HEART-LUNG PREPARATION AND METHOD OF USE

Abstract

An isolated heart or heart-lung preparation in which essentially normal pumping activity of all four chambers of the heart is preserved, allowing for the use of the preparation in conjunction with investigations of electrode leads, catheters, ablation methods, cardiac implants and other medical devices intended to be used in or on a beating heart. The system can be designed to be used within a Magnetic Resonance Imaging (MRI) unit or a X-ray computed tomography (CT) scanner. The preparation may also be employed to investigate heart and lung functions, in the presence or absence of such medical devices. In order to allow comparative imaging visualizations of either or simultaneously the heart and/or lung structures and devices located within the chambers of the heart or vessels or bronchi within the lungs, a clear perfusate such as a modified Krebs buffer solution with oxygenation is circulated through all four chambers of the heart and thus the coronary and/or pulmonary vasculatures. A ventilator with intubation tube can be used to inflate/deflate the lungs and/or provide oxygen to the isolated organs. The preparation and recordings of the preparation may be used in conjunction with the design, development and evaluation of devices for use in or on the heart and/or lungs, as well as for use as an investigational and teaching aid to assist physicians and students in understanding the operation of the cardiopulmonary system.

Claims

1. A method of use of an isolated heart-lung preparation comprising: obtaining an excised heart with one or two lung(s) including corresponding coronary arteries and veins; delivering a transparent perfusate through several and/or all four chambers of the heart via a cannulated attached aorta, inferior vena cava, pulmonary artery and pulmonary vein; wherein the perfusate flows through the coronary arteries and veins of the heart and oxygenates the heart with trachea being intubated and employing a ventilator to inflate/deflate the lung with carbogen or other gaseous mixtures.

2. The method of claim 1 further comprising inserting an optical viewing instrument into one or more chambers of the heart or locations in a lung.

3. The method of claim 1 further comprising applying a medical device to the heart or lung.

4. The method of claim 1 further comprising coupling a physiologic parameter monitor coupled to the heart or lung.

5. The preparation of claim 3 wherein the medical device is implanted within the heart to monitor and control heart rhythm corresponding to the flow of perfusate.

6. The method of claim 1 further comprising coupling a physiologic parameter monitor coupled to the heart or lung.

7. The method of claim 1 further comprising using hydraulic or servo controlled valves to control flows of perfusate to the heart chambers.

8. The method of claim 1 further comprising monitoring the perfusate composition.

9. The method of claim 1 wherein delivering the perfusate further includes delivering the perfusate through the one or two lung(s).

10. The method of claim 1 wherein obtaining an excised heart with one or two lung(s) further included pulmonary arteries and veins.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is an exemplary flow chart illustrating the steps involved in preparing an isolated heart/lung preparation according to the present invention.

[0013] FIG. 2 is a block functional diagram illustrating an exemplary interconnection of the isolated heart/lung preparation according to the present invention and associated support equipment.

[0014] FIG. 3 is a functional diagram illustrating the preparation of the isolated heart /lung preparation according to the present invention in conjunction with monitoring and imaging equipment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] FIG. 1 is a flow chart illustrating the various steps involved in producing the isolated heart/lung preparation of the present invention. The exemplary procedure, which follows, has parameters that are appropriate for use in conjunction with an excised swine heart/lung. These parameters would of course need to be adjusted appropriately in conjunction with isolated heart/lung preparations using hearts obtained from human or other animal donors.

[0016] The first step, indicated at 10, is the initiation of anesthesia. Atropine may be employed to act as an anticholinergic, which dries up secretions and stabilizes the heart.

[0017] The next step, indicated at 20, is to monitor the blood pressure and the cardiac electrogram of the animal and establish IV access. This is accomplished by positioning the animal and securing it to the operating table, attaching electro cardiac leads to the animal to monitor the ECG and inserting an intravenous line into the animal's ear vein. The intravenous drip may comprise two to three liters of Ringer's solution continuously administered through the operation, containing 20 milligrams per kilogram of Thiopental, a short acting anesthetic. 5-milligram doses of Pancuronium or Vecuronium (or other non-depolarizing muscle relaxants) may also be administered to temporarily paralyze the animal's muscles.

