Dromotropic

Dromotropic Effects

Diagram of the cardiac conduction system

Dromotropic effects refer to the influence on the conduction speed of the electrical impulses through the heart's conduction system. These effects are crucial in the regulation of the heart's rhythm and are primarily mediated by the autonomic nervous system.

Cardiac Conduction System

The cardiac conduction system is responsible for the initiation and propagation of electrical impulses that result in the contraction of the heart muscle. It includes the sinoatrial node (SA node), atrioventricular node (AV node), bundle of His, bundle branches, and Purkinje fibers.

• Sinoatrial Node (SA Node): Often referred to as the heart's natural pacemaker, the SA node generates electrical impulses that initiate each heartbeat.
• Atrioventricular Node (AV Node): The AV node receives impulses from the SA node and delays them slightly before passing them to the bundle of His, allowing the atria to contract and fill the ventricles with blood.
• Bundle of His and Bundle Branches: These structures conduct impulses from the AV node to the ventricles.
• Purkinje Fibers: These fibers distribute the electrical impulse throughout the ventricles, causing them to contract.

Autonomic Nervous System

The autonomic nervous system plays a significant role in modulating dromotropic effects. It consists of the sympathetic nervous system and the parasympathetic nervous system.

• Sympathetic Nervous System: Activation of the sympathetic nervous system increases the conduction velocity through the AV node, resulting in positive dromotropic effects. This is mediated by the release of norepinephrine, which binds to beta-adrenergic receptors.
• Parasympathetic Nervous System: The parasympathetic nervous system, primarily through the vagus nerve, decreases conduction velocity, resulting in negative dromotropic effects. This is mediated by the release of acetylcholine, which acts on muscarinic receptors.

Clinical Significance

Dromotropic effects are important in the context of various cardiac arrhythmias. For instance, conditions such as atrial fibrillation or supraventricular tachycardia may require interventions that alter dromotropic properties to restore normal rhythm or control heart rate.

Another view of the cardiac conduction system

Pharmacological agents, such as beta-blockers and calcium channel blockers, are often used to exert negative dromotropic effects, slowing conduction through the AV node and controlling heart rate in arrhythmias.

Related Pages

• Chronotropic effects
• Inotropic effects
• Cardiac electrophysiology
• Heart rate

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