Cerebral angiography using transauricular access in a rabbit model: a new technique

Introduction

Brain research on topics such as stroke and central nervous system diseases require appropriate animal models. For interventional radiology or hemodynamic research, rabbit models have become popular because they are easily handled, are anatomically similarity to humans, and provide a suitable balance between size and practicality (1). Conventionally, the femoral artery is used for cerebral angiography in radiology departments. The procedure starts with shaving the groin hair, sanitization, and local anesthesia at the puncture sites. However, angiographic studies using rabbit models require surgical cutdown of the femoral artery to obtain intra-arterial access; that procedure is technically difficult and requires clinical experience. In addition, puncture of the femoral artery using the Seldinger technique can be problematic due to mismatch between puncture needle size and the femoral artery lumen and to difficulties associated with the transmural introduction of the needle tip.

Recently, a transauricular hepatic angiography technique in a rabbit model was described for hepatic angiography and reported to be feasible and to have several advantages over the transfemoral technique. Common carotid arterial angiography via the central auricular artery in a rabbit model using an intravenous (i.v.) catheter has also been reported (2,3). However, Miscolczi et al. (2) and Ding et al. (3) described only their imaging technique; further vascular intervention or research using a selective approach to the internal carotid artery is not possible using their technique. In addition, transauricular arterial access has been reported to be feasible for use in cardiovascular studies in a rabbit model (4,5). Karnabatidis et al. (4) used serial step-by-step tract dilation to accomplish transauricular endovascular access in a rabbit model by undertaking 22-gauge i.v. catheter insertion, 0.018-inch guide wire advancement, incision of the auricular dermis, and final 4-F vascular sheath advancement. However, this technique seems to require considerable time and effort to achieve transauricular access. Chang et al. (5) used transauricular access for hepatic angiography. However, superselective internal carotid or vertebral angiography for brain research purposes has not been previously reported in a rabbit model using a transauricular approach.

The aim of the present study was to evaluate the technical feasibility of transauricular access for superselective cerebral angiography and review its merits and drawbacks relative to those of transfemoral arterial access in a rabbit model.

Material and Methods

Results

The application of manual pressure to the distal portion and tapping of arteries enabled successful puncture with one or two attempts using a 20-gauge i.v. catheter in all 20 rabbits. After approaching the aortic arch, the microcatheter tip and guide wire were manipulated to select the common carotid or vertebral artery (Fig. 1). For three right auricular and two left auricular approaches, selection of the contralateral common carotid artery was successful only by applying guide wire manipulation. In the other 15 rabbits, selection of the target arteries by applying guide wire manipulation alone was difficult due to the acute angles between the carotid and vertebral arteries. This problem was solved by manual angulation of the tip of guide wire or by using a looping technique within the cardiac chamber, which involved microcatheter/guide wire advancement into the heart, creation of a loop within the left cardiac chamber, and movement of the microcatheter/guide wire back and forth, thereby enabling straightforward superselection of the common and internal carotid or vertebral artery (Fig. 2). During this procedure, intracardiac catheter loops disappeared in six and persisted in nine of the 15 rabbits in which the looping technique was used (Fig. 3).

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Fig. 1.

Contralateral internal carotid angiography performed without the looping technique. Superselection of the right internal carotid artery was successfully achieved by directly passing the microcatheter/guide wire through the aortic arch (a, arrows). Oblique internal carotid angiogram (b).

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Fig. 2.

Contralateral internal carotid angiography performed using the looping technique. The tip of the microcatheter/guide wire is shown in the right common carotid artery and the microcatheter/guide wire is shown to form a loop within the left ventricle (a, arrows). During superselection of the right internal carotid artery, the loop within the left cardiac chamber disappeared (b, arrows). Oblique internal carotid angiogram (c).

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Fig. 3.

Contralateral internal carotid angiography with a sustained loop in the cardiac chamber. Single posteroanterior view showing the tip of the microcatheter/guide wire in the left common carotid artery and a loop remaining within the left ventricle (a, arrows). Oblique common carotid angiogram (b).

