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Related Concept Videos

Disturbances in Heart Rhythm01:29

Disturbances in Heart Rhythm

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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.
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Dysrhythmias V: Evaluating Dysrhythmias01:30

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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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ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias01:25

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Arrhythmia is a condition characterized by an irregular heart rhythm, with ECG changes that differ based on its origin and nature. The types of arrhythmias discussed below include atrial, junctional, and ventricular arrhythmias.Atrial ArrhythmiasPremature Atrial Complexes (PACs): PACs are early atrial beats caused by stress, caffeine, alcohol, electrolyte imbalances, hypoxia, hyperthyroidism, or certain medications (e.g., bronchodilators and decongestants). The ECG shows early P waves with an...
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Electrocardiogram01:29

Electrocardiogram

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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.
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Electrocardiogram Fundamentals01:28

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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
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ECG Interpretation of Rhythms01:24

ECG Interpretation of Rhythms

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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.
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Related Experiment Video

Updated: Nov 5, 2025

Evaluation of Hydration Status by Bioelectrical Impedance Vector Analysis in Patients with Ischemic Heart Disease Undergoing Exercise Stress Test
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Electrocardiographic changes associated with haematocrit variations.

G Oreto1, F Luzza, A Donato

  • 1Università di Messina, Istituto Pluridisciplinare di Clinica Medica, Italy.

European Heart Journal
|May 1, 1992
PubMed
Summary
This summary is machine-generated.

Higher hematocrit levels in blood decrease the voltage of the QRS complex on electrocardiograms. This study in thalassemia patients shows increased red blood cells after transfusion led to lower QRS voltage, impacting cardiac force transmission.

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

  • Cardiology
  • Biophysics

Background:

  • Intracardiac blood has lower electrical resistivity than surrounding tissues.
  • This difference influences cardiac force transmission to the body surface, known as the Brody effect.
  • Blood resistivity is linked to hematocrit, suggesting hematocrit changes affect electrocardiogram (ECG) voltage.

Purpose of the Study:

  • To investigate the hypothesis that changes in hematocrit affect cardiac force transmission, altering QRS complex voltage.
  • To assess the relationship between hematocrit levels and QRS voltage in patients with thalassemia.

Main Methods:

  • A 12-lead ECG was recorded in 40 thalassemia patients before and after red blood cell transfusion.
  • QRS component voltages were measured, and the sum of R wave amplitudes (sigma R) was calculated.
  • Correlation analysis was performed between hematocrit ratios and sigma R values.

Main Results:

  • Post-transfusion ECGs showed a significant decrease in R wave amplitude across all leads.
  • The sum of R wave amplitudes (sigma R) decreased, while S wave amplitude in lead V6 increased.
  • A negative correlation was found between the pre/post-transfusion hematocrit ratio and the corresponding sigma R values (r = -0.434; P < 0.01).

Conclusions:

  • Increased hematocrit is associated with decreased QRS R wave amplitude.
  • These findings help explain low voltage QRS complexes observed in patients with high hematocrit.
  • Hematocrit levels significantly influence the electrical manifestation of cardiac forces on the body surface.