The medical term for the electrical activity of the heart is electrocardiography, and the recording or graphical representation of this activity is called an electrocardiogram (ECG or EKG). The heart's electrical system controls the rhythm and rate of heartbeats, ensuring that the heart pumps blood effectively throughout the body.

How the Heart's Electrical System Works

The heart's electrical activity begins in the sinoatrial (SA) node, often referred to as the heart's natural pacemaker. The SA node is located in the right atrium and generates electrical impulses that initiate each heartbeat. These impulses spread through the atria, causing them to contract and push blood into the ventricles.

The electrical signal then travels to the atrioventricular (AV) node, located between the atria and ventricles. The AV node acts as a gatekeeper, slowing down the electrical impulse to allow the ventricles time to fill with blood. From there, the signal moves through the bundle of His, which divides into the right and left bundle branches, and finally into the Purkinje fibers. These fibers distribute the electrical impulse throughout the ventricles, causing them to contract and pump blood to the lungs and the rest of the body.

The Electrocardiogram (ECG/EKG)

An electrocardiogram is a non-invasive test that records the heart's electrical activity over a period of time. It is performed using electrodes placed on the skin, typically on the chest, arms, and legs. The ECG machine detects and amplifies the tiny electrical changes on the skin caused by the heart muscle depolarizing during each heartbeat.

The ECG produces a series of waves and intervals that correspond to specific electrical events in the heart:

1. P wave: Represents atrial depolarization (contraction of the atria).
2. QRS complex: Represents ventricular depolarization (contraction of the ventricles).
3. T wave: Represents ventricular repolarization (recovery of the ventricles).

The ECG also measures intervals such as the PR interval, QRS duration, and QT interval, which provide information about the timing and coordination of the heart's electrical activity.

Clinical Significance

The ECG is a critical diagnostic tool in cardiology. It can help identify:

• Arrhythmias: Abnormal heart rhythms, such as atrial fibrillation, bradycardia, or tachycardia.
• Ischemia or infarction: Reduced blood flow to the heart muscle, often due to coronary artery disease.
• Structural abnormalities: Enlargement of the heart chambers or thickening of the heart muscle.
• Electrolyte imbalances: Abnormal levels of potassium, calcium, or magnesium, which can affect the heart's electrical activity.
• Medication effects: Certain drugs can alter the heart's electrical conduction.

Types of ECGs

1. Resting ECG: Performed while the patient is lying down and relaxed.
2. Stress ECG (Exercise ECG): Conducted while the patient exercises on a treadmill or stationary bike to assess the heart's response to physical stress.
3. Holter Monitor: A portable device worn for 24–48 hours to record continuous ECG data during daily activities.
4. Event Monitor: Similar to a Holter monitor but used for longer periods to capture intermittent symptoms.

Limitations of ECG

While the ECG is a valuable tool, it has limitations. It provides only a snapshot of the heart's electrical activity at the time of the test. Some conditions, such as intermittent arrhythmias, may not be detected during a standard ECG. In such cases, additional monitoring or diagnostic tests may be required.

In summary, the electrical activity of the heart is a complex and precisely coordinated process that ensures efficient blood circulation. The ECG is a fundamental tool for assessing this activity and diagnosing a wide range of cardiac conditions. Understanding the heart's electrical system and its representation on an ECG is essential for healthcare professionals in managing heart health.