Читать книгу Interventional Cardiology - Группа авторов - Страница 101

The left anterior oblique (LAO) view is most useful for intubation of the left and right coronary arteries, because the left and right coronary sinuses are maximally separated and there is minimal overlap between the ostia and the coronary sinuses (Figure 4.1). For intubation of the left system the J‐wire is advanced up to just above the aortic leaflets. The catheter is advanced over the wire and, when the tip nears the aortic sinuses, the J‐wire is withdrawn to allow it to come close to or intubate the coronary ostium. Slow J‐wire withdrawal is recommended to avoid the catheter tip flicking into the ostium which can cause dissection, plaque dislodgement, or spasm, and also to avoid sucking air into the proximal catheter hub. The right coronary is intubated by advancing the JR catheter over the J‐wire until the tip is just above the aortic leaflets. The wire is then partially withdrawn, often leaving it inside the distal catheter to facilitate manipulation. Taking and holding a deep breath can also help straightening proximal tortuosities, especially of the subclavian arteries when using a radial approach. Gentle counterclockwise rotation aiming the catheter tip toward the left with concomitant withdrawal is usually required. Gentle movements are emphasized to avoid sudden or deep intubation, which can precipitate spasm, and to avoid catheter kinking, especially using a radial approach. Before proceeding to inject dye the pressure trace is checked: if it is damped or ventricularized, there is the possibility of ostial right or LMS disease, spasm, complete occlusion of a non‐dominant RCA, or that the catheter tip is abutting the vessel wall. Forceful contrast injection during any of these scenarios could result in dissection or plaque dislodgement. Contrast injection with an occlusive catheter with contrast remaining at the end of the injection, for instance holding up into the conus branch, should also be avoided because this can precipitate ventricular fibrillation. Spasm can be reversed with intracoronary nitrate, for example isosorbide dinitrate (ISDN) 100–200 μg. Rapid but gentle catheter withdrawal is indicated until the coronary ostium is extubated or the pressure trace normalizes. A small dose of intracoronary nitrate can be required to counteract any coronary vasospasm (e.g. ISDN 100–500 μg depending on the blood pressure). On occasion, smaller (e.g. 5F or 4F) catheters are required to avoid damping caused by spasm in hyper‐reactive arteries or when there is ostial plaque.

The active support offered by deep intubation is frequently used also during interventions. However, this technique presents several relative limitations. The obstruction of flow during deep cannulation can induce severe ischemia, not always prevented by the presence of side holes. There is a potential risk of air embolism because of aspiration of air (cavitation) while the wire is withdrawn if the catheter is damped inside the artery with a low back pressure. It is recommended to wait for backbleeding before connection of the angiographic catheter with the tubes, injecting saline or contrast only when the presence of air is fully excluded. Filling the catheter with contrast before intubation of the ostia also reduces the risk of coronary embolism and makes the catheters more visible at fluoroscopy. Injection of contrast before coronary intubation and repeated tests during cannulation should be avoided in patients with poor renal function. An effective way to confirm cannulation, usable by all the operators with an initial angioplasty experience, is to insert a wire into the proximal coronary arteries, a manoeuvre which is also helpful to stabilize the system during injection.