Canine Model of Ischemia-Induced Ventricular Tachycardia

INTRODUCTION

Despite advances in antiarrhythmia therapies, ventricular tachycardia (VT) is a leading cause of sudden cardiac death. Investigation into the characteristics and new treatments for this arrhythmia is required to improve outcomes and a reproducible model of VT would be useful in these endeavors. We therefore created a canine model of ischemia-induced VT.

MATERIALS AND METHODS

A pacing lead was implanted in the right ventricle in canines (n = 13) and the left anterior descending artery was occluded in two locations for 2 h and subsequently released to create an ischemia-reperfusion injury. In the 10 dogs that survived the first 48 h following the initial study, a terminal study was conducted 4-7 d later and VT was induced using premature stimulation or burst pacing through the right ventricle lead. The arrhythmia was terminated using either antitachycardia pacing or a defibrillatory shock. Multiple inductions into sustained VT were attempted.

RESULTS

Sustained VT was induced in eight of 10 dogs with an average cycle length of 335 ± 70 bpm. Multiple episodes of VT were induced. Episodes of VT exhibited different electrocardiogram morphologies and cycle lengths in individual animals.

CONCLUSIONS

This canine model provides a consistent technique for inducing multiple episodes of sustained VT. It may be useful for investigating VT mechanisms and testing novel therapeutics and treatments for patients with VT.

Evaluation of esophageal injuries after defibrillation with transesophageal ultrasound probe in the mid-esophagus in pigs

OBJECTIVE

Transesophageal echocardiography (TEE) is becoming increasingly utilized by emergency medicine providers during cardiac arrest. Intra-arrest, TEE confers several benefits including shorter pauses in chest compressions and direct visualization of cardiac compressions. Many ultrasound probe manufacturers recommend against performing defibrillation with the TEE probe in the mid-esophagus for fear of causing esophageal injury or damage to the probe, however no literature exists that has investigated this concern. To assess this, we performed cardiopulmonary resuscitation (CPR) and multiple defibrillations in 8 swine with a TEE probe in place.

METHODS

We performed TEE on 8 adult swine during CPR and performed multiple 200 J defibrillations with the TEE probe in the mid-esophagus. Post-mortem, esophagi were dissected and inspected for evidence of injury.

RESULTS

On macroscopic inspection of 8 esophagi, no evidence of hematoma, thermal injury, or perforation was noted.

CONCLUSION

Our study suggests that performing defibrillation during CPR with a TEE probe in place in the mid-esophagus is likely safe and low risk for significant esophageal injury. This further bolsters the use of TEE in CPR and would enable continuous visualization of cardiac activity without the need to remove the TEE probe for defibrillation.

Real-Time Monitoring and Modulation of Blood Pressure in a Rabbit Model of Ischemic Stroke

Control of blood pressure, in terms of both absolute values and its variability, affects outcomes in ischemic stroke patients. However, it remains challenging to identify the mechanisms that lead to poor outcomes or evaluate measures by which these effects can be mitigated because of the prohibitive limitations inherent to human data. In such cases, animal models can be utilized to conduct rigorous and reproducible evaluations of diseases. Here we report refinement of a previously described model of ischemic stroke in rabbits that is augmented with continuous blood pressure recording to assess the impacts of modulation on blood pressure. Under general anesthesia, femoral arteries are exposed through surgical cutdowns to place arterial sheaths bilaterally. Under fluoroscopic visualization and roadmap guidance, a microcatheter is advanced into an artery of the posterior circulation of the brain. An angiogram is performed by injecting the contralateral vertebral artery to confirm occlusion of the target artery. With the occlusive catheter remaining in position for a fixed duration, blood pressure is continuously recorded to allow for tight titration of blood pressure manipulations, whether through mechanical or pharmacological means. At the completion of the occlusion interval, the microcatheter is removed, and the animal is maintained under general anesthesia for a prescribed length of reperfusion. For acute studies, the animal is then euthanized and decapitated. The brain is harvested and processed to measure the infarct volume under light microscopy and further assessed with various histopathological stains or spatial transcriptomic analysis. This protocol provides a reproducible model that can be utilized for more thorough preclinical studies on the effects of blood pressure parameters during ischemic stroke. It also facilitates effective preclinical evaluation of novel neuroprotective interventions that might improve care for ischemic stroke patients.

