Patent Publication Number: US-2021186602-A1

Title: Respiration control during cardiac ablation

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to invasive medical procedures, and specifically to cardiac ablation. 
     BACKGROUND 
     Ablation of cardiac tissue, which is used, for example, to treat cardiac arrhythmias, is complicated by the fact that the heart is not a stationary object, and any device used for the ablation has to contend with the heart&#39;s motion. 
     For example, U. S. Patent Application 2003/0018251 to Solomon provides a system for superimposing the position and orientation of a device on a previously acquired three-dimensional anatomic image such as a CT or MRI image, so as to enable navigation of the device to a desired location. A plurality of previously acquired three-dimensional images may be utilized to form a “movie” of a beating heart, and these can be synchronized with a patient&#39;s EKG in the operating room, and the position of the device can be superimposed on the synchronized “movie” of the beating heart. 
     SUMMARY 
     An exemplary embodiment of the present invention provides a method for invasive cardiac treatment, comprising: 
     inserting a catheter via a transvascular route into a beating heart of a patient who is anesthetically paralyzed and intubated for ventilation; 
     after inserting the catheter, temporarily halting ventilation of the patient; 
     moving the catheter between a plurality of locations of myocardial tissue of the heart while the ventilation is halted; and ablating the myocardial tissue of the heart at the plurality of locations while the ventilation is halted. 
     In a disclosed exemplary embodiment, the method includes measuring an oxygen level and a carbon dioxide level of the patient, and ensuring that the oxygen level and the carbon dioxide level are within acceptable limits when ablating tissue while the ventilation is halted. The method may also include halting ablation and resuming ventilation of the patient when the oxygen level and the carbon dioxide level are not within the acceptable limits. 
     In another disclosed exemplary embodiment, the catheter is selected from one of a balloon, a basket, a lasso, a focal, and a multi-spline catheter. 
     In a further disclosed exemplary embodiment, the catheter includes an electrode, and ablating the myocardial tissue consists of ablating the tissue with radio-frequency energy, injected into the tissue via the electrode, configured to cause cell necrosis. 
     In a yet further disclosed exemplary embodiment, the catheter includes an electrode, and ablating the myocardial tissue consists of ablating the tissue with radio-frequency energy, injected into the tissue via the electrode, configured to cause irreversible electroporation so as to cause cell apoptosis. 
     In an alternative exemplary embodiment, the catheter includes a magnetic position sensor, and inserting the catheter consists of tracking a position of the catheter within the beating heart using the magnetic position sensor. 
     In another alternative exemplary embodiment, the catheter includes an electrode, and inserting the catheter consists of tracking a position of the catheter within the beating heart in response to at least one of currents traversing the electrode and impedances measured between the electrode and conducting patches positioned on the patient. 
     In a further alternative exemplary embodiment, the method includes measuring an oxygen level of the patient, and increasing the oxygen level using the ventilation prior to halting the ventilation. 
     In a yet further alternative exemplary embodiment, ablating the myocardial tissue of the heart at a given location of the plurality of locations includes ablating the tissue at the given location for up to 4 seconds. 
     Ablating the myocardial tissue of the heart at the plurality of locations may consist of ablating the tissue at the plurality of locations for up to 4 minutes. 
     There is further provided, according to an exemplary embodiment of the present invention, apparatus for invasive cardiac treatment, including: 
     a ventilator, which is configured to supply ventilation to a patient who is anesthetically paralyzed and intubated; 
     a catheter, which is configured to be inserted via a transvascular route into a beating heart of the patient and to be moved between a plurality of locations of myocardial tissue of the heart while the ventilation is halted; and 
     a power source, which is configured to ablate myocardial tissue of the heart at the plurality of locations while the ventilation is halted. 
     There is further provided, according to an embodiment of the present invention, a method for invasive cardiac treatment, including: 
     inserting a catheter via a transvascular route into a beating heart of a patient who is anesthetically paralyzed and intubated for ventilation;
         after inserting the catheter, temporarily inducing hyperventilation in the patient;       

     moving the catheter between a plurality of locations of myocardial tissue of the heart while the hyperventilation is induced; and 
     ablating the myocardial tissue of the heart at the plurality of locations while the hyperventilation is induced. 
