The black hole: echolucent tissue observed following intracoronary radiation.

Aims: Recent trials in humans have given us insight into some of the consequences of intracoronary radiation. The authors describe a new observation noted on intravascular ultrasound: that of intraluminal echolucent tissue, dubbed the 'black hole', noted at six-month follow-up.
Methods and Results: One hundred and twenty-eight consecutive patients enrolled in brachytherapy protocols were analyzed. The control group (C) consisted of individuals who underwent percutaneous transluminal coronary angioplasty with (n = 48) and without (n = 22) stent implantation. Radiation groups included those who underwent low activity (LA) (n = 18), high activity (HA) (n = 26) and cold-end (CE) (n = 18) radioactive stenting. The Novoste Betacath (n = 39) and Guidant (n = 27) catheter-based radiation systems were also employed. At six-month follow-up echolucent tissue was identified in a total of 28 cases (22%). Angiographic restenosis occurred in 17 cases (61%). No echolucent tissue was seen in the control group or in the LA group. HA and CE radioactive stents were most commonly associated with echolucent tissue. Echolucent tissue was seen in all groups treated with catheter-based radiation with and without stenting. Pathology after atherectomy demonstrated smooth muscle cells scattered in extracellular matrix containing abundant proteoglycans and an absence of elastin and mature collagen.
Conclusions: Echolucent tissue is common after radioactive stenting. It is composed of tissue rich in proteoglycans while poor in mature collagen and elastin.