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 Each catheter was passed into the esophagus to a location aboral to the heart and slowly withdrawn until atrial pacing was achieved. Then, catheters were withdrawn in 5-mm increments until pacing could not be achieved.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.

Effect of pulse width on transesophageal atrial pacing in dogs.

OBJECTIVE: To determine the impact of stimulus pulse width (PW) on pacing threshold (PT), zone of capture (ZOC) and extraneous muscular stimulation (EMS). STUDY DESIGN: Experimental trial in client-owned dogs. ANIMALS: Seventeen dogs, median weight 16.1 kg (interquartile range: 11.4-21.5). METHODS: Transesophageal atrial pacing (TAP) involved a 6 Fr pacing catheter inserted trans-orally into the esophagus to a position aboral to the heart in anesthetized dogs. The catheter was slowly withdrawn until atrial pacing was noted on an electrocardiogram. The catheter was withdrawn in 1 cm increments until TAP could not be achieved. PTs were recorded at each pacing site using PWs of 10.0, 5.0, 2.0 and 1.8 ms, always in that order. RESULTS: The overall lowest mean PTs for all dogs were 6 ± 3 mA, 9 ± 4 mA, 11 ± 5 mA and 13 ± 5 mA at PWs of 10.0, 5.0, 2.0 and 1.8 ms, respectively. A significant decrease in overall minimum PT was noted using a PW of 10.0 ms compared with either 2.0 or 1.8 ms (p = 0.043 and p = 0.001, respectively) and pacing using 5.0 ms compared with 1.8 ms (p = 0.028). A significant increase in ZOC was noted using a PW of 10.0 ms compared with PWs of 5.0, 2.0 and 1.8 ms (p = 0.0047, p = 0.0006 and p = 0.0003, respectively), using a PW of 5.0 ms compared with PWs of 2.0 and 1.8 ms (p = 0.0011 and p = 0.0003, respectively) and using a PW of 2.0 compared with one of 1.8 ms (p = 0.0084). CONCLUSIONS AND CLINICAL RELEVANCE: Use of 10.0 or 5.0 ms PW to perform TAP minimized the power required to pace the atria, while a PW of 10.0 ms maximized the size of the ZOC.

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.

Partial pericardial defect with left auricular herniation in a dog with syncope.

Pericardial defects are rare in both people and dogs. They may be congenital or acquired in origin, and partial or total in extent. Commonly, pericardial defects are incidental findings at autopsy; however, diagnostic methods such as thoracic radiography and echocardiography can be useful in the ante mortem diagnosis of pericardial defects. This report describes the first case of a dog with syncope, supraventricular tachycardia, and a partial left pericardial defect with herniation of the left auricle for which extensive ante mortem diagnostic information was available. Partial absence of the pericardium should be considered in dogs with disproportionate enlargement of cardiac chambers for which other congenital and acquired heart diseases are ruled out.

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.