الفهرس 
Anatomy Of The Conductive System Of The HeartOnly 14 pages are availabe for public view
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Abstract
Cardiac arrhythmia is an abnormality in the timing or sequence of cardiac depolarization. There are two predominant types of cardiac arrhythmias: tachyarrhythmia, an abnormally rapid cardiac rhythm (heart rate above 100 beats per minute); and bradyarrhythmia, a slow cardiac rhythm (heart rate below 60 beats per minute).
The mechanisms of cardiac tachyarrhythmias can be grouped into two general categories, abnormalities of impulse formation and re-entry. Abnormalities of impulse formation can be subdivided further into abnormal automaticity and triggered activity. Reentry is the most common mechanism of cardiac arrhythmias.
Cardiac bradyarrhythmias may result from either abnormalities in impulse formation or abnormalities in impulse conduction. Sinus bradycardia is the most common type of bradyarrhythmia.
Most of the available antiarrhythmic drugs can be classified according to whether they exert blocking actions predominantly on sodium, potassium, or calcium channels and whether they block receptors.
Class IA. This includes drugs that reduce V.max and prolong action potential duration: quinidine, procainamide, disopyramide.
Class IB. This class of drugs shortens action potential duration: mexiletine, phenytoin, and lidocaine.
Class IC. This class of drugs can reduce V.max, primarily slow conduction, and prolong refractoriness minimally: flecainide, propafenone, and moricizine.
Class II. These drugs block beta-adrenergic receptors, and include: propranolol, timolol, and metoprolol.
Class III. This class of drugs predominantly blocks potassium channels, included are: sotalol, amiodarone, and bretylium.
Class IV. This class of drugs predominantly blocks the slow calcium channel: verapamil, diltiazem, nifedipine, and others.
After an arrhythmia is recognized, it is important to determine whether it produces a hemodynamic disturbance, what type of treatment is required, and how urgently therapy should be instituted. Treatment should be initiated promptly if the arrhythmia results in marked hemodynamic impairment. Treatment should be instituted if the arrhythmia is a precursor of a more severe arrhythmia or the arrhythmia may be detrimental to the patient’s underlying cardiac disease. For the detection of rhythm disturbances, the standard limb lead II is preferred because it usually displays large P waves.
The anesthesiologist must learn, preoperatively, the following information about any implanted pacemaker:
o The indication for placement of the pacemaker, the default rhythm and the type of pacemaker.
o How to detect deterioration in battery function.
o How to change the mode or fire the pacemaker if it is of the radiofrequency type.
o The current rate and sensitivity settings of the pacemaker.
o Whether the pacemaker is currently functioning and how well.
Anaesthesia in patients with ion channel disease is a matter of concern because it is usually a condition for risk of recurrence of precipitating factors such as adrenergic Stimulation of surgery, autonomic nerve modulation, hemodynamic side effects of the anaesthetic and analgesic drugs and changes in body temperature. The difficulty in perioperative management is represented by the doubt in quantified risk for the patient at intermediate risk who arrives in the operating room without a definite therapy.