 10 minutes apart. Dogs were randomly assigned to two groups and studied weekly for a minimum of 6 weeks. Group 1 dogs had pacemakers programmed to a rate of 80 beats/min for the duration of the study. Group 2 dogs were paced at 80 beats/min for weeks 1-3, then increased to 140 beats/min for weeks 4-6. The difference between paired QT-HR ramps within 1 day was <3 ms. QT-HR ramps were statistically indistinguishable over the 6-week study for group 1 dogs. Group 2 dogs experienced a slight flattening in the slope of the QT-HR ramps from week 3 to week 6 due to a reduction in QT interval at low HRs (50 and 80 beats/min) only. This conscious HIS-pacing model in dogs is a sensitive, stable, and reproducible method to define ventricular repolarization characteristics over a range of programmable HRs and experimental conditions.

Pharmacogenetic aspects of drug-induced torsade de pointes: potential tool for improving clinical drug development and prescribing

Drug-induced torsade de pointes (TdP) has proved to be a significant iatro-genic cause of morbidity and mortality and a major reason for the withdrawal of a number of drugs from the market in recent times. Enzymes that metabolise many of these drugs and the potassium channels that are responsible for cardiac repolarisation display genetic polymorphisms. Anecdotal reports have suggested that in many cases of drug-induced TdP, there may be a concealed genetic defect of either these enzymes or the potassium channels, giving rise to either high plasma drug concentrations or diminished cardiac repolarisation reserve, respectively. The presence of either of these genetic defects may predispose a patient to TdP, a potentially fatal adverse reaction, even at therapeutic dosages of QT-prolonging drugs and in the absence of other risk factors. Advances in pharmacogenetics of drug metabolising enzymes and pharmacological targets, together with the prospects of rapid and inexpensive genotyping procedures, promise to individualise and improve the benefit/risk ratio of therapy with drugs that have the potential to cause TdP. The qualitative and the quantitative contributions of these genetic defects in clinical cases of TdP are unclear because not all of the patients with TdP are routinely genotyped and some relevant genetic mutations still remain to be discovered. There are regulatory guidelines that recommend strategies aimed at uncovering the risk of TdP associated with new chemical entities during their development. There are also a number of guidelines that recommend integrating pharmacogenetics in this process. This paper proposes a strategy for integrating pharmacogenetics into drug development programmes to optimise association studies correlating genetic traits and endpoints of clinical interest, namely failure of efficacy or development of repolarisation abnormalities. Until pharmacogenetics is carefully integrated into all phases of development of QT-prolonging drugs and large-scale studies are undertaken during their post-marketing use to determine the genetic components involved in induction of TdP, routine genotyping of patients remains unrealistic. Even without this pharmacogenetic data, the clinical risk of TdP can already be greatly minimised. Clinically, a substantial proportion of cases of TdP are due to the use of either high or usual dosages of drugs with potential to cause TdP in the presence of factors that inhibit drug metabolism. Therefore, choosing the lowest effective dose and identifying patients with these non-genetic risk factors are important means of minimising the risk of TdP. In view of the common secondary pharmacology shared by these drugs, a standard set of contraindications and warnings have evolved over the last decade. These include factors responsible for pharmacokinetic or pharmacodynamic drug interactions. Among the latter, the more important ones are bradycardia, electrolyte imbalance, cardiac disease and co-administration of two or more QT-prolonging drugs. In principle, if large scale prospective studies can demonstrate a substantial genetic component, pharmacogenetically driven prescribing ought to reduce the risk further. However, any potential benefits of pharmacogenetics will be squandered without any reduction in the clinical risk of TdP if physicians do not follow prescribing and monitoring recommendations.

Increased QT dispersion in patients with alcoholic pancreatitis

OBJECTIVES

Increased dispersion of the QT interval has been proposed to be a novel marker for increased risk of ventricular arrhythmia and sudden cardiac death. This study examined whether QT dispersion is affected in patients with alcoholic pancreatitis.

METHODS

We measured the QT interval, corrected QT interval, activation recovery interval, activation time, recovery time, and their respective dispersions in 3 age- and gender-matched groups: patients with alcoholic pancreatitis [age, 58.9 +/- 11.8 years; male/female (M/F), 33/3], patients with alcohol dependence (age, 59.3 +/- 8.9 years; M/F, 33/4), and a healthy control group (age, 55.8 +/- 8.8 years; M/F, 33/3).

