Intravascular ultrasound can predict events, PROSPECT shows



A large proportion of patients with acute coronary syndrome successfully treated with stents and contemporary medical therapy develop major adverse cardiac events (MACE) within three years. The results of the PROSPECT (Providing regional observations to study predictors of events in the coronary tree) trial showed that the identification of lesions can be enhanced by intravascular ultrasound (IVUS).

Gregg W Stone, professor of medicine and the director of research and education at the Center for Interventional Vascular Therapy at the Columbia University Medical Center/New York-Presbyterian Hospital, presented the results of PROSPECT at the 21st annual Transcatheter Cardiovascular Therapeutics (TCT) scientific symposium in San Francisco, US during a late-breaking trial session.

In the 700-patient prospective, multicentre, natural history study, investigators performed quantitative coronary angiography (QCA) of the coronary tree, IVUS, virtual histology and palpography in patients with acute coronary syndrome who had undergone successful percutaneous coronary intervention (PCI) to quantify the clinical event rate due to atherosclerotic progression, and to identify those lesions which place patients at risk for unexpected adverse cardiovascular events. Over a three-year follow-up period, the investigators assessed the patients for the primary endpoint of MACE (a composite of cardiac death, cardiac arrest, myocardial infarction, unstable angina and increasing angina) attributable to rapid angiographic progression of a non-culprit lesion. Stone told the audience that the investigators found that culprit and non-culprit lesions caused similar levels of MACE (11.6% for non-culprit lesions vs. 12.9% for culprit lesions at three years), with half of these events occurring within one year and the other half between one and three years.

Stone told the assembled delegates that, of the non-culprit lesion-related MACE group, none of the patients died and none suffered cardiac arrest, 1% had a myocardial infarction and 3.3% had unstable angina, with 8.5% suffering increasing angina. Stone said that if all the deaths that were due to indeterminate causes (2.7%) were attributed to non-culprit lesions, the worst-case scenario would be a combined cardiac death/cardiac arrest/MI rate of 3.3% in that group.

The investigators looked at baseline characteristics to determine whether there would be any way to predict non-culprit lesion events and found that, apart from insulin-dependent diabetes, baseline variables were poor predictors. However, when they looked at IVUS data, they were able to identify much more successfully those who were at risk, with plaque burden and lesion length in particular being indicators of events.

To conclude, Stone summarised the findings of the study: Approximately 20% of patients with acute coronary syndrome successfully treated with stents and contemporary medical therapy develop MACE within three years. Approximately 12% of these are due to non-culprit lesions. While plaques which are responsible for unanticipated future MACE are frequently angiographically mild, most untreated plaques which become symptomatic have a large plaque burden and a small lumen area (which are detectable by IVUS but not by angiography).

The prospective identification of non-culprit lesions prone to develop MACE within three years can be enhanced by characterisation of underlying plaque morphology with virtual histology. The combination of large plaque burden (IVUS) and a large necrotic core without a visible cap (VH-TCFA) identifies lesions which are at especially high risk for future adverse cardiovascular events.