Jun 25th 2019 Clinical Observations

Today, we had the privilege of observing the implant of one pacemaker and two ICDs at the Philadelphia VA Medical Center. The patients all had different underlying conditions, with each condition treated with a slightly different device and device setup. The patients were awake and anesthetized throughout the procedure.

Overall Process

1. Prep the patient
2. Cut a pocket in the upper left chest area, between the left pectoral muscle and the left deltoid.
3. Use a needle to find the axillary vein, with ultrasound sensing to visualize the needle in real time.
4. Put a wire through the needle tip, and into the vein to hold the place.
5. Repeat steps 3 and 4 for each catheter that is to be inserted.
6. Feed the catheter, which contains the leads, into locations in the heart
7. Test the sensing voltage, pacing voltage, and impedance of the leads.
8. Screw in or otherwise affix the leads. Right atrium and ventricular leads have a small screw which is used to fasten the lead to the myocardium. Left ventricular leads have small mechanical protrusions that keep the lead in place in the coronary sinus.
9. Retest the sensing voltage, pacing voltage, and impedance of the leads.
10. Plug the leads into the ICD or pacemaker
11. Place the device inside the pocket made in the skin
12. Close the pocket.

1st Procedure (~1hr)

The first procedure we observed was a dual-chamber pacemaker implant (DDDR). This was in response to paroxysmal complete AV block. This means that the patient had sudden onset cases where beats from the atrium would not conduct to the ventricles. The patient had episodes where ventricular beats were not observed for up to 8 seconds. The dual chamber pacemaker, is DDDR model. The first D means that it paces in both chambers, the second means that it senses in both chambers. The third D means that it does inhibition and triggered pacing, meaning it will not pace if it sees a natural beat, and pace if it notices a missing beat. The R means the algorithm is rate-responsive. The pacemaker will adapt the heart rate based on what it senses.

The two leads were standard bipolar leads, and were inserted through the vein in a fairly straightforward manner. The surgeons used tools called stylettes to change the way the leads moved through the heart. This device was made by St. Jude’s.

2nd Procedure (~3hrs)

The second procedure was a CRT-D implant, manufactured by Biotronik. This was in response to LBBB or Left Bundle Branch Block. The patient also had a wider QRS complex on a surface electrogram. This happens when an atrial beat would be conducted through the right ventricle, but slow conduction of the signal to the left ventricle would result in an asynchronous beat. This patient was at risk for sudden cardiac death, which is why a CRT-D was implanted.

CRT-D devices have three leads, one in the right atrium, one in the right ventricle, and one in the left ventricle. The D refers to defibrillator, which means that the device can function as an ICD, which should prevent sudden cardiac death. The right atrium lead is identical to that used for the pacemaker. The right ventricle lead has a coil on it. That coil is used to deliver a defibrillating shock. The left ventricular lead is sent through the coronary sinus, near the tip of the left ventricle. This lead has four poles.

For sensing and pacing, a pole must be chosen, and a bipole configured. During the selection of a pole, pacing delivered from the L1 pole, or the farthest pole on the lead, closest to the “tip” of the heart, caused the patients diaphragm to contract. This was due to electrical activation of the phrenic nerve. L2 was chosen because a vector from the right ventricular coil to L2 would not generate a diaphragm response.

Credit: Boston Scientific

3rd Procedure (~1hr)

The implant was for a dual-chamber ICD, made by Medtronic. The patient exhibited signs of cardiomyopathy, with an ejection fraction of less than 35%. This means that on each heart beat, less than 35% of the volume of blood in the heart is expelled. The doctors postulated that it could be caused by AV block, and so opted to install a dual chamber ICD. This only required a right atrial and ventricular lead. This procedure was very similar to the implant of the dual chamber pacemaker that was done in the first procedure.

We’d like to thank the physicians, nurses, and OR team at the Philadelphia VA Hospital for graciously permitting our observation. We found it remarkably informational, and are grateful for the warm reception we received.