AV nodal reentrant tachycardia

AV nodal reentrant tachycardia Reentrant circuit within or near AV Adenosine AV nodal block... 

Toxicity of Ca Channel Blockers The major adverse effect of intravenous verapamil or diltiazem is hypotension, particularly with bolus administration. This is a particular problem if the drugs are used mistakenly in patients with ventricular tachycardia misdiagnosed as AV nodal reentrant tachycardia. Hypotension also is frequent in patients receiving other vasodilators, including quinidine, and in patients with underlying left ventricular dysfunction, which the drugs can exacerbate. Severe sinus bradycardia or AV block also occurs, especially in patients also receiving P blockers. With oral therapy, these adverse effects tend to be less severe. 

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.)... 

O Paroxysmal supraventricular tachycardia is caused by reentry that includes the AV node as a part of the reentrant circuit. Typically, electrical impulses travel forward (antegrade) down the AV node and then travel back up the AV node (retrograde) in a repetitive circuit. In some patients, the retrograde conduction pathway of the reentrant circuit may exist in extra-AV nodal tissue adjacent to the AV node. One of these pathways usually conducts impulses rapidly, while the other usually conducts impulses slowly. Most commonly, during PSVT the impulse conducts antegrade through the slow... 

Type IV drugs inhibit calcium entry into the cell, which slows conduction, prolongs refractoriness, and decreases SA and AV nodal automaticity. Calcium channel antagonists are effective for automatic or reentrant tachycardias that arise from or use the SA or AV nodes. 

Paroxysmal supraventricular tachycardia (PSVT) arising by reentrant mechanisms includes arrhythmias caused by AV nodal reentry, AV reentry incorporating an anomalous AV pathway, SA nodal reentry, and intraatrial reentry. AV nodal reentry and AV reentry are by far the most common of these tachycardias. 

Ca + CHANNEL BLOCK The major electrophysiological effects resulting from block of cardiac Ca + channels are in slow-response tissues, the sinus and AV nodes. Dihydropyridines such as nifedipine, which are used commonly in angina and hypertension, preferentially block Ca + channels in vascular smooth muscle their cardiac effects, such as heart rate acceleration, result principally from reflex sympathetic activation secondary to peripheral vasodilation. Only verapamil, diltiazem, and bepridil block Ca + channels in cardiac cells at clinically used doses. These drugs generally slow heart rate, although hypotension can cause reflex sympathetic activation and tachycardia. The velocity of AV nodal conduction decreases, so the PR interval increases. AV nodal block occurs as a result of decremental conduction and increased AV nodal refractoriness, which form the basis for the use of channel blockers in reentrant arrhythmias whose circuit involves the AV node, such as AV reentrant tachycardia. 

Type II drugs include /Tadrenergic antagonists clinically relevant mechanisms result from their antiadrenergic actions. /3- Blockers are most useful in tachycardias in which nodal tissues are abnormally automatic or are a portion of a reentrant loop. These agents are also helpful in slowing ventricular response in atrial tachycardias (e.g., AF) by their effects on the AV node. 

Nodal tachycardia A common reentrant arrhythmia that travels through the AV node it may also be conducted through atrial and ventricular tissue as part of the reentry circuit... 

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