Twenty-four hour continuous transvenous temporary right ventricular pacing in healthy horses.

BACKGROUND: The ability to perform transvenous temporary cardiac pacing (TV-TP) is critical to stabilize horses with symptomatic bradyarrhythmias. Reports of successful TV-TP in horses are limited, and only briefly describe short-term pacing. OBJECTIVE: To describe temporary, medium-term (24 h) transvenous right ventricular pacing in awake horses using a bipolar torque-directed pacing catheter. ANIMALS: Six healthy adult institutional teaching horses. METHODS: Prospective experimental study with 2 immediately successive TV-TP lead placements in each horse with a target location of the RV apex. One placement was performed primarily with echocardiographic guidance and 1 primarily with fluoroscopic guidance. In all placements, corresponding images were obtained with both imaging modalities. Horses were then paced for 24 h, unrestricted in a stall with continuous telemetric ECG monitoring. Echocardiographically determined lead position, episodes of pacing failure in the preceding 6 h, and pacing thresholds were recorded every 6 h. Pacing failure was defined as a period of loss of capture longer than 20 s. RESULTS: Pacing leads were placed with both guidance methods and maintained for 24 h with no complications. Two horses with leads angled caudally in the right ventricular apex had no pacing failure, the remaining 4 horses had varying degrees of loss of capture. Leads located in the right ventricular apex had longer time to pacing failure and lower capture thresholds P < 0.05. CONCLUSIONS AND CLINICAL IMPORTANCE: Medium-term TV-TP is feasible and has potential for stabilization of horses with symptomatic bradyarrhythmias. Lead position in the right ventricular apex appears optimal. Continuous ECG monitoring is recommended to detect pacing failure.

EFFICACY OF TOLAZOLINE AND VATINOXAN IN REDUCING ADVERSE EFFECTS OF BUTORPHANOL-AZAPERONE-MEDETOMIDINE IMMOBILIZATION IN ROCKY MOUNTAIN ELK (CERVUS CANADENSIS).

A mixture of butorphanol, azaperone, and medetomidine (BAM) is frequently used for immobilization of North American hoofstock. Common adverse effects include respiratory depression, hypoxemia, and bradycardia. In this nonblinded crossover study the efficacy of two a-2 adrenergic antagonists, tolazoline and vatinoxan, were evaluated in alleviating adverse effects of BAM in Rocky Mountain elk (Cervus canadensis). Early administration of these antagonists was hypothesized to cause an increase in heart rate, respiratory rate, partial pressure of oxygen (PaO2) and hemoglobin oxygen saturation (SpO2), as well as reduction in mean arterial blood pressure without affecting sedation levels. Eight captive adult female elk were immobilized on three separate occasions at least 14 d apart with 0.15 mg/kg butorphanol, 0.05 mg/kg azaperone, and 0.06 mg/kg medetomidine. Tolazoline (2 mg/kg IM), vatinoxan (3 mg/mg medetomidine IV) or sterile saline (2 ml IM) were administered 20 min postinduction. The BAM caused hypoxemia, bradycardia, and moderate hypertension, and because of the severe hypoxemia observed, all animals received intratracheal oxygen throughout immobilization. Heart rate, respiratory rate, rectal temperature, SpO2, PaO2, and systolic, diastolic, and mean arterial blood pressure were monitored every 5 min throughout the immobilization. Intramuscular tolazoline caused a brief but significant drop in mean arterial pressure compared with controls and a brief but nonsignificant increase in heart rate. Vatinoxan caused a significant drop in blood pressure and a brief significant increase in heart rate. Changes in respiratory rates and PaO2 were not observed with either antagonist; however, all animals received oxygen, which may have influenced this result. The depth of sedation was unchanged after administration of either drug.

Perioperative analgesic efficacy of lumbar erector spinae plane block in dogs undergoing hemilaminectomy: a randomized blinded clinical trial.

