CT guidance held its own against ultrasound for planning coronary stents

Before a cardiologist props open a narrowed coronary artery with a stent, they need a map: how long the narrowing is, how much plaque sits in the wall, how wide the healthy artery is on either side. The standard way to get that map from inside the artery is intravascular ultrasound, or IVUS — a tiny ultrasound probe threaded into the vessel, which improves outcomes over an angiogram alone [s1]. A randomised trial published in the New England Journal of Medicine on 1 November asked whether a CT scan taken beforehand can do the same job [s1].

The two approaches

Intravascular ultrasound is done during the procedure: the probe goes into the artery and images the vessel wall from within, guiding how the stent is sized and positioned [s1]. Coronary CT angiography, by contrast, is a scan done before the patient reaches the catheterisation lab. It images the arteries from outside and, with modern processing, can also estimate fractional flow reserve — whether a narrowing is actually choking blood flow — and lay out a stenting plan in advance [s1].

The appeal of planning from the CT is practical: the roadmap is ready before the procedure begins, without threading an extra device into the artery. The open question was whether a plan drawn from a scan taken outside the body holds up against ultrasound taken from inside it. P4 was built to test that head-to-head [s1].

How the trial was built

P4 was an investigator-initiated, international, open-label, randomised non-inferiority trial with blinded end-point adjudication, registered as NCT05253677 [s1][s2]. It enrolled patients who needed revascularisation and had at least one artery with a diameter narrowing of more than 70% and a CT-derived fractional flow reserve of 0.80 or less — a lesion both tight and flow-limiting [s1]. A total of 1105 patients were randomly assigned 1:1: 556 to CT-guided PCI and 549 to IVUS-guided PCI [s1]. Their median age was 65 years and 21.7% were women [s1].

The primary endpoint was target-vessel failure — a composite of death from cardiac causes, a heart attack in the treated vessel, or a repeat procedure to reopen it driven by ischaemia — at 12 months [s1]. Because the question was whether CT guidance is "no worse," the trial was designed as a non-inferiority study, with a margin of 4.5 percentage points on the absolute risk difference and a prespecified test for superiority to follow [s1].

What it found

The two strategies came out level. At 12 months, target-vessel failure had occurred in 23 patients (4.1%) in the CT-guided group and 25 patients (4.6%) in the IVUS-guided group — a risk difference of −0.42 percentage points (95% CI −2.82 to 1.99) [s1]. That met the bar for non-inferiority (p<0.001), while the formal test for superiority was not significant (p=0.73) [s1]. Clinical procedural complications were few in both arms: 6 patients in the CT-guided group and 9 in the IVUS-guided group [s1].

In plain terms, planning the stent from a CT scan taken before the procedure produced much the same one-year outcome as guiding it with ultrasound from inside the artery.

What is, and is not, established

What P4 supports is that, for patients with a tight, flow-limiting coronary narrowing, a CT-guided stenting strategy was non-inferior to IVUS guidance for target-vessel failure at one year [s1]. That is a finding about equivalence, not a hint that one is better: the trial was explicitly designed to detect "no worse," and the superiority test was negative [s1].

The qualifications matter. Non-inferiority was judged against a 4.5-percentage-point margin the investigators set in advance; a reader who would consider a smaller difference important should keep that margin in mind [s1]. Entry required a CT-derived fractional flow reserve of 0.80 or less, so the result applies to lesions selected that way, not to every artery a cardiologist might stent [s1]. Follow-up was 12 months; longer-term differences cannot be ruled out [s1]. The trial was open-label, with blinded adjudication of events as the safeguard, and was funded by companies that make CT and flow-analysis technology [s1].

Red flags: anyone who has had a stent and develops chest pain, breathlessness, or pain spreading to the arm or jaw should seek emergency care, as these can signal the treated vessel narrowing again. This article describes research and is not medical advice. How to plan and guide a stenting procedure is a decision for the treating cardiology team.