Initial Challenges with the Animal DSA Procedures
Animal Selection
It is crucial to select an appropriate animal model that could be easily handled,
technically feasible to perform catheterization and a repeat study could be achieved.
We selected the New Zealand white rabbit for this purpose. The main reasons were easy
availability at our hospital, easy to handle the animal, similar coagulation profile
and blood pressure to humans.[1]
In addition, the profile, size and diameter of rabbit neck vessels are similar to
human cerebral vasculature. The New Zealand white rabbit is an already established
experimental animal for research and innovation in neurovascular interventions.[1]
[2]
Anesthetic Considerations
One of the key challenges is to provide adequate anesthesia to animals for completion
of the diagnostic or therapeutic research procedure. Many different types of anesthesia
protocols have been described previously.[1]
[2]
[3] With limited experience and technical hardware for animal resuscitation, we had
to decide on an anesthesia protocol that was feasible, safe, provides immobilization
for 45 to 60 minutes, and the animal can be maintained on room air. New Zealand rabbits
were anesthetized intramuscularly in the groin muscles ([Fig. 1]) with ketamine HCl (50 mg/kg) and xylazine (5 mg/kg) and maintained on room air.
This provides adequate sedation and immobilization for our procedures.
Fig. 1 (A) Intramuscular injection of anesthetic agents to the New Zealand white rabbit. (B) Securing the limbs prior to procedure on the custom-made wooden holding table.
Animal Positioning
After sedation, it is important to place the animal in an adequate position for proper
exposure of the vascular access site. For this, a custom-made wooden table was used
that allowed each of the four extremities to be fixated with straps ([Fig. 1]).
Vascular Access
Another key challenge is to get vascular access for selective catherization in New
Zealand white rabbits as the vessels are tiny in diameter. We employed transauricular
([Fig. 2]) and transfemoral ([Fig. 3]) routes for access. The techniques for these have been previously described.[2]
[3] Transfemoral route requires a cut down procedure, which is technically challenging
during the initial learning phases. A 3F sheath or 18 G cannula was used for the initial
puncture and arterial access.
Fig. 2 (A) The presence of a 3F sheath in the central auricular artery of the left ear. (B) Placement of a 1.7-F microcatheter through the 3F sheath for selective angiography.
Fig. 3 (A) The presence of a 3F sheath in the right femoral artery after careful dissection.
(B) Placement of a 1.7-F microcatheter through the 3F sheath for selective angiography.
Selective Catheterization
Maneuvering the catheter in small vessels is challenging initially and requires technical
expertise. Using 3-F catheters or coaxial systems with 1.7-F or 1.9-F micro catheters,
we could easily navigate and perform intracranial angiography with excellent images
([Fig. 4]). The technical steps for selective catheterization of intracranial vessels have
been previously described.[2]
[3]
Fig. 4 (A) Fluoroscopic image showing guidewire and microcatheter in the arch of aorta. (B) Aortogram run shows opacification of major branches. Selective common carotid angiogram
taken on right (C) and left (D) sides.
Current Projects
Multiple projects are currently running from the department of Radio-diagnosis and
Imaging that are approved by the institutional animal ethical committee.
These include performing transfemoral angiography, transauricular angiography, to
study variations of Circle of Willis in New Zealand white rabbits and creation of
aneurysm flow models.
Conclusion and Future Direction
A vast literature is available depicting the clinical utility of pre-clinical studies
performed on large animals.[4] With the establishment of biplane DSA, we hope for increasing our technical expertise
in animal vascular procedures. The aim is to provide models for research and development
to conduct pre-clinical studies.