OBJECTIVE: To evaluate the perioperative analgesic effect of the unilateral lumbar erector spinae plane block (ESPBL) in dogs undergoing hemilaminectomy. STUDY DESIGN: Randomized, blinded clinical study. ANIMALS: A total of 30 client-owned dogs undergoing thoracolumbar or lumbar hemilaminectomy for intervertebral disc extrusion (IVDE). METHODS: Dogs were randomly assigned to receive a unilateral ESPBL, performed either with 0.4 mL kg-1 ropivacaine 0.5% [group ROPI (n = 15)] or with saline solution [CNT group (n = 15)]. Dogs were premedicated intravenously (IV) with acepromazine 5 µg kg-1 and methadone 0.2 mg kg-1, general anaesthesia was induced by administering IV midazolam 0.2 mg kg-1 and propofol to effect and maintained with isoflurane. Fentanyl was administered as rescue analgesia. Bradycardia [heart rate (HR) < 60 beats minute-1] with hypotension was treated with atropine IV. The Short-Form of the Glasgow Composite Pain Scale was used pre- and postoperatively at 1, 2, 4, 8, 12, 16, 20 and 24 hours after extubation, and methadone 0.2 mg kg-1 was administered IV when pain score was ≥ 5/20. HR and end-tidal concentration of isoflurane (Fe'Iso) were compared between groups with anova combined with a Dunnet's post hoc test. Time to the first rescue methadone and total dose of fentanyl (FENtot, µg kg-1 hour-1) and methadone (METtot, mg kg-1) in the first 24 postoperative hours were compared using unpaired Student's t test. Postoperative pain scores were compared with the Mann-Whitney test and atropine administration with a Fisher's exact test; p < 0.05. RESULTS: HR, Fe'Iso, FENtot, METtot and atropine administration were significantly lower in group ROPI compared to CNT. Postoperative analgesic effect was significantly longer, and pain scores were significantly lower in group ROPI for all time points. CONCLUSIONS AND CLINICAL RELEVANCE: Unilateral ESPBL with ropivacaine reduced perioperative opioid consumption and the occurrence of bradycardia in dogs undergoing hemilaminectomy.

Effect of dexmedetomidine added to retrobulbar blockade with lignocaine and bupivacaine in dogs undergoing enucleation surgery.

OBJECTIVE: To investigate the effect of the addition of dexmedetomidine (BLD) to retrobulbar blockade with combined lignocaine and bupivacaine on nociception. ANIMALS: A total of 17 eyes from 15 dogs. METHODS: Prospective, randomized, masked clinical comparison study. Dogs undergoing unilateral enucleation were randomly assigned into two groups; a retrobulbar administration of lignocaine and bupivacaine in a 1:2 volume ratio combined with either BLD or 0.9% saline (BLS). The total volume of the intraconal injection was calculated at 0.1 mL/cm cranial length. Intraoperative parameters were recorded: heart rate (HR), respiratory rate (RR), end-tidal CO2 (EtCO2 ) arterial blood pressure (BP), and inspired isoflurane concentration (ISOinsp). Pain scores, heart rate and RR were recorded postoperatively. RESULTS: Dogs receiving BLD (n = 8) had significantly lower intraoperative RR (p = 0.007), and significantly lower ISOinsp (p = 0.037) than dogs in the BLS group (n = 9). Postoperatively heart rate was significantly lower in the BLD group at 1 min (p = 0.025) and 1 h (p = 0.022). There were no other significant differences in intraoperative or postoperative parameters, or in postoperative pain scores (p = 0.354). Dogs receiving BLD had a higher rate of anesthetic events of bradycardia and hypertension (p = 0.027). Analgesic rescue was not needed in either group. CONCLUSIONS: The addition of BLD to retrobulbar anesthesia did not result in a detectable difference in pain scores relative to blockade with lignocaine and bupivacaine alone. Dogs receiving retrobulbar BLD had a significantly lower intraoperative RR and isoflurane requirement and an increased incidence of intraoperative bradycardia and hypertension.

