Heart rate distribution in dogs with third degree atrioventricular block and rate responsive pacemakers.

INTRODUCTION: In dogs, single lead ventricular pacing, ventricular sensing, inhibition response, rate adaptive (VVIR) pacemakers are routinely used to treat third degree atrioventricular block. The objectives of this study were to investigate the heart rate distribution in dogs with VVIR pacemakers, and report changes when activity settings were adjusted. ANIMALS: Eighteen client-owned dogs with VVIR pacemakers for third degree atrioventricular block. MATERIALS AND METHODS: This observational study consisted of a review of medical records of dogs with VVIR pacemakers. For dogs with >50% of paced beats at the lower pacing rate, the activity daily living (ADL) and exertion responses were increased. Re-evaluations were performed after 6-12 months. RESULTS: Heart rate distribution similar to healthy dogs was absent for all dogs. In nine dogs, the ADL and exertion responses were increased to the highest level. Of these, three dogs showed no improvement in heart rate distribution; for two dogs, one with an epicardial pacemaker, several activity settings were adjusted and pacing at higher heart rates was observed at re-evaluation. Four dogs died or were lost to follow-up. Clinical signs had resolved for all dogs after pacemaker implantation. CONCLUSION: Default activity settings of VVIR pacemakers do not result in heart rate distribution equivalent to healthy dogs. Increasing the ADL and exertion response settings to the highest levels did not improve the pacemaker rate response. Further investigations into the role of dog size, generator positioning, pacemaker settings, and whether rate responsiveness is required for dogs' quality and quantity of life are warranted.

Characteristics and outcomes of cats with and without pacemaker placement for high-grade atrioventricular block.

INTRODUCTION: Available information on characteristics and outcome in cats with high-grade atrioventricular block (AVB) that receive a pacemaker is limited. ANIMALS: Twenty-two privately owned cats presenting with high-grade AVB. MATERIALS AND METHODS: Medical records were retrospectively examined. Cats were grouped as having received a pacemaker (PACE group) or not having received a pacemaker (non-PACE group). Clinical characteristics and outcomes of groups were evaluated. RESULTS: There were 10 cats in the PACE group and 12 cats in the non-PACE group. At presentation, syncope or seizure-like behavior (p = 0.004) and bradycardia (p = 0.043) were more common in the PACE than the non-PACE group. Historical lethargy (p = 0.015) and dull mentation (p = 0.045) were more common in the non-PACE group, as was clinically relevant systemic disease. Pacemaker placement improved syncope or seizure-like behavior in 100% of cats. The degree of AVB at presentation was not associated with pacemaker placement nor the future degree of AVB. The major complication rate of pacemaker placement was 40%. Intergroup survival was not significantly different (PACE group 1278 days, 95% confidence interval: 0-2145 days; non-PACE group 213 days, confidence interval: 1-not available, p = 0.77). CONCLUSIONS: Pacemaker placement improved clinical signs in cats with high-grade AVB. A difference in survival time could not be demonstrated between cats that received and did not receive a pacemaker in this retrospective study. High-grade AVB can be transient and accompanied by systemic disease in some cats.

Echocardiographic parameters for the assessment of congestive heart failure in dogs with myxomatous mitral valve disease and moderate to severe mitral regurgitation.

The objective of this study was to evaluate the influence of congestive heart failure (CHF) on echocardiographic variables in dogs with moderate or severe mitral valve regurgitation (MR) secondary to myxomatous mitral valve disease (MMVD). The secondary objective was to investigate the preliminary use of left ventricular early inflow-outflow index (LVEIO) and L-waves as indicators of CHF. Forty-five dogs with moderate or severe MR without (n = 23) or with (n = 22) CHF were retrospectively included. Echocardiographic variables of elevated left ventricular (LV) filling pressures and cardiac function, LVEIO and the presence of L-waves were obtained and statistically compared between the two groups. On general linear model analysis, mitral inflow peak E-wave velocity, E:A ratio, ratio of E to isovolumic relaxation time (IVRT) and LVEIO were increased, while left atrium (LA) fractional shortening was reduced, in dogs with CHF. Peak E-wave velocity, peak A-wave velocity, E:A ratio, LA minimum diameter, LA diameter before the P-wave, LA fractional shortening and LVEIO were found to be predictive of CHF. The absence of L-waves indicated a reduced risk of CHF. Several echocardiographic variables may be useful in identifying elevated LV filling pressures, consistent with CHF, in dogs with moderate and severe MR. Left ventricular early inflow-outflow index and L-waves might be of interest as clinical and prognostic markers in dogs with MMVD and require further investigation.

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.

Effect of high altitude on the visual evoked responses in humans on Mt. Everest.

Cerebral visual evoked potentials (VEPs) were collected over a 1-year period from the summer of 1983 through the summer of 1984 from 16 members of the American Ultima Thule Everest Expedition at sea level and at altitudes of 7,100 ft, 16,800 ft, and 21,300 ft. VEPs in response to 100 unilateral LED flashes were processed by a modified Nicolet CA-1000 computer of average transients with an analysis time of 250 ms and were recorded by an X-Y plotter. Readings of oxygen saturation, tetrapolar impedance pulmonary plethysmography, and clinical signs and symptoms of acute mountain sickness (AMS) were recorded. The latency of the major waves of the VEPs increased on initial arrival at higher altitude and returned toward base line over time with acclimatization. There were more acute latency changes in individuals who suffered from symptoms of AMS, which reversed with amelioration of symptoms.

Phenytoin and acute mountain sickness on Mount Everest.

Twenty-one climbers who were members of the American Ultima Thule Everest Expedition participated in a double-blind, randomized clinical trial of phenytoin prophylaxis for acute mountain sickness during the approach to the northeast ridge of Mount Everest. The study was carried out between Beijing and base camp at 16,800 feet. Time spent ascending from Beijing to base camp averaged 13 days. High-altitude symptom questionnaires were filled out beginning in Lhasa at 11,800 feet and in Xigatse at 12,000 feet, in Xegar at 14,000 feet, and at base camp. Computer analysis of the questionnaire answers performed by an impartial analyst revealed that climbers who took phenytoin were less likely to have headaches at base camp. No other statistically significant differences were observed, but the power of the sample size was low.

Cerebral etiology of acute mountain sickness: a case report.

The authors report a case of acute mountain sickness (AMS) experienced by a support member of the Ultima Thule Everest Expedition. The subject arrived at the 17,000-ft base camp by truck and then developed the symptoms of AMS over the following 72 hours. Flash-induced visual evoked responses (VERs), tetrapolar impedance pulmonary plethysmography, and oxygen saturation measurements were performed. These changed from normal before the onset of his symptoms to abnormal during the height of the symptoms and reverted to normal after treatment. This is the first reported case of AMS monitored with VERs. It has been postulated that AMS may be an early form of cerebral edema, and this report corroborates this hypothesis.