Robert A. Sanders

Effects of Pulmonary Vein Ablation on Regional Atrial Vagal Innervation and Vulnerability to Atrial Fibrillation in Dogs

Introduction: Pulmonary vein (PV) isolation has proven to be an effective therapy for atrial fibrillation (AF). However, clinical evidence suggests that suppression of AF after PV isolation could not be fully attributed to the interruption of electrical conduction in and out of the PVs. Furthermore, little is known regarding the effects of ablation around the PVs on the atrial electrophysiological properties. We aimed to study the changes in atrial response to vagal stimulation (VS) after PV ablation (PVA).

Efficacy of two commercially available cardiac pacing catheters for transesophageal atrial pacing in dogs

OBJECTIVE Compare the efficacy of two cardiac pacing catheters for transesophageal atrial pacing (TAP). ANIMALS Ten healthy dogs. METHODS Transesophageal atrial pacing was attempted in left lateral recumbency under general anesthesia. In series, a curved electrophysiologic (EP) catheter and a straight transesophageal pacing (TP) catheter were passed transorally into the distal esophagus, caudal to the heart. Each catheter was slowly withdrawn until pacing was initiated. The catheter continued to be withdrawn in 5 mm increments until capture was no longer achieved at maximal pacing setting creating a total zone of capture (tZOC). Minimum pacing threshold (Th(min)) and degree of extraneous muscle stimulation (EMS) were determined at each site. RESULTS The EP catheter achieved TAP in 10/10 dogs with a Th(min) of 8.8 ± 4.8 mA and tZOC of 4.0 ± 1.7 cm. The TP catheter achieved TAP in 7/10 dogs with a Th(min) of 22.5 ± 5.6 mA and tZOC of 1.2 ± 1.6 cm. No EMS was noted during TAP at Th(min) using the EP catheter. Of the 7 dogs in which TAP was successful, 3/7 experienced considerable EMS at Th(min). There was no significant relationship between patient body weight and Th(min) with either catheter (EP catheter P = 0.09; TP catheter P = 0.81). CONCLUSIONS The electrophysiology catheter captured the atria of more dogs over a larger area without EMS as compared to the TP catheter. The electrophysiology catheter is recommended for transesophageal atrial pacing in dogs.

Use of transesophageal atrial pacing to provide temporary chronotropic support in a dog undergoing permanent pacemaker implantation.

A 14.5-kg, 13-year-old female spayed Cocker spaniel was evaluated because of episodic hind limb weakness. Results of examination were consistent with sick sinus syndrome with intermittent second-degree atrioventricular block. Transesophageal atrial pacing was successful in providing chronotropic support during permanent pacemaker implantation. Transesophageal atrial pacing appears to be a viable option for temporary atrial pacing in dogs with hemodynamically marked bradycardia without significant atrioventricular blockade.

Utility of transesophageal electrocardiography to guide optimal placement of a transesophageal pacing catheter in dogs

OBJECTIVE To determine if the transesophageal atrial (A) wave amplitude or ventricular (V) wave amplitude can be used to guide optimal positioning of a transesophageal pacing catheter in dogs. STUDY DESIGN Prospective clinical study. ANIMALS Fourteen client owned healthy dogs with a median weight of 15.4 kg (IQR = 10.6-22.4) and a median age of 12 months (IQR = 6-12). MATERIALS AND METHODS Transesophageal atrial pacing (TAP) using a 6 Fr pacing catheter was attempted in dogs under general anesthesia. The pacing catheter was inserted orally into the esophagus to a position caudal to the heart. With the pulse generator set at a rate 20 beats/minute(-1) above the intrinsic sinus rate, the catheter was slowly withdrawn until atrial pacing was noted on a surface electrocardiogram (ECG). Then the catheter was withdrawn in 1 cm increments until atrial capture was lost. Minimum pacing threshold (MPT) and transesophageal ECG were recorded at each site. Amplitudes of the A and V waves on transesophageal ECG were then measured and their relationship to MPT was evaluated. RESULTS TAP was achieved in all dogs. In 9/14 dogs the site of lowest overall MPT was the same as the site of maximal A wave deflection. In dogs with at least three data points, linear regression analysis of the relationship between the estimated site of the lowest overall MPT compared to estimated site of the maximal A and V waveform amplitudes demonstrated a strong correlation (R(2) = 0.99). CONCLUSION AND CLINICAL RELEVANCE Transesophageal ECG A and V waveforms were correlated to MPT and could be used to direct the placement of a pacing catheter. However, the technique was technically challenging and was not considered to be clinically useful to guide the placement of a pacing catheter.

