Cardiac Pressure-Volume Loop Analysis Using Conductance Catheters in Mice

The overall goal of this procedure is to assess the load dependent and independent measures of ventricular, systolic and diastolic function. This is accomplished first by the placement of a conductance catheter into the left ventricle of a mouse heart. In the second step, the aorta is constricted to change afterload, followed by the alteration of preload via the constriction of the inferior vena cva.

In the final step, the conductance catheter is carefully calibrated to accurately assess the changes in the cardiac chamber volume. Ultimately, cardiac pressure volume analysis is used to obtain the load dependent and independent measures of cardiac function. The implications of this technique extend towards the therapy of cardiac dysfunction, as it allows both a rigorous evaluation of cardiac function and the potential in masking of functional phenotypes missed by non-invasive testing.

Demonstrating this procedure will be Dr.Lan Mao, a mouse neurosurgeon from our laboratory 30 minutes before placing a conductance catheter into the left ventricle chamber. Soak the tip of the catheter in warm saline while the tip is soaking. Shave the neck and chest of an anesthetized adult mouse and place the animal on a heated pad.

After applying ointment to the animal's eyes, make a midline incision in the neck and dissect the tracheal muscles to expose the trachea. Then place an endotracheal tube through the mouth, visualizing the trachea for the correct placement of the tube, and connect the tube to the respirator. Set the ventilator settings based on the animal's weight as indicated.

Then to place the catheter by a carotid approach, make an incision over the right carotid from the mandible to the sternum, and dissect the surrounding tissue to expose the right carotid. Next, cut the vagus nerve that runs adjacent to the carotid and secure a six oh silk suture around the distal end of the carotid artery. Place two additional sutures beneath the carotid artery proximal to the first suture loosely tying the middle suture.

Then gently pull the proximal suture and use a clamp to secure the suture to the skin. When the carotid artery has been clamped, both proximally and distally make a small incision in the right carotid artery proximal to the first suture and extending longitudinally toward the chest. Now insert the saline soaked conductance catheter tip into the vessel through the incision using the middle suture to secure the catheter.

Then gently advance the catheter into the left ventricle through the carotid. Watching the pressure volume loop tracing to ensure a correct placement, optimal placement of the catheter will yield pressure volume loops that appear rectangular for five to 10 minutes after placement record Baseline pressure volume loops until a steady state is achieved to place the catheter by an apical approach. Make the starting incision from the xiphoid process through the chest wall laterally until the diaphragm is visible.

Cut through the diaphragm to visualize the apex of the heart and use a 25 to 30 gauge needle to make a stab wound in the apex of the left ventricle. Then insert the conductance catheter through the stab wound until the proximal electrode is just inside the ventricle. And record the baseline pressure volume loops as just demonstrated to vary the afterload with the transient aortic occlusion.

Begin by making a small horizontal incision in the upper chest and dissect the surrounding tissue to expose the transverse aorta. Place a 6.0 silk ligature underneath the transverse aorta. Then when the pressure volume loops have returned to baseline, place both ends of the ligature in a small segment of PE 50 tubing class both ends of the suture with a needle clamp and gently and slowly raise the suture over a period of one to two seconds, followed by a slow release of the tension on the vessel.

Optimal recordings should have at least five pressure volume loop cycles and exhibit a steady rise in the end systolic pressures during the application of the tension on the suture. To vary the preload with the transient inferior vena CVA occlusion. Make a vertical incision below the xiphoid process and underneath the diaphragm to expose the inferior vena cva.

Place a six oh silk ligature underneath the inferior vena cva. Then after the pressure volume loops have returned to baseline, clasp both ends of the suture with a needle clamp and gently and slowly raise the suture over a period of one to two seconds, followed by a slow release of the tension on the vessel. Optimal recordings should have at least five pressure volume loop cycles and exhibit a steady drop in the left ventricular and diastolic pressures during the application of the tension on the suture to perform a saline calibration.

At the conclusion of the study, inject a 10 microliter bolus of hypertonic saline into the animal through the jugular vein to obtain a parallel conductance value. An apparent increase in volume will be observed with no change in the pressure as a result of the change in blood pool conductance. To perform a vete calibration, warm a vete with wells of known diameter to 37 degrees Celsius and fill the first three holes with fresh, warm heparinized.

Blood from mice undergoing hemodynamic assessments fit a plastic adapter provided by the manufacturer to the vete. This will hold the conductance catheter stationary during the calibration. Then insert the conductance catheter into the first well until all of the electrodes are submerged.

Finally, record the conductance in the volume channel to test whether the beta arrestin biased angiotensin two receptor type one ligand TR RV 1 2 0 0 2 3 affects cardiac function. In vivo pressure volume loop analysis was performed on wild type mice receiving conventional or novel angiotensin receptor blockers. Indeed, in this experiment, intravenous infusion of TR RV 1 2 0 0 2 3 increased the cardiac contractility significantly compared to conventional and control treatments.

After watching this video, you should have a good understanding of how to perform pressure volume loop analysis using both aortic and inferior vena cava constriction to l obtain both load dependent and independent measures of cardiac function.