Transonic’s monthly Research Webinar Series on the 9th December, 2020 presented the interesting story of two young MDs from Aarhus University in Denmark who are dedicated to finding solutions for the challenges they face in the clinic.

Dr. Mads Dam Lyhne recently completed his PhD studies, focusing on right ventricular function in large porcine models of acute pulmonary embolism. He will soon be returning to his clinical duties, while trying to stay involved in research whenever he can. Dr. Niels Moeslund is in the middle of his PhD studies that are dedicated to organ donation and transplantation. He is currently focusing on reanimation of the heart after circulatory death, also in a large porcine model. Both use Admittance PV loop technology in right and left ventricle simultaneously to answer some of their research questions.

Biventricular pressure-volume loop instrumentation and data collection is feasible in large animals. However, it is not always straight forward and easy. The focus of this webinar was to introduce the audience to the technical aspects of inducing a pulmonary embolism and the instrumentation necessary to investigate the cardiac consequences of the pulmonary embolism in a closed chest approach by Dr. Lyhne. In addition, Dr. Moeslund investigates the best approach to optimize heart donation after circulatory death. An open chest approach is combined with a vascular access in line with the clinical setting he is aiming to mimic.

Acute pulmonary embolism model and closed chest instrumentation

For this model, an acute pulmonary embolism is introduced en bloc as large autologous blood clots to the central venous circulation. The blood clot follows the blood stream and settles in the lungs. This results in a phenotype showing increased pulmonary pressure, impaired right ventricular function, troponin release with maintained mean arterial pressure - clinically comparable to intermediate-high risk. As the complete instrumentation is closed chest, ultrasound is used for vessel puncture followed by fluoroscopy to place the appropriate sheaths and catheters.

For right ventricle PV catheter placement, a 7F sheath is placed in the left external jugular vein. A guide wire is moved all the way down into the inferior vena cava. Subsequently, the 7F sheath is exchanged for a 16F sheath that is extra-long ~ 35cm. The tip of this sheath is pushed to the center level of right atrium. Putting downwards pressure on the outside end of this long sheath results in directing the atrial end of the sheath towards the right ventricle. This helps guide the PV catheter into the right ventricle. Retracting the 16F sheath leaves the PV catheter in place in the RV. Left ventricle PV loop catheter placement is performed by inserting an 8F sheath into the left carotid artery. The catheter is inserted and in the systolic phase of the cardiac cycle is advanced to pass the aortic valve into to left ventricle. An explanation of the complete instrumentation can be found in the webinar.

Right ventricle pressure-volume loop data showing in red baseline values. Light to dark blue represents increased severity of pulmonary embolisms.

Heart donation after circulatory death and open chest instrumentation

The clinical setting investigated here is one of a patient on life support suffering from severe neurological damage that is not sustainable with life. A decision was made to withdrawal life support by turning off the ventilator. This results in a warm ischemia period as the heart continues to work under increased hypoxic conditions. The heart will stop beating approximately 10 min after life support is withdrawn. At this moment there are several options about how to proceed. Dr. Moeslund focusses on the donor phase of transplantation and he uses normothermic regional perfusion (NRP), practically comparable with extra-corporal membrane oxygenation (ECMO), to restore circulation to the thoracoabdominal organs for 30 min followed by a cardiac function assessment. To see if NRP restored cardiac function and, therefore, eventual increased transplantation success.

Although the model is one of open chest via sternotomy, instrumentation occurs via vascular access, taking advantage of the anatomy of the heart guiding the pressure-volume catheters to central positions in the ventricles. The left ventricle pressure-volume catheter is inserted via the right carotid artery, passed through the aortic valves during systole until the pigtail of the catheter touches the apex. Subsequently, the catheter is retracted a few millimeters, assuring measurement of the full length of the ventricle. The right ventricle pressure-volume catheter is inserted via the right external jugular vein. Closing the ostium of the inferior vena cava by hand guides the catheter through the tricuspid valve into the right ventricle until the pigtail is felt at the bottom of the apex. Withdrawal of the catheter a few millimeters again assures full coverage of the ventricle length. This is followed by placement of NRP cannulas and subsequent optimization of PV catheter placement.

Points of attention for data collection in bi-ventricular set-ups

• In general, the right ventricle volume signal is much more influenced by the ventilator, compared to left ventricle. 
• When performing vena cava occlusions, pay close attention to the data of both ventricles. As the ventricles are serially connected, the left ventricle takes a couple of cardiac cycles longer to show a response compared to the right ventricle. 
• Bi-ventricular measurements in large animals can easily be performed for 12 hours non-stop; however, one needs to assure that the PV catheter position doesn’t shift during the experiment.

For a more in-depth review of this unique application – including the data collected - we encourage you to watch the webinar in full here. During the webinar, both Dr. Mads Dam Lyhne and Dr. Niels Moeslund took time to answer the questions of fellow researchers. They also welcome researchers to contact them.

• Dr. Mads Dam Lyhne can be reached via email mads.dam@clin.au.dk, LinkedIn or Twitter @MadsDam_MD.
• Dr. Niels Moeslund can be reached at nielsmoeslund@clin.au.dk.

This webinar was the final one for 2020. We at Transonic would like to thank all our speakers and the audience for being part of this webinar series. For 2021 we wish you all that is good and hope to see you again when this series returns in February.