What is magnetic navigation?

Magnetic navigation works via two permanent magnets positioned on both sides of the patient to create a uniform magnetic field in the chest.  A smaller magnet embedded at the tip of a thin catheter or guidewire has to align in parallel to the outer magnetic field lines.  

By changing the direction of the outer magnets, and thereby the magnetic field lines, the catheter/guidewire can be steered freely in across three dimensions.

How strong are the magnetic fields?

The magnetic navigation system operates with permanent magnets of a field strength of 0.08 Tesla.  In comparison, the field strength of the terrestrial magnetic field in the UK is much smaller (about 4,8 · 10^-5 T).  But one has to be very close to experience a magnetic effect.  On the other hand, the field strength of a magnetic resonance imaging system is much stronger (1,5 T and higher).

What kind of magnetic catheters are available?

Since 2002 when this technology was first used, a whole family of cardiac guidewires (for coronary care interventions) and ablation catheters (for catheter ablation of arrhythmias) have become available. 

All the guidewires have a highly flexible shaft material in common: this new flexible technology has superseded the stiff pullwire mechanism that previously allowed the steering of conventional catheters. 

The risk of perforation of the heart wall is therefore dramatically reduced.

What kinds of arrhythmias are treatable with magnetic navigation?

All arrhythmias that are amenable to conventional catheter ablation are also treatable using the magnetic navigation system. Since all kinds of ablation catheters are available (including so-called irrigated tip catheters), no exemption is necessary.

Thus far this technology has been most widely employed for the treatment of supraventricular tachycardia and accessory pathway ablation.  However, in particular patients with atrial fibrillation will benefit from the magnetic navigation procedure, since the integration of 3D mapping and imaging information will lead to reduced procedure duration and fluoroscopy exposure. 

Exclusion criteria for magnetic navigation

• As for all invasive studies, the existence of an intracardiac thrombus excludes a magnetic navigation procedure.
• Patients that have been implanted with a pacemaker system, can not be investigated magnetically (Magnet-mode of pacemaker).
• Patients with ICD implants need to be carefully investigated since older systems may not allow exposure to magnetic fields.
• Patients with cochlear implants.
• Patients with large metal implants.
• Patients with claustrophobia.
• Patients with a body weight above 150 kg. 

How many patients have been treated so far using magnetic navigation?

Since the introduction of magnetic navigation in clinical cardiology and invasive electrophysiologic studies more than 10,000 patients have undergone such a procedure.  The team at Royal Brompton Hospital includes some of the longest experience using this system in the world,  due to the inclusion of specialist consultant Dr Sabine Ernst who previously lead the first European magnetic navigation laboratory in Hamburg, Germany (opened in May 2003).

What are the benefits for the patient?

Since the navigation of the ablation catheter is guided by the magnetic field, the movement of the soft catheter inside the body is very precise. This allows the operator to navigate with little fluoroscopy (about 20 per cent) and virtually no collateral damage (such as perforation). A dedicated integration of 3D mapping information on the fluoroscopy screens further facilitates the orientation of the operator.

For some supraventricular tachycardias, the number of additional diagnostic catheters has been reduced from typically four in conventional procedures to a single one for magnetic navigation. This reduces the risk of local complications at the puncture sites and increases patient comfort in the follow-up period.

Is the ablation technique different from the conventional ablation procedure?

No, the difference lies in the method of navigation for the ablation catheter to the target site.  In conventional procedures, the operator is positioned next to the patient and steers the catheters manually under fluoroscopic guidance.  Using magnetic navigation, the operator will insert the diagnostic catheters in a conventional way, but will steer the ablation catheter remote-controlled via the magnetic navigation workstation from the control room.  The ablation itself, which is the heating of the cardiac tissue that is responsible for the abnormal heartbeat, is exactly the same in both catheter procedures.

How can I find out if an arrhythmia is eligible for magnetically guided ablation procedure?

We first need to obtain sufficient medical information about an individual and their arrhythmia before we decide whether it is appropriate to offer a magnetically guided ablation procedure.

Before accepting a referral we need a short summary of the prospective patient's medical history and contact details for their GP or other referring physician.  It is important that if the patient's arrhythmia has been documented on an electrocardiogram (ECG) that we are supplied with a copy.