Correction of the QT interval for heart rate: review of different formulas and the use of Bazett's formula in myocardial infarction

The comparison in reduction of QT dispersion after primary percutaneous coronary intervention according to existence of thrombectomy in ST-segment elevation myocardial infarction

BACKGROUND

Primary percutaneous coronary intervention (PPCI) is the standard treatment in patients with ST-segment elevation myocardial infarction (STEMI). Thrombectomy devices are used to remove thrombus or to prevent embolization of thrombus and plaque during PPCI. QT dispersion (the difference between maximal and minimal QT interval calculated on a standard 12-lead electrocardiogram) represents the regional nonuniformity of ventricular repolarization. It may reflect early coronary reperfusion in reducing electrophysiological instability by decreasing QT dispersion in the recovery phase after acute STEMI.

HYPOTHESIS

Our aim was to show whether an additional effect of thrombectomy on reducing QT dispersion will be seen in patients undergoing PPCI for STEMI.

METHODS

The study population included 80 consecutive patients who were admitted to the hospital within 12 hours after the onset of acute STEMI and angiographic evidence of intraluminal thrombus in the infarct-related artery. Patients with atrial fibrillation or flutter, intraventricular conduction abnormalities, pre-excitation, cardiogenic shock, cardiomyopathy, ventricular hypertrophy, and severe valvular heart disease were excluded from the study.

RESULTS

There were no significant differences between groups regarding gender, age, cardiovascular risk factors, and time from symptom onset to treatment, except for smoking, which was much higher in the PPCI plus thrombectomy group. Infarct-related artery distribution (left anterior descending artery [LAD] to non-LAD), and neither the rate of balloon predilatation nor stent implantation were different between groups. Successful coronary patency was achieved in each case. QT interval measurements were similar between groups at admission. However, at 24 hours, QT and QTc dispersions were less in the PPCI plus thrombectomy group (41 ± 9 vs 33 ± 7 ms, P < 0.05 and 45 ± 8 vs 35 ± 7 ms, P = 0.03, respectively), but not in the other QT interval measurements. When patients were divided into 2 groups according to infarct-related artery (LAD and non-LAD groups), QT interval measurement parameters did not show any significant differences.

CONCLUSIONS

Thrombectomy additional to PPCI helps more effective reperfusion at the microvascular level and provides additional prognostic information.

Cigarette Smoking Is Associated with Prolongation of the QTc Interval Duration in Patients with Type 2 Diabetes Mellitus

Aims. Aim of the study was to evaluate the effect of smoking on autonomic nervous system (ANS) activity and QTc interval duration in patients with Type 2 diabetes mellitus (T2DM). Methods. A total of 70 patients with T2DM (35 chronic smokers, 35 nonsmokers) treated with oral antidiabetic medications underwent continuous ECG Holter monitoring for 24 hours and analysis of time- and frequency-domain measures of heart rate variability (HRV). HRV over short time was also assessed using the deep breathing test. In addition, baroreflex sensitivity (BRS) was evaluated using the spontaneous sequence method. The mean QTc interval was measured from the 24-hour ECG recordings. Results. Smokers had lower body mass index (BMI) and exhibited higher 24-hour mean heart rate. There was no difference regarding all measures of ANS activity between the two groups. Smokers showed increased mean QTc duration during the 24 hours (439.25 ± 26.95 versus 425.05 ± 23.03 ms, P = 0.021) as well as in both day (439.14 ± 24.31 ms, P = 0.042) and night periods (440.91 ± 32.30 versus 425.51 ± 24.98 ms, P = 0.033). The association between smoking status and mean QTc interval persisted after adjusting for BMI. Conclusions. Cigarette smoking is associated with prolongation of the QTc interval in patients with T2DM by a mechanism independent of ANS dysfunction.

Value of electrocardiogram in the differentiation of hypertensive heart disease, hypertrophic cardiomyopathy, aortic stenosis, amyloidosis, and Fabry disease

Left ventricular hypertrophy is 1 of the most frequent cardiac manifestations associated with an unfavorable prognosis. However, many different causes of left ventricular hypertrophy exist. The aim of the present study was to assess the diagnostic value of common electrocardiographic (ECG) parameters to differentiate Fabry disease (FD), amyloidosis, and nonobstructive hypertrophic cardiomyopathy (HC) from hypertensive heart disease (HHD) and aortic stenosis (AS). In 94 patients with newly diagnosed FD (n = 17), HHD (n = 20), amyloidosis (n = 17), AS (n = 20), and HC (n = 20), common ECG parameters were analyzed and tested for their diagnostic value. A stepwise approach including the Sokolow-Lyon index, corrected QT duration, and PQ interval minus P-wave duration in lead II to overcome P-wave abnormalities was applied. A corrected QT duration <440 ms in combination with a PQ interval minus P-wave duration in lead II <40 ms was 100% sensitive and 99% specific for the diagnosis of FD, whereas a corrected QT duration >440 ms and a Sokolow-Lyon index ≤1.5 mV were found to have a sensitivity and specificity of 85% and 100%, respectively, for the diagnosis of amyloidosis and differentiation from HC, AS, and HHD. Moreover, a novel index ([PQ interval minus P-wave duration in lead II multiplied by corrected QT duration]/Sokolow-Lyon index) proved to be highly diagnostic for the differentiation of amyloidosis (area under the curve 0.92) and FD (area under the curve 0.91) by receiver operator characteristic analysis. In conclusion, a combined analysis of PQ interval minus P-wave duration in lead II, corrected QT duration, and Sokolow-Lyon index proved highly sensitive and specific in the differentiation of FD, amyloidosis, and HC compared to HHD and AS. Analysis of these easy-to-assess ECG parameters may be of substantial help in the diagnostic workup of these 5 conditions.

