Cardiac Electrophysiology and Conduction

Cardiac electrophysiology and conduction is the study of how each heartbeat is electrically generated and spread across the heart. Specialized pacemaker and conducting tissues — the sinoatrial node, atrioventricular node, bundle of His, bundle branches, and Purkinje fibers — set the rhythm and route the impulse so that atria and ventricles contract in the correct sequence.

Definition

Cardiac electrophysiology and conduction refers to the generation of the cardiac action potential and its orderly propagation through the specialized conduction system, coordinating the timing of atrial and ventricular contraction.

Scope

The topic covers the cardiac action potential and the ion currents that shape it, the automaticity of pacemaker cells, the anatomy and physiology of the conduction system, the orderly propagation of the impulse from the sinoatrial node to the ventricular myocardium, and the role of gap junctions in cell-to-cell conduction. It is descriptive physiology, not a guide to arrhythmia diagnosis or management.

Core questions

• How do pacemaker cells generate spontaneous impulses?
• What ion currents shape the cardiac action potential and refractoriness?
• How does the impulse travel from the sinoatrial node to the ventricles?
• Why is conduction delayed at the atrioventricular node?

Key concepts

• Cardiac action potential and its phases
• Pacemaker automaticity and the funny current
• Sinoatrial and atrioventricular nodes
• His-Purkinje system
• Gap junctions and cell-to-cell conduction
• Refractory period and conduction velocity

Mechanisms

The sinoatrial node depolarizes spontaneously through pacemaker currents, setting the heart rate. The impulse spreads across the atria, converges on the atrioventricular node where conduction is deliberately slowed to allow ventricular filling, then passes rapidly through the bundle of His, the bundle branches, and the Purkinje network to activate the ventricular myocardium from apex toward base. Propagation depends on regenerative sodium and calcium currents and on low-resistance gap junctions that electrically couple adjacent myocytes (Kleber & Rudy, 2004). The shape and duration of the action potential, governed by the interplay of inward and outward ion currents, determines conduction velocity and refractoriness (Bers, 2002). Optical mapping techniques have made it possible to visualize impulse propagation across cardiac tissue directly (Efimov et al., 2004).

Clinical relevance

Normal conduction is the reference against which arrhythmias, conduction blocks, and pre-excitation are defined, and it underpins the interpretation of the electrocardiogram. This topic describes the healthy conduction system and is educational; it does not offer guidance on diagnosing or treating rhythm disorders.

Evidence & guidelines

Conduction physiology rests on classic and modern electrophysiology reviews (Kleber & Rudy, 2004) and standard texts (Katz, 2010). This topic summarizes normal electrophysiology and is not a clinical guideline.

History

The conduction system was mapped in the early twentieth century: His described the atrioventricular bundle, Tawara the node and Purkinje connections, and Keith and Flack the sinoatrial node. The biophysical basis of the action potential, building on the Hodgkin-Huxley framework, and modern optical and computational methods later linked this anatomy to the ionic mechanisms of propagation.

Key figures

• Wilhelm His Jr.
• Sunao Tawara
• Arthur Keith
• Andre G. Kleber
• Yoram Rudy

Seminal works

• kleber-rudy-2004
• efimov-2004

Frequently asked questions

What sets the normal heart rate?

The sinoatrial node, which depolarizes spontaneously faster than other pacemaker tissue, is the heart's normal pacemaker and sets the rate.

Why is there a delay at the atrioventricular node?

Slow conduction through the atrioventricular node delays ventricular activation just long enough for the atria to finish filling the ventricles before they contract.