RESULTS

The QT dispersions in patients with alcoholic pancreatitis (62.4 +/- 19.9 milliseconds; P < 0.001) or alcohol dependence (58.2 +/- 19.6 milliseconds; P < 0.001) were significantly greater than in the control group (41.4 +/- 13.3 milliseconds). Similarly, the corrected QT dispersions in patients with alcoholic pancreatitis (68.5 +/- 22.8 milliseconds; P < 0.001) or alcohol dependence (65.3 +/- 23.6 milliseconds; P < 0.001) were significantly greater than in the control group (42.8 +/- 13.2 milliseconds). Both QT dispersion and QTc dispersion were longer in patients with alcoholic pancreatitis than those with alcohol dependence (P = 0.011 and P = 0.039, respectively). Simple linear regression analysis of the relationship between the RR and QT intervals revealed that the regression lines for patients with alcoholic pancreatitis and alcohol dependence were almost parallel. However, the slope of the regression line for the control group was significantly greater (P < 0.05) than for the other 2 lines.

CONCLUSION

The findings demonstrate increased QT and QTc dispersions in patients with either alcoholic pancreatitis or alcohol dependence. The QT dispersion and QTc dispersion were longer in patients with alcoholic pancreatitis than those with alcohol dependence.

Pharmacokinetic Factors in the Adverse Cardiovascular Effects of Antipsychotic Drugs

Antipsychotics may cause serious adverse cardiovascular effects, including prolonged QT interval and sudden death. This review considers antipsychotic-induced cardiovascular events from three perspectives: high-risk drugs, high-risk individuals and high-risk drug interactions. Pharmacokinetic drug interactions involving the cytochrome P450 (CYP) enzymatic pathway and pharmacodynamic interactions leading to direct cardiotoxic effects are discussed. Original reports on antipsychotic-induced drug interactions are reviewed, with consideration of management guidelines. The literature was reviewed from 1 January 1966 to 1 February 2002. The literature search revealed only 12 original articles published on antipsychotic drug interactions leading to cardiovascular adverse events. Only 4 of the 12 reports were prospective studies; the remainder were either retrospective or anecdotal.Although poor study designs preclude a definitive statement, it appears that pharmacokinetic interactions primarily involved the CYP2D6 and CYP3A4 enzymatic pathways. Those involving the CYP2D6 isozyme included interactions with tricyclic antidepressants, selective serotonergic reuptake inhibitors and beta-blockers. Among these drug interactions, tricyclic antidepressants were most likely to reach clinical significance because of their limited therapeutic index. Drug interactions related to the CYP3A4 pathway were generally less severe, and involved high-potency antipsychotics coadministered with inhibitors such as clarithromycin. Strategies are discussed for the management of adverse cardiovascular events related to antipsychotic drug interactions, including the use of an algorithm. Large, randomised, placebo-controlled studies with strict inclusion criteria are needed to determine the role that antipsychotics play in QT prolongation and sudden death.

Dopamine receptor agonists differ in their actions on cardiac ion channels

Four dopamine receptor agonists used for the treatment of Parkinson's disease (apomorphine, pergolide, ropinirole and sumanirole) were evaluated for the ability to block human ether-a-go-go related gene (hERG) K(+) channels and to modify the duration of canine Purkinje fiber action potentials. Apomorphine, pergolide and ropinirole blocked the hERG-mediated currents with IC(50) values of 2.4, 0.12 and 1.2 microM, respectively. When evaluated in an action potential duration assay, pergolide significantly shortened action potential duration at 90% repolarization (APD(90)) whereas apomorphine and ropinirole significantly prolonged repolarization. Sumanirole only partially blocked hERG K(+) channels at the highest tested concentration (10 microM) and did not modify action potential duration over the tested concentration range (0.65-65 microM). Taken together, these data provide evidence that dopamine receptor agonists developed for the treatment of Parkinson's disease differentially influence hERG K(+) channel function and cardiac action potential duration.

Electrocardiographic changes during migraine attacks

OBJECTIVES

To clarify whether electrocardiographic (ECG) changes can be identified during a migraine attack and to determine whether there are ECG differences between periods with and without headache.

BACKGROUND

The clinical signs and symptoms of migraine point to involvement of the autonomic nervous system, and especially to disrupted regulation of the circulatory system and autonomic balance. This disruption may be more marked during a migraine attack. During a migraine attack, autonomic imbalance within the heart and its vessels conceivably may result in ECG abnormalities.

METHODS

In 30 patients with migraine, the ECG variables of heart rate, abnormalities of rhythm, PR interval, QRS duration, corrected QT interval, T inversion, and ST-segment changes were recorded during migraine attacks and pain-free periods.