     There is further provided, according to an exemplary embodiment of the present invention, apparatus for invasive cardiac treatment, including: 
     a ventilator, which is configured to supply ventilation to a patient who is anesthetically paralyzed and intubated; 
     a catheter, which is configured to be inserted via a transvascular route into a beating heart of the patient and to be moved between a plurality of locations of myocardial tissue of the heart while the ventilator induces hyperventilation in the patient; and 
     a power source, which is configured to ablate myocardial tissue of the heart at the plurality of locations while the hyperventilation is induced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully understood from the following detailed description of the exemplary embodiments thereof, taken together with the drawings in which: 
         FIG. 1  is a schematic, pictorial illustration of a system for cardiac ablation, according to an exemplary embodiment of the present invention; 
         FIG. 2  is a flowchart of steps of an algorithm performed in operation of the system, according to an exemplary embodiment of the present invention; and 
         FIG. 3  is a flowchart of steps of an alternative algorithm performed in operation of the system, according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Overview 
     Radio-frequency (RF) ablation of tissue in the heart relies on good contact between an ablation electrode and the tissue being ablated. However, the contact is complicated by the fact that the tissue is not stationary. The tissue moves because of the beating of the heart, and also because of the patient breathing. While catheter positioning may be configured to reduce the effects of the two motions on the electrode-tissue contact, it may not completely nullify the effects of the motions. 
     Exemplary embodiments of the present invention effectively nullify the breathing motion during ablation as follows. A catheter is inserted into a beating heart of a patient who is anesthetically paralyzed and intubated for ventilation. The ventilation is temporarily halted, and the catheter is moved to a plurality of locations within the heart. Ablation is then performed at the plurality of locations. 
     Exemplary embodiments of the present invention use the fact that each ablation where RF is injected may typically be for approximately four seconds or even less. In some exemplary embodiments, prior to an ablation procedure, the patient may be ventilated to bring the patient oxygen level up, and the ventilation is switched off. The ablation procedure is then performed, and while it is being performed, the patient O 2  and CO 2  levels are monitored. So long as the O 2  and CO 2  levels remain within permissible limits, which is typically the case because the patient is comatose, ablation is continued. 
     By temporarily stopping patient breathing during ablation, the catheter is much more stable. In some cases a complete set of ablations may be performed, without the need for switching the ventilation back on. 
     In an alternative exemplary embodiment of the present invention, rather than switching ventilation off, hyperventilation is induced in the patient. The hyperventilation causes motion of the catheter due to breathing to be shallow and at a high frequency, so that any such motion can be easily filtered. 
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic, pictorial illustration of a catheter-based system  20  for ablation of the heart, according to an exemplary embodiment of the present invention. System  20  comprises a focal catheter  21 , comprising an insertion tube  22  for transvascular insertion into a beating heart  26  of a patient  28 , who is shown lying on a table  29 . A distal tip  40  is deployed at a distal end of insertion tube  22  (as seen in the inset in  FIG. 1 ). In the illustrated exemplary embodiment, tip  40  is applied for a therapeutic procedure, comprising ablating tissue around an ostium  51  of a pulmonary vein in the left atrium of heart  26 . To implement the ablation, tip  40  has one or more electrodes  55  disposed on a surface of the tip. The proximal end of catheter  21  is connected to a control console  24  comprising a power source  45 , which typically includes radio-frequency (RF) signal generation circuitry. Power source  45  supplies RF electrical signals via electrical wiring running through insertion tube  22  to electrodes  55  so as to ablate the tissue with which the electrodes are in contact. Depending on the voltage, frequency and power of the RF electrical signals, the ablation may be by RF energy injection to the heart tissue or by irreversible electroporation (IRE) of the heart tissue. RF energy injection causes necrosis of cells in the tissue by heating; IRE causes apoptosis of the cells. In the disclosure and in the claims, the term “ablation” is assumed to comprise either form of application of the RF signals supplied by power source  45 . Additionally or alternatively, electrodes  55  may be used in electrophysiological (EP) sensing and mapping of electrical signals in heart  26 . 
     To carry out the ablation procedure, patient  28  is first anesthetically paralyzed, intubated with a tube  70 , and then ventilated with a ventilator  72 . The anesthetization and ventilation may be carried out by a qualified practitioner, such as an anesthesiologist (not shown in  FIG. 1 ). During ventilation of patient  28 , the oxygen (O 2 ) and carbon dioxide (CO 2 ) levels in the patient&#39;s blood are checked by respective meters  74 ,  76 , to ensure that they are within acceptable bounds, and that the ventilation is satisfactory. In an exemplary embodiment, the oxygen level is in an approximate range 75-100 mm Hg, and the carbon dioxide level is approximately 35-40 mm Hg. 
