An electrocardiogram (ECG or EKG) is a diagnostic test that records the electrical activity of the heart over a specific period. The resulting graph, known as an electrocardiogram, displays the heart’s rhythm and can provide important information about the heart’s health. Here are the key aspects of an ECG:

1. Electrode Placement:
   • Small adhesive electrodes are placed on the skin at specific locations, typically on the chest, arms, and legs. These electrodes detect the electrical signals generated by the heart.
2. Lead Systems:
   • The electrodes are connected to the ECG machine, which records the electrical impulses from different angles. Different lead systems, such as the standard 12-lead ECG, provide various perspectives on the heart’s activity.
3. Recording the Heart’s Activity:
   • The ECG machine records the electrical signals as waves on a paper or digital display. The waves represent different phases of the cardiac cycle.
4. Standard 12-Lead ECG:
   • The standard 12-lead ECG involves recording electrical signals from 12 different perspectives, providing a comprehensive view of the heart’s activity. These leads include limb leads (I, II, III, AVL, AVR, AVF) and precordial leads (V1-V6).
5. Clinical Applications:
   • Diagnosis of Arrhythmias: ECGs help diagnose irregular heart rhythms.
   • Ischemia and Infarction: Changes in the ST segment can indicate myocardial ischemia or infarction.
   • Conduction Abnormalities: ECGs can identify disturbances in the electrical conduction system of the heart.
   • Monitoring:
     • Continuous ECG monitoring is used in critical care settings.
     • Holter monitors record ECG data over an extended period for ambulatory monitoring.

6. Exercise Stress Testing:
   • ECG is often used during exercise stress tests to assess how the heart responds to physical activity and to detect any abnormalities in blood flow to the heart.
7. Ambulatory ECG Monitoring (Holter Monitoring):
   • ECG is recorded continuously over an extended period, usually 24 to 48 hours, using a portable device known as a Holter monitor.

ECGs are crucial in diagnosing a variety of cardiac conditions and are widely used in clinical practice. Interpretation of an ECG requires expertise, typically provided by healthcare professionals, especially cardiologists. It plays a vital role in routine check-ups, emergency situations, and ongoing cardiac care.