Effect of shock strength on survival and acute cardiac damage induced by open-thorax defibrillation of dogs

The safety of open thorax defibrillation with single damped sine-wave shocks and 6-cm-diameter electrodes was evaluated in healthy anesthetized dogs. Twenty-one dogs were allotted to 6 groups: Group A were nonshocked controls and groups B through F were given single shocks of 4-, 7-, 12-, 19-, or 32-fold, respectively, greater than a defibrillation threshold dose (30 mA/g of heart). Immediate postshock death resulted in group F dogs; group A through E dogs survived and were killed after 2 days. The incidence and severity of cardiac morphologic damage increased with shock strength (mild damage occurred in 1 of 3 dogs in group C and in 3 of 4 dogs in group D and severe damage occurred in 2 of 3 dogs in group E). The cardiac lesions were characterized grossly and microscopically. In dogs that died immediately after shocking, damage was apparent as pale circular zones of edema and myofibrillar degeneration in the ventricular free walls beneath the electrode placement sites on the cardiac surface. In the dogs that survived 2 days, the defibrillator-induced areas of myocardial necrosis and calcification were concentrated in arc or ringlike patterns beneath the periphery of the electrode placement sites. All dogs that were studied 2 days after shocking had mild fibrinous pericarditis. Postshock electrocardiographic changes were not good indicators of cardiac damage because the mild epicardial inflammatory reaction associated with the surgical procedure produced large ST and T wave changes which masked any changes associated with myocardial necrosis induced by the electric shocks. It was concluded that a substantial safety margin exists between the required defibrillation threshold shock dose and the large shocks required to produce marked cardiac damage or death in healthy dogs.     

Evaluation of gastrointestinal permeability and mucosal absorptive capacity in dogs with chronic enteropathy

OBJECTIVE: To assess intestinal mucosal function by measuring permeability and absorptive capacity in dogs with chronic enteropathy (CE) before and after treatment and to determine whether those variables were correlated with clinical disease activity or histologic scoring of intestinal biopsy specimens. ANIMALS: 29 dogs with CE. PROCEDURE: Dogs were designated as having dietresponsive CE or CE requiring glucorticoid treatment. Severity of clinical signs was assessed by calculating the canine inflammatory bowel disease activity index (CIBDAI). Histologic severity of intestinal infiltration was assessed before and after 4 weeks of treatment in the diet-responsive group and before and after 10 weeks of treatment in the glucocorticoid group. Gastrointestinal permeability and mucosal absorptive capacity were assessed by use of intragastric administration of a solution containing lactulose, rhamnose, xylose, 3-O-methylglucose, and sucrose. Urine was collected 6 hours after administration of the sugar solution to determine urinary lactulose-to-rhamnose (L:R), xylose-to-methylglucose (X:M), and sucrose-to-methylglucose (S:M) ratios. RESULTS: Median CIBDAI scores decreased significantly in both groups of dogs after treatment. However, the median histologic grade of intestinal biopsy specimens did not change with treatment in either group. There were no significant differences in L:R, X:M, or S:M ratios after treatment in either group and no significant correlations between L:R, X:M, or S:M ratios and CIBDAI or histologic scores. CONCLUSIONS AND CLINICAL RELEVANCE: Results of tests for intestinal permeability and mucosal absorptive capacity were not useful indicators of clinical disease activity as assessed by the CIBDAI or the sever ity of infiltration as indicated by histologic evaluation.     

The efficacy and safety of external biphasic defibrillation in toy breed dogs

Objective: To evaluate the efficacy and safety of biphasic (BP) defibrillation in toy breed dogs (<5 kg of body weight).
Design: Prospective, clinical experimental study.
Setting: Veterinary teaching hospital.
Animals: Five dogs (pilot study) and 10 dogs (comparison study of biphasic versus monophasic defibrillation).
Measurements and main results: The efficacy of defibrillation was compared by estimating E80 (80% probability of successful defibrillation) after biphasic (BP) and monophasic (MP) defibrillations. The E80 for BP defibrillation was 7.24±1.33 J (2.24±0.41 J/kg) and 10.24±1.34 J (3.18±0.12 J/kg) for MP defibrillation. BP waveform required 30% less shock energy for a successful defibrillation. In order to compare the safety of defibrillation, we evaluated changes in cardiac biomarkers, electrocardiogram, echocardiographical left ventricular index, and aortic pressure during and after BP and MP defibrillation. All dogs treated by either BP or MP defibrillation survived. Pulseless electrical activity occurred in 2 of 5 dogs during MP defibrillation. The levels of cardiac biomarkers were elevated and sustained for longer periods in the MP defibrillation group. Electrocardiographic changes (e.g., QT prolongation, the time to return to an isoelectric ST segment after shocks) were more severe and longer in the MP defibrillation group. In addition, overall left ventricular cardiac performance was severely depressed in the MP group compared with the BP group.
Conclusion: Our findings suggest that BP defibrillation is more effective and safer than MP defibrillation. We determined the acceptable shock energy to be 2–4 J/kg for toy breed dogs.     