     Once the intubation described above has been performed, a physician  30  inserts a sheath  23  into heart  26  of patient  28  via a transvascular route, and then passes insertion tube  22  through the sheath. Physician  30  advances tip  40  of insertion tube  22  toward a target location in heart  26 , for example, in proximity to ostium  51 , by manipulating catheter  21  using a manipulator  32  near the proximal end of the catheter. 
     Once tip  40  of insertion tube  22  has reached the left atrium in heart  26 , physician  30  retracts sheath  23 , and further manipulates catheter  21  so as to navigate the tip to the target location within ostium  51  of the pulmonary vein. When tip  40  has reached the target location, electrodes  55  contact tissue around the ostium. Console  24  may verify that the electrodes are in good contact with the tissue by measuring the impedance between each of the electrodes and the tissue. Once good contact has been established, physician  30  actuates power source  45  to apply RF power to the tissue. 
     During this procedure, system  20  applies magnetic position sensing in tracking the location and orientation of insertion tube  22  and tip  40  within heart  26 , and thus guides physician  30  in maneuvering the distal tip to the target location (within ostium  51  in the present example) and verifying that the tip is properly in place. For this purpose, as shown in the inset in  FIG. 1 , tip  40  of insertion tube  22  contains a magnetic position sensor  39 . One or more magnetic field generators  36  are fixed in known positions in proximity to the body of patient  28 , for example under bed  29  as shown in  FIG. 1 . A driver circuit  34  in console  24  applies drive signals to the magnetic field generators so as to produce multiple magnetic field components directed along different, respective axes. 
     During navigation of tip  40  in heart  26 , magnetic sensor  39  outputs signals in response to the magnetic field components. Position sensing circuitry, such as a processor  41  in console  24 , receives these signals via interface circuits  44 , and processes the signals in order to find the location and orientation coordinates of tip  40 . 
     Processor  41  presents the coordinates of tip  40  on a display  27 , for example by superimposing a graphical representation of the tip, in the location and orientation indicated by position sensor  39 , on a three-dimensional map of the heart chamber in which the tip is located. 
     The methods and apparatus for magnetic position sensing that are implemented in system  20  are based on those that are used in the CARTO® system, produced by Biosense Webster, Inc. (Irvine, Calif.). The principles of operation of this sort of magnetic sensing are described in detail, for example, in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all hereby incorporated by reference herein in their entireties as though set forth in full. Alternatively or additionally, system  20  may implement other magnetic position sensing technologies that are known in the art. 
     Further alternatively or additionally, system  20  may implement current and/or impedance position sensing technologies, that measure the position of electrodes  55  in response to currents traversing the electrodes, and/or impedances of the electrodes, using an impedance/current measuring module  46 . Module  46  is connected by a cable  37  to a plurality of conducting patches  38  positioned on the skin of patient  28 . When configured in a current position measuring mode, module  46  injects current into electrodes  55 , and measures the currents traversing the electrodes to patches  38 . From the measured currents, a processor such as processor  41  calculates the location and orientation of electrodes  55 . When configured in an impedance position measuring mode, module  46  measures impedances between electrodes  55  and patches  38 . From the measured impedances, the location and orientation of electrodes  55  may be calculated. 
     The methods and apparatus for current or impedance position sensing that are implemented in system  20  are also based on those that are used in the CARTO® system. The principles of operation of these systems are described in detail, for example, in U.S. Pat. Nos. 7,756,576, 7,869,865, 7,848,787, and 8,456,182, whose disclosures are all hereby incorporated by reference herein in their entireties as though set forth in full. 
     In some exemplary embodiments, processor  41  comprises a general-purpose computer, with suitable interface circuits  44  for receiving signals from catheter  21  (including low-noise amplifiers and analog/digital converters), as well as for receiving signals from and controlling the operation of the other components of system  20 . Processor  41  typically performs these functions under the control of software stored in a memory  48  of system  20 . The software may be downloaded to the computer in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. Additionally or alternatively, at least some of the functions of processor  41  may be carried out by dedicated or programmable hardware logic. 
       FIG. 2  is a flowchart  90  of steps of an algorithm performed in operation of system  20 , according to an exemplary embodiment of the present invention. In an initial step  100 , patient  28  is prepared for an ablation procedure by being anesthetized, intubated, and ventilated as described above. In addition, as is also described above, tip  40  is inserted into patient  28  so that electrodes  55  contact desired locations of ostium  51  of heart  26 . During the insertion, the ventilation of the patient is checked by monitoring the levels of O 2  and CO 2  in the patient&#39;s blood, and the ventilation is adjusted accordingly to maintain the levels at satisfactory values. 
