Heart

Published on 12/06/2015 by admin

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Last modified 12/06/2015

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8

Heart

Angiocardiography

Diagnostic catheterization has largely been replaced by echocardiography (including transoesophageal echocardiography), radionuclide ventriculography and MR imaging. Angiocardiography is usually used as part of an interventional therapeutic procedure and can be performed simultaneously with cardiac catheterization during which pressures and oximetry are measured in the cardiac chambers and vessels that are under investigation. The right heart, left heart and great vessels are examined together or alone, depending on the clinical problem.

Technique

1. Right-sided cardiac structures and pulmonary arteries are examined by introducing a catheter into a peripheral vein. In babies the femoral vein may be the only vein large enough to take the catheter. If an atrial septal defect is suspected, the femoral vein approach offers the best chance of passing the catheter into the left atrium across the defect. In adults the right antecubital or basilic vein may be used. The cephalic vein should be avoided as it can be difficult to pass the catheter past the site where the vein pierces the clavipectoral fascia to join the axillary vein. The catheter, or introducer, is introduced using the Seldinger technique. (The NIH catheter must be introduced via an introducer as there is no end hole for a guidewire.)

2. In children it is usually possible to examine the left heart and occasionally the aorta by manipulating a venous catheter through a patent foramen ovale. In adults the aorta and left ventricle are studied via a catheter passed retrogradely from the femoral artery.

3. The catheter is manipulated into the appropriate positions for recording pressures and sampling blood for oxygen saturation. Following this, angiography is performed.

Image acquisition

Using digital angiography at 7.5 frames s–1 with alignment to the anatomical axes of the heart, i.e. the X-ray beam is angulated relative to the axial planes of the heart rather the orthogonal planes of the body. The long axis of the heart is usually oblique to the long axis of the patient’s body and cardiac angiography suites have movable C-arms which allow correct positioning by movement of the equipment alone without disturbing the patient. Supplementary angulations of the X-ray beam from the cardiac axes are used to profile those areas of the heart under examination. Useful views are:

Coronary arteriography

Indications

Diagnostic arteriography can be supplemented by intravascular ultrasound (US) to determine the nature and extent of plaque within the vessel wall and, in some centres, with angioscopy. Pressure wire studies to determine fractional flow reduction (FFR) across stenoses prior to angioplasty/stenting can be performed; particularly useful in assessment of intermediate lesions.

Equipment

1. Digital angiography with C-arm

2. Pressure recording device and ECG monitor

3. Selective coronary artery catheters:

(a) Judkins (Fig. 8.4) or Amplatz (Fig. 8.5) catheters – the left and right coronary artery catheters are of different shape. These can be used for both femoral or radial approaches (usually utilizing smaller Judkins for the left coronary artery)

(b) Tiger II catheter (Fig. 8.6) – specifically designed for right radial approach. Single catheter used for both left and right coronary arteries (reduces procedure time, radiation exposure and less manipulation leading to less radial artery spasm)

(c) For assessment of grafts: Judkins, Simmons and others (for both femoral and radial approaches).

Cardiac CT

The rapid evolution of multi-detector CT scanner technology over the last 5 years has resulted in cardiac CT and coronary CT angiography becoming well-established techniques in the investigation and management of cardiovascular disease. Greater temporal resolution, sophisticated ECG-gating software and post processing algorithms and, very importantly, radiation dose-reducing strategies allow cardiac CT to be used widely. CT has a high accuracy in detecting coronary vessel stenoses and a very high negative predictive value in excluding significant disease.

Patient preparation

1. Avoid caffeine – this includes tea, coffee and caffeine-containing soft drinks (including ‘decaffeinated’ varieties), ‘energy’ pills and Viagra-type medication.

2. Drugs – patients should take all their normal cardiac medication as usual on the day of the test.

3. Thorough explanation of the procedure to the patient aids compliance, particularly with regard to breath-hold (suggest patient takes a ‘image breath’ when instructed – less likely to move during scan and avoids ‘Valsalva’ manoeuvre affecting contrast bolus entering chest).

4. 18G cannula in right antecubital fossa – siting cannula in right arm reduces artefact as contrast crosses the mediastinum. For graft studies this avoids streak artefact obscuring origin of LIMA grafts.

5. Assess suitability for administration of β-blockers and sublingual nitrates (see below).

Beta-blockers

Optimal imaging quality and radiation dose are significantly influenced by heart rate, which ideally should be between 55–65 bpm. With basic precautions and simple monitoring, safe and dose-titratable heart rate reduction can be achieved in the majority of patients using β-blocker administered within the radiology department. Metoprolol is commonly used and can be given orally or intravenously, or in combination.

(Contraindications to β-blockade include heart failure, significant aortic stenosis, heart block, asthma/COPD, use of other antiarrhythmic medication including calcium channel blockers and digoxin.)

Scan protocol

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