Evaluation of the anti-endotoxic effects of polymyxin-E (colistin) in dogs with naturally occurred endotoxic shock

Endotoxin is a potent stimulator of the inflammatory response and is believed to initiate the pathology in gram-negative sepsis. Agents are being searched for that bind and neutralize or block the effects of endotoxin. The aim was to study the anti-endotoxic effects of polymyxin-E (colistin) in endotoxaemic dogs. The study included a total of 30 endotoxaemic dogs, which were divided into two groups (control = 15; test = 15) of both sexes, different breeds and ages. Hetastarch colloid solution (Expahes,10 mL/kg, i.v.) with lactated Ringer's solution (20 mL/kg, i.v., Q12 h) was given to all dogs. While ampicillin was administered (Alfasilin, 10 mg/kg, i.m., Q12 h) as an antibacterial to the control group, colistin (12,500 IU/kg, i.m., Q12 h) + ampicillin were administered to the test group. The clinical examination (body temperature, pulse and respiration rates, capillary filling times, peripheral pulse qualities, dehydration degrees), hematological and biochemical examinations (WBC, RBC, HGB, HCT, thrombocyte, serum urea, creatinine and TNF-alpha) were performed both before the treatment, and 2, 4, 12 and 24 h after the treatment. In comparison with the control group, it was observed that test group had shorter capillary filling time at 24 h (P < 0.001). Moreover, the degree of dehydration in test group, was significantly improved at 24 h (P < 0.01). While the differences in peripheral pulse qualities significantly differed between 0 and 2 h in controls, at 2, 4, 24 h after treatment it was found to be significantly increased when compared with 0 h in the test group. Serum TNF-alpha concentrations were statistically decreased in the test group between 0 h and other times (P < 0.01). When compared with controls, serum TNF-alpha concentrations were lower at 2, 4, 12 and 24 h in test group (P < 0.05). Results of the study indicated that polymyxin-E (colistin) has an anti-endotoxic effect and is safe for the dogs with endotoxemia at the dosage used in this study.     

Spectral waveform analysis of major arteries in conscious dogs by Doppler ultrasonography

Normal values of arterial blood flow velocity and waveforms in major arteries of 10 healthy conscious Beagle dogs were determined using Doppler ultrasonography. Peak systolic, early diastolic, and end-diastolic velocities of the basilar artery, common carotid artery, abdominal aorta, external iliac artery, femoral artery, and peak ejection velocity of the valvular aorta were evaluated. Pulsatility index (PI) of the basilar artery and blood pressure were recorded. All arteries had a high-resistance flow pattern with triphasic flow velocity except the basilar artery, which had a low-resistance pattern. Mean peak systolic velocities of the basilar artery, common carotid artery, abdominal aorta, external iliac artery, and femoral artery were 72 +/- 19, 115 +/- 17, 121 +/- 24, 105 +/- 25, and 110 +/- 17 cm/s, respectively. The PI of the basilar artery and peak ejection velocity of the valvular aorta were 1.37 +/- 0.13 and 96 +/- 16 cm/s, respectively. Mean systolic and diastolic blood pressures were 137 +/- 13 and 78 +/- 15 mmHg, respectively. Present findings may be used as references in future studies on vascular diseases and hemodynamics in dogs.     

Role of histamine in heartworm extract-induced shock in dogs

OBJECTIVE: To determine whether heartworm (HW) extract-induced shock in dogs is consistent with anaphylactic shock by examining the role of histamine. ANIMALS: 6 mixed-breed dogs (3 without and 3 with HW infections) and 4 specific pathogen-free (SPF) Beagles. PROCEDURE: Four experiments were performed as follows: 1) 6 mixed-breed dogs were treated IV with 2 ml of HW extract, and plasma histamine concentrations were determined; 2) 4 SPF dogs were treated IV with 2 ml of HW extract and examined for shock; 3) sera from 6 dogs of experiment 1 and from 4 SPF dogs of experiment 2 that were obtained before HW extract treatment were tested for heterologous passive cutaneous anaphylaxis (PCA), using rabbits during a sensitization period of 48 to 72 hours; and 4) mast cell degranulation by HW extract was tested, using rat mesentery and canine cultured mast cells. RESULTS: Experiment 1: 6 dogs developed shock, and plasma histamine concentrations increased significantly from 0.3 +/- 0.2 (mean +/- SD) ng/ml before HW extract treatment to 44.6 +/- 68.9 ng/ml at the onset of shock; experiment 2: all SPF dogs developed shock and had an increase in plasma histamine concentrations; experiment 3: sera from mixed-breed dogs without HW infection and from SPF dogs had negative PCA reactions; experiment 4: HW extract degranulated rat mesentery mast cells and released histamine directly from canine mast cells. CONCLUSIONS AND CLINICAL RELEVANCE: Results of our study indicate that an unknown mast cell-degranulating substances contained in HW extract may degranulate mast cells directly, consequently releasing histamine that may participate in the onset of shock in HW extract-induced shock in dogs.     

