An exponential formula for heart rate dependence of QT interval during exercise and cardiac pacing in humans: Reevaluation of Bazett's formula

Abstract Background Targeted hypothermia, as used after cardiac arrest, increases electrical and mechanical systolic duration. Differences in duration of electrical and mechanical systole are correlated to ventricular arrhythmias. The electromechanical window (EMW) becomes negative when the electrical systole outlasts the mechanical systole. Prolonged electrical systole corresponds to prolonged QT interval, and is associated with increased dispersion of repolarization and mechanical dispersion. These three factors predispose for arrhythmias. The electromechanical relations during targeted hypothermia are unknown. We wanted to explore the electromechanical relations during hypothermia at 33 °C. We hypothesized that targeted hypothermia would increase electrical and mechanical systolic duration without more profound EMW negativity, nor an increase in dispersion of repolarization and mechanical dispersion. Methods In a porcine model (n = 14), we registered electrocardiogram (ECG) and echocardiographic recordings during 38 °C and 33 °C, at spontaneous and atrial paced heart rate 100 beats/min. EMW was calculated by subtracting electrical systole; QT interval, from the corresponding mechanical systole; QRS onset to aortic valve closure. Dispersion of repolarization was measured as time from peak to end of the ECG T wave. Mechanical dispersion was calculated by strain echocardiography as standard deviation of time to peak strain. Results Electrical systole increased during hypothermia at spontaneous heart rate (p < 0.001) and heart rate 100 beats/min (p = 0.005). Mechanical systolic duration was prolonged and outlasted electrical systole independently of heart rate (p < 0.001). EMW changed from negative to positive value (− 20 ± 19 to 27 ± 34 ms, p = 0.001). The positivity was even more pronounced at heart rate 100 beats/min (− 25 ± 26 to 41 ± 18 ms, p < 0.001). Dispersion of repolarization decreased (p = 0.027 and p = 0.003), while mechanical dispersion did not differ (p = 0.078 and p = 0.297). Conclusion Targeted hypothermia increased electrical and mechanical systolic duration, the electromechanical window became positive, dispersion of repolarization was slightly reduced and mechanical dispersion was unchanged. These alterations may have clinical importance. Further clinical studies are required to clarify whether corresponding electromechanical alterations are accommodating in humans.

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Electrocardiographic characteristics and associated outcomes in patients with Takotsubo syndrome. Insights from the RETAKO registry

European Heart Journal ◽

10.1093/ehjci/ehaa946.1816 ◽

2020 ◽

Vol 41 (Supplement_2) ◽

Author(s):

I Martin-Demiguel ◽

I Nunez-Gil ◽

A Perez-Castellanos ◽

O Vedia ◽

A Uribarri ◽

...

Keyword(s):

Heart Rate ◽

Primary Endpoint ◽

Qt Interval ◽

Protective Factor ◽

Independent Predictor ◽

Prognostic Significance ◽

Takotsubo Syndrome ◽

St Segment Elevation ◽

Corrected Qt Interval ◽

St Segment

Abstract Background Our aim was to describe the prevalence and prognostic significance of electrocardiographic features in patients with Takotsubo syndrome (TTS). Methods Our data come from the Spanish Multicenter REgistry of TAKOtsubo syndrome (RETAKO). All patients with complete electrocardiogram were included. Results 246 patients were studied, mean age was 71.3±11.5 and 215 (87.4%) were women. ST-segment elevation was seen in 143 patients (59.1%) and was present in ≥2 wall leads in 97 (39.8%). Exclusive elevation in inferior leads was infrequent (5 - 2.0%). After 48 hours, 198 patients (88.0%) developed negative T-waves in a median of 8 leads with a mean amplitude of 0.7±0.5 mV. Mean corrected QT interval was 520±72 ms and it was independently associated with the primary endpoint of all-cause death and nonfatal cardiovascular events (p=0.002) and all-cause death (p=0.008). A higher heart rate at admission was also an independent predictor of the primary endpoint (p=0.001) and of developing acute pulmonary edema (p=0.04). ST-segment elevation with reciprocal depression was an independent predictor of all-cause death (p=0.04). Absence of ST-segment deviation was a protective factor (p=0.005) for the primary endpoint. Arrhythmias were independently associated with cardiogenic shock (p<0.001). Conclusion Prolonged corrected QT interval, arrhythmia, heart rate at admission and broader repolarization alterations are associated with a poor outcome in TTS. Typical ECG at admission and after 48h. Funding Acknowledgement Type of funding source: None

