An electrocardiogram (ECG or EKG) is a diagnostic tool that records the heart's electrical activity, providing vital information about heart rate, rhythm, conduction pathways, and overall cardiac function.

By capturing the electrical impulses that trigger heart contractions, the ECG translates complex bioelectrical signals into a visual waveform pattern on a graph.

The Electrical Activity of the Heart

The heart relies on a coordinated electrical system to contract and pump blood effectively. This process begins in the sinoatrial (SA) node, a cluster of specialized pacemaker cells located in the upper right atrium. The SA node generates rhythmic electrical impulses that propagate through atrial muscle tissue, causing atrial contraction.

Electrocardiogram: Capturing Surface Electrical Potentials

As the heart produces electrical impulses, tiny voltage changes occur on the skin's surface. Since the body's tissues conduct electricity to a degree, electrodes placed on the limbs and chest capture these voltage fluctuations from multiple perspectives, termed leads.

A standard 12-lead ECG uses ten electrodes to measure the heart's electrical potentials from twelve different angles, providing comprehensive information about the heart's electrical conduction system and muscular activity. The varying voltage recordings are plotted over time to form the characteristic ECG waveform.

Interpreting the Key Waves and Complexes

The ECG waveform consists of several distinct components that correspond to specific electrical activities within the heart:

- The P wave represents atrial depolarization, indicating electrical activation spreading through atrial muscle, preparing it to contract.

- The QRS complex reflects ventricular depolarization, a rapid process where ventricular muscle fibers receive the electrical stimulus to contract, pumping blood to the lungs and body.

- The T wave corresponds to ventricular repolarization, when ventricular muscle cells recover electrically, preparing for the next contraction.

These components appear in a defined sequence and duration, reflecting normal cardiac electrical function. Deviations in wave shape, timing, or amplitude can signify conduction abnormalities, arrhythmias, ischemia, or electrolyte disturbances.

Clinical Applications of ECG Monitoring

ECG monitoring serves multiple critical roles in clinical practice. It allows healthcare providers to measure heart rate and rhythm, detect arrhythmias such as atrial fibrillation or ventricular tachycardia, and identify signs of myocardial ischemia or infarction through changes in the ST segment or T wave morphology.

Continuous ambulatory ECG monitoring systems, like Holter monitors or event recorders, extend evaluation beyond the brief snapshot of a standard ECG. These devices record electrical activity over extended periods, capturing intermittent or transient abnormalities that may elude detection during routine exams.

Advanced ECG interpretations also assist in diagnosing electrolyte imbalances, drug effects on cardiac conduction, and the functioning of implanted devices like pacemakers.

Dr. Alaa Alahmadi states "An ECG is a window into the activity of the human heart and is used widely in clinical practice, mostly in hospitals."

An electrocardiogram monitors the heart by detecting and graphing its electrical impulses as they initiate and coordinate contractions. By translating these signals into waveform patterns, the ECG reveals crucial information about cardiac status, rhythm, and potential abnormalities.

Through both standard and prolonged monitoring, it provides indispensable diagnostic and surveillance capabilities that aid in ensuring cardiovascular health and guiding therapeutic interventions.