Heterogeneity of ventricular repolarization in newborns with severe aortic coarctation

Sudden death is a possible occurrence for newborns younger than 1 year with severe aortic coarctation (CoA) before surgical correction. Basic research and animal experiments have shown electrophysiologic changes during mechanical ventricular pressure overload. The current study aimed to evaluate the effect of severe CoA on the heterogeneity of ventricular repolarization by examining corrected QT and JT interval dispersion (respectively, QTc-D and JTc-D) and electrocardiographic parameters of spatial heterogeneity of ventricular repolarization in newborns with no associated congenital cardiac malformations. The study enrolled 30 isolated severe CoA neonates (age, 45 ± 15 days; 17 males) with normal size and wall thickness of the left ventricle before surgical correction and 30 age- and sex-matched healthy newborns used as control subjects. Heart rate, QRS duration, maximum and minimum QT and JT intervals, and QTc-D and JTc-D measurements were performed. The healthy control group did not significantly differ from the CoA group in terms of heart rate, weight, height, and echocardiographic parameters. Compared with the healthy control group, the CoA group presented significantly increased values of QTc-D (109.7 ± 43.4 vs. 23 ± 15 ms; P = 0.03) and JTc-D (99.1 ± 43.3 vs. 65.8 ± 24.1 ms; P = 0.04). A statistically significant correlation was found between the Doppler peak pressure gradient across the coarctation site and the values of QTc-D (r = 0.48; P = 0.03) and JTc-D (r = 0.42; P = 0.04). Our study showed significantly increased QTc-D and JTc-D in isolated CoA newborns with normal left ventricular geometry.

Prospective cohort study of lead exposure and electrocardiographic conduction disturbances in the Department of Veterans Affairs Normative Aging Study

BACKGROUND

No studies have examined the association between cumulative low-level lead exposure and the prospective development of electrocardiographic conduction abnormalities, which may mediate the association between lead and several cardiovascular end points.

OBJECTIVE

We prospectively examined the association between lead exposure and the development of electrocardiographic conduction abnormalities.

METHODS

We assessed blood lead, bone lead--a biomarker of cumulative lead exposure--measured with K-shell X-ray fluorescence, and electrocardiographic end points among 600 men in the Normative Aging Study who were free of electrocardiographic abnormalities at the time of the baseline ECG. Of these men, we had follow-up data from a second electrocardiogram for 496 men 8.1 (SD = 3.1) years later, on average. We used repeated measures linear regression to analyze change in electrocardiographic conduction timing and logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for developing specific conduction disturbances and adjusted for potential confounders.

RESULTS

Mean (± SD) blood (5.8 ± 3.6), patella bone (30.3 ± 17.7), and tibia bone (21.6 ± 12.0) lead concentrations were similar to those found in samples from the general U.S. population and much lower than those reported in occupationally exposed groups. Compared with those in the lowest tertile of tibia lead, those in the highest had a 7.94-ms (95% CI, 1.42-14.45) increase in heart rate-corrected QT (QTc) interval and a 5.94-ms increase in heart rate-corrected QRS (95% CI, 1.66-10.22) duration > 8 years. Those in the highest tertile of tibia lead also had increased odds of QT prolongation (QTc ≥ 440 msec; OR = 2.53; 95% CI, 1.22-5.25) and JT prolongation (heart rate-corrected JT > 360 msec; OR = 2.53; 95% CI, 0.93-6.91). Results were weaker for patella lead. No associations were identified with blood lead.

CONCLUSIONS

This study suggests that low-level cumulative exposure to lead is associated with worse future cardiac conductivity in the ventricular myocardium, as reflected in QT interval characteristics.

Henry Cuthbert Bazett (1885-1950)--the man behind the QT interval correction formula

The "Bazett formula" is used for correcting the observed QT interval and is named after Henry Cuthbert Bazett who was born in England in 1885. He studied medicine and worked in Oxford and served in the British Medical Corps during World War I. In 1920, Bazett published his seminal paper on the different intervals length of the electrocardiogram recordings in a small group of healthy individuals, and proposed a formula for correcting the QT length for heart rate. Later, he moved to the University of Pennsylvania, in Philadelphia, and from 1931 until his death in 1950, he served as head of the Department of Physiology and a leader of the American Society of Physiology. Bazett's scientific work was largely concerned with temperature control, circulation, and blood volume, and he contributed greatly to the study of circulation in humans by using invasive catheterization.

The role of ECG screening in the evaluation of risk of sudden cardiac arrest in the young

We have the opportunity to answer the questions that have been raised and obtain answers by prospective evaluation. ECG screening does not need an all-or-none approach in the current era. It needs a commitment to obtain the relevant data that will be accepted as applicable in the United States. Multiple populations, genders, ages, ethnicities, and races should be screened in a prospective ECG screening study. The actual costs should be obtained and cost utility analysis should be performed. Models of screening should be developed and tested. It is no longer acceptable to say "It can't be done here"; or "It costs too much"; or any of the scores of excuses used unless one can support the statements with trials or scientific data. A study of 100,000 children ages 5-19 years would cost $500,000-750,000. Is it not worth finding out who is correct, how to better identify those at risk, and how to do it in the most cost-efficient manner? No one wants to waste $2 billion a year. However, a one-time investment of 25% of that amount would determine how best to use our health care resources in the future to identify children and youth at risk for SCA.

The measurement of the QT and QTc on the neonatal and infant electrocardiogram: a comprehensive reliability assessment

BACKGROUND

An electrocardiogram has been proposed to screen for prolonged QT interval that may predispose infants to sudden death in the first year of life. Understanding the reliability of QT interval measurement will inform the design of a screening program.

METHODS

Three pediatric cardiologists measured the QT/RR intervals on 60 infant electrocardiograms (median age 46 days), from leads II, V5 and V6 on three separate occasions, 7 days apart, according to a standard protocol. The QTc was corrected by Bazett's (QTcB), Fridericia's (QT(CFrid)), and Hodges' (QTcH) formulae. Intraobserver and interobserver reliability were assessed by intraclass correlation coefficients (ICC), limits of agreement and repeatability coefficients for single, average of two and average of three measures. Agreement for QTc prolongation (> 440 msec) was assessed by kappa coefficients.

