Anna Hazelwood - Dr. Evelyn Horn - Week 4

Dr. Horn was not seeing patients this week so I bounced between the cardiac catheterization lab and the electrophysiology (EP) lab.  In the cath lab, I was able to see 2 percutaneous coronary interventions (PCIs). These are procedures where the doctor enters the coronary arteries with a catheter, uses a balloon to open them up, and then places a stent to keep the artery open. They also utilize intravascular ultrasound (IVUS) imaging to visualize the inside of the artery to determine what pressure to use when opening the artery with the balloon and eventually the stent. This also helps them confirm that the stent is properly in place and will not dislodge.

In the EP lab, I saw three very interesting procedures this week. The first one was an atrial ablation case where the patient already had prior "gold standard" ablations but was still experiencing atrial flutter. Therefore, the doctor needed to map out the electrical conductivity of the atria to determine where the atrial flutter was occurring to then plan where to ablate. The hospital pairs with a company Carto which is able to map out the heart using a special catheter. They also use intra-cardiac ultrasound to match up a 3D CAT scan image of the heart with the actual positions in space. This allows the doctor to visualize their ablation catheter in a 3D image of the heart with the conductance of the tissue overlayed. They can also map out each spot that was ablated for the patient's medical records. In this case, they used electrical stimulation to push the heart into a stressed state, to see when the atrial flutter appears. Then, during the atrial flutter, they mapped the conductivity and determined their ablation path. In the image below, red indicates non-conducting tissue which is what the doctor wants to see in the atria to ensure the flutter will not come back. The purple indicates healthy, conductive tissue.

The second procedure I saw was a more "gold standard" atrial ablation but this time they used pulse field ablation (PFA) instead of radiofrequency. This patient had no prior ablations so the plan was to map out the conductivity of the atria, and then use both a "flower" and "basket" shaped ablation catheter to outline the major vessels in the atria. These vessels are typically where an atrial flutter occur from, so in a typical case where the patient has had no prior ablations, this is where the doctor targets. The procedure was relatively straightforward and used the same Carto mapping software.

The last procedure was the most interesting because it was a ventricular ablation for supraventricular tachycardia (SVT). This procedure started with a stress test where they stimulated the heart and tried to induce SVT in order to be able to map out where to ablate. However, this patient was not able to be induced into SVT. This then led them to use a magnetic catheter that can be controlled in the observation room by the doctor on a computer. This catheter can sense the conductance of the tissue it is over and the carto software can match up the heart monitor results with this catheter's readouts to determine the optimal location to ablate. After finding a 99% match spot, the doctor ablated around that area and then tested the patient again to determine if this ablation worked. This procedure was the most fascinating because all of the exploration and actual ablating was done using a computer mouse controlled by the doctor.