Single center retrospective clinical audit and comparison of outcome between epicardial and transvenous endocardial permanent pacemaker implantations in dogs.

The aim of this retrospective cohort study was to provide a single-center clinical audit of complications for single chamber permanent pacemaker implantation (PPI) techniques and determine if the clinical parameters, PPI technique or complications were associated with outcome. The electronic medical records were searched for dogs treated for bradyarrhythmia with PPI. Data related to presenting complaint, signalment of the dog, ECG diagnosis, echocardiographic findings, PPI technique, and programing of the pacemaker were recorded. Survival length (days) was recorded as the last veterinary visit; if the dog was dead the reason was documented. Cumulative survival of each pacemaker was examined by a Kaplan-Meier survival curve and the two techniques compared with a logrank test. Chi-square was used to determine the association between major complications and death. A total of 66 dogs with 52 transvenous and 30 epicardial PPIs were included. All epicardial pacemakers were implanted via transdiaphragmatic approach. A total of 31 life-threatening complications were reported. There were nine deaths related to major complications (13.6% of the study sample). The median follow-up period was 366 days, with a median survival of 255 days, and a significant difference in cumulative survival of each pacemaker (P = 0.01) between epicardial (93 days, range 0-1882 days) and transvenous (334 days, range 0-2745) PPIs but no significant difference in cumulative survival between the two techniques when only the first pacemaker was considered (p = 0.07). The presence of a major complications had a significant association with death due to pacemaker complications (P<0.001). The decision to perform epicardial PPI in failed transvenous PPI patients may have skewed the cumulative survival as was evident in the lack of significant difference in survival when only first PPI were examined. Major complication rates between the two techniques were similar and the authors consider both techniques equally reliable to manage symptomatic bradycardia in dogs.

Sedative effects and changes in cardiac rhythm with intravenous premedication of medetomidine, butorphanol and ketamine in dogs.

OBJECTIVE: To determine the sedative effects and characteristics of cardiac rhythm with intravenous (IV) premedication of medetomidine, butorphanol and ketamine in dogs. STUDY DESIGN: Prospective, blinded, randomized clinical trial. ANIMALS: A total of 116 client-owned healthy dogs undergoing elective surgery. METHODS: Dogs were randomly allocated one of four groups: group M, medetomidine 5 µg kg-1; group B, butorphanol 0.2 mg kg-1; group MB, medetomidine 5 µg kg-1 and butorphanol 0.2 mg kg-1; or group MBK, medetomidine 5 µg kg-1, butorphanol 0.2 mg kg-1 and ketamine 1 mg kg-1 IV. Sedation was assessed using a numerical descriptive scale. Heart rate (HR) and rhythm were monitored; propofol dose (mg kg-1 IV) to allow orotracheal intubation was documented. Data were analysed using anova, accounting for multiple testing with the Tukey honest significant difference test. RESULTS: Sedation scores varied significantly between all groups at all time points, except between groups MB and MBK at four time points. HR decreased in all groups: most in groups M and MB, least in group B. HR was initially higher in group MBK than in groups M and MB. Arrhythmias occurred in all groups: group B showed second-degree atrioventricular blocks occasionally, all other groups showed additionally ventricular escape complexes and bundle branch blocks. Dose of propofol required for orotracheal intubation was significantly higher in group B (5.0 ± 2.0 mg kg-1) than in group M (2.6 ± 0.6 mg kg-1). Although no difference could be demonstrated between groups MB (1.4 ± 0.6 mg kg-1) and MBK (0.9 ± 0.8 mg kg-1), both groups required significantly less propofol than group M. CONCLUSION AND CLINICAL RELEVANCE: Medetomidine-based premedication protocols led to various bradyarrhythmias. Addition of subanaesthetic doses of ketamine to medetomidine-based protocols resulted in higher HRs, fewer bradyarrhythmias and fewer animals that required propofol for intubation without causing side effects in healthy dogs.