RESULTS

QT interval intraobserver ICC was 0.86 and repeatability coefficient was 25.9 msec; interobserver ICC increased from 0.88 for single observations to 0.94 for the average of 3 measurements and repeatability coefficients decreased from 22.5 to 16.7 msec. For QTcB, intraobserver ICC was 0.67, and repeatability was 39.6 msec. Best interobserver reliability for QTcB was for the average of three measurements (ICC 0.83, reproducibility coefficient 25.8 msec), with further improvement for QTcH (ICC 0.92, reproducibility coefficient 16.69 msec). Maximum interobserver kappa for prolonged QTc was 0.77. Misclassification around specific cut points occurs because of the repeatability coefficients.

CONCLUSIONS

Uncorrected QT measures are more reliable than QTcB and QT(CFrid). An average of three independent measures provides the most reliable QT and QTc measurements, with QTcH better than QTcB.

New aspects on the assessment of left ventricular dyssynchrony by tissue Doppler echocardiography: comparison of myocardial velocity vs. displacement curves

The purpose of this study is to assess the incremental value of tissue Doppler (TDI) derived displacement curves (TDint) compared to TDI velocity curves (TDvel) for the evaluation of left ventricular (LV) dyssynchrony (LVD). About 25 patients (pts.) with systolic heart failure were studied by TDvel and TDint. Four TDI sample volumes were placed at the basal and four at the mid ventricular myocardium, utilising two imaging planes. LV dyssynchrony (LVD) was defined as an interregional delay of >40 ms corrected for heart rate. 10 pts. had synchronous contraction, 15 pts. LVD as defined by two experts (EC). To determine diagnostic accuracy and intra-observer variability two identical sets of 100 documents (25 pts. x two imaging planes x two modalities) were produced and presented in random order to one trained (TR) and two untrained (UR) readers. The TR more frequently classified documents as unreadable (7.5 vs. 3.5%, P < 0.05) but more often as correct, i.e., consistent with EC (72.0 vs. 57.8%, P < 0.001). 8.7% of the documents were classified as unreadable using TDvel, 1.0% when applying TDint (P < 0.001). The mean value of correct classification of all 3 readers was 54.3% (TDvel only), 70.7% (TDint only), and 77.7% (combining both modalities), (P < 0.001). The kappa value for TR and TDint was 0.68, for TDvel 0.29. For UR, kappa did not differ (TDint: 0.58; TDvel 0.51). TDint is superior to TDvel in accuracy, reproducibility, and applicability for skilled and unskilled investigators when evaluating LVD by TDI. The combined application of TDint and TDvel is optimal.

A study of the association between the prolongation of the QT interval in the resting ECG and myocardial infarction

The relationship between the incidence of myocardial infarction in the 10 year follow-up period and the length of the QT interval and its two components (the time elapsing between the Q wave and the beginning of the T wave, and the duration of the T wave) was investigated in a study of the records of a group of men drawn from a random sample of all 55-year-old men living in Göteborg, Sweden. A significant association was found between the incidence of myocardial infarction and the first component but not with the second component or the QT interval itself. The two components were found to be independent and thus to have the potential to act as confounding factors if the QT interval is examined alone. Further, our results suggest that correcting the QT interval for heart rate needs careful reassessment.

QRS amplitudes, QTc intervals and ECG abnormalities in pheochromocytoma patients before, during and after treatment

QRS amplitudes (S1 + R5), Minnesota Code ECG abnormalities and QTc intervals were analyzed in ECGs from 31 pheochromocytoma patients on admission to hospital, after 17 +/- 7.2 (SD) days of preoperative phenoxybenzamine therapy in a dosage of 148 +/- 45.0 (SD) mg/day and after a mean postoperative follow-up of 6 years. QRS voltage decreased significantly from 3.37 +/- 1.48 on admission, to 2.26 +/- 0.69 mV at postoperative follow-up (p less than 0.001). The prevalence of total Minnesota Code changes increased or was unchanged on the different occasions. Severe to moderate changes, however, became less prevalent, while mild changes increased. The QTc interval was 0.44 +/- 0.04 s on admission and 0.41 +/- 0.02 s at follow-up (p less than 0.01). No significant differences were observed during treatment with phenoxybenzamine. Pathological ECGs are common findings in patients with pheochromocytoma and significant improvements occur after surgery. Significant effects of phenoxybenzamine therapy were only found in patients with sustained hypertension.

Changes of the corrected QT interval in healthy boys and girls over day and night

AIMS

The study was designed to detect changes in corrected QT intervals over day and night in both sexes in healthy children.

METHODS AND RESULTS

The corrected QT interval was calculated from 24 h ECGs obtained from 282 healthy children aged 6 months to 18 years. The QTc interval as measured by the 24 h recording differs to the standard ECG measurement which is in average of 40-50 ms shorter. The QTc interval changes little over a 24 h period and is remarkably constant despite significant heart rate changes in healthy children.

CONCLUSION

The routine ECG-even if the calculated values differ markedly from those obtained over 24 h-seems to be a good screening method for the measurement of corrected QT intervals, because the corrected QT interval is kept constant over the whole day in healthy children.

Bias and variance evaluation of QT interval correction methods

There is an increasing regulatory emphasis on assessing drug-induced QT interval prolongation. Since QT interval is correlated with heart rate (HR), assessment of drug-induced QT interval prolongation should be made at a standardized HR, resulting in the need to correct QT interval (QTc) for HR. This study investigates the statistical properties of QTc intervals using individual based correction (IBC), population based correction (PBC), or fixed correction (FC) methods under both the linear and log-linear regression models for the QT-RR relationship where RR is the time elapsing between two consecutive heart beats (inversely related to HR through RR = 60/HR). This study shows that QTc intervals using PBC and FC methods are conditionally biased. The QTc interval using the IBC method is conditionally unbiased under the linear regression model, but is conditionally biased under the log-linear regression model. It also shows that under both the linear and log-linear regression models, the conditional variances of the QTc intervals using the three correction methods satisfy the order FC < or = PBC < or = IBC. Suggestions for analyzing QT intervals based on these findings are discussed.

