Angiography and DSA Basics
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Direct answer
Seldinger's 1953 technique — puncture, wire through the needle, needle out, catheter over the wire — still anchors every angiogram performed today. Digital subtraction angiography then removes background anatomy by acquiring a mask image before contrast and electronically subtracting it from contrast-filled frames, leaving isolated vessels; because bone and bowel gas move between frames, the patient must hold still and images are obtained in apnoea. The common femoral artery punctured over the femoral head below the inguinal ligament is the classic access (radial access is now common), and 4-6 F sheaths carry diagnostic catheters such as the pigtail flush catheter. Beyond diagnosis — aneurysms, stenoses, tumour blush, bleeding — the same platform is therapeutic: coiling, stenting, embolisation and thrombectomy, which is why catheter angiography remains the reference standard that CT and MR angiography are measured against.
What you must remember
- Seldinger sequence: vessel punctured, guidewire advanced through the needle, needle withdrawn, tract dilated, catheter or sheath placed over the wire — never memorised as "needle then catheter" alone.
- Access anatomy: common femoral artery over the femoral head, below the inguinal ligament, over the femoral vein (medial) and nerve (lateral) — puncture over bone allows effective compression afterwards; a high puncture risks retroperitoneal haemorrhage.
- Subtraction principle: mask image plus post-contrast frame subtracted pixel-by-pixel; roadmapping and mask-fade are refinements; patient motion degrades the mask, hence apnoea and immobilisation.
- Contrast and alternatives: non-ionic iodinated contrast 300-370 mg iodine/mL is standard; carbon dioxide gas contrast is an option in renal failure or allergy but contraindicated above the diaphragm (cerebral and coronary circuits).
- Catheter vocabulary: pigtail flush catheter for aortic runs, selective catheters (Simmons, Cobra, Headhunter shapes) for branch vessels, microcatheters for superselective embolisation.
- Complication clusters: access-site haematoma (commonest), pseudoaneurysm and arteriovenous fistula; catheter-related dissection, perforation, distal embolisation and vasospasm; systemic contrast reactions and nephropathy.
- Post-procedure care: manual compression about 10-15 minutes (longer on anticoagulation) or closure device, bed rest with the limb straight, and regular pulse and puncture-site checks.
- Anticoagulation during the procedure: intravenous heparin (often as an activated clotting time-guided bolus) for neurointervention and long manipulations, and continuous catheter flushing to prevent thrombus build-up.
Walking through a cerebral angiogram
A 54-year-old with a subarachnoid haemorrhage and a middle cerebral aneurysm suspected on CT angiography is taken for digital subtraction angiography with a view to coiling. Under ultrasound and fluoroscopic guidance the right common femoral artery is punctured over the femoral head; a 6 F sheath is seated. A pigtail or selective catheter rides a hydrophilic wire to the aortic arch; each carotid and vertebral artery is catheterised in turn. Mask images are taken in apnoea, contrast injected, and subtracted runs display the circulation free of skull base — the aneurysm's neck, dome and relationship to the parent vessel measured in working projections. Heparin is given once the decision to treat is firm; a microcatheter is navigated coaxially into the aneurysm and detachable coils packed until the dome is excluded, with a final run confirming patency of the parent artery and no residual neck. Sheath out, compression or closure, and neurological observation. Every element of the examinable vocabulary — Seldinger, mask, roadmapping, microcatheter, coil — appears in this one pathway, which is why learning it as a story outperforms learning it as a list.
Access-site viva favourites
Believing angiography is purely diagnostic is dated: the majority of modern neurovascular and peripheral work is therapeutic at the same sitting, and MCQs now phrase "reference standard" versus "treatment" as complementary. Second, access-site anatomy errors: puncturing above the inguinal ligament enters the external iliac artery, where no bone backs compression and retroperitoneal haematoma develops silently — the dreaded post-procedure hypotension with a clean groin. Third, forgetting that DSA quality depends on the mask: a restless patient or bowel gas produces misregistration artifacts mimicking stenoses, so "check the subtraction before the stenosis" is the reader's rule. Finally, carbon dioxide contrast has a hard ceiling — never above the diaphragm — because gas embolism in the cerebral or coronary circulation is catastrophic; this single contraindication is a recurring one-liner.
Frequently asked questions
What are the steps of the Seldinger technique?
Arterial puncture, guidewire insertion through the needle, needle removal, tract dilation, and catheter or sheath placement over the wire — the universal platform of angiography.
How does digital subtraction angiography work?
A pre-contrast mask image is electronically subtracted from each contrast-filled frame, cancelling bone and soft tissue so only opacified vessels remain, demanding an immobile patient and apnoea.
Why is the common femoral artery punctured over the femoral head?
The underlying bone permits effective post-procedure compression, while a puncture above the inguinal ligament cannot be compressed and risks retroperitoneal haemorrhage.
When is carbon dioxide used as contrast and when is it contraindicated?
In iodinated-contrast allergy and renal impairment for peripheral venography and aortic runs, but never above the diaphragm because cerebral or coronary gas embolism can be fatal.
What are the common complications of catheter angiography?
Access-site haematoma, pseudoaneurysm and arteriovenous fistula, catheter-induced dissection or vasospasm, distal embolisation, and systemic contrast reactions or nephropathy.