Sudden death in the presence of overt beta-adrenergic receptor activation in guinea pigs immediately following isoflurane anesthesia

Acute isoproterenol leads to age-dependent arrhythmogenesis in guinea pigs

Sudden cardiac death from ventricular arrhythmias is more common in adult patients with with heart failure compared with pediatric patients with heart failure. We identified age-specific differences in arrhythmogenesis using a guinea pig model of acute β-adrenergic stimulation. Young and adult guinea pigs were exposed to the β-adrenergic agonist isoproterenol (ISO; 0.7 mg/kg) for 30 min in the absence or presence of flecainide (20 mg/kg), an antiarrhythmic that blocks Na⁺ and ryanodine channels. Implanted cardiac monitors (Reveal LINQ, Medtronic) were used to monitor heart rhythm. Alterations in phosphorylation and oxidation of ryanodine receptor 2 (RyR2) were measured in left ventricular tissue. There were age-specific differences in arrhythmogenesis and sudden death associated with acute β-adrenergic stimulation in guinea pigs. Young and adult guinea pigs developed arrhythmias in response to ISO; however, adult animals developed significantly more premature ventricular contractions and experienced higher arrhythmia-related mortality than young guinea pigs treated with ISO. Although there were no significant differences in the phosphorylation of left ventricular RyR2 between young and adult guinea pigs, adult guinea pigs exposed to acute ISO had significantly more oxidation of RyR2. Flecainide treatment significantly improved survival and decreased the number of premature ventricular contractions in young and adult animals in association with lower RyR2 oxidation. Adult guinea pigs had a greater propensity to develop arrhythmias and suffer sudden death than young guinea pigs when acutely exposed to ISO. This was associated with higher oxidation of RyR2. The incidence of sudden death can be rescued with flecainide treatment, which decreases RyR2 oxidation. NEW & NOTEWORTHY Clinically, adult patients with heart failure are more likely to develop arrhythmias and sudden death than pediatric patients with heart failure. In the present study, older guinea pigs also showed a greater propensity to arrhythmias and sudden death than young guinea pigs when acutely exposed to isoproterenol. Although there are well-described age-related cardiac structural changes that predispose patients to arrhythmogenesis, the present data suggest contributions from dynamic changes in cellular signaling also play an important role in arrhythmogenesis.

Effects of subcutaneous alfaxalone alone and in combination with dexmedetomidine and buprenorphine in guinea pigs (Cavia porcellus)

OBJECTIVE

To characterize alfaxalone administered subcutaneously (SC) in guinea pigs, both alone and in combination with dexmedetomidine and buprenorphine.

STUDY DESIGN

Prospective, blinded, crossover study.

ANIMALS

A total of 15 healthy female guinea pigs weighing 400-600 g.

METHODS

Alfaxalone (10, 20 and 40 mg kg^-1) was administered SC to three guinea pigs as a pilot dose-finding study. Alfaxalone (20 mg kg^-1; A₂₀) was selected for comparison against combination protocols of alfaxalone (15 and 20 mg kg^-1) with dexmedetomidine (0.25 mg kg^-1) and buprenorphine (0.05 mg kg^-1; A₁₅DB, A₂₀DB). Each protocol was randomly administered to 12 guinea pigs separated by ≥7 days. Time and quality of induction and recovery, heart rate, respiratory rate, peripheral hemoglobin oxygen saturation, rectal temperature, pedal withdrawal reflex and adverse effects were recorded.

RESULTS

The median time to induction for A₂₀, A₁₅DB and A₂₀DB was 6.8-8.0 minutes with no significant difference between treatments. Mean duration of recumbency for A₂₀ was 73.6 ± 19.6 minutes. Recumbency duration for A₁₅DB and A₂₀DB extended to 90 minutes, at which time dexmedetomidine was antagonized using atipamezole (0.025 mg kg^-1 SC). Physiological variables were within normal limits with the exception of one animal that died 45 minutes following treatment with A₂₀DB. Pedal withdrawal reflex remained intact with all treatments. Minor side effects such as twitching or bruxism occurred sporadically with treatment A₂₀ but not with A₁₅DB and A₂₀DB.

CONCLUSIONS AND CLINICAL RELEVANCE

SC alfaxalone produced uncomplicated sedation that may be recommended for nonpainful procedures that do not require complete immobility. The addition of dexmedetomidine and buprenorphine increased the duration of sedation and immobility, but did not result in general anesthesia. This combination sedation protocol may be useful for nonpainful procedures requiring extended immobility.

Sedative effects of intramuscular alfaxalone in pet guinea pigs (Cavia porcellus)

OBJECTIVE

To evaluate the efficacy and side effects of alfaxalone administered intramuscularly (IM) as a sedative agent in guinea pigs undergoing survey radiographs.

STUDY DESIGN

Prospective clinical trial.

ANIMALS

A total of 30 client-owned guinea pigs.

METHODS

Following baseline assessments, 5 mg kg^-1 alfaxalone was administered IM. Heart rate, arterial haemoglobin oxygen saturation, respiratory rate, rectal body temperature, palpebral reflex, response to toe and ear pinch, righting reflex, posture, jaw tone and reaction to manipulation were assessed before and after sedation at 5-minute intervals. The time elapsed from onset of sedation to return of locomotion and coordinated limb movements, the quality of recovery and the occurrence of undesired effects were observed and recorded.

RESULTS

The mean ± standard deviation onset of sedation was 2.7 ± 0.6 minutes. The physiological variables remained within normal ranges until completion of the procedure. Palpebral reflex and responsiveness to both ear and toe pinch were maintained during sedation. Neither hypoxaemia nor hypothermia was observed. The duration of sedation was 29.3 ± 3.2 minutes. Sedation and recovery were uneventful, and adverse effects were not observed.

CONCLUSIONS AND CLINICAL RELEVANCE

In conclusion, 5 mg kg^-1 of IM alfaxalone represents a valuable sedation protocol for healthy guinea pigs undergoing minor noninvasive procedures. Further trials are required to investigate its cardiovascular effects, clinical usefulness in unhealthy patients and its combined use with analgesics for procedures associated with nociception.