Pharmacokinetics of a 503B outsourcing facility-produced theophylline in dogs.

Theophylline is an important drug for treatment of canine chronic bronchitis and bradyarrhythmias, but new products require validation since pharmacokinetics in dogs can vary by formulation. A new, 503B outsourcing facility-produced theophylline product (OFT) is available for veterinary use. Outsourcing facilities have many advantages over traditional compounding sources including current good manufacturing practice compliance. The purpose of this study was to establish the pharmacokinetics of OFT in dogs. Eight healthy dogs received 11 mg/kg intravenous aminophylline and 10 mg/kg oral OFT followed by serial blood sampling in a two-way, randomized, crossover design with 7-day washout. Plasma theophylline concentrations were quantified by liquid chromatography-mass spectrometry. Bioavailability, maximum concentration, time to maximum concentration, half-life and area under the curve were: 97 ± 10%, 7.13 ± 0.71 µg/mL, 10.50 ± 2.07 h, 9.20 ± 2.87 h, and 141 ± 37.6 µg*h/mL, respectively. Steady-state predictions supported twice daily dosing of the OFT, but specific dosage recommendations are hindered by lack of a canine-specific therapeutic range for plasma theophylline concentration. These findings suggest that the OFT is well absorbed and can likely be dosed twice daily in dogs, but future pharmacodynamic and clinical studies are needed to establish a definitive therapeutic range for theophylline in this species.

Reversal effects of atipamezole, flumazenil, and 4-aminopyridine on bradycardia and increases in blood pressures induced by medetomidine, midazolam, and ketamine in isoflurane-anesthetized cats.

OBJECTIVE: To investigate the effects of a fixed dose of atipamezole (AT), flumazenil (FL), and 4-aminopyridine (AP), both alone and in combination, on changes in arterial blood pressure and heart rate induced by medetomidine (ME), midazolam (MI), and ketamine (KE) under isoflurane anesthesia with controlled ventilation in healthy cats. DESIGN: Prospective experimental study. SETTING: University animal research facility. ANIMALS: Healthy adult mixed-breed cats were used for 8 investigation groups (6 cats per group), with ≥2 weeks between interventions. INTERVENTIONS: Cats were anesthetized with an end-tidal isoflurane concentration of 2% under controlled ventilation. A catheter was inserted into the right or left femoral artery for arterial pressure monitoring and blood gas sampling, and ECG electrodes were placed. Upon completed preparations, cats were administered a mixture of ME (0.05 mg/kg) and MI (0.5 mg/kg), followed 10 minutes later by intramuscular KE (10 mg/kg). Twenty minutes after KE injection, the cats received IV injection with either a physiological saline solution at 0.1 mL/kg (control), or 1 of 7 variations of experimental drugs, alone or in combination: AT (0.2 mg/kg), FL (0.1 mg/kg), AP (0.5 mg/kg), AT+FL, FL+AP, AT+AP, and AT+FL+AP. Arterial blood pressure and heart rate were continuously measured over 120 minutes after administration of potential antagonists. MEASUREMENTS AND MAIN RESULTS: ME+MI+KE induced an increase in blood pressure and bradycardia. Potential antagonists alone or in combination did not significantly alter the bradycardia. FL, AP alone, and FL+AP did not significantly alter the changes in blood pressures induced by ME+MI+KE. Meanwhile, administration of AT alone or in combination reversed the increase in blood pressure induced by ME+MI+KE but transiently caused excessive hypotension. CONCLUSION: These results revealed that AT alone or in combination is effective for antagonizing hypertension induced by ME+MI+KE; however, attention should be paid to temporary hypotension in cats anesthetized with isoflurane.

Effect of fentanyl, with or without treatment of bradycardia, on the minimum alveolar concentration of isoflurane and cardiovascular function in dogs.

