CT Coronary Angiogram — ECG-Synchronised
Carina to below the cardiac apex; extended cranially when arterial or venous grafts are in question.
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
Premedication
Given to make the acquisition work, not to treat the patient. Doses are typical — confirm against your local protocol and prescribe within your own governance.
Rate control. Motion is the leading cause of a non-diagnostic coronary CT, and the right coronary artery moves most, so a regular rate at or below roughly 60 bpm is part of the protocol rather than an optimisation.
- Dose and route
- Typically oral metoprolol 50-100 mg about an hour before, and/or intravenous metoprolol in 5 mg increments to a usual maximum of around 15-20 mg, titrated to rate at the scanner. Regimens vary substantially between centres — confirm locally.
- When
- Oral roughly 60 minutes before; intravenous immediately before, allowing 3-5 minutes between increments to judge effect. Do not begin acquisition until the rate is both low enough and regular.
- Do not give if
- Avoid in decompensated heart failure, high-grade AV block without a pacemaker, marked bradycardia, and systolic hypotension.
- AVOID in asthma or a history of bronchospasm. The BNF position is that beta-blockers should usually be avoided in these patients, and metoprolol’s own label lists severe asthma as a contraindication — cardioselectivity is dose-dependent and falls away at the doses used here (up to 100 mg orally plus 20 mg intravenously). This is the contraindication a radiographer meets most often on an outpatient list, and it belongs with the absolute ones rather than below them.
- Suspected aortic dissection is a different scan and a different rationale: rate control there is treatment, not image optimisation.
- If unsuitable
- Ivabradine is the alternative where the contraindication to beta-blockade is BRONCHOSPASTIC DISEASE, and only there. It is not a general substitute: it shares the conduction and haemodynamic contraindications listed above — sick sinus syndrome, sinoatrial block, second- or third-degree AV block without a pacemaker, resting rate below about 60, significant hypotension, decompensated heart failure — so reaching for it because of those is swapping one contraindicated drug for another. It also acts on the sinus node funny current and therefore does NOTHING in atrial fibrillation, which is the commonest reason a coronary CT is non-diagnostic. Published CCTA regimens are typically 5 mg twice daily for a few days, or a single oral dose. Modern high-pitch and wide-detector systems tolerate higher rates, so scanner capability changes the threshold — which is exactly why this is confirm-locally.
Coronary vasodilatation. Without it the distal vessels are under-distended and distal disease is systematically over-called — the artefact looks like the finding.
- Dose and route
- Typically 400-800 micrograms sublingually, as spray or tablet.
- When
- Roughly 3-5 minutes before acquisition, so the effect is at its maximum during the scan rather than arriving after it.
- Do not give if
- Absolutely contraindicated with a phosphodiesterase-5 inhibitor — sildenafil or vardenafil within about 24 hours, tadalafil within about 48 — because the combination causes profound hypotension. Also absolutely contraindicated with RIOCIGUAT (Adempas), which is a soluble guanylate cyclase stimulator rather than a PDE5 inhibitor and so is missed by a question that asks only about the latter. Ask by indication as well as by drug name: sildenafil is dispensed as Revatio for pulmonary hypertension, and that patient will not describe it as an erectile-dysfunction tablet. This is the single question that must be asked before it is given.
- Avoid in significant aortic stenosis, hypertrophic obstructive cardiomyopathy, and systolic hypotension.
- Warn the patient about headache and transient flushing, which are expected rather than adverse.
When to use it
- Stable chest pain with low-to-intermediate likelihood of obstructive coronary disease, as a first-line anatomical test.
- Acute chest pain in the emergency department with a non-diagnostic troponin and electrocardiogram, in a selected low-to-intermediate risk group.
- Assessment of coronary anomalies and of graft patency after bypass surgery.
- Planning before structural intervention where coronary anatomy is needed alongside the valve assessment.
Technique
- Heart rate control is part of the protocol: society guidance targets a regular rate at or below approximately 60 bpm, most often with oral or intravenous beta-blockade.
- Sublingual nitrate is the recommended default for coronary dilatation unless contraindicated, and acquisition should not begin until several minutes after administration so the effect is maximal.
- Prospective ECG-triggered axial acquisition is the default mode in a rate-controlled patient with a regular rhythm; retrospective gating is reserved for arrhythmia or when functional data are required, at higher dose.
