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Related Concept Videos

Special considerations while measuring pulse01:13

Special considerations while measuring pulse

Assessing a patient's pulse is a fundamental skill in healthcare, but certain situations require special attention:
Electrocardiogram01:29

Electrocardiogram

An electrocardiogram (ECG or EKG) is a critical diagnostic tool that records the electrical signals produced by the heart during each heartbeat. This recording is achieved through electrodes placed strategically on the arms, legs, and chest. The electrocardiograph amplifies these signals and produces 12 distinct tracings, offering a comprehensive understanding of the heart's electrical activity.
Three major waveforms are present in a typical ECG recording: the P wave, the QRS complex, and the T...
Correlation between ECG and Cardiac Cycle01:25

Correlation between ECG and Cardiac Cycle

The electrical signals recorded on an electrocardiogram (ECG) occur before the mechanical processes of contraction and relaxation during the cardiac cycle.
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...
Disturbances in Heart Rhythm01:29

Disturbances in Heart Rhythm

Arrhythmia or dysrhythmia refers to an abnormal heart rhythm caused by a defect in the heart's conduction system. It can cause the heart to beat irregularly, too quickly, or too slowly, leading to symptoms like chest pain, shortness of breath, and fainting. Factors such as stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte abnormalities can trigger arrhythmias.
Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart...
ECG Interpretation of Rhythms01:24

ECG Interpretation of Rhythms

An electrocardiogram (ECG)graphically represents the heart's electrical activity on ECG paper or a monitor.
Components of the Electrocardiogram
The primary components of a normal ECG waveform in Normal sinus rhythm(NSR) include the P wave, PR interval, QRS complex, ST segment, T wave, and occasionally a U wave.
ECG waveforms are divided by vertical and horizontal lines at standard intervals.
The horizontal axis measures time and rate, and the vertical axis measures amplitude or voltage. When...
Dysrhythmias IV: Characteristics of Bradyarrhythmias01:18

Dysrhythmias IV: Characteristics of Bradyarrhythmias

Bradyarrhythmias are cardiac rhythm disorders characterized by a slower-than-normal heart rate, typically defined as fewer than 60 beats per minute. Some of which are discussed here:Sinus BradycardiaSinus bradycardia presents a heart rate lower than 60 beats per minute, with a regular rhythm originating from the SA node. The ECG typically shows normal P waves preceding each QRS complex, a normal PR interval (0.12 to 0.20 seconds), and a normal QRS duration (0.06 to 0.10 seconds).First-Degree AV...

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Related Experiment Video

Updated: Jul 16, 2026

Methods for ECG Evaluation of Indicators of Cardiac Risk, and Susceptibility to Aconitine-induced Arrhythmias in Rats Following Status Epilepticus
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Significant difference in beat-to-beat QT interval variability among different leads.

Vikram Kumar Yeragani1, Manuel E Tancer, Debra Glitz

  • 1Department of Psychiatry, Wayne State University School of Medicine, Detroit, Michigan, USA. vikramyershr@yahoo.com

Heart Disease (Hagerstown, Md.)
|November 21, 2002
PubMed
Summary

QT interval variability differs significantly between ECG leads, impacting cardiac mortality risk assessment. Consistent lead selection is crucial for accurate QT variability calculations in sudden cardiac death prediction.

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Area of Science:

  • Cardiology
  • Electrophysiology
  • Medical Instrumentation

Background:

  • QT interval on ECG reflects cardiac repolarization; prolonged QTc is linked to sudden cardiac death.
  • Increased QT dispersion between ECG leads correlates with higher cardiac mortality risk.
  • Beat-to-beat QT interval variability, influenced by the autonomic nervous system, predicts sudden cardiac death.

Purpose of the Study:

  • To investigate significant differences between QT variability (QTv) and QT interval variability index (QTvi) measures.
  • To assess the impact of lead configuration on QT variability calculations.
  • To evaluate the implications for local versus global cardiac repolarization assessment.

Main Methods:

  • Analysis of 17 continuous ECG datasets from ambulatory monitoring.
  • ECG data digitized at 1,000 Hz across three channels (leads V(5), V(1), and V(3)).
  • Calculation and comparison of detrended QT variance (QTv) and QTvi.

Main Results:

  • A highly significant difference (P < 0.0001) was found between QTv and QTvi measures.
  • This difference was observed in two of the three lead configurations (V(5) and V(1) vs. V(3)).
  • Findings suggest lead-dependent variations in QT variability quantification.

Conclusions:

  • The choice of ECG lead is critical for consistent QT variability calculations.
  • Further research is needed to definitively establish conclusions.
  • Results highlight the importance of considering lead selection in QT variability studies for cardiac risk assessment.