Transit time thermodilution guidewire system for measuring coronary flow velocity

Abstract

The system for measuring coronary blood flow velocity, comprises a guidewire shaft of a size suitable for “over the wire” placement of intervention devices in a coronary artery, with several equally spaced thermal sensors mounted in sequence, along its extreme distal segment, to detect and report thermal changes to an external monitoring apparatus. When the guidewire has been inserted at a segment of interest in the coronary artery, a steady infusion of room temperature saline or other suitable miscible infusion is introduced for 10 to 15 seconds at the ostium of the coronary artery. The infusion generates a thermal indicator by lowering the basal coronary blood by a fraction of a degree centigrade. The phasic nature of the relatively warmer coronary flow from the aorta, with its large diastolic and small systolic components, modulates the lowered temperature level in a cyclical, wavy pattern that simulates rectified sine waves. These waves are detected in sequence by the equally spaced downstream thermal sensors. The phase shift between successive waves represents the transit time of blood flowing between the sensors, a value which is inversely proportional to the average flow velocity during a single cardiac cycle. Lead wires from the thermal sensors extend along the guidewire shaft, ending proximally as sleeve electrodes that are externally connectable to a monitoring system that includes amplifiers, a fast sweep color-coded digital monitor and a microprocessor. This monitoring system translates readings of the fluid's interphasic transit time between the thermal sensors into digital real-time values of average flow velocity. These measures can be obtained at basal conditions, before, during and after intervention procedures, or before and after induced coronary hyperemia so as to determine coronary reserve. If the artery's diameter is known, the monitoring system may also generate values for coronary volume flow. Qualitative indications of transmyocardial flow velocity may also be obtained by observing the rate of return of the transient blood temperature change to its normal level.

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