Intracardiac Pressures

A pressure wave is the cyclical force generated by cardiac muscle contraction. Its amplitude and duration are influenced by various mechanical and physiological parameters. The pressure waveform of a cardiac chamber is influenced by the following factors:

1) Force of contraction of the contracting chamber

2) Its surrounding structures

3) Contiguous chambers of the heart

4) The pericardium

5) The lungs

6) The vasculature

7) The heart rate

8) The respiratory cycle

For the assessment of intracardiac pressures, two systems are currently in use:

1) Fluid filled systems

2) Micromanometer catheters

Atrial Pressure

The RA pressure wave form has three positive deflections — “a”, “c”, and “v” waves. The “a” wave is due to atrial systole and follows the P-wave on surface ECG. The “x” descent follows the “a” wave and represents atrial relaxation and downward pulling of the tricuspid annulus by RV contraction. The “x” descent is interrupted by the “c” wave, which is a small positive deflection caused by protrusion of the closed tricuspid valve into the RA. The pressure in the RA rises after the “x” descent due to passive atrial filling. The atrial pressure then peaks as the “v” which represents ventricular systole.

The LA pressure waveform is similar to that of the RA although normal LA pressure is higher representing the high pressure system of the left side of the heart. In LA pressures, unlike RA pressures, the “v” wave is generally higher than the “a” wave.

Normal pressure waveforms

 

Normal pressure waveform

Pulmonary Capillary Wedge Pressure

The PCW waveform is similar to LA pressure waveform except that it is damped and delayed due to transmission through the lungs. The “c” waves may not be seen. Normally the PA diastolic pressure is similar to the mean PCW pressure as the pulmonary circulation has a low resistance.

Ventricular Pressure

RV and LV waveforms are similar in morphology but different in magnitude. The duration of systole and isovolumic contraction and relaxation are longer and the ejection period shorter in the LV than in the RV. End diastolic pressure in generally measured at the “C” point which is the rise in ventricular pressure at the onset of isovolumic contraction.

Great Vessel Pressures

The contour of the central aortic pressure and PA pressure tracing consists of a systolic wave, the incisura (indicative of closure of the semilunar valves) and a gradual decline in pressure until the following systole. The pulse pressure reflects the volume and compliance of the arterial system.The mean aortic pressure more accurately reflects the peripheral resistance.