AV node. Some of those with AVNRT may be able to stop their attack by using physical manoeuvres that increase the activity of the vagus nerve on the heart, specifically on the atrioventricular node. These manoeuvres include carotid sinus massage (pressure on the carotid sinus in the neck) and the Valsalva manoeuvre (increasing the pressure in the chest by attempting to exhale against a closed airway by bearing down or holding one's breath). Medications that slow or briefly halt electrical conduction through the AV node can terminate AVNRT, including adenosine, beta blockers, or non-dihydropyridine calcium channel blockers (such as verapamil or diltiazem). 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. Less commonly used drugs for this purpose include antiarrhythmic drugs such as flecainide or amiodarone. If the fast heart rate is poorly tolerated (e.g. the development of heart failure symptoms, low blood pressure or coma) then AVNRT can be terminated electrically using a cardioversion. In this procedure, after administering a strong sedative or general anaesthetic, an electric shock is applied to the heart to restore a normal rhythm. Arrhythmia prevention While preventative treatment may be very helpful at stopping the unpleasant symptoms associated with AVNRT, as this arrhythmia is a benign condition, preventative treatment is not essential. Some of those who choose not to have further treatment will eventually become asymptomatic. Those who wish to have further treatment can choose to take long term antiarrhythmic medication. The first line drugs are calcium channel antagonists and beta blockers, with second line agents including flecainide, amiodarone, and occasionally digoxin. These drugs are moderately effective at preventing further episodes but need to be taken long term. Alternatively, an invasive procedure called an electrophysiology (EP) study and catheter ablation can be used to confirm the diagnosis and potentially offer a cure. This procedure involves introducing wires or catheters into the heart through a vein in the leg. The tip of one of these catheters can be used to heat or freeze the slow pathway of the AV node, destroying its ability to conduct electrical impulses, and preventing AVNRT. The risks and benefits are weighed up before this is performed. Catheter ablation of the slow pathway, if successfully carried out, can potentially cure AVNRT with success rates of >95%, balanced against a small risk of complications including damaging