Effects of bandage configuration on paw pad pressure in dogs: a preliminary study

Seven bandage configurations were placed on the right forepaw of six English pointer dogs to evaluate the effects that configurations have on reducing pad pressure. The "clam shell" configuration resulted in less pressure being applied to all palmar pad surfaces. For the major weight-bearing pad, a basic paw bandage with an intermediate compressible foam sponge that had a hole under the major weight-bearing pad, combined with a metal splint paw cup under the sponge, resulted in a significantly lower pressure recording than for other bandage configurations. Digital pads 3 and 5 had the greatest pressure in a basic bandage configuration. Based on pressures on these pads, a basic paw bandage with an intermediate compressible foam sponge under the major weight-bearing pad, with or without a metal splint paw cup under the sponge, helped elevate the digits to relieve pressure on them. Placing a foam sponge pad, with or without a splint paw cup under the palmar paw surface, also provided less pressure on these pads.     

Effect of posture and anaesthesia on the distribution of pulmonary perfusion and lung configuration in beagle dogs

To investigate the effect of posture and anaesthesia on the topographical distribution of pulmonary perfusion in canine lungs, the changes in lung shape, configuration and regional perfusion were assessed in healthy beagle dogs, using a repeated 99mTc perfusion scintigraphic procedure. The general shape of the lung images was similar in standing and prone postures, except for a relative increase of the more ventral zone in the prone posture, ascribed to vertical flattening of the lung associated with enlargement of the ventral zones. Configuration changes revealed a shift of the parenchyma towards the more caudal parts in the prone posture, which suggests a parenchymal compression of the paradiaphragmatic lung zones. The prone posture induced a decreased perfusion to the caudal third of the lung. Anaesthesia induced significant changes in lung shape without an obvious direction. The perfusion to the more ventral as well as to the more cranial zones was reduced. Differences in the perfusion distribution are thought to be mainly due to the pressure exerted by the abdominal content through the diaphragm and to the shift of the blood towards better ventilated lung regions.     

Evaluation of the six-minute walk test in dogs

OBJECTIVE: To determine the feasibility for use of a 6-minute walk test (6-MWT) in dogs with congestive heart failure (CHF) and document that the distance walked in 6 minutes decreases when a dog has CHF. ANIMALS: 16 young mature male hound-crossbred dogs weighing between 25 and 37 kg. PROCEDURE: An unobstructed path (22.73 m) was measured in a hallway. Each dog was walked on a leash for 6 minutes; each dog was allowed to set its own pace. At the end of 6 minutes (as measured by use of a stopwatch), the total distance walked was measured. Heart rate (HR) obtained by auscultation and mean systemic arterial pressure (MAP) obtained by oscillometry were recorded before and after the 6-MWT. Heart failure was induced by use of rapid ventricular pacing. Mean of the distance walked, HR, and MAP before and after the 6-MWT were compared between the control period and after dogs developed induced CHF. RESULTS: Dogs with CHF had a significant increase in resting HR, significant decrease in MAP, and a significant decrease in the distance walked in 6 minutes. The MAP increased slightly after exercise during the control period but decreased slightly after exercise during the CHF period. Fractional shortening decreased significantly when dogs had CHF. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of these results indicated that the distance walked in 6 minutes decreased significantly when a dog had CHF. The 6-MWT requires little time, space, or equipment and may replace the treadmill exercise test.     

