Cardiac Arrhythmias: Difference between revisions

The cardiac conduction system (figure 3) is the highway though which the electric activity of the heart spread from the atria to the ventricle. The characteristics of the different parts of the conduction system are a result of the different characteristics of the individual myocytes. On a larger level, function is controlled predominantly by the autonomic nerve system (both vagal and sympathetic nerve system). Especially the sinus node and atrioventricular node are responsive to the autonomic nerve system. The ganglionic plexi, a conglomeration of both vagal and sympathetic nerves, form the intrinsic cardiac nerve system and innervate through a network of nerve fibers the atria and ventricles. The vagal and sympathetic nerve system are both continually active in the heart, but vagal activity dominates the tonic background stimulation of the autonomic nerve system. Moreover the heart is more susceptible to vagal stimulation. Vagal stimulation provokes a rapid response and the effect dissipates swiftly in contrast to sympathetic stimulation which has a slow onset and offset. Vagal stimulation results in a reduction is in sinus node activation frequency and prolongs AV nodal conduction. These effects can occur simultaneously or independent of each other.  Sympathetic stimulation exerts reverse effects, accelerating the sinus node firing frequency and improving AV nodal conduction. The autonomic nerve system has a small effect on cardiomyocytes. Vagal stimulation tends to prolong the refractory period and decreasing the myocardial contractility. Sympathetic stimulation has opposite effects on the cardiac tissue. Whereas the physiological modulation of cardiac conduction is vital to adaptation of the heart to rest and exercise it  can attribute to the pathologic substrate in a diseased myocardium.

===Sinus node===