Threading a catheter to the heart
Cardiac catheterization is the most direct way to study the coronary arteries. A thin, flexible tube is inserted through an artery — usually at the wrist or groin — and gently steered up to the heart under X-ray guidance. When dye is injected into the coronary arteries and filmed, you get a coronary angiogram: a sharp, moving road map showing exactly where an artery is narrowed or blocked. It is invasive and carries small risks, so it is used when the answer truly matters — and especially when treatment may follow immediately.
The same catheter does more than draw arteries. It can measure pressures inside the chambers and great vessels, sample oxygen levels, and — by injecting dye into the left ventricle — perform ventriculography to watch the main pumping chamber squeeze. This is why the procedure is broadly called catheterization, not just angiography: angiography is one of the things a catheter does.
Is a narrowing actually important?
A picture of a narrowing does not always prove it is causing trouble. A borderline 50–70% narrowing may or may not be starving the muscle. Two tools settle it from inside the artery. Fractional flow reserve measures the pressure drop across the narrowing — if blood flow falls below a threshold, the lesion is significant. Intravascular ultrasound puts a tiny ultrasound probe inside the artery to see the plaque and true vessel size directly. Together they keep treatment matched to lesions that genuinely matter.
Fractional flow reserve (FFR) — deciding if a stent is needed
FFR = pressure beyond the narrowing / pressure before it
(measured at maximal flow, both in mmHg)
Example:
pressure before narrowing (aortic) = 100 mmHg
pressure beyond narrowing (distal) = 72 mmHg
FFR = 72 / 100 = 0.72
Decision threshold (commonly used):
FFR > 0.80 .... lesion not flow-limiting -> defer stent
FFR <= 0.80 ... lesion flow-limiting -> stent benefits
0.72 is below 0.80 -> the narrowing is significant;
relieving it (e.g., a stent) is expected to help.Diagnosis and treatment in one sitting
What sets catheterization apart from every other imaging test is that it can fix what it finds. Through the same catheter, a blocked artery can be opened by percutaneous coronary intervention — a balloon widens the narrowing and a stent is left to hold it open. In a STEMI — a heart attack from a fully blocked artery — this is the emergency treatment, and getting the artery open fast saves muscle. No other test in this track both diagnoses and treats in a single procedure.