Medicine
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Closed Chest Biventricular Pressure-Volume Loop Recordings with Admittance Catheters in a Porcine Model
Chapters
Summary May 18th, 2021
Here we present a closed chest approach to admittance-based bi-ventricular pressure-volume loop recordings in pigs with acute right ventricular dysfunction.
Transcript
This closed chest approach to obtain biventricular pressure-volume loop recordings enables state-of-the-art hemodynamic evaluation in an en vivo porcine model. The main advantage of this minimally invasive method is that it allows for thorough and load-independent evaluation of the cardiovascular system while maintaining near-intact thoracic physiology. This method of biventricular evaluation is very important for most experimental cardiovascular models because the left and the right heart may act differently, for instance, on pharmacological stimulation.
And at the same time, there can be interdependency between the left and the right heart, so it's very important to assess both cardiac ventricles at the same time. After anesthetization, use a 17 gauge sterile venous catheter to puncture the skin. Guide the needle to intravascular positioning with the help of the ultrasound.
Use the Seldinger technique to replace the needle with a guide wire. Remove the venous catheter and leave only the guide wire in the intravascular lumen. To ease the insertion of the sheath, make a small skin incision adherent to the guide wire.
Then place an appropriately-sized sheath over the guide wire and into the vessel of choice using the Seldinger technique. Insert the Swan-Ganz catheter in the right jugular vein through the eight French sheath. Use thoracoscopy to observe when the distal part of the Swan-Ganz catheter is out of the sheath by resistance-free inflation of the balloon.
Slowly advance the Swan-Ganz catheter. Observe the changes in the pressure signal from the distal port as it enters the right ventricle and shortly after the distal port passes through the pulmonary artery. Deflate the balloon and ensure that the distal pressure port is still in the main pulmonary artery using thoracoscopy and the pressure signal.
Insert a long guide wire through the seven French sheath in the left jugular vein, then advance the guide wire through the upper central veins, the right atrium, and the inferior vena cava, monitoring the movements using thoracoscopy. Leaving the guide wire in the venous circulation, extract the seven French sheath and compress the entry point to avoid bleeding. Then use the Seldinger technique to exchange the seven French sheath for the 16 French sheath.
Advance the 16 French sheath over the guide wire until the tip of the sheath has reached the level of the superior vena cava. Insert the pressure volume catheter in the 16 French sheath, then advance it into the right atrium. Point the external end of the 16 French sheath downwards and medially, which will point the internal end of the sheath anteriorly.
Advance the pressure volume catheter from the right atrium into the more anteriorly positioned right ventricle. Verify this by the change in pressure signal from the pressure volume catheter to a classic ventricular shape and by the tactile resistance as the pressure volume catheter meets the right ventricular apex. Finally, to avoid any hemodynamic or electrical influence of the device located close to the heart, retract the 16 French sheath outside the thoracic cavity once the catheter is in the right ventricle.
Insert the pressure-volume catheter in the eight French sheath into the left carotid artery. Advance the pressure volume catheter through the eight French sheath towards the aortic valves guided by fluoroscopy. To advance the pressure volume catheter through the open aortic valves, synchronize the quick advancement of the pressure-volume catheter to a systolic phase of the cardiac cycle.
Verify the success by observing a change in the pressure signal from the PV catheter to a classic ventricular shape. Advance the guide wire from the femoral vein to the inferior vena cava at the diaphragm level, then insert the balloon over the guide wire advancing it to the diaphragm level at the end expiration. Check that the optimal phase and magnitude signals are received from both ventricles.
Ensure both ventricular pressure-volume loops have the proper shape, realistic pressures and volumes. Record pressure-volume loops over 30 to 60 seconds of continuous ventilation and use the average value of all respiratory cycles to perform analysis. For load-independent pressure-volume variables, do a breath hold.
Wait for a few heartbeats and then slowly inflate the inferior vena cava balloon with the chosen liquid. Observe as the right ventricular pressure-volume loops become progressively smaller and shift leftward. Keep the inferior vena cava balloon inflated long enough to reduce right ventricular output and thereby the left ventricle preload and observe the progressive decrease in the left ventricular pressure and volume.
Acceptable pressure-volume loops obtained from the left ventricle should have a classic square shape, and those from the right ventricles should have the classic triangular shape. The pressure-volume catheters need to be adjusted to improve the quality of loops if suboptimal loops are obtained from the left or the right ventricle. It is more difficult to obtain the classic triangular loops from the right ventricle and some static noise due to blood turbulence in the end diastole is acceptable.
The two ventricles are serially connected, causing a time-wise shift in preload reduction as the inferior vena cava balloon quickly reduces right ventricular preload, but left ventricular preload is not reduced until the right ventricular output has decreased by its lack of preload. A gradual reduction in the preload causes a family of loops with a gradual reduction in volume and pressure to both the left ventricle and right ventricle. Insertion of the right-sided pressure-volume catheter can be difficult, but with practice, anyone can learn it.
Importantly, necessary time must be spent optimizing catheter positioning to obtain reliable data. This method can thoroughly evaluate cardiovascular animal models and the effects of interventions. The hemodynamic investigations may be supplemented by imaging and blood samples to mimic clinical workup.
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