Greg Ikonnikov and Dominique Yelle

Clin Anat.2009 Jan;22(1):99-113. Can J Anaesth.1993 Nov;40(11):1053-64.

An organized rhythmic contraction of the heart requires adequate propagation of electrical impulses along the conduction pathway. Of note, the impulses in the His-Purkinje system travel in such a way that papillary muscle contraction precedes that of the ventricles, thereby preventing regurgitation of blood flow through the AV valves.

Physiol Rev.2005 Oct;85(4):1205-53.

Heart Rhythm.2010 Jan;7(1):117-26.

Note: The different types of cardiac ion channels are discussed below, throughout the description of the phases of action potentials in different cardiac cells.

Physiol Rev.2005 Oct;85(4):1205-53.

Action potential: electrical stimulation created by a sequence of ion fluxes through specialized channels in the membrane (sarcolemma) of cardiomyocytes that leads to cardiac contraction.

The action potential in typical cardiomyocytes is composed of 5 phases (0-4), beginning and ending with phase 4.

Pharmacol Ther.2005 Jul;107(1):59-79. Drugs.2007;67 Suppl 2:15-24. (The funny current)

Table 1. Cardiac cell types displaying pacemaker behavior.

Pacemaker

Location

Inherent rate (beats per minute, BPM)

Sinoatrial (SA) node

Right atrium (RA) at junction with superior vena cava (SVC)

60-100 BPM

Atrioventricular (AV) node

RA at posteroinferior area of interatrial septum

40-60 BPM

Purkinje fibers and ventricular cardiomyocytes

Throughout the ventricles

20-40 BPM

The sequence of events for pacemaker action potential:

Nature.2002 Jan 10;415(6868):198-205.

Excitation-contraction coupling represents the process by which an electrical action potential leads to contraction of cardiac muscle cells. This is achieved by converting a chemical signal into mechanical energy via the action of contractile proteins.

Calcium is the crucial mediator that couples electrical excitation to physical contraction by cycling in and out of the myocytes cytosol during each action potential.

Main contractile elements:

Regulatory elements:

The initial influx of Ca2+ into myocytes through L-type Ca2+ channels during phase 2 of the action potential is insufficient to trigger contraction of myofibrils. This signal is amplified by the CICR mechanism, which triggers much greater release of Ca2+ from the sarcoplasmic reticulum.

As with myocyte contraction, this process is synchronized with the electrical activity of the cell.

Adv Physiol Educ.2011 Mar;35(1):28-32.

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Physiology of cardiac conduction and contractility ...