Method for pressure guidewire equalization
The present document describes a system for equalizing the pressure of a pressure guidewire against the pressure of an aortic pressure device: the system comprising two methods of equalizing the pressure against each other, one method that involves a gain adjustment and another method that involves the addition of an offset; the method further comprising a method for detecting which method should be applied to the situation, the detecting methods including: the contribution of the operator; an algorithm detecting the first equalization from subsequent post procedure equalizations, the algorithm including various factors such as incrementing the equalization requests, measuring the elapsed time and others.
1. A method for equalizing one of a pressure of a distal intravascular pressure measuring device (a distal pressure) and a pressure of an aortic pressure measuring device (an aortic pressure), the method comprising:
measuring an initial aortic pressure (Pa 1 ) at a site of aortic pressure using a guidewire comprising the aortic pressure measuring device and measuring an initial distal pressure (Pd 1 ) at the site of aortic pressure using the guidewire comprising the distal intravascular pressure measuring device, the guidewire comprising an optical connection to transmit a signal to undergo equalization;
calculating a gain factor (K) by dividing the initial aortic pressure (Pa 1 ) by the initial distal pressure (Pd 1 );
measuring the aortic pressure (Pa′) and the distal pressure (Pd′) at a site that is distal to the site of the aortic pressure; and
repeatedly equalizing the pressure by performing one of:
if gain-equalizing was not previously performed, gain-equalizing by adjusting a gain of one of:
the measured distal pressure by multiplying Pd′ by the gain factor (K), thereby producing a gain-equalized distal pressure (Pd eq ); and
the measured aortic pressure by dividing Pa′ by the gain factor (K), thereby producing a gain-equalized aortic pressure (Pa eq ); and
if the gain-equalizing was previously performed, adding an offset value (A) to the pressure.
2. The method of claim 1 , wherein gain-equalizing comprises gain-equalizing the measured distal pressure, further comprising averaging the distal pressure, either before or after the gain-equalizing, thereby generating an average gain-equalized distal pressure ([Pd]); averaging the aortic pressure, thereby generating an average aortic pressure ([Pa]); and calculating fractional flow reserve (FFR) by calculating the minimum value of ratio [Pd]/[Pa].
3. The method of claim 2 , wherein the averaging is performed over one of:
a given number of cardiac cycles; and
a given time period.
4. The method of claim 1 , wherein adding the offset value to the pressure comprises performing an offset equalization of the gain-equalized distal pressure, comprising:
verifying that the gain factor (K) has been used for the gain-equalizing to determine if gain-equalizing was not previously performed;
measuring an aortic pressure (Pa 2 ) using the aortic pressure measuring device and measuring a distal pressure (Pd 2 ) at the site of aortic pressure using the distal intravascular pressure measuring device;
calculating the offset value (A) by subtracting the gain-equalized distal pressure from the aortic pressure (Pa 2 ); and
offset-equalizing by calculating a gain-and offset-equalized distal pressure (Pd offset ) by adding the offset value (A) to the gain-equalized distal pressure (Pd eq ).
5. The method of claim 4 , further comprising averaging the distal pressure, either before or after the gain-equalizing, thereby generating an average gain-equalized distal pressure ([Pd]); averaging the aortic pressure, thereby generating an average aortic pressure ([Pa]); and calculating fractional flow reserve (FFR) by calculating the minimum value of ratio [Pd]/[Pa].
6. The method of claim 4 , further comprising determining whether the offset-equalizing is required, the determining comprising: verifying at least one of a set of criteria, the set of criteria comprising: an existence of a bubble on a surface of the distal intravascular pressure measuring device; a manipulation of the distal intravascular pressure measuring device during more than 2 minutes; and a recording of data for a first FFR measurement.
7. The method of claim 5 , wherein verifying that the distal pressure is gain-equalized comprises verifying that a recording has been performed at least once by a monitoring device.
8. The method of claim 1 , further comprising determining whether another gain-equalizing is required after performing a first gain-equalizing.
9. The method of claim 8 , wherein the determining whether another gain-equalizing is required comprises determining whether a second equalizing step is required, measuring a period after the first gain-equalizing and, upon determining that a second equalizing step is required and that the period is less than a given period, performing once more the calculating a gain factor (K), the measuring a distal pressure (Pd′) and the gain-equalizing the measured distal pressure (Pd′).
10. The method of claim 9 , wherein the given period is between 5 seconds and 2 minutes.
11. The method of claim 1 , wherein the measuring a distal pressure (Pd′) at a site that is distal to the site of aortic pressure comprises measuring a distal pressure (Pd′) at a site that is distal to an intravascular lesion using the distal intravascular pressure measuring device.
