Localization and characterization of atrial depolarization waves on the surface electrocardiogram in dogs with rapid supraventricular tachycardia.

BACKGROUND: Supraventricular tachycardias (SVTs), despite having various anatomical substrates and pathophysiological mechanisms, frequently show similar electrocardiographic presentations. OBJECTIVES: To locate and characterize atrial deflections (ADs) on 12-lead electrocardiograms in dogs with sustained rapid SVT and assess the utility of different electrocardiographic variables in differentiating types of tachycardia. ANIMALS: Ninety-two dogs with orthodromic atrioventricular reciprocating tachycardia, 17 with atrial flutter, 33 with focal atrial tachycardia recorded and confirmed by electrophysiological study, and 40 dogs with sinus tachycardia. METHODS: Atrial deflection position on the 12-lead surface electrocardiogram was assessed according to the sequence of intracardiac activation. Its features were evaluated together with the relationship between AD and QRS complex interval (AD-R) and QRS complex and AD interval (R-AD). RESULTS: Orthodromic atrioventricular reciprocating tachycardia was characterized by an AD-AD interval of 213 ± 30 ms, mean electrical axis (MEA) of AD of -90 (-90/-78)°, R-AD interval of 75 (65-80) ms, and R-AD/AD-R of 0.54 (0.45-0.64). Atrial flutter was characterized by an AD-AD interval of 199 ± 57 ms, MEA of 76° (72/81), R-AD of 120 (72-144) ms, and R-AD/AD-R of 0.81 (0.63-1.13). Focal atrial tachycardia was characterized by an AD-AD interval of 270 ± 38 ms, MEA of 49 (-72/76)°, R-AD of 160 (120-200) ms, and R-AD/AD-R of 1.45 (0.92-1.67). Sinus tachycardia was characterized by an AD-AD interval of 292 ± 31 ms, MEA of 66° (52/73), R-AD of 215 (192-222) ms, and R-AD/AD-R of 2.68 (2.25-3.08). CONCLUSIONS AND CLINICAL IMPORTANCE: Analyzing AD on 12-lead electrocardiogram is helpful in differentiating the most common SVTs in dogs.

Lidocaine for chemical cardioversion of orthodromic atrioventricular reciprocating tachycardia in dogs.

BACKGROUND: Typical atrioventricular accessory pathways (APs) are composed of myocardial cells. They provide electrical connections between atria and ventricles separate from the normal conduction system. Accessory pathways can participate in a macroreentrant circuit resulting in orthodromic atrioventricular reciprocating tachycardia (OAVRT). HYPOTHESIS: Because of ultrastructural similarities of typical AP cells to ventricular myocardial cells, we hypothesized lidocaine would be effective in blocking AP conduction, thus terminating OAVRT. ANIMALS: Thirty-two consecutive client-owned dogs presenting with narrow complex tachyarrhythmias were confirmed to have OAVRT by electrophysiologic study (EPS). METHODS: Prospective, nonrandomized, single-arm study with lidocaine administered IV to dogs during OAVRT in 2 mg/kg boluses to a cumulative dose of 8 mg/kg or development of adverse effects. Electrocardiograms were monitored continuously. Subsequent EPS was performed to confirm OAVRT and the absence of other tachycardia mechanisms. RESULTS: Twenty-seven dogs experienced OAVRT cardioversion with lidocaine, before or at the time of adverse effects. Orthodromic atrioventricular reciprocating tachycardia in 5 dogs did not cardiovert before adverse effects, precluding additional dosing. Median total lidocaine dose for cardioversion was 2 mg/kg (interquartile range, 2-5.5 mg/kg). Dogs with right free wall APs had a significantly higher rate of cardioversion than did dogs with right posteroseptal APs. CONCLUSIONS AND CLINICAL IMPORTANCE: Lidocaine successfully cardioverted OAVRT in 84.4% of dogs in our study before adverse effects precluded additional dosing. In 5 dogs with dose limited by adverse effects, it is unknown whether cardioversion would have occurred at a higher cumulative dose.