[0018] The next step, indicated at 30, is intubation and beginning of mechanical ventilation. This step is accomplished by inserting an endotracheal tube for mechanical ventilation and use of inhalation anesthetics. Any mode of general anesthesia or muscle relaxants may be employed to anesthetize the animal. Exhaled carbon dioxide is monitored according to standard operating room procedures and the levels of the administered gas components are titrated to maintain normal hemodynamic parameters.

[0019] The next step, indicated at 40, is the placement of monitoring probes. This is accomplished using standard operating room pressure measurement probes such as a Swan-Ganz catheter, Millar pressure transducer catheter, etc. for in-vivo blood pressure measurements.

[0020] The next step, indicated at 50, is the opening of the chest cavity. This is accomplished by making a longitudinal incision along the midline, cutting the sternum along the midline, and retracting the ribcage to expose the heart and great vessels. A lateral approach may also be employed. The pericardium may then be excised and pericardial fat and other connective tissues removed. Alternatively, the pericardium may be left intact if evaluation of devices employed in the pericardial space is desired.

[0021] The next step, indicated at 60, includes the isolation of superior and inferior vena cava, the aorta, the pulmonary artery and pulmonary vein of the lung to be removed, along with the insertion of the aortic cannula. This is accomplished by dissecting out the major blood vessels listed above for clamp placement and transsection, followed by introduction of an aortic cardioplegic cannula, for example a nine French double lumen cannula. Prior to placement of the aortic cannula, heparin is delivered to prevent coagulation. If desired, adenosine may be introduced to dilate coronary vessels and prepare the heart for cardioplegia. The inferior vena cava is then tied off at one or two spaced locations, the superior vena cava is clamped at one or two spaced locations and the aorta is clamped distally from the insertion site of the aorta cardioplegic cannula.

[0022] The next step, indicated at 70, comprises arresting the heart and initiating the cardioplegia procedure. This step is accomplished by initiating antegrade coronary flow of cardioplegia solution through the aortic cannula, for example one to two liters of St. Thomas Hospital cardioplegia solution. Delivery of the cardioplegia solution stops the electrical activity of the heart, due to the high potassium content. Topical cold in the form of ice or a slurry of buffers is applied to the heart to slow any remaining myocardial activity, and the left ventricle is decompressed through a pulmonary artery puncture.

[0023] The next step, indicated at 80, comprises the removal of the heart/lungs and transfer of the heart in ice to a fluid bath to maintain the heart/lungs in a cooled condition. In this step, continuous low flow cardioplegia may be maintained by means of the aortic cannula. The inferior vena cava and superior vena cava are then cut. The aorta is cut as distal to the clamp as possible (e.g. beyond the arc so that a portion of the descending aorta is removed) and the pulmonary vein of the lung to be removed is excised.

[0024] The next step, indicated at 90, is to cannulate the major vessels. This step is accomplished by recannulating the aorta using a larger cannula, for example a 40-50 French cannula secured directly into the aorta. The pulmonary artery and vein of the dissected lung are cannulated, for example using a 28-40 French cannula. The right atrium is cannulated, for example with a 36-40 French cannula inserted into the inferior vena cava. The superior vena cava, any viewing equipment passing through the wall of any heart chamber and any other remaining openings are sutured to eliminate leaks of perfusate.

[0025] The next step, indicated at 100, is the attachment of the heart/lung to the associated apparatus for oxygenating and delivering the clear perfusate. This step is discussed in more detail in conjunction with the description of the equipment associated with the heart in FIG. 2, below. The associated apparatus includes two perfusion pumps for delivering perfusate to the right and left chambers of the heart, fluid columns to adjust input (pre-load) to the right and left atria to appropriate physiologic pressures and to mimic vascular resistance (after-load), a ventilator for inflation/deflation of the lung, and an optional water bath, in which the heart may be located to control the overall temperature of the preparation.

