Place the patient in a supine position to improve cerebral perfusion and reduce the odds of syncope. Placing the patient in Trendelenburg position may actually terminate the rhythm.

Cardiology

Some people with known AVNRT may be able to stop their attack by using various maneuvers to activate the vagus nerve. This includes carotid sinus massage (pressure on the carotid sinus in the neck), submersion of the face in ice water to trigger the diving reflex, putting the patient in Trendelenburg position or the Valsalva maneuver (increasing the pressure in the chest by attempting to exhale against a closed airway). Vagal maneuvers are contraindicated in the presence of hypotension.

Cardiology

Medical therapy to terminate and prevent AVNRT includes drugs that slow AV nodal conduction.

Adenosine is generally considered first line therapy for AVNRT.

Treatment of AVNRT with adenosine can be complicated by:

• The development of shortness of breath due to bronchospasm
• In some cases there can be asystole which is transient given the short half life of adenosine
• Atrial fibrillation may be induced by adenosine administration
• Ventricular fibrillation is rarely induced by adenosine. When it does occur it is due to block of the AV node with rapid antegrade conduction of atrial fibrillation down the bypass tract. It is for this reason that defibrillation equipment be available.
• Adenosine should not be used in heart transplant patients
• Dipyridamole may potentiate the effect of adenosine
• Theophylline may reduce the effectiveness of adenosine

Administration:

• Place a large bore (18 gauge and larger) intravenous line
• The initial dose is 6 mg and this should be followed a saline flush with elevation of the arm to assure that the drug is infused
• If this is not effective, then 12 mg or 18 mg of adenosine can be admininistered

A short acting beta-blocker such as esmolol (half life of 8 minutes) can be used to terminate an episode of AVNRT. Longer acting beta-blockers such as atenolol, metoprolol, and propranolol can also be used to reduce the risk of recurrent episodes. Atenolol may be preferable among patients with bronchospasm as it selectively blocks beta-1 receptors with little effect on beta- 2 receptors.

Numerous other antiarrhythmic drugs may be effective if the more commonly used medications have not worked; these include flecainide or amiodarone. Both adenosine and beta blockers may cause tightening of the airways, and are therefore used with caution in people who are known to have asthma. Calcium channel blockers should be avoided if there is a wide complex tacycardia and the diagnosis of AVNRT is not clearly established in so far as calcium channel blockers should be avoided in ventricular tachycardia. If the diagnosis of AVNRT is established, then non-dihydropyridine calcium channel blockers (such as verapamil) may be administered to terminate the rhythm if other agents are not effective. Verapamil acts longer than adenosine and acts rapidly. Its administration can be complicated by hypotension, bradycardia and negative inotropic effects.

Cardiology

In very rare instances, cardioversion (the electrical restoration of a normal heart rhythm) is needed in the treatment of AVNRT. This would normally only happen if all other treatments have been ineffective, or if the fast heart rate is poorly tolerated (e.g. the development of heart failure symptoms, hypotension (low blood pressure) or unconsciousness).

Cardiology

After being diagnosed with AVNRT, patients can also undergo an electrophysiology (EP) study to confirm the diagnosis. Catheter ablation of the slow pathway, if successfully carried out, and cures 95% of patients with AVNRT. The risk of complications is quite low.

Cardiology

The following triggers should be avoided:

• Alcohol
• Caffeine
• Chocolate
• Hyperthyroidism
• Hypokalemia
• Hypomagnesemia
• Myocardial ischemia
• Psychological stress
• Tea
• Theobromine in foods like tea, coffee and chocolate
• Theophylline

Cardiology