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.

Atrioventricular accessory pathways in 89 dogs: Clinical features and outcome after radiofrequency catheter ablation.

BACKGROUND: Atrioventricular accessory pathways (APs) in dogs have been reported rarely. Data regarding clinical presentation and long-term outcome after radiofrequency catheter ablation (RFCA) are limited. HYPOTHESIS/OBJECTIVES: To study clinical features, electrophysiologic characteristics, and outcome of RFCA in dogs with APs. ANIMALS: Eighty-nine dogs presented consecutively for RFCA of APs. METHODS: Case series. RESULTS: Labrador retrievers (47.2% of dogs) and male dogs (67.4% of dogs) were most commonly affected. Labrador retrievers were more likely to be male than non-Labrador breeds (P = .043). Clinical signs were nonspecific and most commonly included lethargy and gastrointestinal signs. Concealed APs were more prevalent in Labrador retrievers than other breeds (P = .001). Right-sided APs (91.7%) predominated over left-sided (8.3%). Tachycardia-induced cardiomyopathy (TICM) occurred in 46.1% of dogs, with complete resolution or substantial improvement noted on one-month postablation echocardiograms. Radiofrequency catheter ablation successfully eliminated AP conduction long term in 98.8% of dogs in which it was performed. Complications occurred in 5/89 dogs. Recurrence in 3 dogs was eliminated long term with a second procedure. CLINICAL IMPORTANCE/CONCLUSIONS: Accessory pathways are challenging to recognize in dogs because of nonspecific clinical signs, frequency of concealed APs that show no evidence of their presence during sinus rhythm, and intermittent occurrence of tachyarrhythmias resulting from APs. Tachycardia-induced cardiomyopathy commonly occurs with AP-mediated tachycardias and should be considered in any dog presenting with a dilated cardiomyopathic phenotype because of its good long-term prognosis with rhythm control. Radiofrequency catheter ablation is a highly effective method for eliminating AP conduction and providing long-term resolution.

When, why, and how to perform cardiac radiofrequency catheter ablation.

Radiofrequency catheter ablative techniques provide a unique opportunity to cure dogs of certain supraventricular tachyarrhythmias, rather than simply controlling the rhythm with drug therapy. Accessory pathways, which can participate as one limb of a rapid, narrow complex tachyarrhythmia circuit, have a particularly high cure rate with radiofrequency catheter ablation. Focal atrial tachycardias also provide a substrate that can be amenable to ablation. Tachycardia-induced myocardial dysfunction resulting from frequent tachyarrhythmic episodes will resolve after a successful ablation. This report outlines the indications, equipment, and techniques used in dogs for performing catheter ablation with temperature-controlled radiofrequency energy delivery.

Interventional catheterization for tachyarrhythmias.

Catheter ablation of cardiac tachyarrhythmias is unique among our therapeutic armamentarium because it offers the ability to cure certain tachyarrhythmias permanently without implanted devices. TICM that is not distinguishable from idiopathic DCM can also resolve once the underlying tachyarrhythmia is eliminated. Current techniques are best suited to tachyarrhythmias in which a point lesion or small linear burn would result in disruption of the tachyarrhythmia's substrate. The equipment and expertise required limit the availability of this treatment modality in veterinary medicine. Its success with SVTs (particularly those secondary to accessory pathways), however, make it a viable option for many owners, even if they must travel some distance to reach a center performing these procedures.