RESULTS

Of the 30 patients studied during a migraine attack, 9 (30%) had one or more abnormalities of rhythm (including sinus arrhythmia, atrial premature contraction, and ventricular premature contraction), 20% had PR intervals greater than 0.20 seconds, 40% had corrected QT intervals greater than 0.44 seconds, 66% had T inversion, and 40% had ST-segment abnormalities. No patient had arrhythmia, PR intervals greater than 0.20 seconds, or corrected QT intervals greater than 0.44 seconds during a pain-free period. No differences were noted for ST-segment changes, T inversion, and total ECG changes between periods with and without headache, but both PR and corrected QT intervals were significantly longer during migraine attacks than during pain-free periods.

CONCLUSIONS

We conclude that ECG abnormalities often are present during a migraine attack, and for most of these, particularly PR and corrected QT interval lengthening, these abnormalities will be absent or less prominent during pain-free intervals.

Prognostic value of QT interval parameters for mortality risk stratification in Chagas' disease: results of a long-term follow-up study

BACKGROUND

QT interval parameters are potential prognostic markers of arrhythmogenicity risk and cardiovascular mortality and have never been evaluated in Chagas' disease.

METHODS AND RESULTS

Outpatients (738) in the chronic phase of Chagas' disease were enrolled in a long-term follow-up study. Maximal heart rate-corrected QT (QTc) and T-wave peak-to-end (TpTe) intervals and QRS, QT, JT, QTapex, and TpTe dispersions and variation coefficients were measured manually and calculated from 12-lead ECGs obtained on admission. Clinical, radiological, and 2-dimensional echocardiographic data were also recorded. Primary end points were all-cause, Chagas' disease-related, and sudden cardiac mortalities. During a follow-up of 58+/-39 months, 62 patients died, 54 of Chagas' disease-related causes and 40 suddenly. Multivariate Cox survival analysis revealed that the QT-interval dispersion (QTd) (hazard ratio, 1.45; 95% confidence interval, 1.29 to 1.63; P<0.001, for 10-ms increments) and left ventricular (LV) end-systolic dimension (hazard ratio, 1.36; 95% confidence interval, 1.21 to 1.53; P<0.001, for 5-mm increments) were the strongest independent predictors for all end points. The maximum QTc interval (QTcmax) could substitute for QTd with a worse predictive performance. Other predictors were heart rate, presence of pathological Q waves, frequent premature ventricular contractions (PVCs), and isolated left anterior fascicular block (LAFB) on the ECGs. Kaplan-Meier survival curves demonstrated that a QTd > or =65 ms or a QTcmax > or =465 ms1/2 discriminated the 2 groups with significantly different prognoses.

CONCLUSIONS

Electrocardiographic QTd and echocardiographic LV end-systolic dimension were the most important mortality predictors in patients with Chagas' disease. Heart rate, the presence on ECG of pathological Q waves, frequent PVCs, and isolated LAFB refined the mortality risk stratification.

Does QTc interval predict the response to beta-blockers and calcium channel blockers in hypertensives?

The QT interval corrected for heart rate (QTc) is believed to reflect sympathovagal balance. It has also been established that beta-blockers and dihydropyridine-type calcium channel blockers (DHPCCB) influence the autonomic nervous system. This study tested the hypothesis that QTc interval length is a predictor of the blood pressure reduction induced by beta1-selective beta-blockers or DHPCCB. The predictive values of pretreatment heart rate and of the heart rate change with therapy were also evaluated. The authors conducted an historical reanalysis of 5 clinical trials that looked at the antihypertensive effects of beta-blockers (nebivolol) or DHPCCB (amlodipine, felodipine, isradipine, nifedipine). Correlation and quintile analyses were performed to measure the association between QTc interval, heart rate, or heart rate change and therapeutic blood pressure response. Separate analyses were undertaken for beta-blockers and DHPCCB. Seventy-three and 98 hypertensive subjects respectively were included in the beta-blocker and DHPCCB analyses. QTc interval, pretreatment heart rate, and heart rate change with therapy were not associated with therapeutic blood pressure response. In this study, QTc interval length, pretreatment heart rate, and heart rate change with therapy were not good predictors of the blood pressure response to beta1-selective beta-blockers or DHPCCB in hypertensive subjects.

