GLOSSARY

The electrical conductivity of the heart is the heart’s ability to generate and transmit electrical signals in an orderly way, enabling coordinated contraction of the atria and ventricles.

Electrical Properties of Cardiac Muscle

• Automaticity: the ability to generate action potentials without external stimulation.
• Excitability.
• Conductivity: signal transmission through gap junctions.
• Long refractory period: preventing tetanus and preserving rhythm.

Action Potential of Ventricular Muscle Cells

• Phase 0: rapid depolarisation by sodium entry.
• Phase 2 (plateau): calcium entry; the long cardiac action potential (about 250–300 milliseconds) is due to this phase.
• Phase 3: repolarisation by potassium efflux.

Pacemaker Cell Action Potential

Sinoatrial node cells have no stable resting potential and spontaneously depolarise slowly (funny current), which gives them automaticity.

Conduction Pathway

Sinoatrial node → atria → atrioventricular node (delay) → bundle of His → right and left bundle branches → Purkinje fibres → ventricular myocardium.

Relevance to Sport

• Electrolyte disorders: severe low or high potassium and magnesium, for example in severe dehydration or excessive salt-free fluid intake, may disrupt conduction and cause arrhythmias.
• Channelopathies: genetic ion-channel diseases such as long QT syndrome and Brugada syndrome are causes of sudden death in athletes with a structurally normal heart.