Induction of atrial fibrillation and flutter in dogs using methacholine

Identification of two preclinical canine models of atrial fibrillation to facilitate drug discovery

BACKGROUND

Atrial fibrillation (AF) is the most common arrhythmia occurring in humans, and new treatment strategies are critically needed. The lack of reliable preclinical animal models of AF is a major limitation to drug development of novel antiarrhythmic compounds.

OBJECTIVE

The purpose of this study was to provide a comprehensive head-to-head assessment of 5 canine AF models.

METHODS

Five canine models were evaluated for the efficacy of AF induction and AF duration. We tested 2 acute models: short-term atrial tachypacing (AT) for 6 hours with analysis of AF at hourly increments, and carbachol injection into a cardiac fat pad followed by short-term AT. We also tested 3 chronic models: pacemaker implantation followed by either 4 weeks of AT and subsequent atrial burst pacing or intermittent long-term AT for up to 4-5 months to generate AF ≥4.5 hours, and finally ventricular tachypacing to induce heart failure followed by atrial burst pacing to induce AF.

RESULTS

Careful evaluation showed that acute AT, AT for 4 weeks, and the heart failure model all were unsuccessful in generating reproducible AF episodes of sufficient duration to study antiarrhythmic drugs. In contrast, intermittent long-term AT generated AF lasting ≥4.5 hours in ∼30% of animals. The acute model using carbachol and short-term AT resulted in AF induction of ≥15 minutes in ≥75% of animals, thus enabling testing of antiarrhythmic drugs.

CONCLUSION

Intermittent long-term AT and the combination of local carbachol injection with successive short-term AT may contribute to future drug development efforts for AF treatment.

Cardiac activity during airway resistance alterations with intravenous and inhaled methacholine

Measurement of airway contractile responses to methacholine (MCh) is an important investigational tool in humans and mice. However, i.v. administration of MCh in murine models may suffer from potential cardiac sequelae produced by stimulation of cholinergic receptors within cardiac muscle. Therefore, we studied the i.v. (0-10,000 microg/kg) and aerosolized (inhaled; 0-25 mg/ml) administration of MCh, to determine their effects on pulmonary resistance (RL) and cardiac muscle activity (as heart rate; HR) in anesthetized, mechanically-ventilated C57Bl6 mice. MCh, i.v., increased RL but produced: (1) prolonged asystole (29-47 sec); (2) subsequent overshoot of baseline HR; and (3) prolonged HR recovery times (7-25 min), suggestive of sympathetic modulation after cholinergic stimulation. In contrast, inhaled MCh aerosol produced no change in HR, while increasing RL similar to i.v. MCh. These results suggest that, for specific instances utilizing the plethysmographic technique, inhaled MCh aerosol may be superior to i.v. administration, due to the avoidance of potential bouts of asystole that can confound experimental results and lead to premature death of mice.