Electrocardiographic ventricular repolarization parameters in chronic Chagas' disease as predictors of asymptomatic left ventricular systolic dysfunction

Electrocardiographic repolarization parameters are potential markers of arrhythmogenic risk and have not been evaluated in Chagas' disease. The aim of this report was to investigate their associations with LV systolic function assessed by two-dimensional echocardiography. In a cross-sectional study involving 738 adult outpatients in the chronic phase of Chagas' disease, maximal QTc and T wave peak-to-end (TpTe) intervals, and QT, QTapex (QTa), IT and TpTe interval dispersions, and variation coefficients were measured and calculated from 12-lead standard ECGs. Clinical, radiological, ECG, and echocardiographic data were recorded. In bivariate statistical analysis, all repolarization parameters were significantly increased in patients with moderate or severe LV systolic dysfunction, and these patients showed more clinical, radiologic, and ECG abnormalities. Receiver operating characteristic curve analysis demonstrated that isolatedly QTd had the best predictive performance for LV dysfunction, with an 80% specificity and 67% sensitivity for values >60 ms in the subgroup of chagasic patients with abnormal ECGs and no heart failure. Multivariate logistic regression selected, as the best predictive model for LV dysfunction in this subgroup of patients, the presence of cardiomegaly on chest X ray (OR 14.06, 95% CI, 5.54-35.71), QTd >60 ms (OR 9.35, 95% CI, 4.01-21.81), male gender (OR 7.70, 95% CI, 2.98-19.91) and the presence of frequent premature ventricular contractions (PVCs) on ECG (OR 4.06, 95% CI, 1.65-9.97). This model showed 90% specificity and 71% sensitivity. In conclusion, QTd was associated to LV systolic function and could be used to predict asymptomatic dysfunction in chronic Chagas' disease. The presence of cardiomegaly, frequent PVCs, and male sex refined LV function stratification in these patients.

Abnormalities of rate-corrected QT intervals in Parkinson's disease-a comparison with multiple system atrophy and progressive supranuclear palsy

A number of patients with Parkinson's disease (PD) and multiple system atrophy (MSA), in whom sudden death does occur occasionally, have QT or rate-corrected QT (QTc) interval prolongation on electrocardiogram (ECG). Although these QT or QTc interval abnormalities are likely related to autonomic dysfunction, the pathophysiology remains unknown. The aim of this study was to compare the degree of QTc interval prolongation among akinetic-rigid syndromes, namely PD and related disorders, and to evaluate the relationship between QTc prolongation and severity of autonomic dysfunction. Thirty-four patients with PD, 22 with MSA, 11 with progressive supranuclear palsy (PSP) and 30 healthy controls underwent standard autonomic function tests, and electrocardiography variables (RR, QT and QTc intervals) were measured by an ECG recorder with an automated analyzer. The relationship between QTc interval and cardiovascular reflex tests were also analyzed. Orthostatic hypotension and decreased heart rate in response to respiratory stimuli were prominent in MSA, while these were relatively mild in PD. Unlike the RR and QT intervals, the QTc interval significantly differed among all groups (p<0.01). The QTc interval was significantly prolonged in PD (409+/-17 ms; p<0.001) and MSA (404+/-14 ms; p<0.05) compared with healthy controls (394+/-19 ms). Neither autonomic dysfunction nor QTc interval prolongation was evident in PSP. QTc intervals and cardiovascular reflexes did not correlate, except for Valsalva ratio. The QTc interval was obviously prolonged in PD patients to an extent that could not be accounted for simply by autonomic dysfunction levels. MSA patients showed slightly prolonged QTc intervals in spite of marked cardiovascular autonomic dysfunction. Abnormalities of the QTc may reflect the degeneration of cardioselective sympathetic and parasympathetic neurons that cannot be fully captured by cardiovascular autonomic function tests.

Value of corrected QT interval dispersion in identifying patients initiating dialysis at increased risk of total and cardiovascular mortality

Cardiovascular disease remains the most common cause of premature death in end-stage renal disease (ESRD). Although several predictors of cardiac death have been reported, identifying individuals most at risk remains difficult. Previous studies in nonuremic populations have associated cardiac mortality, in particular sudden death, with increased QT dispersion (QTd); defined as the difference between the maximal and minimal QT interval on a standard electrocardiogram. The present study aimed to determine the prognostic value of QTd and corrected QTd (QTdc) in predicting total, cardiovascular, and arrhythmia-related mortality in ESRD patients initiating dialysis. The study was a retrospective cohort of adult ESRD patients starting peritoneal dialysis or hemodialysis between 1990 and 1994. Statistical analysis was by Cox proportional hazard modeling and Kaplan-Meier analysis. Primary study endpoints were total, cardiovascular, and arrhythmia-related mortality. Nonfatal cardiovascular events were a secondary endpoint. A total of 147 patients were studied for a period of 5 to 9 years. In Cox modeling, QTdc was an independent predictor of total (relative risk [RR] = 1.53; difference for RR = 50 msec; P = 0.0001) and cardiovascular mortality (RR = 1.57; difference for RR = 50 msec; P = 0.028) and trended toward arrhythmia-related mortality (P = 0.061). Total mortality also was predicted independently by lack of renal transplantation, radiographic cardiomegaly, and predialysis serum albumin. In multivariate analysis, QTdc was associated weakly with serum calcium, mean QT interval, and presence of diabetes mellitus. QTdc may be a useful marker for identifying dialysis patients at an increased risk for overall and cardiovascular mortality.

