Simultaneous assessment of ischaemia-induced ventricular fibrillation (VF) and contractile function by intraventricular balloon inflation (IVB) in rat isolated heart

W. M. Pickles, C. D. Wilder, M. J. Curtis. Cardiovascular division, King's College London, London, United Kingdom.

Introduction: A model that allows simultaneous assessment of VF and contractile function would halve animal requirements. Unfortunately, in Langendorff perfused rat hearts, IVB inflation inhibits the ability of regional ischaemia to elicit VF(1). However, perfusion with catecholamines facilitates ischaemia-induced VF (I-IVF) in IVB-free hearts when risk of VF is low due to a small ischaemic territory (2). Here we tested whether catecholamines can surmount the antiarrhythmic effect of IVB inflation.

Methods: Male Wistar rat (285-400g) hearts were Langendorff-perfused with an IVB positioned in the left ventricle and minimally inflated (0.01 ml) to give a detectable developed pressure (∼30 mmHg; ‘IVB’ groups) or inflated substantially (0.12 ml) to give a developed pressure >100 mmHg (‘IVB inflated’). Baseline assessment (-11 min) during perfusion with Krebs’ (modified to contain 4mM K⁺) was followed by randomized and blinded switch to test solution at -10 min, then left coronary artery ligation at time zero, with ischaemia maintained for 60 min. Test solution comprised Krebs’ containing catecholamines (93.9 nM noradrenaline and 22.5 nM adrenaline in 15 mM ascorbate vehicle) or vehicle alone (n = 9/group). Design (blinded and randomized) and data analysis (e.g. use of ANOVA for Gaussian-distributed data and Fisher’s exact test for VF incidence) accorded with BPS guidelines (3).

Results: Heart rate and developed pressure were increased by catecholamines (Cat) from 1 min before ligation (-1 min), and the effect on pressure was exacerbated by IVB inflation (Table 1). Ischaemia reduced developed pressure, with effects sustained during ischaemia (Table 1). Mean ischaemic zone size varied between groups from 53±2 to 59±1 (P>0.05). Cats increased VF incidence and extended the susceptibility time window past 30 min of ischaemia, but IVB inflation was antiarrhythmic during ischaemia and surmounted the arrhythmia facilitating effect of catecholamines (Table 1).

Conclusion: IVB inflation suppressed the Cat-induced facilitation of ischaemia-induced VF. Unfortunately this rendered VF incidence too low to permit the assay to be suitable for evaluating drug effects on VF and contractile function contiguously.

References:

(1) Wilder CDE, et al., (2016). Br J Pharmacol 173, 39-522.

(2) Wilder CDE et al., (2016). http://www.pa2online.org/abstracts/vol13issue3abst245p.pdf.

(3) Curtis MJ, et al., (2015). Br J Pharmacol 172:2671-2674, 2015