Ectopic foci

An overview of ectopic foci in cardiac physiology

Ectopic foci are abnormal pacemaker sites within the heart that can cause irregular heart rhythms. These sites are not the primary pacemaker of the heart, the sinoatrial node, but can initiate impulses that lead to premature heartbeats or arrhythmias. Understanding ectopic foci is crucial for diagnosing and treating various cardiac conditions.

Physiology

In a healthy heart, the sinoatrial node (SA node) is the primary pacemaker, generating electrical impulses that travel through the atrioventricular node (AV node) and the His-Purkinje system to coordinate the contraction of the heart muscle. However, under certain conditions, other cells in the heart can become pacemakers, creating ectopic foci.

Ectopic foci can occur in the atria, ventricles, or the atrioventricular junction. These foci can generate impulses due to increased automaticity, triggered activity, or reentry mechanisms.

Increased Automaticity

Increased automaticity occurs when cardiac cells outside the SA node spontaneously depolarize at a faster rate than normal. This can be due to changes in the resting membrane potential or alterations in ion channel function.

Triggered Activity

Triggered activity is caused by afterdepolarizations, which are abnormal depolarizations that occur during or after repolarization. These can be early afterdepolarizations (EADs) or delayed afterdepolarizations (DADs), often linked to electrolyte imbalances or drug effects.

Reentry Mechanisms

Reentry occurs when an electrical impulse travels in a loop within the heart, reactivating tissue that has already been depolarized. This can create a continuous circuit of excitation, leading to tachycardia.

Clinical Significance

Ectopic foci can lead to various arrhythmias, including premature atrial contractions, premature ventricular contractions, atrial fibrillation, and ventricular tachycardia. These arrhythmias can range from benign to life-threatening, depending on their location and frequency.

Diagnosis

Diagnosis of ectopic foci involves electrocardiography (ECG) to identify abnormal rhythms. Holter monitoring or event recorders may be used for intermittent arrhythmias. Electrophysiological studies can help localize the ectopic focus.

Treatment

Treatment depends on the type and severity of the arrhythmia. Options include lifestyle modifications, medications such as beta-blockers or antiarrhythmics, and invasive procedures like catheter ablation.

Also see

• Sinoatrial node
• Atrioventricular node
• Cardiac arrhythmia
• Electrocardiography
• Catheter ablation

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