Vertebral angiography was possible when using the looping technique (Fig. 4). In two cases of right auricular access and one of left auricular access, the contralateral vertebral artery was selected directly without applying the looping technique (Fig. 5). Internal carotid angiography with same side access was also possible when using the looping technique (Fig. 6), although a little more time was required to select the target artery, as the tip of the microcatheter/guide wire moved sympathetically with cardiac beats, which sometimes made it difficult to select the target artery, especially when using the looping technique.

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Fig. 4.

Ipsilateral vertebral angiography with a sustained loop in the cardiac chamber. Right vertebral angiogram with right transauricular access showing the tip of the microcatheter/guide wire in the right vertebral artery and a remaining loop in the left ventricle (a, arrows). Posteroanterior vertebral angiogram (b).

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Fig. 5.

Contralateral vertebral angiography with direct artery selection. The image shows the tip of the microcatheter/guide wire in the right vertebral artery (a) without a microcatheter/guide wire loop. Oblique vertebral angiogram (b).

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Fig. 6.

Ipsilateral internal carotid angiography with a sustained loop in the cardiac chamber. Single posteroanterior view showing the tip of the microcatheter/guide wire in the left common carotid artery and loop in the left atrium (a, arrows). Oblique internal carotid angiogram (b).

Mean procedure times from puncture of the central auricular artery to microcatheter removal from the artery were similar: 15 ± 0.35 min for right ear approaches and 13 ± 0.58 min for left ear approaches (P = 0.135).

Discussion

Rabbit models have been widely used in various fields, including the angiographic field, such as stroke-related studies (1), investigations into saccular aneurysm creation at carotid arteries (2), chemoembolization of hepatic carcinoma studies (7,8), and studies into the central nervous system (9). Traditionally, the femoral artery has been used as an intra-arterial route for angiography in rabbit models (1), but transfemoral access in animal models presents difficulties associated with surgical cutdown in the inguinal area and femoral artery exposure and cannulation. Bleeding, transmural catheter advancement, and occlusion or dissection of the femoral artery are potential causes of transfemoral access failure. Another less serious problem associated with transfemoral access is that repeat angiography is not straightforward due to anatomical disarrangement and surgical occlusion of the femoral artery resulting from the initial transfemoral approach. In comparative studies on auricular and femoral artery approaches to cardiovascular experimentation (3), pressure monitoring (10), and hepatic angiography (5), the transauricular arterial access has been reported to be as good as or better than the femoral approach in terms of reducing the time to complete the procedure. Carotid angiography of the right side with forceful injection of contrast media into the left auricular artery has been reported in multiple follow-up studies to be straightforward in a rabbit aneurysm model (2). However, this technique is unsuitable for interventional purposes or brain research, and its use is restricted to simple visualization of the vascular anatomy of the common carotid artery. The internal carotid artery is small in caliber; thus, it is barely visible during normal common carotid angiography. Superselective internal carotid angiography is essential when creating a stroke model or researching central nervous system drug development. However, to the best of our knowledge, superselective internal carotid angiography via the transauricular access route has not been previously reported.

In the present study, transauricular access for cerebral angiography was evaluated to be feasible in a rabbit model. A highly attractive advantage of the transauricular access is that it does not require a cutdown procedure. In addition, a 20-gauge i.v. catheter is sufficient for the 2.0-F microcatheter application, and the technique of looping the microcatheter/wire within the cardiac chamber simplified the selection of the carotid or vertebral artery on right and left sides of the neck. In animal research, the traditional Seldinger method via the femoral artery requires skillful manipulation for successful cannulation of the microcatheter. Transmural advancement of the needle is a highly annoying problem associated with femoral access and is probably due to the relatively small luminal diameters compared to that of the needles used for cannulation. Bleeding from the cutdown field also extends procedural times. However, when the transauricular arterial approach is used, no cutdown procedure is needed, resulting in a reduction of procedure time. The diameter of the central auricular artery appears to be too small for a large-sized i.v. catheter, although Chang et al. (5) reported the successful use of an 18-gauge i.v. catheter. In the present study, a 20-gauge i.v. catheter was suitable. Moreover, tapping arteries several times increased lumen diameters and eased cannulation.