Phenotypic spectrum and clinical characteristics of apical hypertrophic cardiomyopathy: multicenter echo-Doppler study

OBJECTIVES

The aim of this study was to define the phenotypic spectrum of apical hypertrophic cardiomyopathy (ApHCM) and clinical characteristics pertaining to identified subtypes.

METHODS

In 182 consecutive ApHCM patients (58.9 +/- 11.2 years; 142 men) with left ventricular ejection fraction > or =50%, we measured end-diastolic wall thickness of all 16 left ventricular segments to determine patterns of hypertrophy. Echo-Doppler parameters, electrocardiography patterns, and clinical findings were analyzed.

RESULTS

ApHCM was classified into three types as pure focal (n = 81), pure diffuse (n = 70) and mixed type (n = 31) according to patterns of hypertrophy. Incidence of atrial fibrillation (5% for pure focal vs. 11% for pure diffuse vs. 23% for mixed type, p < 0.05) and left atrial volume index (30.9 +/- 11.8, 35.7 +/- 14.8, and 41.3 +/- 15.9 ml/m(2), respectively, p < 0.001) were significantly different among subtypes. Peak systolic (6.6 +/- 1.0 vs. 6.3 +/- 1.2 vs. 5.9 +/- 1.1 cm/s, respectively, p < 0.05), diastolic (5.1 +/- 1.8 vs. 5.0 +/- 1.2 vs. 4.1 +/- 1.3 cm/s, respectively, p < 0.05) mitral annular velocity, E/E' (13.3 +/- 4.2 vs. 13.7 +/- 5.4 vs. 16.1 +/- 6.1, respectively, p < 0.05) were also significantly different.

CONCLUSIONS

ApHCM contains three morphologically distinct phenotypes and detailed subtyping is important in the prediction of development of atrial fibrillation, left atrial volume index and left ventricular longitudinal function.

Effect of slow coronary flow on electrocardiographic parameters reflecting ventricular heterogeneity

QT interval dispersion reflects regional variations in ventricular repolarization and cardiac electrical instability. Previous studies have showed that QT interval dispersion changes during episodes of myocardial ischemia. Slow coronary flow (SCF) in epicardial coronary arteries is a rare and unique angiographic finding. Whether this pattern of flow is associated with electrocardiographic abnormalities is unknown. Therefore, this study was designed to investigate whether SCF results in electrocardiographic (ECG) changes compared to normal coronary flow. For this aim 24 patients with angiographically proven SCF who had no obstructive coronary lesion (group I) and 25 patients without coronary artery disease (group II) were included in the study. Both groups underwent a routine standard 12-lead surface electrocardiogram recorded at 50 mm/s during rest. QT dispersion (QTd), corrected QT (QTc), and corrected QT dispersion (QTcd) were calculated. Distributions of sex, age, body mass index (BMI), and cardiac risk factors were similar in the 2 groups. Mean heart rate was similar in the 2 groups (74 +/-8 vs 77 +/- 7 p > 0.05). Mean QRS interval durations were similar in the groups (92 +/-7 vs 90 +/-6 ms p > 0.005). In group I, QTd, QTcd, and QTc, were significantly higher than in group II (QTd: 73 +/-14 vs 40 +/-14; QTcd: 71 +/-15 vs 42 +/-9; QTc: 414 +/-14 vs 388 +/-13, respectively p <0.05). In conclusion, SCF was found to be associated with prolonged QT interval and increased QT dispersion. Ischemia in microvascular level and/or altered autonomic regulation of the heart may be responsible mechanisms.

Fishing for an ECG: a student-directed electrocardiographic laboratory using rainbow trout

Cardiac physiology is emphasized in many undergraduate physiology courses, but few nonmammalian vertebrate model systems exist that 1) can be studied fairly noninvasively, 2) are well suited for controlled experimentation, and 3) emphasize principles characteristic of the vertebrate heart. We have developed an inquiry-based undergraduate/graduate-level laboratory in cardiac physiology and electrocardiography using rainbow trout (Oncorhynchus mykiss Walbaum) and the BioPac MP30 data-acquisition system (other fish species and/or electrocardiographic recording devices can be substituted). This laboratory facilitates intensive study of vertebrate electrocardiograms (ECGs) under a variety of environmental and physiological perturbations and is ideal for use in multi-session, inquiry-based laboratory projects in animal physiology. Furthermore, students gain valuable experience in scientific inquiry, study design, following and/or developing scientific protocols, and animal care. This laboratory requires the ability to keep captive fish of at least 100 g and equipment to record ECGs. Departments meeting these requirements can adopt this technique at modest expense. Student enthusiasm and feedback were positive, and several students commented that the nonlethal methods used added to the laboratory's perceived value.

Effects of isolated coronary artery ectasia on electrocardiographic parameters reflecting ventricular heterogeneity

Isolated coronary ectatic but otherwise normal epicardial coronary arteries are an infrequent angiographic finding. We sought to determine whether coronary artery ectasia (CAE) may alter QT-interval duration and dispersion. The study population consisted of 24 patients with isolated CAE and otherwise normal epicardial coronary arteries (group 1) and sex- and age-matched subjects with atypical chest pain and otherwise normal coronary flow (group 2). Both groups underwent a routine standard 12-lead surface electrocardiogram recorded at 50 mm/s during rest. QT dispersion (QTd), corrected QT (QTc), and corrected QT dispersion (QTcd) were calculated. Distribution of sex, age, body mass index, and cardiac risk factors were similar in the 2 groups. Mean heart rate was similar in the 2 groups (74 +/- 10 vs 70 +/- 7, P > .05). In group 1, QTd, QTcd, and QTc were significantly higher than those of group 2 (QTd, 40 +/- 17 vs 29 +/- 10 milliseconds [P < .05]; QTcd, 43 +/- 19 vs 30 +/- 10 milliseconds [P < .05]; QTc, 410 +/- 21 vs 397 +/- 19 milliseconds [P < .05]). In conclusion, CAE was found to be associated with prolonged QT interval and increased QTd. Microvascular dysfunction and/or ischemia may be responsible mechanisms.

