September 01, 2013

There can be little doubt that future electrophysiologists will scoff at the notion of leaving permanent hardware in the human heart. Pacemakers will become as dumb as Swan-Ganz catheters. Yet until pacemaker cells are implanted instead of silicone and titanium, patients with bradycardia have only two options—device or disease.

Cardiac pacing is one of the oldest aspects of electrophysiology. There were pacemakers well before there were electrophysiologists. It's harder now to generate much interest in pacing; the niftiness of catheter ablation, cardiac resynchronization therapy, and novel anticoagulants have overshadowed the simple pacemaker. New stuff replaces old stuff—as in a blog (grin).

Worry Not

I have found a couple of thought-provoking issues surrounding modern-day cardiac pacing. Snaking leads, ablating aberrant tissue, and delivering shocks aren't the only cool aspects of electrophysiology. Thinking ranks up there, too.

For the Village 1 crowd (EP) at ESC Congress 2013 , two important issues in cardiac pacing rose to the level of notation:

Avoiding Harm: Are We Killing Our Patients Softly With RV Pacing?

One of the most important aspects of cardiac pacing is avoiding harm. Minimalism rules—especially when it comes to the RV lead. Dr C Butter from Berlin, Germany, gave an excellent presentation: Is there a role for alternate RV apical pacing?

If you are like me, you worry about the RV lead—especially in the apex. Although technically easier to simply let the lead fall into the apex, I worry about an increased risk of perforation and subsequent harmful effects of dyssynchrony. Do no harm.

It makes sense, therefore, to get the RV lead closer to the intrinsic conduction system in the septum. Septal means closer approximation to normal conduction. Truth be told, when V-pacing percentage is going to be high (AV block), I strive for septal lead positioning. But what does the evidence say? You know the danger of doing stuff only because it makes sense

The first thing Dr Butter taught us was to avoid RV pacing if possible. RV pacing associates with worse outcomes, including mortality. We knew that, of course, but I had forgotten that RV pacing causes unfavorable changes in protein expression, mitochondrial density, and myocardial disarray. For some reason, references to cell biology get my attention.

He showed a neat case in which contractility improved with discontinuation of RV pacing even with a PR interval of 400 ms. The issue of how long to wait for intrinsic ventricular activation comes up a lot in patients with both sinus- and AV-node disease. His message was to wait; a late QRS was better than a paced QRS.

Then he went on to the main question: Is RV septal lead positioning worth the trouble?

I'll make it short: the results of clinical trials are inconsistent. We simply do not know. Reasons for trial inconsistencies included undefined sites of lead placement, lack of fluoroscopy controls, undefined pacing percentages, and short follow-up. One thing we do know is that nonapical RV pacing has never looked worse than standard apical placement.

Three other useful facts I learned from his update:

  1. You need multiple fluoroscopy views to confirm a true septal lead position. (See attached reference to EuroPace review.) Look for the RV lead to point posteriorly toward the spine.

  2. RV outflow tract does not equal septal. Given the superior aspect of the RVOT above the true septum, and the possibility of free wall pacing, the "high" outflow tract may not be an ideal location for pacing.

  3. A recent review of data from the  MADIT-RIT trial (Heart Rhythm ) tells us that in patients with CRT, there are no obvious differences in outcomes between RV lead positions—although there was a mysterious increase in ventricular arrhythmia in patients implanted with nonapical sites.

I'd point those interested to this excellent review in the journal Europace . Australian professors Richard Hillock and Harry Mond do more than just a nice job reviewing the literature; they also provide a useful hands-on tutorial.  Although they agree the literature is inconclusive, their belief is obvious:

It seems unfortunate that with the weight of evidence of harm from RV apical pacing and the evidence for benefit from RVOT septal pacing that thousands of patients in the near future will be exposed to the adverse effects of RV apical pacing while we dally. We encourage all cardiologists to actively review their current right ventricular lead positioning preferences.

