Ventricular tachycardia is the most common life-threatening arrhythmia, defined as a series of three or more ventricular contractions occurring at a rate of 100-250 beats per minute. VT may lead to sudden cardiac death and together with ventricular fibrillations result in an estimated 300,000 deaths per year in the United States. While acute therapeutic options include defibrillation and cardioversion, drug regimens and surgical ablation of the problematic cardiac tissue are more permanent options.
This latter – cardiac ablation – has just recently become more appealing from the dual perspectives of safety and efficacy. A multi-center study called STOP-VT (Study To Obliterate Persistent Ventricular Tachycardia) found the use of the Stereotaxis Robotic Ablation System, which features remote magnetic navigation, to be an extremely promising therapeutic intervention for VT. The press release reports:
The acute success rate in the study was an impressive 94 percent, and no patients suffered a major complication. The acute success results obtained from the STOP-VT study are 10-15 percent higher than similar published studies using conventional ablation techniques.
We at Medgadget wanted to find out more about the Stereotaxis system, so we spoke with Dr. Zyad Younan, a leading electrophysiologist at the Robert Wood Johnson University Hospital who has extensive experience with Stereotaxis, having performed the world’s first ablation using the Stereotaxis and Impella Heart Pump systems together.
Shiv Gaglani, Medgadget: Good afternoon, Dr. Younan. Would you please start off by explaining what may cause ventricular tachycardia and why ablation is used as a treatment?
Dr. Zyad Younan: There are many potential causes of electrical abnormalities in general and tachycardia in specific. These include congenital abnormalities of the heart – such as Wolf-Parkinson-White syndrome – as well as de novo and improper electrical circuits formed by scar tissue after damage to heart tissue (e.g. myocardial infarction). These problematic circuits can cause decreased cardiac output because of improperly timed contraction. Ablation can be used as a treatment because it allows us to physically destroy these abnormal circuits so that the contractions are more normal.
Medgadget: Can you walk us through a typical ablation procedure?
Dr. Younan: We prepare the patient in the operating room by anesthetizing him or her. We then sequentially insert 3-5 catheters, each specially designed for diagnosis or treatment, into either the right or left femoral vein near the groin. The catheters are carefully positioned into the heart through the inferior vena cava and into the right atrium. Depending upon where we believe the aberrant tissue to be, we can navigate the catheters into the right ventricle or even into the left atrium and left ventricle by boring a small hole through the wall between the atria (the fossa ovalis, which used to be an open hole during fetal development when pulmonary circulation was not necessary). An alternative is to pass the catheters into the femoral artery (not the femoral veins) and go retrograde, meaning up the aorta directly into the left ventricle. However, we generally steer away from that because in elderly patients there is a small risk that it may cause plaques near the aorta to come loose and embolize in the brain, leading to all sorts of other issues (like stroke).
In any case, once the catheters are positioned using real-time intercardiac echocardiography images, the diagnostic catheters are used to localize the aberrant tissue by measuring electrical activity and signals. After problematic areas are found, the ablation catheter applies radiofrequency (RF) energy to destroy them. Hopefully the problem is fixed after that point, though of course we closely follow the patient’s progress to make sure it works.
Medgadget: How does the traditional ablation procedure compare to the remote magnetic navigation (Stereotaxis) system?
Dr. Younan: Whether we were dealing with a tachycardic or fibrile atrium or ventricle, the traditional manual procedure requires a lot more time and care to seed the catheters into the heart and localize the problem. In contrast, the Stereotaxis system features catheters with small magnetic tips that can be positioned incredibly accurately using an external tri-axial magnetic field (about 0.8 to 1.0 T). Then, using a computer mouse in another room we can move the catheter throughout the heart in search for the problematic tissue, and subsequently ablate it with the radiofrequency energy (40-50 watts; generally higher than that used for the traditional method).
Medgadget: Do these differences in operation result in any unique advantages and disadvantages?
Dr. Younan: With the traditional methods there’d be a lot of radiation exposure as well as the persistent risk of perforating the heart since the traditional catheter is stiffer. In contrast, Stereotaxis’ remote controlled magnetic navigation technology features a catheter that bends like a noodle when it touches the heart wall, decreasing the risk of perforation. As a result we can navigate more quickly and both the patient and physician are exposed to less radiation.
From the physician’s perspective, fatigue is also much less with the remote magnetic navigation system. Whereas the traditional methods require us to stand up often for hours at a time while we position the catheters, the Stereotaxis system can be controlled sitting in front of a computer in another room.
In addition, the traditional methods require us to shift our focus between controlling the catheter position and looking at the computer showing electrical activity. I like to use the analogy that it is sort of like texting while driving. The divided attention made us more prone to errors.
As a result, the Stereotaxis system has a significantly higher success rate for VT ablations. At this point though, the systems have comparable success rates for ablating atrial fibrillations, but a positive is that with the remote magnetic navigation system there are less complication risks and decreased radiation exposure. I believe this system will eventually become the gold standard to do ablations.
Medgadget: That’s really interesting. What was also interesting was hearing that you were the first person to do an ablation procedure using both the Stereotaxis system as well as the Impella Ventricular Assist Device in combination. Did the magnetic field not interfere with the VAD, and why was it necessary to use both?
Dr. Younan: Fortunately the field was not strong enough to be problematic for the Impella system. The room and other devices, like the pulse oximeter, are magnetically compatible. In terms of the VAD, when doing these operations we actually induce ventricular tachycardia in order to be able to map it. The problem is that the patient’s blood pressure and cardiac output drop, so we decided to pioneer the use of placing the Impella device into the ventricle to maintain cardiac output.
Medgadget: Fascinating. It’d be great to see a procedure sometime. Thank you for your time and explanations!
Dr. Younan: My pleasure, and you’re welcome to visit the OR to see how it works for yourself.