[0026] The next step is to initiate ventilation of the lung. The primary bronchus of the dissected lung is ligated, clamped, or otherwise sealed shut to recreate a closed volume airway. The trachea is intubated with a standard medical balloon tipped intubation tube to maintain airway control. The intubation tube is subsequently connected to a ventilator that is set to similar physiological ventilation parameters as the respective species being used. For swine it is set to approximately 15 breaths per minute and a volume of 300-400 milliliters.

[0027] The next step, indicated at 110, is the reinitiation of normal rhythm. This may be accomplished by placing a epicardial defibrillation electrode on the surface of the left ventricle, cannulating the superior vena cava and passing a defibrillation lead through the cannula, through the right atrium and into the right ventricle and thereafter delivering a defibrillation shock between the two electrodes to initiate normal rhythm. The cannula located in the superior vena cava preferably extends upward a sufficient distance to prevent leakage from the right atrium and may be employed to introduce additional or alternative leads, catheters or viewing equipment into the right atrium or ventricle. The defibrillation lead preferably includes cardiac pacing and sensing electrodes that may be used to moderate and control the heart rhythm as necessary in conjunction with an associated external cardiac pacemaker.

[0028] The last step, indicated at 120 is to maintain the isolated heart. This is accomplished by employing the associated equipment to deliver a clear, oxygenated perfusate such as a modified Krebs buffer solution adjusted to physiological conditions of pH and calcium. In addition, epinephrine, milrinone or other ionotrope may be added to the perfusate if the heart is not beating to increase the sensitivity to defibrillation. Lidocaine or other anesthetic may be added to the perfusate as a local anesthetic, reducing likelihood of ventricular arrhythmias. Other pharmacological treatment as appropriate may be administered in order to support the preparation. The flow of clear perfusate can be controlled, for example via a series of automated pinch valves around the tubes leading to and from any cannulations of the preparation and/or via automated level changes of load chambers at 210, 212,256. This may serve the purposes of extending the preparation's viability when full physiological mimicry is unnecessary, isolating a fluid volume of perfusate to maintain temperature and/or chemical content control, adjusting physiological stressors or maintaining constant experimental conditions with loading pressures.

[0029] Once the preparation is established, it may be employed at 130 to generate information with regard to heart/lung function alone or in conjunction with medical devices inserted in or mounted to the preparation. Monitoring of heart/lung function may comprise the insertion of optical viewing equipment into a chamber or a blood vessel of the preparation and/or imaging the preparation using an external video camera, fluoroscope, infrared camera, chemical imaging system (e.g. Ramon spectroscopy), ultrasound, MRI or other imaging method, and/or monitoring the physiologic performance of the heart, including hemodynamic and electrical functioning of the heart. Equipment for monitoring hemodynamic and electrical heart functions may for example include heart sound monitors such as phonocardiograph equipment or other microphones, electrogram sensors, heart rate sensors, pressure sensors, gas concentration sensors, and/or flow sensors located in the chambers and/or in the coronary vasculature and/or lung(s) of the preparation. The outputs of the various imaging devices and sensors may be recorded at 140 to provide a record of the monitored parameters alone or in conjunction with one another. The recorded outputs of the optical viewing equipment, imaging devices and/or sensors may be combined at 150 to provide a recording, which will allow for simultaneous display of the obtained images and/or monitored cardiac and lung parameters. The recordings obtained may be duplicated and distributed at 160, in the form of CD ROMs, video tape, electronic files, movies, or the like, allowing for the information obtained using the preparation to be widely available to physicians and students.