Magnetic Resonance Imaging With Cardiac Devices:

Referring physicians often ask me to implant an MRI-safe pacemaker. It goes something like this: "this young patient will likely 'need' (gasp) an MRI some day." These words activate my frontal lobe; I don't verbalize the thought . . . "the marketing worked."

The topic of safety with MRI and pacemakers highlights some of my favorite issues to think and write about: making medicine more difficult than it has to be; embracing dogma; big marketing that capitalizes on dogma and fear, and of course, the trade-offs of being "safe."

Prof Ariel Roguin from Haifa, Israel, guided us through 20 minutes on safe MRI imaging with both conventional and conditional pacemakers. That's right; the words safe, MRI, and conventional pacemaker can indeed go together.

A true/false question:

Most patients with conventional pacemakers can undergo MRI without incident?

You can tell where I am going, but I suspect many US physicians would stumble on this one. ProfRoguin's talk helped clarify the issues.

The background here is relevant: The same diseases that lead to MRI scans also increase the risk of having a cardiac device. A rough estimate holds that one in three patients might be indicated for an MRI over the lifetime of their device. This is an important clinical problem.

MRI scanning in patients with devices creates potential trouble through four mechanisms: heating at the lead tip, rotational force (torque) on the device, functional impairment of electronics, and image distortion. Reports of adverse MRI-pacemaker events date back to the 1980s. Though small in number, these events generated tremendous fear. And few things market better than fear.

In the US, one device maker has marketed an MRI-safe pacemaker system. In Europe, multiple device companies have MRI-compatible pacing systems with CE Mark. (No ICDs have CE Mark.) Favorable data from randomized trials of the Medtronic EnRhythm and Advisa pacing systems led to FDA approval for these devices. (In May of this year, Medtronic gained CE Mark for its reliable 5076 lead when paired with a MRI-safe generator.)

We can agree that MRI-compatible devices are backed by solid safety data. The surprise came when Dr Roguin presented data on conventional devices. You know, the dangerous devices, the prohibited ones.

Conventional pacemakers look to be MRI-safe:

Dr Roguin informed us that between 2000 and 2006, over 300 cases have made the published literature. None of these trials report any significant morbidity or mortality. The most recent and largest published series involved 555 MRI scans in 438 patients, with 46% ICDs ( Annals of Internal Medicine ). Using a careful protocol, this group of researchers demonstrated safety in a 1.5-Tesla MRI. No significant morbidity or morality was noted. Only three patients had power-on-reset events.

The most striking safety data, however, come from the MagnaSafe registry (reported previously on heartwire ). Dr Roguin provided the most recent update of this ongoing prospective registry of nonthoracic MRI scans:

  • 1100 MRIs.

  • 816 pacemakers.

  • 284 ICDs.

  • 2141 leads.

  • 21% of patients were pacemaker-dependent.

Significant clinical events, including death, device failure, lead failure, or loss of capture occurred in ZERO cases.

The lack of media coverage of this data is striking. Although Dr Roguin emphasized that a lack of statistical significance does not equal clinical significance, the safety data on doing MRI scans in conventional device patients paints a different story than does dogma and fear.

Trade-offs of Device Selection

Another factor in the equation of device selection are the tradeoffs of choosing MRI-compatible systems. Let's reconsider that young patient who might need an MRI in the future. Would shorter device longevity be important? How about fewer programming features? Or would reports of higher rates of perforations and dislodgements with stiffer MRI-compatible leads matter to the patient?

Conclusion 

Please don't misunderstand; I'm not negative on MRI-compatible pacing systems. In the future, all new devices will be MRI-compatible. What I see as important here are the lessons:

The evidence is clear that most patients with conventional devices can undergo MRI scans. Real data refutes dogma. Second, there are trade-offs to be made with current MRI-safe devices. How to balance these risks must be made with knowledge of real data, not just fear and legend.

JMM

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