Diagnostic Angiography and Catheter Design

What features are desirable for a diagnostic angiographic catheter in the cardiac catheterization laboratory? In general, we require both safety and efficacy. More specifically, tip deformability or “softness”, and tip radiopacity are features that make for a safer catheter. Intrinsic to safety but usually not a feature of catheter design is the ability to monitor pressure at the catheter tip to be certain that the tip is not “wedged” under a plaque or in a hemodynamically significant ostial LMCA or RCA obstruction. One of the cardinal teachings in the cardiac catheterization laboratory is to always carefully monitor pressure when performing coronary angiography, as the pressure waveform is an important clue regarding the presence of ostial disease or being wedged under a plaque. Performing a non-selective injection prior to selective angiography is always a safe maneuver, particularly in left coronary angiography, as a forceful injection in a critical LMCA stenosis can be a terminal event. Regarding efficacy, torquability and resistance to kinking as well as lumen size required to deliver adequate contrast to visualize the coronary anatomy are specific desirable characteristics that make for a good diagnostic catheter. Recent advances in plastic polymer technology have allowed for a reduction in catheter size with preservation of lumen size due to the development of “thinwall” catheter designs. Obviously, there are limits to the reduction of catheter size with simultaneous preservation of an adequate lumen. Also, as the catheter and lumen size decrease, there is an increased pressure at the catheter tip with coronary injection, resulting in a “jet” of contrast that may cause dissection or the catheter to dislodge from the coronary ostium. The article by Ootomo and colleagues in this issue of the Journal of Invasive Cardiology elegantly demonstrates See Ootomo et al. on pages 379–384 the relationships between force and pressure at a constant injection rate and between injection rate and pressure in catheters with and without side-holes. This is something that Mason Sones must have intuitively known as his original coronary catheters had side-holes incorporated into their design. The presence of side-holes may improve safety and no doubt efficacy in delivering contrast, but there is a trade-off as you lose the ability to monitor tip pressure and the clue that there may be a significant LMCA obstruction. With this type of catheter, it would behoove the operator performing the diagnostic angiography to meticulously perform a preliminary non-selective injection of the coronary artery to be certain that there is not a significant ostial stenosis. There is also a question of “how low do you need to go?” in terms of catheter size. Five French is usually small enough, except in patients with small radial arteries. It is not certain that 4 French, as compared to 5 French, improves the safety in studies performed via the radial approach. The smaller catheter size might be an improvement in studies performed via the femoral or brachial approach, where hemostasis can be a more significant problem. Smaller thin-wall catheters tend to be more rigid in an effort to prevent kinking and to simultaneously maintain torquability and lumen size. Catheter stiffness or rigidity is potentially more of a problem via the radial or brachial approach as generally more manipulation is required for engagement of the coronary artery compared to femoral access. Composite catheters with different materials at the “working end,” compared to the shaft, can help to obviate these problems, but these catheters are more difficult to manufacture, therefore, more expensive. A more deformable catheter, like the old Sones catheters, would allow for a single catheter to be used for both left and right coronary injections. Currently, there are catheter designs that attempt to achieve this, but they remain imperfect.