Introduction
FIGURE 243-1 Common mechanisms underlying paroxysmal supraventricular tachycardia along with typical R-P relationships. A. Schematic showing a four-chamber view of the heart with atrioventricular node in green and an accessory pathway between the lex atrium and lex ventricle in blue. Atrial tachycardia (AT; red circuit) is confined completely to atrial tissue. Atrioventricular nodal reentry tachycardia (AVNRT; blue circuit) uses atrioventricular (AV) nodal and perinodal atrial tissue. Atrioventricular reentry tachycardia (AVRT; black circuit) uses atrial and ventricular tissue, accessory pathway, AV node, and specialized conduction fibers (His-Purkinje) as part of the reentry circuit. B. Typical relation of the P wave to QRS, commonly described as the R-P to P-R relationships for the diwerent tachycardia mechanisms. 
FIGURE 243-2 Location of focal atrial tachycardia focus estimated by P-wave morphology. LAA, lex atrial appendage; LIV, lex inferior pulmonary vein; LSV, lex superior pulmonary vein; RAA, right atrial appendage; RIV, right inferior pulmonary vein; RSV, right superior pulmonary vein; SVC, superior vena cava. 
FIGURE 243-3 Atrial tachycardia (AT) with 1:1 and 2:1 atrioventricular (AV) conduction. Arrows indicate P waves. A. AT with 1:1 AV relationship and R-P > P-R. B. Same AT with 2:1 AV relationship axer AV nodal–blocking agent administered.
# Antiarrhythmic agents
TABLE 243-1 Commonly Used Antiarrhythmic Agents—Intravenous Dose Range/Primary Indication
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