A case of PARSON: ??????

I walked into my office one morning and found a pacemaker printout on my desk. Shortly thereafter I was enthusiastically engaged by a Medtronic employee asking me whether I had seen the printouts, I had not so I hastily reviewed them. Over the past couple of months, it seems like every chance a Medtronic employee gets to tell me about their atrialATP (aATP) therapies, they jump at the opportunity to do so. These poor folks however have been repeatedly stonewalled by me whenever they try to talk about these aATP therapies. Truth is, I did try these aATP therapies after the publication of the MINERVA trial. But despite the trials purported significant reductions in greater than 1 day, 7 day or progression to permanent atrial fibrillation, I failed to see even one patient with successful termination using aATP therapies. Ostensibly, someone recently in Medtronic Sales/Marketing has instructed their employees to highlight Medtronic's aATP therapies; whereas in reality, someone needs to tell Sales/Marketing at Medtronic that currently the greatest 'highlight' for Medtronic pacemakers is their lack of remote monitoring (not to be confused with remote interrogation), which unlike MRI or aATP therapies, has clearly demonstrated morbidity and mortality benefits in the patients we care for. Irrespective, with great joy this Medtronic employee was disproving my hollow assessment that aATP therapies never work by placing this provocative tracing on my desk. I initially sarcastically offered congratulations for finding an actual patient in whom this algorithm worked and told them something to the effect of "even a blind squirrel finds a nut". As time allowed and since this successful therapy was such a novelty, I decided to take a closer look at the tracings. After this review, I defiantly handed the tracings back to the Medtronic employee and told them that they should be embarrassed for having placed this on my desk. Why did I react with such contempt?

My Explanation (see marked up tracings below)

In this printout we do see the successful termination of a tachycardia using atrialATP (aATP). As we examine the event graph, we identify "railroad tracks" in the atrial signal. This is usually due to far-field oversensing of the ventricular signal on the atrial channel however we also see this when we have short-coupled atrial events on the marker channel, as in this case atrial-refractory:atrial-paced (AR-AP). We then see a sudden discontinuation of the "railroad tracks" followed by a tachycardia at approximately 280 ms. Interestingly we then notice what looks like "narrow railroad tracks" followed by our unsuccessful aATP Ramp1. These "narrow railroad tracks" suggests that perhaps alternating flutter circuits are maintaining the tachycardia at this point. After the failed aATP, the tachycardia becomes more regular, with some intermittent "narrow railroad tracks", followed by the successful aATP Ramp2.

 As I mentioned, the "railroad tracks" are attributable to the AR-AP events. While we cannot see the electrograms to say with certainty, what presumably happens is that the final AP event occurring prior to the initiation of tachycardia captures the atrium. This atrial capture results in short-coupling of the sensed AR-captured AP and thus the induction of atrial flutter. My supposition is that the prior short coupled events were sensed AR-noncaptured AP events, which is why the flutter was not being induced; without electrograms however we cannot say for sure.

 While the Medtronic employee was correct in that the aATP was in fact successful, what they failed to recognize was that this is another case of what I have termed PMF: pacemaker mediated fibrillation, or in this case pacemaker mediated flutter. Instead of touting aATP, the correct intervention would have been to shorten the post-ventricular atrial refractory period (PVARP) such that the AR is properly sensed (AS). This adjustment would prevent the subsequent AP event from occurring short-coupled and presumably the induction of this PMF event. Conversely, Medtronic has an algorithm termed NCAP, noncompetitive atrial pacing, whereby an AR event results in a programmed delay in the next delivered AP event; if available on this device, NCAP should have been initiated or the programmed delay extended.

 I suggested that this was a case of arson, whereby the pacemaker set the fire (PMF) and then played the role of hero (aATP). You do not get credit for being a hero if you are an arsonist. A case of PARSON: Pacemaker ARSON.