Combined fluid-filled and micromanometer-tip catheter system for high-fidelity pressure recordings in infants.

Investigation of pressure-derived indices of systolic and diastolic function in infants and young children has been limited, in part due to difficulty in obtaining high-fidelity pressure recordings. Standard fluid-filled catheter-manometer systems have a frequency response which is inadequate for this purpose, whereas high-frequency response micromanometer-tip catheters systems are difficult to use in this age group. Therefore, a system was investigated whereby a micromanometer-tip catheter (Millar) was connected directly to a standard pigtail catheter. The frequency response of this combined system was defined using 3.2 Fr pigtails of 40, 50, and 65 cm, 4.0 Fr pigtails of 50, 65, and 80 cm, and 5.0 Fr pigtails of 80 and 100 cm. In three different catheters of each diameter and length, minimal variation in response was seen. The 3.2 Fr-40-cm system demonstrated a flat line (100%) response to 90 Hz with a resonant frequency of 130 Hz. This is certainly adequate for determination of pressure derivatives for heart rates up to 120 beats per minute. The longer 3.2 Fr catheters demonstrated a poorer frequency response. The 4.0-Fr-50-cm system was flat line to 60 Hz, rising to 175% response at the resonant frequency of 85 Hz. This is adequate for determination of pressure derivatives at heart rates up to 120 beats per minute. Increasing the diameter or length of the pigtail catheter resulted in further deterioration of the frequency response. Thus, this system provides high-fidelity tracings suitable for assessment of pressure-derived indices of systolic and diastolic function in infants and young children.