[0030] FIG. 2 is a schematic diagram of the isolated heart/lung 200 in conjunction with associated equipment employed to maintain the preparation and to evaluate medical devices in conjunction with the preparation. The preparation is maintained in a support apparatus illustrated schematically at 204, which may include a support of surgical netting. The preparation may simply hang suspended in the support netting in a position with the atria located above the ventricles or may be re-oriented to simulate the position of the heart/lung in the donor species in upright, reclining or other positions. The pericardium of the excised heart may also be used as a support, and the heart/lung preparation may be positioned as desired (e.g. vertically or horizontally) to mimic a desired physiological condition. The preparation is maintained at physiological temperature, either by means of the perfusate in combination with the surrounding ambient temperature or optionally by means of an optional temperature control bath. An oxygenator 244 with associated cardiotomy reservoir 246 is coupled to the preparation such that the drain from the pulmonary artery 250 and the output of the aorta 248 both feed the cardiotomy reservoir 246 associated with the oxygenator 244. The right atrium chamber filling pump 242 draws perfusate from the reservoir directly and delivers it to the right atrial preload chamber 210 which comprises a fluid column adjusted to maintain approximately 5 mm Hg pressure going into the right atrium 252 via cannula 208 coupled to the inferior vena cava. The outlet of the pulmonary artery 250, as noted above, drains into the reservoir 246 to complete the circulation path for the right side of the heart. Return flow of perfusate from the coronary sinus is allowed to enter the right atrium or can be separately cannulated to allow periodic sampling or monitoring of the perfusate.

[0031] A second pump 240 pumps perfusate from the reservoir 246, through the oxygenator 244 and to the left atrium 254 by means of the cannula 238 inserted into the pulmonary vein. A left atrium preload chamber 256 comprises a fluid column that maintains approximately a 10 mm Hg input pressure into the left atrium. The outflow from the aorta 248 is delivered via cannula 236 to the reservoir 246, against an aortic afterload chamber 212 which defines a fluid column which maintains an average pressure of approximately 70 mm Hg, opposing outflow of fluid from the aorta and mimicking vascular flow impedance. Perfusate enters the coronary arteries from the aortic root, providing for oxygenation of the heart tissue without separate cannulation of the coronary arteries. A port may optionally also be installed in the aortic cannula to allow periodic sampling or monitoring of the perfusate. Either or both of the preload chambers may be fitted with oxygen bubblers to increase oxygenation of the perfusate if desired. Flow into the left atria may also occur through the lung from the right atria as in the normal physiologic situation. This can be controlled by clamping the root of the lung if desired.

[0032] In the event that both lungs are excised, no pre-load to the left atrium is required and this aspect of the preparation need not be performed.

[0033] The ventilator 500 is illustrated coupled to the primary bronchus 502 of the dissected lung 504. The trachea 506 is intubated with a standard medical balloon tipped intubation tube to maintain airway control. The intubation tube is connected to ventilator 500, set to similar physiological ventilation parameters as the respective species being used.

[0034] The apparatus described above in conjunction with the preparation may, if desired, be powered by means of storage batteries and mounted in a wheeled cabinet, allowing the preparation to be readily moved from one location to another. The preparation so configured may be employed as a teaching aid in multiple classrooms and/or may be conveniently moved between different laboratories or research facilities.

[0035] Also, illustrated in conjunction with the preparation is an optical viewing scope 224, for example a fiber optic viewing scope 224 and associated display 232 and control keyboard 234. Scope 224 is inserted into one or more of the chambers of the heart, for example by means of a T-fitting 226 associated with one of the four cannulas coupled to the heart. In the drawing as illustrated, the T-fitting is associated with the cannula 258 coupled to the pulmonary artery 250, allowing for visualization of the right chambers of the heart. However, the optical scope may as well be inserted into the left side of the heart, for example, via the aorta or pulmonary vein.

[0036] Alternately, the viewing scope 224 may be passed through the wall of a chamber of the heart or lung, for example through the right atrial appendage and secured by means of a purse-string suture to minimize leakage.

[0037] With the optical scope in place allowing observation of a desired chamber of the heart or lung, a medical device intended for use in the heart may be inserted therein. For example, a cardiac pacing lead, cardiac ablation catheter, diagnostic catheter, or other medical device, may be inserted into the heart or lung, and monitored under visual observation using the optical scope, for example by being passed through the cannula 216 coupled to the superior vena cava in the same manner as the pacing/defibrillation lead 220 as illustrated. Additionally, surgical implants such as cardiac valves and atrial septal defect devices may also be tested in conjunction with the isolated heart/lung preparation, under observation of the fiber optic scope. For example, a prosthetic device such as a tricuspid valve may be implanted into the test animal in place of the natural valve 202, weeks, days or months prior to harvesting the animal's heart. Using the isolated heart preparation, the condition and operation of the prosthetic devices may be monitored optically, while the heart beats in an essentially normal fashion.