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Safety and effectiveness of drug therapy for the acutely agitated patient (Part I)

Italian Journal of Medicine ◽

10.4081/itjm.2010.127 ◽

2013 ◽

pp. 127-136

Author(s):

Gianluca Airoldi

Keyword(s):

Heart Rate ◽

Qt Interval ◽

Physical Restraint ◽

Safety Data ◽

Surrogate Marker ◽

Diagnostic Procedures ◽

Torsades De Pointes ◽

Long Qt ◽

Drug Induced ◽

Qt Interval Prolongation

Acute agitation occurs in a variety of medical and psychiatric conditions, and the management of agitated, abusive, or violent patients is a common problem in the emergency department. Rapid control of potentially dangerous behaviors by physical restraint and pharmacologic tranquillization is crucial to ensure the safety of the patient and health-care personnel and to allow diagnostic procedures and treatment of the underlying condition. The purpose of this article (the first in a 2-part series) is to review the extensive safety data published on the antipsychotic medications currently available for managing situations of this type, including older neuroleptics like haloperidol, chlorpromazine, and pimozide as well as a number of the newer atypical antipsychotics (olanzapine, risperidone, ziprasidone). Particular attention is focused on the ability of these drugs to lengthen the QT interval in surface electrocardiograms. This adverse effect is of major concern, especially in light of the reported relation between QT interval and the risk of sudden death. In patients with the congenital long-QT syndrome, a long QT interval is associated with a fatal paroxysmal ventricular arrhythmia knownas torsades de pointes. Therefore, careful evaluation of the QT-prolonging properties and arrhythmogenic potential of antipsychotic drugs is urgently needed. Clinical assessment of drug-induced QT-interval prolongation is strictly dependent on the quality of electrocardiographic data and the appropriateness of electrocardiographic analyses. Unfortunately, measurement imprecision and natural variability preclude a simple use of the actually measured QT interval as a surrogate marker of drug-induced proarrhythmia. Because the QT interval changes with heart rate, a rate-corrected QT interval (QTc) is commonly used when evaluating a drug’s effect. In clinical settings, themost widely used formulas for rate-correction are those of Bazett (QTc=QT/RR^0.5) and Fridericia (QTc=QT/RR^0.33), both of which standardize themeasuredQTinterval to an RRinterval of 1 s (heart rate of 60 bpm).However, QT variability can also be influenced by other factors that are more difficult to measure, including body fat, meals, psycho-physical distress, and circadian and seasonal fluctuations.

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Computational Analysis of Coronary Blood Flow: The Role of Asynchronous Pacing and Arrhythmias

Mathematics ◽

10.3390/math8081205 ◽

2020 ◽

Vol 8 (8) ◽

pp. 1205

Author(s):

Timur Gamilov ◽

Philipp Kopylov ◽

Maria Serova ◽

Roman Syunyaev ◽

Andrey Pikunov ◽

...

Keyword(s):

Heart Rate ◽

Blood Flow ◽

Coronary Blood Flow ◽

Long Qt Syndrome ◽

Premature Ventricular Contraction ◽

Cardiac Pacing ◽

Long Qt ◽

Computational Evaluation ◽

Qt Syndrome

In this work we present a one-dimensional (1D) mathematical model of the coronary circulation and use it to study the effects of arrhythmias on coronary blood flow (CBF). Hydrodynamical models are rarely used to study arrhythmias’ effects on CBF. Our model accounts for action potential duration, which updates the length of systole depending on the heart rate. It also includes dependency of stroke volume on heart rate, which is based on clinical data. We apply the new methodology to the computational evaluation of CBF during interventricular asynchrony due to cardiac pacing and some types of arrhythmias including tachycardia, bradycardia, long QT syndrome and premature ventricular contraction (bigeminy, trigeminy, quadrigeminy). We find that CBF can be significantly affected by arrhythmias. CBF at rest (60 bpm) is 26% lower in LCA and 22% lower in RCA for long QT syndrome. During bigeminy, trigeminy and quadrigeminy, respectively, CBF decreases by 28%, 19% and 14% with respect to a healthy case.