12. The method of claim 1 , wherein gain-equalizing comprises gain-equalizing the measured aortic pressure, further comprising averaging the aortic pressure, either before or after the gain-equalizing, thereby generating an average gain-equalized aortic pressure ([Pa]); averaging the distal pressure, thereby generating an average distal pressure ([Pd]); and calculating fractional flow reserve (FFR) by calculating the minimum value of ratio [Pd]/[Pa].
13. The method of claim 1 , wherein adding the offset value to the pressure comprises performing an offset equalization of the gain-equalized aortic pressure, comprising:
verifying that the gain factor (K) has been used for the gain-equalizing;
measuring an aortic pressure (Pa 2 ) using the aortic pressure measuring device and measuring a distal pressure (Pd 2 ) at the site of aortic pressure using the distal intravascular pressure measuring device;
calculating the offset value (A′) by subtracting the gain-equalized aortic pressure from the distal pressure (Pd 2 ); and
offset-equalizing by calculating a gain-and offset-equalized aortic pressure (Pa offset ) by adding the offset value (A′) to the gain-equalized aortic pressure (Pa eq ).
14. The method of claim 13 , further comprising averaging the aortic pressure, either before or after the gain-equalizing, thereby generating an average gain-equalized aortic pressure ([Pa]); averaging the distal pressure, thereby generating an average distal pressure ([Pd]); and calculating fractional flow reserve (FFR) by calculating the minimum value of ratio [Pd]/[Pa].
15. A method for equalizing a pressure of one of a distal intravascular pressure measuring device and an aortic pressure measuring device against another one thereof, the method comprising:
performing a measurement with a guidewire comprising the distal intravascular pressure measuring device and the aortic pressure measuring device, the guidewire comprising an optical connection or an electric connection to transmit a signal from the distal intravascular pressure measuring device or from the aortic pressure measuring device, the signal to undergo equalization;
repeatedly determining if gain-equalizing the pressure was previously performed; and
based on the determining, repeatedly equalizing the pressure by performing one of:
adjusting a gain of the pressure, if the gain-equalizing was not previously performed; and
adding an offset to the pressure, if the gain-equalizing was previously performed.
16. A system used in performing of fractional flow reserve (FFR) measurements in which takes place an equalizing of a distal pressure against an aortic pressure, the system comprising:
a guidewire comprising an optical connection for transmitting a signal to undergo equalization, the guidewire comprising:
a distal intravascular pressure measuring device for measuring distal pressure; and
an aortic pressure measuring device for measuring aortic pressure;
a monitoring device comprising a computer adapted to execute instructions comprising:
measuring an initial aortic pressure (Pa 1 ) at a site of aortic pressure using the aortic pressure measuring device and measuring an initial distal pressure (Pd 1 ) at the site of aortic pressure using the distal intravascular pressure measuring device;
calculating a gain factor (K) based on the initial aortic pressure (Pa 1 ) and the initial distal pressure (Pd 1 );
measuring a distal pressure (Pd′) at a site that is distal to the site of aortic pressure; and
repeatedly equalizing the pressure by performing one of:
if gain-equalizing was not previously performed, gain-equalizing the measured distal pressure by multiplying Pd′ by the gain factor (K) thereby producing an equalized distal pressure (Pd eq ) and
if the gain-equalizing was previously performed, adding an offset value (A) to the pressure.
17. The system of claim 16 , wherein the computer further executes instructions comprising: averaging the distal pressure, either before or after the gain-equalizing, thereby generating an average gain-equalized distal pressure ([Pd]); averaging the aortic pressure, thereby generating an average aortic pressure ([Pa]); and calculating fractional flow reserve (FFR) by calculating the minimum value of ratio [Pd]/[Pa].
18. The system of claim 16 , wherein the computer further executes instructions comprising:
after the gain-equalizing, measuring an aortic pressure (Pa 2 ) using the aortic pressure measuring device and measuring a post procedure distal pressure (Pd 2 ) at the site of aortic pressure using the distal intravascular pressure measuring device;
calculating the offset value (A) by subtracting a gain-equalized distal pressure from the aortic pressure (Pa 2 ); and
calculating a gain-and offset-equalized distal pressure (Pd offset ) by adding the offset value (A) to the gain-equalized distal pressure (Pd eq ).
19. The system of claim 16 wherein the distal intravascular pressure measuring device comprises a pressure guidewire.
20. The system of claim 19 , wherein the aortic pressure measuring device comprises a catheter for sliding onto the pressure guidewire.