Evaluation of drug-induced QT interval prolongation: implications for drug approval and labelling

Assessment of proarrhythmic toxicity of newly developed drugs attracts significant attention from drug developers and regulatory agencies. Although no guidelines exist for such assessment, the present experience allows several key suggestions to be made and an appropriate technology to be proposed. Several different in vitro and in vitro preclinical models exist that, in many instances, correctly predict the clinical outcome. However, the correspondence between different preclinical models is not absolute. None of the available models has been demonstrated to be more predictive and/or superior to others. Generally, compounds that do not generate any adverse preclinical signal are less likely to lead to cardiac toxicity in humans. Nevertheless, differences in likelihood offer no guarantee compared with entities with a preclinical signal. Thus, the preclinical investigations lead to probabilistic answers with the possibility of both false positive and false negative findings. Clinical assessment of drug-induced QT interval prolongation is crucially dependent on the quality of electrocardiographic data and the appropriateness of electrocardiographic analyses. An integral part of this is a precise heart rate correction of QT interval, which has been shown to require the assessment of QT/RR relationship in each study individual. The numbers of electrocardiograms required for such an assessment are larger than usually obtained in pharmacokinetic studies. Thus, cardiac safety considerations need to be an integral part of early phase I/II studies. Once proarrhythmic safety has been established in phase I/II studies, large phase III studies and postmarketing surveillance can be limited to less strict designs. The incidence of torsade de pointes tachycardia varies from 1 to 5% with clearly proarrhythmic drugs (e.g. quinidine) to 1 in hundreds of thousands with drugs that are still considered unsafe (e.g. terfenadine, cisapride). Thus, not recording any torsade de pointes tachycardia during large phase III studies offers no guarantee, and the clinical premarketing evaluation has to rely on the assessment of QT interval changes. However, since QT interval prolongation is only an indirect surrogate of predisposition to the induction of torsade de pointes tachycardia, any conclusion that a drug is safe should be reserved until postmarketing surveillance data are reviewed. The area of drug-related cardiac proarrhythmic toxicity is fast evolving. The academic perspective includes identification of markers more focused compared with simple QT interval measurement, as well as identification of individuals with an increased risk of torsade de pointes. The regulatory perspective includes careful adaptation of new research findings.

Increased QT dispersion does not reflect the increased regional variation of cardiac sympathetic nervous activity in hypertrophic cardiomyopathy

BACKGROUND

QT dispersion (QTD) reflects regional variation of ventricular repolarization. However, the relationship between QTD and the regional variation of cardiac sympathetic nerve activity in hypertrophic cardiomyopathy (HCM) is not yet elucidated.

METHODS

Cardiac sympathetic nerve activity was evaluated in 25 patients with HCM by iodine 123 metaiodobenzylguanidine (MIBG) myocardial scintigraphy. With planar MIBG imaging, heart and mediastinum ratios (H/M) at early (20 minutes) and delayed (3 hours) acquisition and the washout rate (WR) were calculated. Polar maps of left ventricular myocardium were divided into 20 segments. The SD of early uptake (EU-SD), delayed uptake (DU-SD), and WR (WR-SD) in 20 segments as indices of regional variation were calculated. QT intervals were corrected by use of the Bazett formula.

RESULTS

Maximum QTc correlated positively with H/M early, WR, and left ventricular wall thickness (LVWT). Minimum QTc correlated positively with WR and LVWT. Corrected QTD (QTDc) correlated negatively with EU-SD, DU-SD, and WR-SD and positively with the interventricular septal thickness/posterior wall thickness ratio. Stepwise regression analysis revealed that the most powerful determinants for maximum QTc, minimum QTc, and QTDc were WR, LVWT, and EU-SD, respectively.

CONCLUSIONS

QTD correlated negatively rather than positively with the regional variability index of cardiac sympathetic nerve activity. These results suggest that increased QTD in patients with HCM may not reflect increased heterogeneity of cardiac sympathetic nerve activity.