[Clinical significance of dynamic QT-interval-analyses]

Dynamic parameters of ventricular repolarization as Holter derived parameters expressed as QT-interval adaptation to heart rate changes (QT/RR-slope) and QT-interval-variability are being more and more frequently used to identify patients with increased risk for ventricular arrhythmias. Steep QT-RR-slopes, reflecting inadequate adaptation of ventricular repolarization to heart rate changes, as well as increased QT-interval-variability, reflecting temporal inhomogeneity of ventricular repolarization duration, are frequently observed in patients at risk for sudden cardiac death. Additionally, there is strong evidence for significant alterations in the dynamics of action potential duration restitution in patients with structural heart disease. This review gives an up-to-date overview about the current research in methods of assessment and clinical relevance of dynamic parameters of ventricular repolarization.

Accuracy of Uncorrected versus Corrected QT Interval for Prediction of Torsade de Pointes Associated with Intravenous Haloperidol

STUDY OBJECTIVE

To determine if the uncorrected QT interval (QT(u)) more accurately predicts drug-induced torsade de pointes than QT intervals corrected using the Bazett's (QT(B)), Fridericia (QT(Frid)), or Framingham (QT(Fram)) methods.

DESIGN

Retrospective analysis of a previously reported case-control study of risk factors for haloperidol-induced torsade de pointes.

SETTING

Large tertiary care teaching hospital.

PATIENTS

Forty-six critically ill patients who received intravenous haloperidol for sedation; seven developed torsade de pointes.

MEASUREMENTS AND MAIN RESULTS

The QT intervals were measured manually by one investigator from electrocardiograms performed before and during haloperidol therapy. Logistic regression analysis for prediction of torsade de pointes was performed, incorporating QT(u), QT(B), QT(Frid), QT(Fram), and RR intervals measured during treatment. Receiver operating characteristics (ROC) curves were constructed. Primary outcome measures were proportion of explained variation (maximum-rescaled R2); area under the ROC curves for QT(u), QT(B), QT(Frid), QT(Fram), and RR interval; and sensitivity and specificity for prediction of haloperidol-induced torsade de pointes. The QT(u) was associated with the highest R2 compared with QT(Fram), QT(Frid), QT(B), and RR interval (0.77, 0.73, 0.68, 0.53, and 0.30, respectively). No significant differences in areas under the ROC curves were found between any of the QT-interval methods. Areas under the ROC curves for QT(u) and QT(Fram) trended toward being greater than that associated with the RR interval. All QT-interval methods were highly sensitive (100% for each), whereas the RR interval was less sensitive (86%); QT(u) and QT(Fram) were most specific (82%) compared with the QT(Frid) (72%), QT(B) (64%), and RR interval (36%).

CONCLUSION

Compared with QT(B) and QT(Frid), the QT(u) and QT(Fram) best predicted haloperidol-induced torsade de pointes in critically ill patients; the QT(Fram) offered no advantage over the QT(u).

Magnitude of error introduced by application of heart rate correction formulas to the canine QT interval

BACKGROUND

Accurate detection of drug-induced QT interval changes is often confounded by concurrent heart rate changes. Application of heart rate correction formulas has been the traditional approach to account for heart rate-induced QT interval changes, and thereby identify the direct effect of the test article on cardiac repolarization. Despite numerous recent studies identifying the imprecision of these formulas they continue to be applied.

METHODS

Using a chronic atrioventricular dissociated His-paced canine model, heart rate correction methods were evaluated for their ability to generate a corrected QT interval independent of original heart rate. Additionally, His bundle pacing at a heart rate of 60 beats/min allowed calculation of the magnitude of error introduced by application of heart rate correction formulas.

RESULTS

Of the fixed parameter heart rate correction formulas, only Van de Water was able to predict corrected QT values independent of the original heart rate. The magnitude of error discovered by application of heart rate correction formulas varied, but in many cases was very large. Bazett's formula was associated with a mean overcorrection of 67.9 ms; Fridericia's 28.7 ms. Van de Water was the best fixed parameter formula with a mean error of 10.8 ms. As expected, group and individual corrections derived from linear regression of the HR-QT data offered improvement over the traditional formulas. Both were able to predict QTc values independent of the heart rate. However, errors of the magnitude of 10 and 6 ms, respectively, were still introduced.

CONCLUSION

Van de Water and linear regression correction methods were superior to others in this study, but all methods generated QTc errors equal to or much greater than the magnitude of interest for drug safety evaluation.

Randomized dose-ranging controlled trial of AQ-13, a candidate antimalarial, and chloroquine in healthy volunteers

OBJECTIVES

To determine: (1) the pharmacokinetics and safety of an investigational aminoquinoline active against multidrug-resistant malaria parasites (AQ-13), including its effects on the QT interval, and (2) whether it has pharmacokinetic and safety profiles similar to chloroquine (CQ) in humans.

DESIGN

Phase I double-blind, randomized controlled trials to compare AQ-13 and CQ in healthy volunteers. Randomizations were performed at each step after completion of the previous dose.

SETTING

Tulane-Louisiana State University-Charity Hospital General Clinical Research Center in New Orleans.

PARTICIPANTS

126 healthy adults 21-45 years of age.

INTERVENTIONS

10, 100, 300, 600, and 1,500 mg oral doses of CQ base in comparison with equivalent doses of AQ-13.

OUTCOME MEASURES

Clinical and laboratory adverse events (AEs), pharmacokinetic parameters, and QT prolongation.

