Each patient below is alert and oriented and has a BP110/60. In which patient would adenosine constitute appropriate initial therapy?
Adenosine is currently approved for thetermination of paroxysrriat supraventricular tachycardias at doses of 6 mg and, if 6 mg fails, 12 mg. The primary mechanism of adenosine is to decrease conduction velocity through the A V node. As such, it is an ideal drug for acute termination of regular reentrant supraventricular tachycardia involving the A V node) Side effects may include chest discomfort and transier it hypotension. The half-life is extremely short, and the side effects tend to be brief. Patients with wide complex tachycardia suggestive of ventricular tachycardia or known preexcitation syndrome should be treated with agents that decrease automaticity, such as quinidine and procainamide. However, in patients with apparent ventricular tachycardia who have neither a history of ischemic heart disease nor preexcitation syndrome, adenosine may be a useful diagnostic agent to determine whether a patient has a reentrant tachycardia, in which case the drug may terminate it; an atrial tachycardia, in which case the atrial activity may be unmasked; or a true, preexcited tachy-cardia, in which case adenosine will have no effect. While adenosine is not the recommended primary therapy for patients with wide complex tachyarrhythmia, patients with junctional tachycardia who have evidence of poor ventricular function or concomitant β-adrenergic blockademay be reasonable candidates for its use.
A 65-year old man with no ischemic heart disease and wide complex tachycardia
A 65 -year old woman with known ischemic disease and narrow complex tachycardia
A 25-year old woman with known preexcitation syndrome and narrow complex tachycardia
A 28-year-old man with known preexictation syndrome and wide complex tachycardia