OBJECTIVE: To determine the effect of fentanyl on the minimum alveolar concentration of isoflurane (MACISO) and cardiovascular variables in dogs, and how the treatment of bradycardia affects them. STUDY DESIGN: Prospective, randomized crossover-controlled trial. ANIMALS: A total of six male Beagle dogs weighing 9.9 ± 0.7 kg (mean ± standard deviation) and aged 13 months. METHODS: To each dog, two treatments were assigned on different days: fentanyl (FENTA) or fentanyl plus glycopyrrolate (FENTAglyco) to maintain heart rate (HR) between 100 and 132 beats minute-1. Determinations of MACISO were performed with 10 plasma fentanyl target concentrations ([Fenta]Target (0, 0.16, 0.32, 0.64, 1.25, 2.5, 5.0, 10.0, 20.0 and 40.0 ng mL-1) for FENTA and 5 [Fenta]Target (0, 1.25, 2.5, 5.0, 10.0 ng mL-1)) for FENTAglyco. During each MACISO determination, cardiovascular variables [mean arterial pressure (MAP), HR and cardiac index (CI)] were measured, and systemic vascular resistance index (SVRI) calculated. Pharmacodynamic models were used to describe the plasma fentanyl concentration [Fenta]-response relationship for the effect on MACISO and cardiovascular variables. A mixed-model analysis of variance followed by Dunnett's or Tukey's test, and the Bonferroni adjustment were used for comparisons within and between each treatment, respectively. Significance was set as p < 0.05. RESULTS: Fentanyl decreased MACISO by a maximum of 84%. The [Fenta] producing 50% decrease in MAC, HR and CI were 2.64, 3.65 and 4.30 ng mL-1 (typical values of population model), respectively. The prevention of fentanyl-mediated bradycardia caused no significant effect on MACISO, but increased HR, MAP and CI, and decreased SVRI when compared with isoflurane alone. CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl caused a plasma concentration-dependent decrease in MACISO, HR and CI and an increase in SVRI. Cardiovascular improvements associated with fentanyl in isoflurane-anesthetized dogs only occurred when the fentanyl-mediated bradycardia was prevented.

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.

Use of intravenous lidocaine to treat dexmedetomidine-induced bradycardia in sedated and anesthetized dogs.

OBJECTIVE: To assess cardiopulmonary function in sedated and anesthetized dogs administered intravenous (IV) dexmedetomidine and subsequently administered IV lidocaine to treat dexmedetomidine-induced bradycardia. STUDY DESIGN: Prospective, randomized, crossover experimental trial. ANIMALS: A total of six purpose-bred female Beagle dogs, weighing 9.1 ± 0.6 kg (mean ± standard deviation). METHODS: Dogs were randomly assigned to one of three treatments: dexmedetomidine (10 µg kg-1 IV) administered to conscious (treatments SED1 and SED2) or isoflurane-anesthetized dogs (end-tidal isoflurane concentration 1.19 ± 0.04%; treatment ISO). After 30 minutes, a lidocaine bolus (2 mg kg-1) IV was administered in treatments SED1 and ISO, followed 20 minutes later by a second bolus (2 mg kg-1) and a 30 minute lidocaine constant rate infusion (L-CRI) at 50 (SED1) or 100 µg kg-1 minute-1 (ISO). In SED2, lidocaine bolus and L-CRI (50 µg kg-1 minute-1) were administered 5 minutes after dexmedetomidine. Cardiopulmonary measurements were obtained after dexmedetomidine, after lidocaine bolus, during L-CRI and 30 minutes after discontinuing L-CRI. A mixed linear model was used for comparisons within treatments (p < 0.05). RESULTS: When administered after a bolus of dexmedetomidine, lidocaine bolus and L-CRI significantly increased heart rate and cardiac index, decreased mean blood pressure, systemic vascular resistance index and oxygen extraction ratio, and did not affect stroke volume index in all treatments. CONCLUSION AND CLINICAL RELEVANCE: Lidocaine was an effective treatment for dexmedetomidine-induced bradycardia in healthy research dogs.

