Coronary Lesions (PDF)

angiographically visible vessel dissection without reduction of flow is associated with a 6.5-fold increase in the incidence of acute or subacute closure. On the other hand, plaque dissection is the most signi.cant mechanism of lumen enlargement after balloon dilatation, as shown by ultrasound and angioscopy studies, and it is likely that plaque fracture is a prerequisite for achieving effective and persistent plaque compression and redistribution and lumen enlargement. Ultrasound studies suggest that temporary wall stretch in concentric lesions or in eccentric lesions in vessels with a disease-free arc without plaque disruption and dissection has a smaller lumen gain due to a significant immediate elastic recoil after dilatation.

Thus, post-angioplasty dissection may be a desirable finding; however, at the same time, it may also be the expression of a complication and of impending procedure failure.

Alternative imaging techniques in coronary dissection

Intracoronary ultrasound

Intracoronary ultrasound studies have produced a major advancement in the detection of ruptured plaque and dissection. Ultrasound may identify coronary dissections more often than angiography, and it is likely that this improved sensitivity in association with a more detailed definition of the severity of the dissection may have a significant impact on patient treatment and clinical outcome. The lower sensitivity of angiography as compared to intravascular ultrasound in the detection of coronary dissection may be easily explained when considering the two prerequisites for angiographic detection: first, a direct connection between the true and the false lumens, and second, the use of a view that avoids the superimposition of the two lumens. Only on very rare occasions has an angiographically detected dissection not been observed on ultrasound imaging. Dissection may not be visible by ultrasound if the true lumen is severely stenotic and the ultrasound catheter presses the .ap against the arterial wall (Figure 13.1), or if the dissection occurs behind a heavily calci.ed plaque that prevents accurate morphological definition.

Balloon angioplasty produces multiple vascular injuries, including endothelial denudation, cracking and splitting of the intimal and medial layers, compression and redistribution of the plaque, and stretching or tearing of the media. Moreover, intravascular ultrasound studies have shown pre-procedural severe wall dissection due to spontaneous plaque rupture in a substantial minority of patients with stable angina or acute ischemic syndromes.

A major dissection may be defined as a dissection flap resulting in a significant stenotic true lumen, or extending around more than one-third of the circumference of the vessel (Figure 13.2). The severity of dissection, as defined by echographic criteria, seems to be strongly related to subsequent adverse events due to acute or subacute vessel closure.