TEE guided REBOA deflation following ROSC for non-traumatic cardiac arrest

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is most commonly used to manage non-compressible torso hemorrhage. It is also emerging as a promising treatment for non-traumatic refractory cardiac arrest. Aortic occlusion during chest compressions increases cardio-cerebral perfusion, increasing the potential for sustained return of spontaneous circulation (ROSC) or serving as a bridge to extracorporeal cardiopulmonary resuscitation (ECPR). Optimal patient selection and post-ROSC management in such cases is uncertain and not well reported in the literature. We present a case of non-traumatic out-of-hospital cardiac arrest in which REBOA was placed in the emergency department with subsequent ROSC. Transesophageal echocardiography was used to guide post-ROSC REBOA management and balloon deflation.

Comparison of assessment of coagulation in healthy dogs by the TEG 6s and TEG 5000 viscoelastic analyzers

The TEG 6s (Haemonetics) point-of-care viscoelastic analyzer is portable, compact, simple to use, and has the potential for rapid viscoelastic analysis that can guide the treatment of veterinary patients at the site of care. Although approved for use in people, the TEG 6s has yet to be evaluated for hemostatic analysis in veterinary medicine. Citrated whole blood (CWB) was collected from 27 healthy dogs. An aliquot of CWB from each dog was diluted by 33% with an isotonic crystalloid, representing an in vitro model of hemodilution. Unaltered and diluted CWB samples were analyzed using 2 TEG 6s and 6 TEG 5000 (Haemonetics) analyzers. The 6 TEG 5000 analyzers ran duplicate analyses of either unaltered or diluted samples using 1 of 3 reagents (Haemonetics): Kaolin TEG, RapidTEG, or TEG Functional Fibrinogen. Duplicate TEG 5000 analyses were averaged and compared with a single TEG 6s analysis. Lin concordance correlation coefficient and Bland-Altman plots were used to evaluate agreement of reaction time, kinetic time, alpha angle, maximum amplitude (MA), and G value (G) for samples activated with Kaolin TEG, and agreement of MA for samples activated with RapidTEG between the 2 machines. Overall, agreement between the TEG 6s and TEG 5000 analyzers was poor. Viscoelastic measurements by the TEG 6s and TEG 5000 in healthy dogs were not all interchangeable. Agreement was satisfactory only for MA and G measurements of diluted blood samples activated with Kaolin TEG, and MA measurements for both unaltered and diluted blood samples activated with RapidTEG.

Acute kidney injury following resuscitative aortic occlusion

Background: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is an emergent technology for the treatment of non-compressible torso hemorrhage (NCTH). While aortic occlusion (AO) above the site of hemorrhage provides hemostasis and time for surgical intervention, ischemia-reperfusion injury to the kidneys is a known complication. We aimed to report the incidence and factors associated with acute kidney injury (AKI) following AO in patients with NCTH or in similar porcine models. Methods: We searched Pubmed (MEDLINE), Embase, Scopus, and ProQuest Dissertations & Theses from inception to July 2017. We included original studies of trauma patients with NCTH treated with REBOA, or similar porcine studies that included renal parameters, excluding case reports and case series. After duplicate removal, full texts of studies retrieved via the search strategy were evaluated by two authors. Renal parameters (e.g., creatinine concentration, urine output, histopathology) were extracted. Quality of the evidence and risk of bias were assessed. Results: Twelve out of 2,100 records were included (3 trauma patients, 9 porcine studies). While 1/3 human reports described AO in Zone 1, all swine publications reported Zone 1. All human studies reported renal damage. There were nonetheless inconsistencies in definitions used. Evidence of AKI was reported in 3/9 swine studies.  Conclusions: Consistent reporting of AKI incidence is lacking from human clinical studies of AO in NCTH trauma patients. While comorbidities in trauma patients may contribute to AKI, animal models support the association between AO and AKI. As REBOA is growing in popularity as a therapy for NCTH, further studies determining factors associated with the AKI are needed.