Angles between right innominate and left common carotid or left vertebral arteries were so acute that artery selection was not easy in the present study. Thus, we used a looping method within the cardiac chamber, i.e. the microcatheter/guide wire was looped within the cardiac chamber, enabling the tip of the microcatheter to be directed toward the entrances of the carotid or vertebral arteries. When selecting arteries on the same side as the transauricular access, the looping technique was essential. Some researchers may express concern regarding cardiac injury related to using the looping technique. However, as with any invasive procedure, there are specific patient-dependent and procedure-related complications that are inherent to angiography, no matter the technique used. Nonetheless, major complications resulting from cardiac catheterization in clinical coronary angiography occur in < 2% of the population and the associated mortality rate is < 0.08% (11).

Using a preformed microcatheter with a sharp curve in the “J” shape or “Swan neck,” such as that provided by Prowler (Codman, Johnson & Johnson Medical, Wokingham, UK), Phenom (Medtronic Neurovascular, Irvine, CA, USA), or Direxion (Boston Scientific, Natick, MA, USA) microcatheters, might have made the need for looping in the heart unnecessary. However, for precise selection of the ipsilateral cerebral or vertebral artery, the tip of preformed microcatheter needs to be very acute due to angle between the entry and exit arteries at the same site. Thus, careful manipulation seemed to be needed if a preformed microcatheter was used. If the preformed tip is insufficient to resolve the problem, the looping technique, as used in this study, is an appropriate option.

Arrhythmias can occur during diagnostic catheterization. The most common arrhythmia is ventricular premature contraction, which generally lacks clinical importance, can be induced by catheter introduction into the right or left ventricle (12). However, there is a low incidence of serious ventricular arrhythmias during diagnostic cardiac catheterization (13). Ventricular tachycardia (VT) and fibrillation (VF) are rare complications associated with catheterization, reported to occur in approximately 0.4% of cases (14). Such arrhythmias may result from excess catheter manipulation but, more commonly, they are associated with intracoronary contrast injection. The risk of arrhythmia occurrence is greatest following the injection of high-osmolar contrast agents into the right coronary artery and is particularly high during periods of prolonged injection or damped pressure tracing (15). Unfortunately, the mechanisms of VT and VF remain incompletely described. It has been reported that contrast medium can directly lower VF thresholds to 20%–60% of the control level. This phenomenon is not a direct effect of hypoxia; instead, it is a direct effect of the contrast medium (sodium iodide) on myocardial metabolism (16,17). In addition to the direct effects of the contrast medium after its injection into a coronary artery, mechanical factors may also have a role. For example, pressure damping at the catheter tip indicates that the catheter may be a significant obstruction to flow, and a combination of ischemic and contrast medium effects may result in an arrhythmia.

Procedural times were similar for the right and left approaches, which suggests that the choice of site for the initial puncture is unimportant. However, selection of the target arteries depends on vessel morphology and operator skill. In this study, cardiac beats sometimes made it difficult to select the target artery, especially when using the looping technique, as the tip of the microcatheter/guide wire moved sympathetically. Passage of the microcatheter from the auricular artery to the internal maxillary artery was time-consuming because the microcatheter tended to advance to arteries other than the internal maxillary artery. To solve this selection problem, gentle manipulation of the microcatheter/guide wire was required.

In conclusion, transauricular cerebral angiography in rabbits appears to offer a feasible approach to the study of brain and carotid interventions. Selection of the internal carotid or vertebral artery on each side was not difficult when using the described technique of looping the microcatheter/guide wire within the cardiac chamber. Furthermore, the results indicate which ear is chosen as the initial puncture site is unimportant.