RESULTS

No hematologic, hepatic, renal, or other organ toxicity was observed with AQ-13 or CQ at any dose tested. Headache, lightheadedness/dizziness, and gastrointestinal (GI) tract-related symptoms were the most common AEs. Although symptoms were more frequent with AQ-13, the numbers of volunteers who experienced symptoms with AQ-13 and CQ were similar (for AQ-13 and CQ, respectively: headache, 17/63 and 10/63, p = 0.2; lightheadedness/dizziness, 11/63 and 8/63, p = 0.6; GI symptoms, 14/63 and 13/63; p = 0.9). Both AQ-13 and CQ exhibited linear pharmacokinetics. However, AQ-13 was cleared more rapidly than CQ (respectively, median oral clearance 14.0-14.7 l/h versus 9.5-11.3 l/h; p < or = 0.03). QTc prolongation was greater with CQ than AQ-13 (CQ: mean increase of 28 ms; 95% confidence interval [CI], 18 to 38 ms, versus AQ-13: mean increase of 10 ms; 95% CI, 2 to 17 ms; p = 0.01). There were no arrhythmias or other cardiac AEs with either AQ-13 or CQ.

CONCLUSIONS

These studies revealed minimal differences in toxicity between AQ-13 and CQ, and similar linear pharmacokinetics.

Acute effect of methylphenidate on QT interval duration and dispersion in children with attention deficit hyperactivity disorder

Among childhood psychiatric disorders, attention deficit hyperactivity disorder (ADHD) is of greatest interest to practitioners. Methylphenidate (MPH) is a drug that is widely used in the treatment of children in whom ADHD has been diagnosed. Although this treatment has been used for years, its effects on the heart remain the subject of debate. The QT interval comprises the ventricular activation and recovery periods as seen on electrocardiogram (ECG). The acute effect of MPH on QT interval dispersion is unknown. Researchers in the present study sought to investigate the acute effects of MPH on QT interval as seen on ECG. A total of 25 patients with ADHD (mean age, 9.4+/-2.1 y) who were treated with MPH were enrolled in the study. Twelve-lead derivation ECGs were taken before and 2 h after administration of 10 mg of MPH. Maximum QT interval, minimum QT interval, and interval durations were measured, and QT dispersion was calculated, for each ECG. QT dispersion measured after medication administration decreased significantly from 59.6+/-16.3 ms to 50.8+/-10.9 ms (P=.016); corrected QT dispersion decreased significantly from 70.9+/-17.6 ms to 61.3+/-13.3 ms (P=.011). Maximum QT interval duration decreased from 73.7+/-21.8 ms to 361.8+/-29.0 ms (P=.006); minimum QT interval duration rose from 317.0+/-23.3 ms to 322.3+/-21.6 ms (P=.312). In conclusion, the findings of this study show that MPH reduces QT dispersion during the acute period shortly after its administration.

QT-interval dispersion in acute myocardial infarction is only shortened by thrombolysis in myocardial infarction grade 2/3 reperfusion

BACKGROUND

Increased QT interval dispersion (QTd) has been found in patients with acute myocardial infarction (AMI). In previous studies this has been shown to decrease with thrombolysis.

HYPOTHESIS

The aim of this study was to compare the effects of reperfusion by primary percutaneous transluminal coronary angioplasty (PTCA) and by thrombolysis on QTd and correlate these results with the degree of reperfusion.

METHODS

We studied 60 patients with a first AMI. The study cohort included 40 consecutive patients who had received thrombolysis (streptokinase or rt-PA); 20 additional consecutive patients with successful primary PTCA, all with preselected Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow by predefined selection criteria (12 stents); and 20 controls. A 12-lead ECG for QTd calculation was recorded before thrombolysis or PTCA and immediately after the procedure. All values were corrected according to Bazett's formula (QTcd). QTd and QTcd values before and after each procedure in three groups and the respective percent changes of deltaQTd and deltaQTcd were compared separately.

RESULTS

QTd and QTcd were significantly increased before thrombolysis/PTCA versus normals. An angiogram performed after thrombolysis showed adequate reperfusion (TIMI grade 2/3) in 20 patients, while in the other 20 only TIMI 0/1 reperfusion was achieved. Thrombolysis-TIMI flow 2/3 and PTCA significantly reduced QTd (from 68 +/- 10 to 35 +/- 8 ms, p < 0.001, deltaQTd = 48 +/- 11%, in the Thr-TIMI flow 2/3 group,and from 79 +/- 11 to 38 +/- 9 ms, p < 0.001, deltaQTd = 52 +/- 9%, in the PTCA group), while in the Thr-TIMI flow 0/1 group no significant changes were recorded. A percent QTd decrease > 30 s had 96% sensitivity, 85% specificity, and 93% positive and 94% negative predictive value, respectively, for TIMI 2/3 flow.

CONCLUSIONS

A significant decrease in QT dispersion may provide an additional electrocardiographic index for successful (TIMI 2/3) reperfusion.

Simple criteria for differentiation of Fabry disease from amyloid heart disease and other causes of left ventricular hypertrophy

AIMS

Fabry disease may be difficult to differentiate from other causes of left ventricular hypertrophy such as other myocardial storage diseases (including amyloidosis), hypertrophic cardiomyopathy (HCM), or hypertensive heart disease (HHD). We sought to determine simple criteria to best differentiate the above mentioned cardiac diseases.

METHODS AND RESULTS

All patients in a six-year time period with left ventricular hypertrophy due to Fabry disease (13 patients), biopsy proven cardiac amyloidosis (16 patients), non-obstructive HCM (17 patients), and 22 randomly selected patients with advanced HHD were compared. Retrospective analysis of clinical characteristics, findings of electrocardiogram (ECG) and echocardiography by blind review was performed.

RESULTS

No single clinical characteristic or findings of ECG or echocardiography could reliably differentiate between the various diseases. Increased echogenicity/granular sparkling, valvular abnormalities, abnormal renal function, and diastolic function were not helpful discriminators. In a univariate analysis, four criteria (acroparesthesia, anhydrosis, absence of hypertension and presence of Sokolow criteria for left ventricular hypertrophy in the ECG) were significant for Fabry disease. By logistic regression analysis, the following most suitable discriminative parameters were identified: hypertension in HHD (specificity 82%), orthostasis and/or pericardial effusion for amyloidosis (specificity 93%), papillary muscle anomaly in non-obstructive HCM (specificity 92%), and Fabry disease if neither hypertension orthostatis, pericardial effusion nor a papillary muscle anomaly was present (specificity 87%).

