Today our topic of discussion is Cardioversion of Intensive Care.
Cardioversion of Intensive Care
CARDIOVERSION
Cardioversion is the use of electrical energy to convert a cardiac dysrhythmia, other than ventricular fibrillation, to one that is more hemodynamically stable, preferably a sinus rhythm. Defibrillation generally applies to unsynchronized electrical counter shock during a ventricular fibrillation.
It is most effective when the myocardial cells, are not anoxic or acidotic. Therefore defibrillation should ideally be performed within 15-20 seconds of the onset of dysrhythmia. Defibrillation is accomplished by the passage of direct current (DC) electrical shock through the heart that is sufficient to depolarize the cells of the myocardium (Fig. 30.7).
Definition: Cardioversion is a medical intervention used to normalize an abnormal heart rate that occurs in atrial flutter, atrial fibrillation or ventricular tachycardia. In these conditions, the heart rate exceeds 100 bpm and is irregular. The condition can be episodic and indicates an underlying heart condition such as hypertension, cardiomyopathy, etc.
The subsequent repolarization of myocardial cells will allow the SA node to resume the role of the pacemaker. The output of the defibrillator is quantified in joules or watts per second. The recommended energy for initial shock defibrillation is 200 joules with a second shock of 200-300 joules if defibrillation unsuccessful. High doses of electricity during defibrillation have been found to cause myocardial damage thus the lowest effective electric output is the one with which to start.
Cardioversion Types
Electrical cardioversion refers to administration of therapeutic dosage of electric current in a specific moment of the cardiac cycle. The timing is important to avoid ventricular tachycardia. This is a scheduled procedure performed on an out-patient basis on patients who have a history of episodic atrial flutter or atrial fibrillations. Electric current is administered using pads that are placed on the
chest or on the chest and back. They are held in place with the help of saline based gel. The cables are connected to machine that generates shocks and displays the cardiac rhythm. The patient is given sedatives to make the entire procedure more tolerable. Electrical cardioversion can at times be used as a lifesaving intervention in emergencies like ventricular tachycardia (Fig. 30.8).
Pharmacological cardioversion entails the use of antiarrhythmic drugs to restore normal heart rate. Sodium channel blockers, beta blockers, potassium channel blockers or calcium channel blockers are the drugs used. All these drugs act to reduce the conductivity of the heart muscle which in turn reduces the heart rate. This is a good alternate in patients with fibrillation of recent onset.
CARDIAC DEFIBRILLATION
Defibrillator is an emergency resuscitative procedure in which therapeutic doses of high energy electrical shocks are given to patients to restore heart beat in cardiac arrest or
pulse less ventricular tachycardia. They can be administered at any time in the cardiac cycle. Purpose: To treat lethal arrhythmias such as ventricular tachycardia (VT) and ventricular fibrillation (VF).
Types of Defibrillators
Automated external defibrillators generally found in public places like airports, bus station, railway stations, offices, etc. are designed to analyze the disturbed heart rate and administer shocks accordingly. These can be operated by untrained personnel and cannot be manually overridden. The only drawback is that they take around 10-20 seconds to analyze the rhythm which can be critical.
Semi-automated external defibrillators are similar except that they can be controlled manually when operated by a trained paramedic. They can pace the heart rate. These machines have an ECG display which helps in resuscitation.
Internal defibrillators are seen in the operation rooms where they are used to restore heart beat during an open heart surgery. The paddles are placed above and below the heart and the shock is given.
Automatic internal cardiac defibrillator (AICD) is implanted under the skin in the chest area. They constantly monitor the rhythm of the heart. Upon sensing any irregularities in the rhythm, it immediately sends shocks to the heart muscles and restores normal heart rate.
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