The critical decision in the management of a patient with sustained ventricular tachycardia is the urgency with which to treat the rhythm. In a patient who is hemodynamically stable, treatment should be delayed until a 12-lead electrocardiogram has been obtained. During the delay, a brief medical history and baseline laboratory values can be obtained. Specific attention should be paid to a history of myocardial infarction and potentially proarrhythmic drugs. If you are not sure about a drug, look it up.
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Levels of potassium and magnesium and appropriate drugs must be checked. Toxicologic screens should be obtained immediately on arrival in the emergency department.
Why is it important to obtain a 12-lead electrocardiogram?
The axis and morphology help to make the diagnosis of ventricular tachycardia, as well as shed light on the potential mechanism and origin of the rhythm. For example, a rhythm with a right bundle branch block morphology generally originates from the left ventricle and implies that the rhythm is secondary to ischemic heart disease with scar formation and/or aneurysm. Rhythms with left bundle branch block morphology generally originate from the right ventricle. Once the initial electrocardiographic data are obtained, a decision has to be made about the best way to terminate the rhythm. If there is any question about the patient's stability or if the clinical situation deteriorates, it is best to terminate the rhythm by cardioversion.
After the baseline data have been obtained, what method is used to terminate the rhythm?
With any question of hemodynamic instability, termination should be done immediately with synchronized DC electrical cardioversion. Hemodynamic instability is defined as hypotension resulting in shock; congestive heart failure; myocardial ischemia (infarction or angina); or signs or symptoms of inadequate cerebral perfusion. It is important to ensure that the energy is delivered in a synchronized fashion before cardioversion. Failure to do so may introduce the energy in a vulnerable period (into the T wave‚ late phase 3 in repolarization) and accelerate the rhythm or induce ventricular fibrillation.
Energy levels as low as 10 watt-seconds may be successful, but at the risk of ventricular fibrillation due to incomplete defibrillation of a critical mass of the myocardium sufficient to extinguish the rhythm. It is therefore wise to begin at a level of 100 watt-seconds. If the patient is conscious, adequate intravenous sedation should always be provided.