Regenerative medicine research offers promising therapies to regenerate the myocardium after a myocardial infarction (MI) but relevant small animal models are lacking. Rabbit heart has similar coronary circulation, MI scar structure and ventricular electrophysiology to humans and could therefore represent an important small animal model to study electromechanical graft-host coupling in vivo (1). The standard technique to induce MI in rabbits is surgical coronary ligation (CL) but is limited by procedural severity and thoracic adhesions. Percutaneous coronary occlusion avoids these shortcomings and is widely used in large animal models including pigs (2). However, it is currently only applicable to large rabbits (> 3.5kg) because of the limited availability of specialized catheters required for the coronary arteries (CA) of smaller animals (3). 

Here, we describe a new approach to percutaneous coronary occlusion in 2.5-3.5kg rabbits.

New Zealand White rabbits (n=15, male, 2.5-3.5 kg) were sedated using ketamine (s.c.; 15mg/kg) and medetomidine (s.c.; 0.25mg/kg), intubated and anaesthetized using isoflurane (inhalation; 1.5-3%). Cardiorespiratory output was closely monitored, including two ECG-leads, peripheral pulse pressure sensor, pulse oximeter and capnograph. Continuous ECG recordings were used to confirm the presence of ST-segment changes. The carotid artery was accessed through a surgical cut-down, with the direct insertion of a 4F vascular sheath. Anterior-posterior fluoroscopic cardiac projections were acquired to identify the vasculature. A 4F angiographic catheter was positioned near the coronary ostium using a 0.035” guidewire, followed by contrast injections used for angiography. Five mm of the microcatheter tip (≤1.5F), including radiopaque marker, was cut, and used for coronary occlusion. A 0.007/8” wire was then manoeuvred through the 4F catheter into the distal left CA, whereafter the catheter tip was pushed over the wire by the microcatheter. For sham operated animals (n=5), the CA was instrumented with only the wire. Blood samples were taken to measure troponin (cTnI) levels (detection range: 0.02-180 ng/ml). Ejection fraction (EF) was measured at 6-8 weeks post-occlusion. Hearts were then excised and processed for MRI and histology. Outcomes were compared to the CL model (n=18) or respective sham (n=17).

Blood markers were increased in procedural animals at 24 hr (cTnI range: percutaneous 46.8 to ≥180ng/ml; CL 37.1 to ≥180ng/ml) but was negligible in the sham-groups (≤0.02 to 1.6ng/ml).  Left ventricular function was not significantly different between both MI groups (EF: percutaneous 51±10%; CL 49±8%; p=0.89) but was reduced compared to surgical sham (EF: 63±6% p=0.0063). MRI and histological assessment showed comparable scar volume between CL and percutaneous MI hearts. However, the percutaneous procedure resulted in hearts with clean epicardial surface with no adhesions.

The percutaneous MI model is a refinement over the current CL model and can be used to aid the development of post MI therapies including cardiac regeneration. It avoids: 1) post-surgical adhesions that complicate the integration of implanted tissues, 2) the need for a second thoracotomy if cardiac patch implantation is required and finally the procedures allow the option to deliver therapeutic cells or molecules into the coronary circulation at the time of the MI or subsequently.