Respiratory sinus arrhythmia and submersion bradycardia in bottlenose dolphins (Tursiops truncatus).

Among the many factors that influence the cardiovascular adjustments of marine mammals is the act of respiration at the surface, which facilitates rapid gas exchange and tissue re-perfusion between dives. We measured heart rate (fH) in six adult male bottlenose dolphins (Tursiops truncatus) spontaneously breathing at the surface to quantify the relationship between respiration and fH, and compared this with fH during submerged breath-holds. We found that dolphins exhibit a pronounced respiratory sinus arrhythmia (RSA) during surface breathing, resulting in a rapid increase in fH after a breath followed by a gradual decrease over the following 15-20 s to a steady fH that is maintained until the following breath. RSA resulted in a maximum instantaneous fH (ifH) of 87.4±13.6 beats min-1 and a minimum ifH of 56.8±14.8 beats min-1, and the degree of RSA was positively correlated with the inter-breath interval (IBI). The minimum ifH during 2 min submerged breath-holds where dolphins exhibited submersion bradycardia (36.4±9.0 beats min-1) was lower than the minimum ifH observed during an average IBI; however, during IBIs longer than 30 s, the minimum ifH (38.7±10.6 beats min-1) was not significantly different from that during 2 min breath-holds. These results demonstrate that the fH patterns observed during submerged breath-holds are similar to those resulting from RSA during an extended IBI. Here, we highlight the importance of RSA in influencing fH variability and emphasize the need to understand its relationship to submersion bradycardia.

Cardiovascular effects of intravenous vatinoxan (MK-467) in medetomidine-tiletamine-zolazepam anaesthetised red deer (Cervus elaphus).

OBJECTIVE: To determine the effect of intravenous vatinoxan administration on bradycardia, hypertension and level of anaesthesia induced by medetomidine-tiletamine-zolazepam in red deer (Cervus elaphus). STUDY DESIGN AND ANIMALS: A total of 10 healthy red deer were included in a randomised, controlled, experimental, crossover study. METHODS: Deer were administered a combination of 0.1 mg kg-1 medetomidine hydrochloride and 2.5 mg kg-1 tiletamine-zolazepam intramuscularly, followed by 0.1 mg kg-1 vatinoxan hydrochloride or equivalent volume of saline intravenously (IV) 35 minutes after anaesthetic induction. Heart rate (HR), mean arterial blood pressure (MAP), respiration rate (fR), end-tidal CO2 (Pe'CO2), arterial oxygen saturation (SpO2), rectal temperature (RT) and level of anaesthesia were assessed before saline/vatinoxan administration (baseline) and at intervals for 25 minutes thereafter. Differences within treatments (change from baseline) and between treatments were analysed with linear mixed effect models (p < 0.05). RESULTS: Maximal (81 ± 10 beats minute-1) HR occurred 90 seconds after vatinoxan injection and remained significantly above baseline (42 ± 4 beats minute-1) for 15 minutes. MAP significantly decreased from baseline (122 ± 10 mmHg) to a minimum MAP of 83 ± 6 mmHg 60 seconds after vatinoxan and remained below baseline until end of anaesthesia. HR remained unchanged from baseline (43 ± 5 beats minute-1) with the saline treatment, whereas MAP decreased significantly (112 ± 16 mmHg) from baseline after 20 minutes. Pe'CO2, fR and SpO2 showed no significant differences between treatments, whereas RT decreased significantly 25 minutes after vatinoxan. Level of anaesthesia was not significantly influenced by vatinoxan. CONCLUSIONS AND CLINICAL RELEVANCE: Vatinoxan reversed hypertension and bradycardia induced by medetomidine without causing hypotension or affecting the level of anaesthesia in red deer. However, the effect on HR subsided 15 minutes after vatinoxan IV administration. Vatinoxan has the potential to reduce anaesthetic side effects in non-domestic ruminants immobilised with medetomidine-tiletamine-zolazepam.

