Electrocardiogram (ECG)

Overview

An electrocardiogram (ECG) is a medical test that records the electrical activity of the heart. It involves placing electrodes on the chest, arms, and legs to measure the electrical signals produced during each heartbeat. ECGs are commonly used to assess heart health, diagnose heart conditions such as arrhythmias and heart attacks, and monitor the effectiveness of cardiac treatments. The test provides valuable information about the heart’s rhythm, rate, and overall electrical activity. It is a non-invasive procedure that is quick, painless, and widely available in medical settings, making it a valuable tool for cardiovascular assessment and diagnosis.

Introduction

• The electrocardiogram (ECG) records the flow of electrical impulses throughout the heart
• Electrical currents flow from negatively charged areas to positively charged areas
  • depolarization currents flowing towards a positive electrode will lead to an upward deflection seen in the ECG reading 
  • repolarization currents flowing away from the positive electrode will lead to a downward deflection seen in the ECG reading 
  • the ECG records the sum of the electrical forces that flow through the heart
    • the ECG deflections depend on how these electrical forces align to a specific ECG lead 
• e.g., lead aVR, a right-arm electrode, will demonstrate a positive deflection when electrical activity points towards the right arm 

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ECG Lead Reference

• There are 6 limb leads and 6 chest lead, which comprise the 12-lead ECG
  • limb leads 
    • aVR, aVL, and aVF
    • I, II, III
    • the limb leads read electrical forces in the frontal view
  • chest (precordial) leads 
    • V1-V6
• the precordial leads read electrical forces in the perpendicular plane

Conduction Pathway

• Depolarization normally begins at the sinoatrial (SA) node 
  • the SA node is located at the junction of the superior vena cava and right atrium
• Depolarization from the SA node spreads to the right and left atria
• After the right and left atria, the wave of depolarization reaches the atrioventricular (AV) node
  • there is an expected delay in the transmission of depolarization to the ventricles at the AV node
• The impulse then goes to the bundle of His and then the right and left Purkinje fibers
• Pacemaker rates
  • SA > AV > bundle of His/Purkinje/ventricles
• Speed of transmission
  • bundle of His = Purkinje fibers > atria > ventricles > AV node

Treatment

Electrocardiogram (ECG) is a diagnostic test and does not involve direct treatment. It is a tool used by healthcare professionals to assess the electrical activity of the heart and diagnose various heart conditions. The results of an ECG can guide treatment decisions, but the actual treatment will depend on the specific heart condition or issue identified. Treatment options may include medication, lifestyle changes, procedures like cardiac ablation or pacemaker implantation, or surgery, depending on the underlying condition. It is important to consult with a qualified healthcare professional for appropriate diagnosis and treatment recommendations based on the ECG findings.

ECG And Conduction Pathway 

ECG Basics
ECG Finding	Information
P wave	Represents atrial depolarization
PR interval	Represents the time from the start of atrial depolarization to the start of ventricular depolarizationNormally < 200 msec
QRS complex	Represents ventricular depolarizationNormally < 120 msec
ST segment	Represents an isoelectric point in ventricular depolarizationCorrelates with phase 2 (plateau) of ventricular action potential
T wave	Represents ventricular repolarizationBecomes peaked in hyperkalemia and flattened in hypokalemia
U wave	Believed to represent ventricular repolarization but during the late phaseBecomes prominent in hypokalemia
J point	The point between the end of the QRS complex and the beginning of the ST segment

Studies

Electrocardiogram (ECG) studies involve the analysis and interpretation of the electrical activity of the heart recorded during an ECG test. These studies are performed by healthcare professionals, typically cardiologists or trained technicians, to evaluate the heart’s rhythm, rate, and overall electrical patterns.

During an ECG study, the healthcare professional examines various components of the ECG waveform, including the P wave, QRS complex, and T wave, among others. They analyze the intervals and durations of these waveforms to identify any abnormalities or irregularities that may indicate a heart condition or problem.

ECG studies can help in the diagnosis and management of various cardiac conditions, including arrhythmias (abnormal heart rhythms), myocardial infarction (heart attack), ischemia (restricted blood flow to the heart), and conduction system abnormalities.

Interpreting ECG studies requires expertise and knowledge of normal and abnormal ECG patterns. It involves identifying specific abnormalities or patterns that may indicate a particular cardiac condition and correlating them with the patient’s symptoms and medical history.

ECG studies are an essential tool in cardiology, providing valuable information to guide treatment decisions and monitor the effectiveness of interventions. They are commonly performed in hospitals, clinics, and other healthcare settings by trained professionals to assess and manage heart health.

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