CONCLUSION

A combination of symptoms, echocardiographic findings and ECG in unexplained left ventricular hypertrophy may help to differentiate amyloidosis, non-obstructive HCM and hypertensive heart disease from Fabry disease. The results of this preliminary study will have to be confirmed in a prospective study.

Corrected QT variability in serial electrocardiograms in long QT syndrome: the importance of the maximum corrected QT for risk stratification

OBJECTIVES

We evaluated the incremental prognostic information provided by multiple corrected QT (QTc) measurements on serial electrocardiograms (ECGs) in patients with the inherited long QT syndrome (LQTS).

BACKGROUND

A baseline QTc of > or =500 ms has been shown to be associated with increased risk of cardiac events among LQTS patients. However, the value of QTc measurements on follow-up ECGs in risk assessment has not been determined.

METHODS

The risk of a first LQTS-related cardiac event during adolescence was assessed in 375 patients enrolled in the International LQTS Registry for whom serial follow-up ECGs were recorded before age 10.

RESULTS

The mean +/- SD difference between the minimum and maximum QTc values on serial ECGs recorded in study patients was 47 +/- 40 ms. The maximum QTc interval recorded before age 10 was the strongest predictor of cardiac events during adolescence (adjusted hazard ratio [HR] = 2.74; p < 0.001). Other follow-up QTc measures, including the baseline, the mean, and the most recent QTc interval recorded before age 10, were less significant risk factors. After adjusting for the maximum QTc value during follow-up, no significant association remained between the baseline QTc value and the risk of subsequent cardiac events (HR = 1.04; p = 0.91).

CONCLUSIONS

In LQTS patients, there is a considerable variability in QTc measures in serial follow-up ECGs. The maximum QTc interval provides incremental prognostic information beyond the baseline measurement. We suggest that risk stratification in LQTS patients should include follow-up ECG data.

Differential effects of anesthetics on electrical properties of the rainbow trout (Oncorhynchus mykiss) heart

We compared electrocardiographic signals in hatchery-reared, non-spinally-transected, immature rainbow trout (Oncorhynchus mykiss Walbaum) under clove oil (25 ppm), tricaine methanesulfonate (tricaine, 60 ppm), and benzocaine (108 ppm) general anesthesia (35 min, 14 degrees C). For all 3 anesthetics, the mean heart rate (HR) and QRS amplitude did not differ, and QRS duration and QT interval were independent of HR. Heart rate variability (HRV) was significantly (4-fold, P=0.032) higher under benzocaine than under clove oil and tricaine, but did not differ between clove oil and tricaine. QRS duration differed between groups (P<0.001, F=121); benzocaine anesthesia resulted in longer QRS complexes compared to clove oil (P<0.001) and tricaine (P<0.001) anesthesia, and QRS complexes under clove oil were longer than those under tricaine (P<0.001). High HRV and QRS amplitude variation with benzocaine were associated with HR oscillations as anesthetic exposure time increased, and suggest benzocaine toxicity which may influence cardiac function studies. Similar clove oil and tricaine ECG patterns suggest comparable autonomic effects, and maintenance of myocardial excitability. Given its low cost, ease of use, and similar ECG profiles to tricaine, clove oil is a viable alternative for studies of cardiac function in anesthetized rainbow trout.

Double-blind, double-dummy, multinational, multicenter, parallel-group design clinical trial of clinical non-inferiority of formoterol 12 microg/unit dose in a b.i.d. regimen administered via an HFA-propellant-pMDI or a dry powder inhaler in a 12-week treatment period of moderate to severe stable persistent asthma in adult patients

BACKGROUND

Pressurized metered-dose inhalers (pMDIs) have traditionally used CFCs as propellants. However, the worldwide phase-out of CFCs has necessitated the development of new pMDIs that use alternative propellants. One such replacement is the hydrofluoroalkane HFA-134a.

OBJECTIVES

This study sought to establish the clinical non-inferiority of a new HFA-134a-containing pMDI to a conventional dry powder inhaler (DPI) in the administration of formoterol to adult patients with moderate-to-severe, stable persistent asthma. The secondary aim was to collect safety data in a multiple-dose long-term study.

METHODS

During this multicenter, double-blind, parallel study, 500 patients were randomized to receive 12 microg of formoterol twice daily for 12 weeks via either an HFA pMDI or a DPI. If necessary, the dose could be increased to 24 microg twice daily. At baseline, all patients (aged 18-70 years) had an FEV1 40-80% of predicted and a documented positive response to the reversibility test.

RESULTS

After 12 weeks' therapy, the adjusted mean morning PEFR was 343.69 l/min in the formoterol HFA pMDI group and 344.56 l/min in the formoterol DPI group. Because the lower limit of the 95% CI for the between-group difference (-11.64 l/min) was well within the non-inferiority margin (-20 l/min), the HFA device was deemed clinically non-inferior to the DPI device. This finding was confirmed when evening PEFR and FEV1 were assessed. Both formulations of formoterol were well tolerated during prolonged multiple dosing.

CONCLUSIONS

This study provides evidence that the new HFA-formulated formoterol pMDI has a similar efficacy and safety profile to the conventional formoterol DPI in the treatment of patients with moderate-to-severe asthma.

The Combined Use of Ibutilide as an Active Control With Intensive Electrocardiographic Sampling and Signal Averaging as a Sensitive Method to Assess the Effects of Tadalafil on the Human QT Interval

OBJECTIVES

This study was designed to evaluate effects of tadalafil, a phosphodiesterase-5 inhibitor used for the treatment of erectile dysfunction (ED), on the QT interval.