Novel cutaneous use of implantable loop recorders in two dogs with unexplained episodes of collapse

Determining the cause of episodes of collapse can be difficult. Even in patients with frequent collapsing episodes due to cardiac causes, diagnostic surface electrocardiogram and 24 hr ambulatory electrocardiographic (Holter) monitoring are sometimes inconclusive. Event monitors with multiple leads can be challenging to use in veterinary medicine over long periods of time due to lead dislodgment. Implantable leadless loop recorders (ILRs) are useful, but owners are sometimes unwilling to have an ILR implanted due to the associated risks and/or costs. In this case report, the authors describe the use of cutaneously placed ILRs in two dogs with unexplained episodes of collapse/exercise intolerance. Data recorded provided clinically useful information. Cutaneously placed ILRs can be used effectively in veterinary medicine to evaluate patients with unexplained episodes of collapse.

Feasibility of transthoracic echocardiographic imaging in non-sedated ovine subjects using a commercial restraint device

Transthoracic echocardiography (TTE) is a valuable non-invasive imaging research technique. In ovine models of cardiac disease, restraint for TTE often involves sedation even with currently available restraint equipment; our goal was to determine the feasibility of using a commercial restraint device, commonly known as the sheep chair, in minimizing animal stress and the need for sedation while achieving a complete TTE examination. A total of 10 healthy adult Dorset sheep were restrained in a sheep chair for TTE and observed for signs of stress. No animals displayed overt evidence of stress and none required sedation. While individual anatomic variation existed, image quality was sufficient to determine cardiac function. These observations suggest that a sheep chair is a useful aid in minimizing the need for sedation to acquire a full TTE study in ovine subjects.

Echocardiographic imaging options in ovine research subjects

OBJECTIVES To determine the feasibility of acquiring quality transesophageal (TEE), epicardial (EE), and intracardiac (ICE) echocardiographic images in ovine subjects and to discuss the merits of each technique with a focus on ICE image acquisition. ANIMALS Eleven male castrated Dorset adult sheep. METHODS Transesophageal echocardiography was performed under general anesthesia. Epicardial echocardiography was performed as part of an open chest (thoracotomy or sternotomy) experiment. Subjects were recovered with permanent jugular vein indwelling catheter and ICE from this approach was described. Feasibility of each technique was qualitatively assessed based on subjective image quality from three images for each image plane in each sheep. RESULTS Transesophageal echocardiography was technically challenging and did not provide adequate image quality for consistent interpretation. Epicardial echocardiography and ICE had more favorable results with ICE demonstrating unique benefits for post-operative serial monitoring. CONCLUSIONS Epicardial echocardiography and ICE were effective imaging techniques. Epicardial echocardiography required the least specialized training but was considered to have limited feasibility due to its requirement for an open chest procedure. Even with the necessity for permanent indwelling jugular cannulation, ICE was the least invasive of the three imaging techniques and potentially the most practical approach for chronic studies by minimizing post-operative stress. Transesophageal echocardiography was not a feasible technique in this study.

Effects of catheter shape, interelectrode spacing, and electrode size on transesophageal atrial pacing in dogs

OBJECTIVE To determine effects of catheter shape, interelectrode spacing (IS), and electrode size (ES) on pacing threshold (PT), extraneous muscular stimulation (EMS), and zone of capture (ZOC) for dogs undergoing transesophageal atrial pacing (TAP). ANIMALS 10 purpose-bred dogs without cardiac conduction disturbances. PROCEDURES 7 configurations for TAP catheters were tested in each dog to evaluate effects of catheter shape (curved or straight), IS (5, 15, and 25 mm), and ES (2, 4, and 6 mm). Each catheter was passed into the esophagus to a location aboral to the heart and slowly withdrawn until atrial pacing was achieved. Then, catheters were withdrawn in 5-mm increments until pacing could not be achieved. Outcomes measured at each pacing site included PT, degree of EMS, and ZOC. RESULTS There was a significantly lower PT, wider ZOC, and less EMS for the curved catheter than for the straight catheter. An ES of 6 mm induced significantly more EMS than was induced by an ES of 2 or 4 mm. An IS of 5 mm induced significantly less EMS and a significantly narrower ZOC but required a significantly higher PT, compared with results for an ES of 15 or 25 mm. Additionally, there was a significant direct correlation between IS and ZOC. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that a curved catheter with multiple 4-mm electrodes that provides for variable IS would be ideal for TAP in dogs. IMPACT FOR HUMAN MEDICINE TAP catheters currently used in human medicine are straight. The PT in humans may potentially be reduced with curved catheters.