- A calcium score acquisition is often performed first and is a separate exposure — decide in advance whether it is needed.
- Timing is bolus-tracked, not fixed. The monitoring region of interest goes in the descending thoracic aorta at the level of the carina (some protocols use the ascending aorta or the left atrium), the trigger sits at roughly 100 HU above baseline, and the diagnostic acquisition follows after a post-trigger delay of about 5-8 s — long enough to give the breath-hold instruction and move the table, which is why the number is longer here than for a peripheral CTA.
- A test bolus is the accepted alternative and is preferred by some centres for consistency: 10-20 mL at the diagnostic rate with monitoring images at the aortic root every 1-2 s, then a scan delay of the measured time-to-peak plus about 2-4 s.
- Injection duration is matched to acquisition time rather than chosen independently — volume equals rate multiplied by duration, so 5 mL/s for 10-12 s gives the 50-60 mL that covers a prospectively triggered acquisition. On a slower platform needing a longer acquisition, the volume goes up for the same reason.
- A fixed delay has no place in a coronary study: at a heart rate of 60 bpm the diagnostic window is a few seconds wide, and individual transit time varies far more than that.
- Scanner generation moves all of these numbers. A wide-detector single-beat or high-pitch acquisition needs less contrast and a shorter injection than a system acquiring over several heartbeats — confirm the local combination rather than transplanting one.
Where it goes wrong
- Scanning an uncontrolled or irregular rate produces motion artefact that most often degrades the right coronary artery and is the leading cause of a non-diagnostic study.
- Dense contrast in the superior vena cava and right atrium streaks across the right coronary artery; a saline chaser or a diluted second injection phase mitigates it.
- Heavy calcification blooms and overestimates stenosis, an inherent limitation rather than a protocol error — but thin sections and a sharp kernel reduce it.
- Omitting nitrate leaves small vessels under-distended and exaggerates distal disease.
- A breath-hold that is not practised produces diaphragmatic drift through the acquisition.
Clinical questions that reach this study
Contrast
Typically 50-80 mL of high-concentration non-ionic iodinated contrast at 4-6 mL/s with a saline chaser, often as a biphasic or triphasic injection to opacify the right heart without streaking it.
Acquisition
- Breathing
- Single inspiratory breath-hold, practised beforehand.
- Reconstruction
- Thin axial reconstructions at the optimal cardiac phase with multiphase reconstruction where the rhythm is variable, plus curved multiplanar reformats along each coronary artery.
- Preparation
- Caffeine avoided for several hours; heart-rate control per local pathway, commonly oral or intravenous beta-blockade targeting a regular rate around 60 bpm or below. Sublingual nitrate immediately before acquisition unless contraindicated (recent phosphodiesterase inhibitor, severe aortic stenosis, hypotension). Right antecubital cannula of at least 18-20G; ECG electrodes applied clear of the scan field.
Phases
Each phase is authored once and shared across every protocol that uses it, so the physiology below is the same wherever you meet it.
- CT angiography, bolus-trackedNo fixed delay. A monitoring ROI is placed in the target vessel (commonly the aorta) and acquisition triggers at a set attenuation rise — a ~100 HU threshold is widely used — followed by a short diagnostic delay of a few seconds for table movement and breath-hold instruction. Confirm locally.
This is not a separate physiological phase so much as a technique for hitting one reliably. The transferable principle is that a fixed delay assumes an average circulation, and the patients who most need vascular imaging — the shocked, the failing, the arrhythmic, the aneurysmal — are precisely those whose circulation time is furthest from average. Tracking the bolus in the target vessel replaces that assumption with a measurement, so peak arterial opacification is achieved in the individual patient. The trade-off is that the technique commits the scan to whatever the monitoring ROI sees: a badly placed ROI, a mistimed breath-hold or a threshold reached by a contralateral vein produces a systematically mistimed study rather than a slightly degraded one.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Prior contrast reaction and elective premedication· nurse pre scan
- Intravenous access adequate for the planned injection· radiographer at scan
- Metformin and iodinated contrast· radiographer at scan
- Child-sized technique and contrast dose· radiographer at scan
- Sedation or anaesthesia for a child· nurse pre scan
- Kidney function and intravenous iodinated contrast· radiographer at scan