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Principles of Electrophysiology

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  1. Introduction
  2. Cardiac electrophysiology
  3. Mechanisms of cardiac tachyarrhythmias
  4. Mechanism of Bradyarrhythmias
  5. Conclusions
  6. Bibliography

The function of the human heart requires rhythmic beatings occurring on the average 70 times a minute, 24 hours a day, for 80 or more years. The close to 3 billion contractions of the cardiac musculature that must occur without fail are coordinated by an intricate network of specialized electrically active cells that are integrated with the myocytes that comprise the predominant mass of the heart. Any loss of electrical activity, even for a few seconds, results in syncope; loss of electrical activity for a few minutes may end in death.

[...] The basis for poor propagation of the depolarizing wave front in the heart usually results from pathologic changes in patients with structural heart disease, including coronary artery disease, left ventricular hypertrophy, and heart failure. Fibrotic changes in the heart, with increases in collagen and intracellular matrix as seen in hypertrophy or infarction, can lead to areas of slow conduction and provide portals for reentry. Changes in the gap junction proteins have been noted in hypertrophy with increases of connexin43. These changes typically result from advanced age or the presence of structural heart disease, such as a prior myocardial infarction or a cardiomyopathy. [...]

[...] Variations in the duration and shape of the cardiac action potential exist depending on its location in the heart. Likewise, alterations of ion channel expression and activity in disease states contribute to prolongation of the action potential. The atrial action potential has a typical duration of 100 to 200 msec, whereas the ventricular action potential typically lasts 250 to 300 msec. Different layers of the ventricle exhibit marked changes in the action potential. Epicardial cells have a prominent phase 1 compared with endocardial cells, in which phase 1 is blunted. [...]

[...] The AV node is found at the apex of the triangle of Koch, formed by the tendon of Todaro on one side and the tricuspid annulus on the other, on the right side of the heart and anterior to the os of the coronary sinus. The arterial supply of the AV node arises from the right coronary artery in 85 to 90% of cases. The AV node itself is complex and can be divided into three general regions, with further subdivisions possible. [...]

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