Pathological bradyarrhythmia in horses.

Pathological bradyarrhythmia is rare in horses but should be especially considered when presented with a horse that has signs consistent with episodic weakness or collapse. This paper reviews the literature describing our current knowledge of, and possible mechanisms causing, clinically significant bradyarrhythmia in horses.

Survival of a dog with accidental colchicine overdose.

OBJECTIVE: To describe the treatment and clinical course of a dog accidentally prescribed 10 times the recommended dose of colchicine (0.3 mg/kg/d instead of 0.03 mg/kg/d). CASE SUMMARY: After glaucoma surgery, a 1-year-old male neutered Pomeranian weighing 6.8 kg was prescribed 1,000 µg colchicine twice a day per os. The dog presented to the emergency department after the first dose with vomiting and was treated as an outpatient. Two colchicine doses later, the dog represented with vomiting, ocular pain, and increased intraocular pressure. The dog's vital signs were normal, and the dog was admitted for rehydration, analgesia, and revision glaucoma surgery the next day. Two hours after revision surgery, the dog developed vomiting and diarrhea. Postoperatively, the dog was hypothermic (36.3°C), persistently hypertensive (227 mm Hg), and bradycardic (60/min). Biochemistry revealed metabolic acidosis and increased hepatic enzyme activities. Mannitol was administered for presumed cerebral edema. Later, the dog developed bradycardia due to second-degree atrioventricular heart block, which responded to atropine. Total hospitalization was 9 days. Treatment included IV fluids, IV lipid emulsion, N-acetylcysteine, activated charcoal, gastroprotectants, antiemetics, opioids, antimicrobials, and barrier nursing due to transient neutropenia. NEW OR UNIQUE INFORMATION PROVIDED: This is the first report to describe the successful treatment of a dog with colchicine overdose. The systemic effects were presumed to be secondary to colchicine toxicosis rather than diet, infection, or other drug reaction, and may have been compounded by a second anesthetic episode. Gastrointestinal signs, symptoms of cerebral edema, cardiac arrhythmias, and neutropenia were documented. One other report of colchicine overdose in a dog exists, and that patient was euthanized. This report demonstrates that complete recovery with intensive care is possible; however, the prognosis remains guarded.

Extreme bradycardia and tachycardia in the world's largest animal.

The biology of the blue whale has long fascinated physiologists because of the animal's extreme size. Despite high energetic demands from a large body, low mass-specific metabolic rates are likely powered by low heart rates. Diving bradycardia should slow blood oxygen depletion and enhance dive time available for foraging at depth. However, blue whales exhibit a high-cost feeding mechanism, lunge feeding, whereby large volumes of prey-laden water are intermittently engulfed and filtered during dives. This paradox of such a large, slowly beating heart and the high cost of lunge feeding represents a unique test of our understanding of cardiac function, hemodynamics, and physiological limits to body size. Here, we used an electrocardiogram (ECG)-depth recorder tag to measure blue whale heart rates during foraging dives as deep as 184 m and as long as 16.5 min. Heart rates during dives were typically 4 to 8 beats min-1 (bpm) and as low as 2 bpm, while after-dive surface heart rates were 25 to 37 bpm, near the estimated maximum heart rate possible. Despite extreme bradycardia, we recorded a 2.5-fold increase above diving heart rate minima during the powered ascent phase of feeding lunges followed by a gradual decrease of heart rate during the prolonged glide as engulfed water is filtered. These heart rate dynamics explain the unique hemodynamic design in rorqual whales consisting of a large-diameter, highly compliant, elastic aortic arch that allows the aorta to accommodate blood ejected by the heart and maintain blood flow during the long and variable pauses between heartbeats.