Observations at the Hospital of the University of Pennsylvania
This past week Nandan Tumu and I have had the absolute privilege of observing several electrophysiology procedures at the Hospital of the University of Pennsylvania (HUP). Here I will recount my observations of the surgeries we watched on June 27th and 28th, which involved transcatheter ablation surgery. In Nandan’s post he talks about the procedures for device implantation.
June 27, 2019
On Thursday we observed two procedures, each approximately 4.5 hours in length. The first procedure was a pulmonary vein isolation (PVI) for persistent atrial fibrillation. The patient had previously failed treatment on antiarrhythmic drugs and was now eligible for treatment with transcatheter ablation. The indications for surgery for the second patient were unclear, but he/she was also prescribed PVI + cavo-tricuspid isthmus (CTI) ablation to treat atrial flutter. A rough outline of the procedures is as follows:
- 3 mapping electrodes are placed on the patient’s back and 3 on the patient’s front. These 6 electrodes altogether will help create 3D images of the heart with CARTO-3’s advanced mapping technology. A 12-lead ECG setup is also employed to constantly monitor the heart. Defibrillators are on standby in case of an arrhythmic episode.
- The patient is placed under general anesthesia and is given jet ventilation for breathing. A temperature probe is placed down the patient’s esophagus to monitor the temperature of the surrounding area, as ablation procedures can potentially burn the esophagus.
- A hollow, cannulated needle is inserted into the patient’s groin area in an effort to gain access to the femoral vein. The femoral vein begins in the thigh and becomes the external iliac vein in the groin area, which leads directly to the inferior vena cava (IVC) of the heart. The IVC leads directly to the right atrium of the heart.
- A flexible, J-tip guide wire is inserted into the hollow needle and the needle is removed, leaving only the guide wire. The purpose of the rounded J-tip is the ensure that no additional punctures are made in the vein.
5. An apparatus consisting of a hollow dilator inside of a hollow sheath is introduced into the vein by means of the guide wire. The guide wire and dilator are then removed, leaving only the sheath.
6. An intracardiac echo (ICE) catheter is inserted into the hollow sheath and is ready to make its way up to the heart via femoral vein for ultrasound imaging. Preliminary ICE imaging is needed for scoping out the structures of the heart pre-procedure in order to ensure that they remain unscathed post-procedure.
*Steps 3–5 are known as the modified Seldinger technique. An overview of the techinque is provided in the image below. The purpose of the Seldinger technique is to gain venous access for the flimsy catheters needed for ultrasound imaging, 3D mapping, and ablation.
7. Steps 3–5 are repeated for 3 more catheters. In order, the catheters are the coronary sinus (CS) catheter, the lasso, and the ablator. The lasso and ablator catheters have mapping capabilities. The lasso (pictured below) is built to expand and contract as it travels within the pulmonary veins to map them out. The ablator is built to deliver radio frequency (RF) current. The CS catheter is used to access the left atrium without having to puncture through the septum and is used for sensing purposes. The lasso and ablator catheters go transseptal in order to access the left atrium. Throughout the procedure, the patient will have around 4 to 5 catheters inserted into his/her femoral veins.
8. Once all of the catheters are in, electroanatomical mapping of the atria and pulmonary veins can begin. A CARTO-3 representative in the control room adjusts the view and settings of the system while the surgeon navigates his way through the heart. On the screen one can see the structures of the heart begin to take shape as the mapping catheters and mapping electrodes interact and create matrices and whatnot. Point-by-point reference mapping of this sort requires that the patient remain in one position, but CARTO-3 even has compensatory capabilities for if the patient moves a bit off center.
9. A nurse operates the deliverance of RF current at the discretion of the surgeon. The surgeon decides the power and length-of-time at which RF is delivered. The ablator catheter delivers RF in order to create a localized lesion in the tissue at the catheter’s tip, rendering that tissue electrically inert. For PVIs, RF only has to be sufficient to electrically isolate the pulmonary veins. This is accomplished by creating a ring of lesions around the base of the pulmonary veins.
10. The surgeon and nurse begin delivering RF current. CARTO-3 simultaneously creates spherical markers at each point where RF is delivered. The spheres approximate the diameter of the actual lesions being formed. The CARTO-3 rep also landmarks the border at which lesions will either be too close to or far from the pulmonary veins, also at the discretion of the surgeon. Because the surgeon is the only one who feels physical resistance from the structures of the heart, constant communication between doctors and rep is necessary to map those structures out. CARTO-3 is also able to measure the pressure felt by the tip of the ablator catheter and will send warning signals if the pressure becomes too great, to avoid puncturing the heart.
11. Eventually, a perimeter of lesions is created around all four pulmonary veins. The pulmonary veins are paced to test if the impulses can or cannot cross the ablated border. If the pulmonary veins are truly electrically isolated and the impulses can’t cross the border, the surgeon can remove the catheters and close up any openings in the patient.
12. For CTI ablation, lesions are created along the CTI line in an effort to interrupt a macro-reentrant circuit suspected to be causing atrial flutter. Macro-reentrant circuits are circuits involving both the atria and the ventricles. For more on reentry, refer to my article about ventricular tachycardia. The ablation line is created below the crista terminalis of the right atrium. Thus, the ablator catheter needs not access the left heart and CTI ablation can be accomplished from just femoral vein access.
June 28, 2019
On Friday we observed one procedure, approximately 5 hours in length. The patient was experiencing premature ventricular complexes (PVCs). The indications for ablation were a low left ventricular ejection fraction, high PVC burden, manifestation of symptoms due to bradycardia, and previously unsuccessful ablation. The setup for this procedure is the same as for PVI, except this time the patient was under local anesthesia and had no need for jet ventilation. The insertion of catheters was accomplished by the same methods as described above. The catheters involved were ICE, a right ventricular catheter (for pacing), ablator, and later a CS catheter.
A 3D image of the ventricles is constructed in CARTO using still frames taken from the ICE ultrasound. With each frame the CARTO rep traces out the anatomical structures of interest and the system overlays each cross-section on top of the previous.
The minimum pacing threshold needed to depolarize (or capture) ventricular tissue is noted for two reasons: to localize the source of PVCs and in case pacing is needed at any point to terminate a sudden arrhythmia.
How can pacing help localize the source of PVCs? Good question. Once the 3D image is constructed, the area suspected to be the source of PVCs is paced. The resulting ECG is compared to a previously recorded ECG of a natural PVC, and a similarity coefficient is generated by CARTO. If the ECGs are similar enough, the surgeon ablates the area that was just paced. The general area of PVC origin is deduced by watching the 12-lead ECG for deflections in the wrong direction, indicating that an impulse is originating from an unusual place.
The majority of time was spent trying to terminate all natural PVCs with RF ablation. If during ablation PVCs appear suppressed, but the PVCs come back once ablation stops, then more aggressive RF may be required to completely terminate the PVCs. RF deliverance was higher in power and longer in duration for this procedure because suppression was common. The goal is to terminate all PVCs regardless of whether ablation is on or off.
At some point, the patient’s PVCs refused to go away completely. Doctors tried to approach the area of interest from a different angle with a CS ablator catheter, but the CS appeared to be closed off because of scarring from a previous procedure. This is just one example of the imperfect nature of the electrophysiology practice, or any clinical practice for that matter.