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Relation between heart rate and QT interval in exercise-induced myocardial ischemia

The American Journal of Cardiology ◽

10.1016/0002-9149(85)90770-2 ◽

1985 ◽

Vol 56 (13) ◽

pp. 861-862 ◽

Cited By ~ 25

Author(s):

Massimo Romano ◽

Teresa Di Maro ◽

Giovanni Carella ◽

Maria Rosaria Cotecchia ◽

Giuseppe Ferro ◽

...

Keyword(s):

Heart Rate ◽

Myocardial Ischemia ◽

Qt Interval ◽

Exercise Induced

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Mechanisms Underlying QT Interval Adaptation Behind Heart Rate During Stress Test

10.23919/cinc53138.2021.9662880 ◽

2021 ◽

Author(s):

Ruben Cebollada ◽

Cristina Perez ◽

Konstantinos A Mountris ◽

Juan Pablo Martinez ◽

Pablo Laguna ◽

...

Keyword(s):

Heart Rate ◽

Qt Interval ◽

Stress Test

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Abstract 17288: Risk Prediction of 10-Year Cardiovascular Mortality Using Automated Electrocardiographic Analysis in the National Health and Nutrition Examination Survey

Circulation ◽

10.1161/circ.130.suppl_2.17288 ◽

2014 ◽

Vol 130 (suppl_2) ◽

Author(s):

Amit J Shah ◽

Cecile Janssens ◽

Suman Kundu ◽

Emir Veledar ◽

Peter Wilson ◽

...

Keyword(s):

Heart Rate ◽

Risk Prediction ◽

Risk Score ◽

Qt Interval ◽

Validation Cohort ◽

Risk Scores ◽

Older Individuals ◽

Traditional Risk Factors ◽

Ecg Score ◽

Cvd Mortality

Introduction: Several individual ECG parameters are predictive of cardiovascular disease (CVD) mortality, and when combined in a score, may improve risk prediction. Hypothesis: We hypothesized that an ECG risk score (based on automated measures available on many modern ECG machines) can effectively predict CVD mortality, and augment risk classification when added to traditional risk factors (TRF). Methods: We examined 6786 individuals aged 40-79 years without known CVD in NHANES III (1988-1994) followed 10 years for CVD mortality. Six pre-specified ECG variables (“ECG model”), were evaluated including P, R, T axes, QT interval, QRS width, and heart rate. Three risk scores were developed for variables containing: 1) TRF only, 2) ECG factors (including age, sex, and race), and 3) TRF+ECG combined. Validation was performed using a cohort aged 40-74 years from NHANES I (n=3773), enrolled in 1971-1974. Age stratification was performed with cutoff of 65 years because of increased competing risks in older individuals. Results: During 10 years of follow up, 384 CVD deaths occurred. Frontal QRS-T angle, T-axis, wide QRS interval (cutoff 120 ms), heart rate-corrected QT interval, and heart rate were found to be significant predictors (p<0.05) of CVD death. As per the table, the ECG score had similar performance compared to the TRF score for the subgroup < 65 years of age in the derivation and validation cohorts. The score with combined ECG + TRF had the best performance for those aged < 65 years, and resulted in a net reclassification index of 9% in the validation cohort using cutoffs of 7.5% and 20% for low, intermediate, and high risk categories. In those aged ≥ 65 years, the combined score showed improvement vs. the TRF score in the derivation, but not validation cohort. Conclusion: A risk score based on routinely reported automated ECG variables and TRF predicts risk of 10-year CVD death better than TRF alone in a cohort age < 65 years without known CVD.

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