Electrocardiogram — Core Principles

Core Principles

The Electrocardiogram (ECG or EKG) is a non-invasive diagnostic test that records the electrical activity of the heart over time. It works by detecting the tiny electrical impulses generated by the heart's specialized conduction system (SA node, AV node, Bundle of His, Purkinje fibers) as they spread through the cardiac muscle, causing depolarization and repolarization.

The resulting graphical tracing displays characteristic waves and segments: the P wave signifies atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave indicates ventricular repolarization.

The PR interval measures conduction time from atria to ventricles, and the ST segment reflects the plateau phase of ventricular action potentials. By analyzing the rate, rhythm, and morphology of these waveforms, clinicians can diagnose a wide range of cardiac conditions, including arrhythmias, myocardial ischemia, and hypertrophy, making it a fundamental tool in cardiovascular assessment.

Important Differences

vs Echocardiogram

Aspect	This Topic	Echocardiogram
Nature of Test	Electrocardiogram (ECG)	Echocardiogram
What it Measures	Electrical activity of the heart (depolarization and repolarization waves).	Physical structure, movement, and blood flow within the heart using sound waves.
Information Provided	Heart rate, rhythm, electrical conduction pathways, signs of ischemia/infarction, chamber enlargement (indirectly).	Heart chamber size, valve function, pumping strength (ejection fraction), presence of fluid around the heart, congenital defects, blood clot detection.
Technology Used	Electrodes placed on the skin detect electrical potential differences.	Ultrasound transducer emits and receives high-frequency sound waves.
Primary Use Cases	Diagnosing arrhythmias, heart attacks, conduction blocks, electrolyte imbalances.	Assessing heart valve disease, heart failure, congenital heart disease, pericardial effusion, cardiac masses.

While both ECG and Echocardiogram are non-invasive cardiac diagnostic tools, they provide fundamentally different types of information. An ECG is like an 'electrical map' of the heart, tracing the impulses that drive each beat, crucial for understanding rhythm and electrical health. An Echocardiogram, conversely, is a 'structural and functional movie' of the heart, using sound waves to visualize its chambers, valves, and blood flow dynamics. ECG detects electrical problems, while echo detects mechanical and structural issues. Often, both tests are used in conjunction to get a comprehensive picture of cardiac health.