Invasive coronary angiography and physiology

What it is and how it works

Invasive coronary angiography (ICA) uses a catheter placed in the coronary arteries, contrast dye and X-ray imaging. It defines whether an epicardial coronary artery has a luminal obstruction, and how severe it is, where it sits, how long it is and how wide the vessel is, along with coronary blood flow. Its main goal is to detect and characterize high-grade stenoses so the team can judge whether percutaneous or surgical revascularization is feasible and needed Gulati et al., 2021, Section 3.1.2.

A pressure wire adds physiology. Fractional flow reserve (FFR) is the ratio of pressure beyond a stenosis to aortic pressure during maximal hyperemia, which estimates the ratio of flow. The instantaneous wave-free ratio (iFR) is a non-hyperemic alternative, simpler to use and clinically non-inferior in practice Weir-McCall et al., 2026, Section 2.1. The chest pain guideline links revascularization for lesion-specific ischemia (FFR of 0.80 or less, or iFR of 0.89 or less) to better event-free survival than treating by anatomy alone Gulati et al., 2021, Section 5.2.1. The same catheter lab can also offer intravascular imaging, testing for coronary spasm and microvascular disease, and other hemodynamic measurements Winchester et al., 2023, Table A.

What the result tells you

The AUC sort angiography results by the worst stenosis, as in the angiography categories below Winchester et al., 2023, Definitions for Table 1.3.

Anatomy alone is an imperfect guide to ischemia. In the SCCT consensus, compared with invasive FFR of 0.80 or less, the sensitivity of angiographic stenosis was 69% and the specificity 67%Narula et al., 2021, Section 1. For an equivocal angiogram, the AUC assume physiological testing (FFR or non-hyperemic indices), noninvasive stress testing, or intravascular ultrasound for the left mainWinchester et al., 2023, Assumption 8. Physiology values are continuous, from 0 to 1, and should not be read only as above or below a cutoff Winchester et al., 2023, Definitions for Table 1.3.

Many angiograms show no obstructive disease. Nonobstructive CAD is present in more than half of patients undergoing elective angiography and carries an increased risk of death and MI Virani et al., 2023, Section 6.1.2. The chest pain guideline notes that current testing patterns result in a normal angiography rate of upward of 50% to 60% Gulati et al., 2021, Section 5.1.2.

The microvascular catch

Angiography has a spatial resolution of about 0.3 mm, so it cannot show the 0.1 mm arterioles that regulate blood flow to the muscle. A normal angiogram therefore does not exclude abnormal coronary vascular function, which can be tested during the same procedure, including coronary microcirculation and vasomotion Gulati et al., 2021, Section 3.1.2. Ischemia with nonobstructive coronary arteries (INOCA) covers microvascular dysfunction, spasm, or both Virani et al., 2023, Section 6.1.2. In the CorMicA trial, treatment guided by invasive physiology (flow reserve, microvascular resistance, FFR, then acetylcholine testing) improved angina and quality of life at 6 months, with no difference in major adverse events Virani et al., 2023, Section 6.1.2. See also the definition of coronary microvascular dysfunction.

Strengths and limitations

Practical points

• A test, or the first step of treatment? Angiography can answer a diagnostic question, but the guidelines mainly frame it as the step that guides treatment. For patients with chronic coronary disease, ICA is recommended when a change in symptoms or functional capacity persists despite guideline-directed medical therapy (GDMT), to guide therapy aimed at improving angina Virani et al., 2023, Section 3.1. It is also recommended for newly reduced LV function or heart failure, and not routinely recommended for risk stratification alone without LV dysfunction, heart failure, refractory chest pain, or noninvasive testing suggesting significant left main disease Virani et al., 2023, Section 3.2.
• After noninvasive testing. In patients with obstructive CAD and stable chest pain despite GDMT, ICA is recommended when stress testing shows moderate to severe ischemia. It is also effective for guiding therapy when CCTA shows left main stenosis of 50% or more, obstructive CAD with FFR-CT of 0.80 or less, or severe stenosis in all three main vessels. If a patient goes to ICA without prior stress testing, FFR or iFR is of benefit Gulati et al., 2021, Section 5.2.1. SCCT likewise says left main stenosis of 50% or more and severe triple-vessel disease should go to ICA Narula et al., 2021, Table 1.
• Without known CAD. The chest pain guideline notes that, unlike older guidelines, contemporary randomized trials support safely triaging candidates for elective angiography with CCTA or noninvasive stress testing Gulati et al., 2021, Section 5.1.3.
• Symptoms versus outcomes. In ISCHEMIA, an invasive strategy did not change the primary composite outcome over about 3.3 years in stable CAD with moderate to severe ischemia, but angina improved more, particularly in patients with more frequent angina at baseline Virani et al., 2023, Section 3.1.
• Risks. The AUC name procedural complications and radiation, and list sensitivity to iodinated contrast among the inherent risks of testing Winchester et al., 2023, Assumption 21. The sources used here give no complication rates. In pregnancy, imaging with ionizing radiation should generally be avoided, and when it is necessary the risks and benefits of invasive angiography should be discussed with the patient Gulati et al., 2021, Section 3.3.
• Reading the report. Look for the worst stenosis in each major vessel and the left main, whether FFR or iFR was measured for intermediate lesions, and, if the arteries look open, whether coronary function testing was done.

An example from the tool

Angiography is often considered after a noninvasive test has shown significant ischemia. Open the scenario below to see how the criteria rate each test, and why.

The tool also covers what comes after angiography. For the case where angiography shows mild or no CAD, or normal invasive physiology, open scenario 38 →.

Try the scenario builder → for patient-specific questions.