System and method of tissue contact assessment for balloon catheter ablation

A medical method, comprising:

• inserting a catheter into a chamber of a heart of a living subject, the catheter having a longitudinal axis and an inflatable balloon comprising electrodes, the inflatable balloon being configured to press the electrodes against tissue of the chamber and at least partially block blood flow in the chamber;
• inserting an ultrasound probe, separately from and independent of the catheter, into the chamber of the heart in which the catheter is inserted or a different chamber of the heart, the ultrasound probe being configured to provide a plurality of velocity measurements of the blood flow in the chamber over time and further configured to capture an image in an image plane that contains the longitudinal axis of the catheter;
• inflating the balloon of the catheter to press the electrodes against tissue of the chamber and at least partially blocking blood flow in the chamber;
• obtaining from the ultrasound probe a first velocity measurement from the plurality of velocity measurements prior to inflation of the inflatable balloon and a second velocity measurement of the blood flow in the chamber after inflation of the inflatable balloon;
• determining a quality of contact of the electrodes with tissue of the chamber, wherein the determining comprises selecting the first velocity measurement for use in determining the quality of contact responsively to receiving a user input confirming that the ultrasound probe is correctly placed to provide the velocity measurements of the blood flow in the chamber, the quality of contact being determined in response to one of:
• i) a ratio of the first velocity measurement to the second velocity measurement, ii) an absolute reduction or fractional percentage reduction in the first velocity measurement with respect to the second velocity measurement, or iii) a ratio of the second velocity measurement to the first velocity measurement;
• outputting an indication of the quality of contact to an output device;
• and
• providing at least one electrical signal to the electrodes in order to ablate the tissue of the chamber.