[0038] To enhance controllability of the preparation, control valves 400 as illustrated schematically may be placed in the fluid lines to and from the pre-load and after-load chambers as illustrated to allow fine control of pre-load and afterload parameters. The valves may be coupled to a computer 402 via interface 404. Pressure sensors may also optionally be placed in the various fluid lines and corresponding connected to the computer 402. A data Acquisition device 406 may optionally be provided to sense conditions in the reservoir as illustrated and may also be coupled to the computer 402.

[0039] Similarly, computer 402 is coupled to control the ventilator 500 and to adjust the ventilation parameters thereof. Instrumentation and control systems may be varied depending upon the specific purpose for the preparation.

[0040] FIG. 3 illustrates schematically the preparation of the present invention in conjunction with imaging and monitoring equipment and audiovisual processing equipment appropriate for producing recordings combining the outputs of the imaging and monitoring equipment. The heart/lung preparation is illustrated at 300, shown suspended over a cabinet 310 that contains or supports the apparatus illustrated in FIG. 2, with the possible exception of the display 232 and associated control keyboard 234. Interconnection of the chambers of the heart/lung with the equipment illustrated in FIG. 2 is omitted for the sake of simplicity, but corresponds to that illustrated in FIG. 2.

[0041] Illustrated schematically in conjunction with the preparation 300 are examples of the types of available monitoring and imaging equipment that may be used in conjunction with the preparation. For example, a fiber optic viewing scope 314 may be inserted into one or more chambers of the heart/lung, along with monitors 312 of hemodynamic or electrical hear functions, as discussed above which may be inserted into a chamber of the heart/lung, within the vasculature of the heart, or applied to the exterior surface of the heart and or lung. In addition, video imaging by means of a camera 316 of the exterior of the heart/lung may be employed. In addition, or alternatively, an imaging apparatus 318 such as a fluoroscope (X-ray), ultrasound scanner, MRI, or other medical imaging system may also be employed.

[0042] The obtained images and/or signals obtained from the imaging devices and/or monitoring equipment are preferably all provided to processing, display and recording equipment 320, 322, 324 and 326 of the types typically employed with the imaging and monitoring equipment. The recorded images and/or signals may be combined with one another by means of audio-visual processing equipment 328 and provided to a recorder 330 to produce a combined recording allowing for simultaneous observation of visual imaging and/or recorded monitored parameters and/or other types of medical imaging on a single audio-visual recording. The recording may be reproduced and distributed, for example in the form of CD ROMs, video tapes, movies or electronic files, to allow the information obtained from the preparation to be viewed by physicians and/or students at remote locations.

[0043] Also, illustrated at 332 is a pacemaker/defibrillator, coupled to the preparation by means of one or more implantable leads. The operation of the pacemaker/defibrillator or other electronic medical device associated with the heart/lung may also be processed, displayed and recorded by means of associated equipment 334 and provided to audio-visual processing equipment 328. In some cases, particularly in those cases in which the operation of a medical device such as a pacemaker or a defibrillator is of interest with regard to the obtained images and/or other monitored parameters, information with regard to the operation of the medical device may also be combined with obtained images and/or other monitored parameters for display and reproduction. For example, in the context of an implantable pacemaker or cardioverter, the device may provide a signal indicative of the electrogram of the heart and may also provide signals indicative of the operation of the device, including sensing of spontaneous depolarizations by the device, delivery of stimulation pulses to the heart, and information regarding other operational parameters of the device. This information may also be displayed in a combined recording, along with simultaneously obtained images and/or monitored parameters.

[0044] The preparation may also serve as a mechanism for allowing physicians to practice implant techniques while directly observing the operation of the heart and implanted devices in a beating heart/lung model. In this context, the physician would implant the prosthesis or device, as if in an intact animal, and have the opportunity to observe the progress of the device through the heart and its interaction with the various structures of the beating heart and ventilated lung, for example by using a display associated with an optical probe.

[0045] In conjunction with the above specification, we claim the following subject matter.