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Electrocardiogram

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...

Holter Monitor: 24-Hour Monitoring

Holter Monitor: 24-Hour Monitoring

Holter monitoring is a continuous electrocardiography (ECG) recording that tracks the heart's electrical activity over an extended period, generally 24 to 48 hours. This noninvasive diagnostic tool detects irregular heart rhythms that may not be captured during a standard ECG performed in a clinical setting.DeviceThe Holter monitor is a portable, small device connected to several electrodes on the patient's chest. These electrodes detect the heart's electrical signals and transmit them to the...

Pulse rhythm

Pulse rhythm

Pulse rhythm refers to the pattern of pulsations within specific intervals, offering valuable insights into the regularity or irregularity of the heart's beats as observed through the pattern of pulsation within specific intervals. A regular pulse exhibits a consistent heart rate with uniform waveforms and pulsation force, variations of which can be classified as normal, weak, or bounding.
Conversely, an irregular pulse pattern is termed dysrhythmia, stemming from disruptions in cardiac muscle...

Electrocardiogram Fundamentals

Electrocardiogram Fundamentals

Introduction
An electrocardiogram (ECG) is a diagnostic tool for identifying cardiac conditions such as arrhythmias, conduction abnormalities, and myocardial ischemia.
Definition
An electrocardiogram (ECG) visualizes the heart's electrical activity by tracing the electrical movement associated with each heartbeat on a graph or monitor. As the heart beats, an electrical wave passes through it, correlating with the cardiac cycle events.
Parts of an ECG
An ECG utilizes electrodes on the skin to...

Cardiac Action Potential

Cardiac Action Potential

Cardiac action potentials are essential for proper heart function, enabling the rhythmic contractions needed for adequate blood circulation. Nodal cells and Purkinje fibers, specialized for electrical conduction, generate these action potentials.
The cardiac action potential process involves a series of phases characterized by the movement of ions across the cardiac cell membranes, leading to the depolarization and repolarization of the cardiac myocytes.
Ionic Basis of Cardiac Action Potentials

Dysrhythmias V: Evaluating Dysrhythmias

Dysrhythmias V: Evaluating Dysrhythmias

Dysrhythmias, also known as arrhythmias, are disturbances in the heart's rhythm that range from benign to life-threatening. A thorough evaluation is crucial for appropriate management and involves a comprehensive medical history, physical examination, and various diagnostic tests.Medical HistorySymptoms: Collect detailed information on palpitations, dizziness, syncope, chest pain, and fatigue. Note their onset, frequency, and triggers.Previous Cardiac Issues: Document any history of heart...

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Related Experiment Video

Updated: Jun 2, 2026

A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis

A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis

Published on: December 28, 2012

Sedentary long-duration head-down bed rest and ECG repolarization heterogeneity.

Chris Sakowski¹, Vito Starc, Scott M Smith

¹University of Texas Medical Branch, Galveston, TX, USA.

Aviation, Space, and Environmental Medicine

|April 13, 2011

Summary

Ninety days of head-down bed rest (HDBR) significantly increased ECG repolarization heterogeneity, indicating a potential risk for ventricular arrhythmias. These changes were reversible upon resuming ambulation.

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Area of Science:

Cardiovascular Physiology
Space Medicine
Electrocardiography

Background:

Head-down bed rest (HDBR) simulates microgravity effects on the cardiovascular system.
Previous studies noted QTc interval lengthening during spaceflight, suggesting potential repolarization abnormalities.

Purpose of the Study:

To investigate the impact of 90 days of HDBR on cardiac autonomic function and advanced electrocardiographic (ECG) parameters.
To specifically assess changes in repolarization heterogeneity using beat-to-beat QT interval variability (QTV), T-wave complexity, and 3D ECG.

Main Methods:

20 healthy subjects underwent 90 days of 6° HDBR.
High-fidelity 12-lead ECGs were recorded during controlled breathing at multiple time points.
Plasma volume and electrolytes were measured concurrently.

Main Results:

HDBR significantly increased QTV index, unexplained QTV, T-wave complexity, and spatial QRS-T angle.
Spatial ventricular gradient significantly decreased after HDBR.
These ECG changes were largely reversible after ambulation but not directly correlated with electrolyte or plasma volume changes.

Conclusions:

Long-duration HDBR reversibly increases ECG repolarization heterogeneity.
This suggests an elevated risk of ventricular arrhythmias associated with prolonged bed rest.