Hemodynamic characteristics of vasopressin in dogs with severe hemorrhagic shock

The effect of vasopressin was compared with that of the established vasopressor epinephrine in experimentally induced hemorrhagic shock. After rapid crystalloid resuscitation in a ratio of three volumes of 0.9% saline to one volume of blood (3:1 crystalloid resuscitation), six dogs were given 0.4 IU/kg vasopressin and another six dogs were given 0.1 mg/kg epinephrine. Five dogs in the control group were given fluid resuscitation in the same manner as above without administration of any drugs. Administration of vasopressin increased diastolic arterial pressure (DAP) from 45.0 +/- 4.9 to 91.2 +/- 9.6 mmHg within 5 min, compared with epinephrine from 46 +/- 4.0 to 51.8 +/- 7.7, and control from 47.3 +/- 7.5 to 46.3 +/- 7.3. Systolic arterial pressure (SAP) did not increase significantly following vasopressin compared with epinephrine and control group. Results of DAP and systemic vascular resistance index (SVRI) suggested that vasopressin administration was vasoconstrictive after fluid resuscitation in decompensatory hemorrhagic shock in dogs, whereas epinephrine did not compared with control. In addition, epinephrine did not affect the cardiac index (CI) and SVRI, while a significant decrease in CI and increase in SVRI were observed in vasopressin group. The pressor effect of epinephrine in the vascular system was abrupt and only lasted a short period of time (within 5 min), while that of vasopressin was steady and lasted for more than 1 hr, especially regard to in DAP. When compared with epinephrine, vasopressin can be a more effective and safer choice in patients with severe hemorrhagic shock.     

Evaluation of the Accutrend for lactate measurement in dogs

BACKGROUND: Lactate concentrations are increasingly quantified in dogs using point-of-care instruments, but often without canine-specific method evaluation and instrument-specific reference intervals. OBJECTIVES: The objectives of this study were to 1) determine the precision of the Accutrend (Roche Diagnostics) for lactate determination in dogs, 2) determine the accuracy of the Accutrend using the Rapidlab 865 (Bayer Diagnostics) as the reference method, and 3) establish and compare reference intervals for lactate concentration in clinically healthy dogs for both instruments. METHODS: Precision was evaluated using low and high control materials, and variable (1 drop) and fixed (25 microL) sample volumes. Accuracy was determined by comparing lactate concentrations obtained with the Accutrend with those from the Rapidlab 865 in 273 heparinized canine jugular venous blood samples from 100 clinically healthy dogs and 107 systemically ill dogs (173 samples). Lactate reference intervals were established for both analyzers using data from the 100 clinically healthy dogs. RESULTS: The precision of the Accutrend was good (coefficients of variation, < or = 5.3%) for 25-microL samples but not when a drop was used. Lactate concentrations obtained on the Accutrend correlated poorly with those from the Rapidlab 865 (r = 0.864, mean bias = 0.66 mmol/L, 95% confidence interval [CI] = 0.57-0.76 with 95% limits of agreement = -0.87 (lower limit, 95% CI = -1.03 to -0.71) and 2.20 (upper limit, 95% CI = 2.04 to 2.36). The reference interval for canine lactate concentration on the Accutrend was 1.2-3.1 mmol/L compared with 0.46-2.31 mmol/L on the Rapidlab. CONCLUSION: Although precision was good with fixed sample volumes, blood lactate concentrations obtained on the Accutrend were significantly different than those on the Rapidlab 865, with systematic and random errors resulting in a positive bias. Further evaluation of the Accutrend is required before its use in dogs can be recommended.     

Spectral waveform analysis of intranodal arterial blood flow in abnormally large superficial lymph nodes in dogs

OBJECTIVE: To evaluate pulsed-wave Doppler spectral parameters as a method for distinguishing between neoplastic and inflammatory peripheral lymphadenopathy in dogs. SAMPLE POPULATION: 40 superficial lymph nodes from 33 dogs with peripheral lymphadenopathy. PROCEDURES: 3 Doppler spectral tracings were recorded from each node. Spectral Doppler analysis including assessment of the resistive index, peak systolic velocity-to-end diastolic velocity (S:D) ratio, diastolic notch velocity-to-peak systolic velocity (N:S) ratio, and end diastolic velocity-to-diastolic notch velocity ratio was performed for each tracing. Several calculation methods were used to determine the Doppler indices for each lymph node. After the ultrasonographic examination, fine needle aspirates or excisional biopsy specimens of the examined lymph nodes were obtained, and lymphadenopathy was classified as either inflammatory or neoplastic (lymphomatous or metastatic) via cytologic or histologic examination. Results of Doppler analysis were compared with cytologic or histopathologic findings. RESULTS: The Doppler index with the highest diagnostic accuracy was the S:D ratio calculated from the first recorded tracing; a cutoff value of 3.22 yielded sensitivity of 91%, specificity of 100%, and negative predictive value of 89% for detection of neoplasia. Overall diagnostic accuracy was 95%. At a sensitivity of 100%, the most accurate index was the N:S ratio calculated from the first recorded tracing; a cutoff value of 0.45 yielded specificity of 67%, positive predictive value of 81%, and overall diagnostic accuracy of 86.5%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that noninvasive Doppler spectral analysis may be useful in the diagnosis of neoplastic versus inflammatory peripheral lymphadenopathy in dogs.     

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.