action potential conduction disturbances

http://www.siumed.edu/~dwade/phys310/AP'sECG.html

http://www.wpanet.org/sectorial/docs/ST483.pdf

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Note added at 16 hrs 58 mins (2005-08-31 16:13:14 GMT)
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What is an ECG?

The electrocardiogram (ECG or EKG) is a noninvasive test that is used to reflect underlying heart conditions by measuring the electrical activity of the heart.






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Note added at 16 hrs 58 mins (2005-08-31 16:13:18 GMT)
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What is an ECG?

The electrocardiogram (ECG or EKG) is a noninvasive test that is used to reflect underlying heart conditions by measuring the electrical activity of the heart.






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Note added at 17 hrs 11 mins (2005-08-31 16:25:38 GMT)
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Normal Impulse Conduction
The action potentials generated by the SA node spread throughout the atria primarily by cell-to-cell conduction. There is some functional evidence for the existence of specialized conducting pathways within the atria (termed internodal tracts), although this is controversial. The conduction velocity of action potentials in the atrial muscle is about 0.5 m/sec. As the wave of action potentials depolarizes the atrial muscle, the cardiomyocytes contract by a process termed excitation-contraction coupling.

Regulation of Conduction
The conduction of electrical impulses throughout the heart, and particularly in the specialized conduction system, is strongly influenced by autonomic nerve activity. An increase in sympathetic firing increases conduction velocity via neuronal-released norepinephrine binding to beta-adrenoceptors. Activation of parasympathetic (vagal) nerves decreases conduction velocity via the action of acetylcholine on muscarinic receptors.
Because conduction velocity is highly dependent upon the rate of tissue depolarization, which is related to the slope of phase 0 of the action potential, conditions (or drugs) that alter phase 0 will affect conduction velocity. For example, conduction can be altered by changes in membrane potential, which can occur during myocardial ischemia and hypoxia. Cellular hypoxia leads to membrane depolarization, inhibition of fast Na+ channels, a decrease in the slope of phase 0, and a decrease in action potential amplitude. Together, these membrane changes result in a decrease in speed by which action potentials are conducted within the heart. Antiarrhythmic drugs such as quinidine (a Class IA antiarrhythmic) that block sodium channels cause a decrease in conduction velocity.