ECG of the Month

Abstract

A 2-year-old 30-kg (66-lb) sexually intact male Golden Retriever was referred to the Clinica Veterinaria Malpensa because of exercise intolerance and episodic weakness of 1 month' s duration. During 1 episode of weakness, an ECG examination performed by the primary veterinarian revealed a narrow-QRS complex tachycardia with a cycle length of 200 milliseconds. The patient was treated with sotalol a (2 mg/kg [0.9 mg/lb], PO, q 12 h) to control episodic supraventricular tachycardia and to reduce clinical signs.At the initial evaluation, a physical examination revealed no abnormalities. Findings of survey thoracic radiography and transthoracic echocardiography were considered normal. An initial 12-lead ECG revealed short PQ intervals, slurring of the onset of the QRS complexes (delta wave), and alteration of the QRS-ST segment morphology. These findings were consistent with ventricular pre-excitation.The presence of an accessory pathway (AP)-mediated tachycardia was strongly suspected, and an electrophysiological assessment was performed. Sotalol administration was discontinued for 24 hours (ie, a period equivalent to 5 half-lives of the drug) before the procedure. The patient was anesthetized and placed in dorsal recumbency during the entire interventional procedure. Multiple access sites on jugular and femoral veins were used to allow introduction of endocardial catheters by use of the Seldinger technique. The electrophysiological assessment was conducted in accordance with standard techniques. 1,2 A decapolar catheter b was introduced at the level of the coronary sinus and positioned in contact with the epicardal surface, and a quadripolar catheter c was inserted near the bundle of His. An ablation catheter d was used to perform programmed atrial and ven- Figure 1-Surface ECG tracings (6 leads of a 12-lead ECG) obtained during electrophysiological assessment of a dog that was evaluated because of exercise intolerance and episodic weakness of 1 month's duration. On the basis of initial ECG findings, an accessory pathway (AP) was suspected. The electrophysiological examination revealed the presence of an AP that was subsequently ablated by use of a radiofrequency catheter. During the procedure and before the ablation, the dog developed a paroxysm of sustained atrial fibrillation (AF). The first 6 beats of the ECG tracings have features typical of AF with orthodromic conduction through the His-Purkinje system, including absence of the P wave, narrow QRS complex (duration, 60 milliseconds; reference range, < 70 milliseconds), and irregular R-R intervals. From the seventh beat onward, antegrade activation of the AP with signs of ventricular pre-excitation is evident. Wide QRS complexes (duration, 100 milliseconds), the presence of a delta wave preceding each R wave, and persistence of irregular R-R intervals are indicative of the occurrence of pre-excited AF. Paper speed = 50 mm/s; 1 cm = 1 mV.

Electrocardiographic patterns of ventricular pre-excitation in dogs with right-sided accessory pathways

“…In contrast with people, APs in dogs have been reported to be located around the tricuspid valve annulus (Santilli et al 2007; Wright et al 2018) (Santilli et al 2006(Santilli et al , 2010(Santilli et al , 2012. This technique carries a high success rate in veterinary medicine and is associated with a low complication rate (Santilli et al 2006, Wright et al 2018).…”