Cardiac Catheter

The two principle uses are for diagnosis and treatment however with the improvement in non-invasive imaging methods its use in diagnosis is falling.

It is still however helpful in delineating extra cardiac anatomy (principally the great arteries), assessing post-operative complications and remains the gold standard for haemodynamic measurement.

It is usual to come into hospital the night before the procedure and to go home the day after. They may be a little sore where the catheters were placed but are usually able to resume normal activities within a few days.

The risks of diagnostic catheterisation are minimal but as it is an invasive procedure vascular damage can occur, the myocardium can be perforated leading to tamponade, valve tensor apparatus can be damaged and arrhythmias induced.

Procedure

Children are usually given an anaesthetic. A small catheter is passed from a blood vessel (usually in the groin) up into the heart and maneuvered through the various chambers and arteries.

Access to both the venous and arterial side may be gained through septal defects, if present, otherwise the vein and artery must be catheterised. A cannula (or needle) is used to access the vein and/or artery. A wire is then inserted into the vessels, the cannula is withdrawn and a sheath advanced over the wire with a haemostatic valve on the end through which catheters can be introduced into the circulation. The sheaths are usually have an internal diameter of 5 French size (1.65mm).

Haemodynamic Data

Both pressure and oxygen saturation data is collected.

The normal values are depicted on the right. White circles represent the oxygen saturation as a percentage. The mean pressure is given for the atria, the systolic pressure for the ventricles and both systolic and diastolic for the arteries.

Systemic (Qs) & pulmonary (Qp) flows (l/min/m2) are calculated using the Fick Principle from data obtained at cardiac catheterisation. In this example the systemic cardiac output (Qs) is calculated to be 4 l/min/m²compared 8 l/min/m² of pulmonary cardiac output (Qp) due to flow across the VSD. This is thus a 2:1 shunt.

The resistances can also be calculated using Ohm's law of Resistance ∞ Pressure/Flow. The pulmonary vascular resistance (Rap) can thus be calculated by (mean PA pressure- mean LA pressure)/pulmonary flow.

Angiography

Once the pressure and saturation data have been obtained then angiography to delineate the cardiac chambers and great vessels is undertaken. The contrast is injected rapidly with the aid of a pump. Originally the pictures were stored on cine film but it is now normal for them to be captured digitally and stored on a CD rom in DICOM format.

The angiogram on the right shows dye injected into the aorta passing through a patent duct into the pulmonary artery.

The catheters are then removed and pressure is applied to achieve haemostasis.

Interventional Procedures

In most institutions almost half the catheters are now for interventional purposes. The first intervention was balloon atrial septostomy in 1966 followed by pulmonary angioplasty in 1982. Subsequently it became possible to close PDAs, ASD and more recently VSDs. Re-coarctation is also treated by balloon therapy. Abnormal pulmonary vessels can also be coiled. These procedures are dealt with under the relevant conditions.

This page was last edited 16/2/2004

Acknowledgements