Establishing vascular access is essential in interventional Cardiology. In general the ideal access route should be safe and stable and puncture should be possible in a minimum of time and with a minimum of effort while providing a high success rate.
Common contemporary access sites for coronary angiography and Intervention are: - radial - femoral - brachial - ulnar
Classically vascular access is secured and maintained by implantation of an access sheath. Depending on the vessel, different types and sizes of sheaths are available. Usually via side access injection of medication or contrast can be performed through the sheath. Also blood can be drawn from the vessel and invasive blood pressure measurement can be derived. Sheaths are characterized by inner and outer diameter ("french"), length of the tube and sometimes additional features (Special tapering, stiffness, ect). Note: in case of transradial approach the practice of sheath-less catheterization should be mentioned (link).
RADIAL: Most commonly a 5 or 6 French system is used for classic coronary angiography. Because of the smaller Diameter of the radial artery, the sheath sets usually provide an extra floppy, fine guidewire for the Seldinger maneuver and the introducer has extra tapering for smooth advancement. Of note: typically after Implantation of the radial sheaths administration of spasmolytic medications such as nitroglycerine and verapamile will performed to avoid spasm. Radial sheaths are usually of 12 cm length and most types (even 5 Fr) can house up to 6 French guide catheters ("6-in-5 Fr").
FEMORAL: Sheaths used for transfemoral approach are available in a variety of types and sizes. For diagnostic coronary angiography purpose only (no PCI) a 4 or 5 French System with 12 cm length can be used. For PCI, at least 6 Fr should be used. For complex procedures such as left main interventions or CTO some interventionalists prefer 7 Fr access. Larger bore sheaths should be reserved for Special purposes, such as rotational atherectomy, endomyocardial biopsy, valve interventions or percutaneous ventricular assist devices. For percutaneous coronary interventions the majority of cases can be managed via 6 Fr Access. However, there are multiple designs with different lengths to achieve optimal stability and back-up. Apart from 12 cm length, also 25 cm and 45 cm are widely available.
In general, a longer sheath will provide better steerability, better torque response and increased back-up. In patients with severe kinking of femoral and iliac arteries, longer sheats may be extremely helpful, especially when PCI is performed. Furthermore, stress of the femoral of iliac vessel wall e.g. and thereby risk of injury is reduced, when echange of catheters is performed via longer sheaths. This is especially true for patients with severe calcification and tortuous anatomy. In rare cases massive kinking may require extra Long catheters. In such cases, extra Long sheaths can be used to straighten the anatomy and thereby allow use of normal length equipment, which inherits better torque reponse and back up. Note that a 45 cm sheath will "guide the guide catheter" for usually well beyond the diaphragm. Sheer stress and resistance of the guide catheter in the pelvic vessels will be exluded and maneuveribility of the catheter will increase.