BACKGROUND

Cardiovascular disease is common in men with ED. Men with cardiovascular disease and ED may have decreased cardiac repolarization reserve.

METHODS

Effects of tadalafil (100 mg by mouth), ibutilide (0.002 mg/kg intravenously), and placebo on the QT interval in healthy men were compared (placebo and tadalafil [n = 90], with a subset [n = 61] receiving all treatments; mean age 30 years, range 18 to 53 years). Electrocardiographic sampling was done for two days before treatment and on treatment days. The QT was corrected for RR interval with five correction methods, including an individual correction (QTcI). Plasma concentrations of tadalafil were measured to evaluate concentration-QT effect relationships.

RESULTS

At the time corresponding to maximum plasma concentration of tadalafil, the mean difference in the change in QTcI between tadalafil and placebo was 2.8 ms; tadalafil was equivalent to placebo (a priori, upper limit of 90% confidence interval < 10 ms [actual = 4.4 ms]; post hoc, upper limit of 95% confidence interval < 5 ms [actual = 4.8]). The active control, ibutilide, significantly increased QTcI by 6.9 and 8.9 ms compared with tadalafil and placebo, respectively. Similar statistical results were obtained with four additional QT correction methods. No subject had a QTcI > or = 450 ms or an increase in QTcI > or = 30 ms with any treatment.

CONCLUSIONS

Based on the a priori statistical test of equivalence, placebo and high-dose tadalafil produced equivalent effects on the QT interval. This study reliably discerned 5- to 10-ms changes in corrected QT in the ibutilide active control group.

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.

QTc interval and QTc dispersion during haemodiafiltration

BACKGROUND AND AIM

Our aim was to evaluate QTc interval and QTc dispersion in 27 end-stage renal disease (ESRD) patients undergoing Acetate Free Biofiltration (AFB) in order to ascertain any correlations between the electrrocardiographic (ECG) parameters, serum Na+, K+, Ca++, Mg++ and intraerythrocytic Mg++ (Mg++e) concentrations. All measures were made at t0 (session beginning), t1 (first hour), t2 (second hour), t3 (third hour), and t4 (session end).

RESULTS

Blood pressure, heart rate, bodyweight and total ultrafiltration in the three dialysis sessions were constant. A significant progressive increase occurred in serum Ca++ during the sessions, while there was a significant diminution in serum K+. The pattern for Mg++ concentrations in serum and erythrocytes differed: in serum it decreased, whereas Mg++e increased. At t4, the QTc interval was reduced to a significant extent with respect to the baseline value. QTc dispersion significantly increased at t1 without there being significant variations at other times with respect to t0. At t2, t3 and t4, values promptly returned to baseline levels. QTc had a negative correlation with serum Ca++ levels at t4. In contrast, an inverse correlation was found between QTc dispersion and serum K+ at t1. No other correlations could be found between any other electrolytes, QTc interval or QTc dispersion.

CONCLUSION

In conclusion, the decrease observed in the QTc interval at the end of an AFB session was inversely related to serum Ca++ concentrations. Moreover, an increase in QTc dispersion occurred during the first hour of the session, and was negatively correlated with serum K+.

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.

Preoperative Electrocardiographic Risk Assessment of Atrial Fibrillation After Coronary Artery Bypass Grafting

INTRODUCTION

This study evaluated the role of surface ECG in assessment of risk of new-onset atrial fibrillation (AF) after coronary artery bypass grafting surgery (CABG).

METHODS AND RESULTS

One hundred fifty-one patients (126 men and 25 women; age 65 +/- 10 years) without a history of AF undergoing primary elective and isolated CABG were studied. Standard 12-lead ECGs and P wave signal-averaged ECG (PSAE) were recorded 24 hours before CABG using a MAC VU ECG recorder. In addition to routine ECG measurements, two P wave (P wave complexity ratio [pCR]; P wave morphology dispersion [PMD]) and six T wave morphology descriptors (total cosine R to T [TCRT]; T wave morphology dispersion of ascending and descending part of the T wave [aTMD and dTMD], and others), and three PSAE indices (filtered P wave duration [PD]; root mean square voltage of terminal 20 msec of averaged P wave [RMS20]; and integral of P wave [Pi]) were investigated. During a mean hospital stay of 7.3 +/- 6.2 days after CABG, 40 (26%) patients developed AF (AF group) and 111 remained AF-free (no AF group). AF patients were older (69 +/- 9 years vs 64 +/- 10 years, P = 0.005). PD (135 +/- 9 msec vs 133 +/- 12 msec, P = NS) and RMS20 (4.5 +/- 1.7 microV vs 4.0 +/- 1.6 microV, P = NS) in AF were similar to that in no AF, whereas Pi was significantly increased in AF (757 +/- 230 microVmsec vs 659 +/- 206 microVmsec, P = 0.007). Both pCR (32 +/- 11 vs 27 +/- 10) and PMD (31.5 +/- 14.0 vs 26.4 +/- 12.3) were significantly greater in AF (P = 0.012 and 0.048, respectively). TCRT (0.028 +/- 0.596 vs 0.310 +/- 0.542, P = 0.009) and dTMD (0.63 +/- 0.03 vs 0.64 +/- 0.02, P = 0.004) were significantly reduced in AF compared with no AF. Measurements of aTMD and three other T wave descriptors were similar in AF and no AF. Significant variables by univariate analysis, including advanced age (P = 0.014), impaired left ventricular function (P = 0.02), greater Pi (P = 0.012), and lower TCRT (P = 0.007) or dTMD, were entered into multiple logistic regression models. Increased Pi (P = 0.038), reduced TCRT (P = 0.040), and lower dTMD (P = 0.014) predicted AF after CABG independently. In patients <70 years, a linear combination of increased pCR and lower TCRT separated AF and no AF with a sensitivity of 74% and specificity of 62% (P = 0.005).

CONCLUSION

ECG assessment identifies patients vulnerable to AF after CABG. Combination of ECG parameters assessed preoperatively may play an important role in predicting new-onset AF after CABG.