Intracoronary ultrasound: insights into mechanisms and results of coronary interventions

Influence of coronary atherosclerotic remodeling on the mechanism of balloon angioplasty

OBJECTIVES

Intracoronary ultrasonography was used to assess coronary arteries before and after balloon percutaneous transluminal coronary angioplasty (PTCA) to determine whether the mode of coronary atherosclerotic remodeling affects the mechanism of balloon dilation.

BACKGROUND

Coronary arteries may enlarge or shrink in response to atherosclerotic plaque development. The effect of coronary remodeling on the mechanism of balloon PTCA has not yet been studied.

METHODS

Forty-one patients with 47 native de novo coronary artery lesions were studied with a 30 MHz intracoronary ultrasound catheter before and after balloon PTCA. Images were analyzed at the lesion site and the adjacent reference segments. At each site the lumen, vessel, and plaque area and the percent area stenosis were measured. Lesions were separated into two groups based on relative vessel area (lesion vessel area/reference vessel area). A relative vessel area >1.0 defines adaptive enlargement (group 1, n = 25), whereas a relative vessel area < or =1.0 reflects coronary shrinkage (group 2, n = 22). Regression analysis examined whether elastic recoil and the PTCA balloon/vessel area ratio correlated.

RESULTS

After balloon PTCA was performed, both the enlargement and shrinkage groups had similar gains in luminal area (2.3 +/- 1.8 mm2 [mean +/- SD] vs 2.8 +/- 1.7 mm2, p = 0.32), reduction in percent stenosis (-19.2% +/- 11.5% vs -14.4 +/- 12.7, p = 0.18), and final lumen area (4.9 +/- 1.7 mm2 vs 4.7 +/- 1.9 mm2, p = 0.73). However, the mechanism of luminal enlargement was different in each group. Reduction in plaque area was significantly greater in the enlargement group (group 1, -2.0 +/- 1.7 mm2 vs group 2, 0.04 +/- 2.2 mm2; p = 0.001), whereas increased vessel area was more important in the shrinkage group (group 1, 0.8 +/- 1.5 mm2 vs group 2, 2.4 +/- 2.3 mm2; p = 0.009). Positive correlation was seen between elastic recoil and the balloon/vessel area ratio in lesions with vessel enlargement (r = 0.80, p < 0.0001). No such correlation was observed in shrinkage vessels (r = 0.28, p = 0.21 ).

CONCLUSIONS

The acute luminal gain after balloon PTCA is similar regardless of the type of coronary remodeling. However, the mode of remodeling affects the mechanism of balloon dilation such that enlargement vessels exhibit plaque compression, whereas shrinkage arteries demonstrate vessel stretch. The post-PTCA elastic recoil correlates linearly to the balloon/vessel area ratio in arteries that have undergone adaptive enlargement.

Intravascular ultrasound and balloon percutaneous transluminal coronary angioplasty

Intracoronary ultrasound provides unique information during percutaneous transluminal coronary angioplasty (PTCA), including more accurate measurement of vessel size and plaque burden as well as plaque characteristics such as composition and distribution. As a research tool, it has been useful in determining the mechanisms of PTCA, which primarily involves vessel stretch, plaque fracture/dissection, and plaque redistribution. It may be clinically useful in assessing lesion severity in patients with indeterminate clinical and angiographic findings. Plaque characteristics as determined by intracoronary ultrasound may also be helpful in developing an individualized interventional approach for each lesion. Finally, certain intracoronary ultrasound findings after PTCA, such as large dissections and large residual stenosis, are associated with increased risk of short-term and long-term adverse outcomes.