Electrical Impulses Can Reenter To Cause Fibrillation

Normally, the action potentials spread over the entire heart and die out with each beat. In disease states, however, conduction through a region may be depressed to the point that when the conducted wave exits that region, it finds the surrounding myocardium out of its refractory period and ready to respond with another action potential. If this occurs, the wave is said to have reentered and the wave of excitation can go around and around the heart in a condition called fibrillation. In this state the muscle only quivers rather than rhythmically contracting and relaxing.

If the atria fibrillate, the AV node will be stimulated in rapid succession. The AV node's long refractory period, however, prevents the ventricle from being stimulated too rapidly to efficiently pump blood. Whenever the AV node comes out of its refractory period, the next wave of excitation will then be conducted to the ventricle, resulting in a normal QRS complex but at irregular intervals. Figure 7 and panel A in Figure 11 both show atrial fibrillation. Note that P waves are absent from the tracings and that the R-R interval is irregularly irregular. Atrial fibrillation is not a serious condition and is common in the elderly and in patients with mitral valve disease. Unfortunately, blood

A Atrial fibrillation

B Ventricular fibrillation

FIGURE 11 ECG tracing from a patient with atrial fibrillation (A) and a patient with ventricular fibrillation (B).

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Get Rid of Gallstones Naturally

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