     In an ablation preparatory step  104 , ventilation to patient  28  is halted temporarily. Typically, prior to the halting, the ventilation is adjusted to increase the level of oxygen in the patient&#39;s blood to be close to an upper permissible bound of the oxygen level. In one embodiment the upper permissible bound is approximately 100 mm Hg. Increasing the oxygen level provides more time for ablation, described in the following steps of the flowchart, of patient  28 . While ventilation is halted, both the O 2  and CO 2  levels continue to be monitored to ensure that they remain satisfactory. 
     In a decision step  108 , while the ventilation is halted, the O 2  and CO 2  levels of patient  28  are checked to ensure they are within acceptable limits. It will be understood that after ventilation has been halted as prescribed in step  104 , the decrease in O 2  level, and the increase in CO 2  level, occur at a relatively slow rate, because the patient is comatose. In one exemplary embodiment an acceptable limit for the oxygen level is greater than approximately 60 mm Hg, and an acceptable limit for the carbon dioxide level is less than approximately 45 mm Hg. 
     If decision step  108  returns positive, i.e., the O 2  and CO 2  levels of patient  28  are within acceptable limits, in an ablation step  112  physician  30  activates power source  45  so as to ablate the tissue at the site where electrodes  55  of tip  40  are in contact. Once the ablation has been satisfactorily executed, the physician deactivates power source  45 . 
     On conclusion of the ablation in step  112 , in a motion step  114  the physician manipulates tip  40  to move so that electrodes  55  contact a new site. Control of the flowchart then returns, as shown by arrow  116 , to ablation step  112 , via decision step  108 , so that ablation is executed at the new site. 
     Exemplary embodiments of the invention continuously monitor the O 2  and CO 2  levels of patient  28 , so that while decision step  108  returns positive, ablation step  112  and motion step  114  iterate. 
     If decision step  108  returns negative, i.e., the O 2  or CO 2  levels of patient  28  are not within acceptable limits, control continues to a ventilation step  120 , wherein ventilation is resumed and ablation may be halted. 
       FIG. 3  is a flowchart  190  of steps of an alternative algorithm performed in operation of system  20 , according to an exemplary embodiment of the present invention. Apart from the differences described below, the algorithm of flowchart  190  is generally similar to that of flowchart  90 , so that the actions of steps indicated by the same reference numerals in both flowcharts are generally the same. 
     In flowchart  190  a hyperventilation step  204  replaces ablation preparatory step  104  of flowchart  90 . In hyperventilation step  204 , rather than ventilation being halted as in flowchart  90 , patient  28  is hyperventilated, i.e., high frequency ventilation is induced in the patient. The high frequency ventilation may be as much as four times the regular ventilation rate, and in one embodiment the high frequency ventilation is 150 breaths/minute, or even more. While the patient is hyperventilated both the O 2  and CO 2  levels continue to be monitored to ensure that they remain satisfactory. The hyperventilation causes the patient&#39;s breathing motion to be shallow, i.e., to have a smaller amplitude than that of regular breathing or ventilation. The shallow breathing significantly improves the stability of tip  40 . In addition, the low amplitude and the high frequency of the motion enable processor  41  to filter out any such motion. 
     In flowchart  190  a ventilation step  220  replaces ventilation step  120  in flowchart  90 . Ventilation step  220  is invoked when decision  108  returns negative, and the step comprises ceasing hyperventilation and resuming normal ventilation. 
     Reviewing both flowcharts, in some exemplary embodiments the time for each ablation step  112 , i.e., the time during which power source  45  is activated, may be as low as approximately four seconds. Assuming a moving time of approximately six seconds, the time for ablating one site and moving to another site, comprising one pass of steps  112  and  114 , is of the order of approximately 10 s. The time during which steps  112  and  114  iterate may typically be up to approximately four minutes overall, since patient  28  is comatose. Thus, embodiments of the present invention enable a physician to implement ablation accurately at multiple locations, such as around ostium  51 , and even to move tip  40  to one or more alternative locations such as another ostium, and perform ablations at each of the alternative locations. 
     The description above has assumed that ablation is performed using a focal catheter. However, the principles of the present invention may similarly be applied, mutatis mutandis, to other types of catheters such as lasso, basket, balloon, and/or multi-spline catheters having one or more electrodes suitable for ablation. It will also be appreciated that embodiments of the present invention are not just directed for use on a particular region of a heart, but may be applied, mutatis mutandis, to any region of or around a beating heart. 
     It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.