Atrioventricular reentry

FIGURE 6-2. Algorithm for the treatment of acute (top portion) paroxysmal supraventricular tachycardia and chronic prevention of recurrences (bottom portion). Note For empiric bridge therapy prior to radiofrequency ablation procedures, calcium channel blockers (or other atrioventricular [AV] nodal blockers) should not be used if the patient has AV reentry with an accessory pathway. (AAD, antiarrhythmic drugs AF, atrial fibrillation AP, accessory pathway AVN, atrioventricular nodal AVNRT, atrioventricular nodal reentrant tachycardia AVRT, atrioventricular reentrant tachycardia DCC, direct-current cardioversion ECG, electrocardiographic monitoring EPS, electrophysiologic studies PRN, as needed VT, ventricular tachycardia.)... 

Severely depressed conduction may result in simple block, eg, atrioventricular nodal block or bundle branch block. Because parasympathetic control of atrioventricular conduction is significant, partial atrioventricular block is sometimes relieved by atropine. Another common abnormality of conduction is reentry (also known as "circus movement"), in which one impulse reenters and excites... 

Paroxysmal supraventricular tachycardia is usually due to reentry in or proximal to the atrioventricular (AV) node or AV reentry incorporating an extra nodal pathway common tachycardias can be terminated acutely with AV nodal... 

Sung RJ, Lauer MR, Chun H. Atrioventricular node reentry Current concepts and new perspectives. PACE 1994 17 1413-1430. 

Jackman WM, Beckman KJ, McClelland JH, et al. Treatment of supraventricular tachycardia due to atrioventricular nodal reentry by... 

Quinidine, a class 1A antiarrhythmic, depresses myocardial excitability, conduction velocity, and contractility. Therapeutically, it prolongs the effective refractory period and increases conduction time, thereby preventing the reentry phenomenon. In addition, quinidine exerts an indirect anticholinergic effect it decreases vagal tone and may facilitate conduction in the atrioventricular junction. 

C. Clinical Use and Toxicities Calcium channel blockers are effective for converting atrioventricular nodal reentry (also known as nodal tachycardia) to normal sinus rhythm. Their major use is in the prevention of these nodal arrhythmias in patients prone to recurrence. These drugs are orally active verapamil is also available for parenteral use (Table 14—2). The most important toxicity of verapamil is excessive pharmacologic effect, since cardiac contractility, AV conduction, and blood pressure can be significantly depressed. See Chapter 12 for additional discussion of toxicity. Amiodarone has moderate calcium channel-blocking activity. 

---