WHEN IS A GOOD HOLTER REPORT NOT A GOOD HOLTER REPORT?

The short answer to the title question is, “When the Holter recording wasn’t read and interpreted by a board certified veterinary cardiologist.”  But actually, it’s not nearly as simple as that, and this blog is going to be neither a paean to all board certified cardiologists nor an exposé of the commercial services that provide inexpensive, technician-read holter reports with a super-fast turnaround. Hopefully, this account will give other Boxer breeders the same kind of “heads up” I got recently when I had occasion to send the same Holter tape, first to a commercial Holter reading service, and then to a board certified veterinary cardiologist.

A Tale of Two Holter Reports

Before I begin this little cautionary tale, let me say that I don’t pretend to be an expert on heart disease. In fact, beyond a short CPR course that I’ve mostly forgotten, I’ve had no medical training whatsoever. What I’ve learned about Boxer Cardiomyopathy, or ARVC as it’s now called, was “absorbed” from listening (and taking notes) to the presentations of researchers and other experts as secretary to the ABC Health & Research Committee and the ABCF Board of Trustees, and by taking advantage of the expert knowledge of the cardiologist who treats my own dogs and who is never too busy to answer questions or explain heart disease to his clients.

This saga began with a 5 year-old health-tested bitch that had never been bred and a very promising young dog whose parents had been health tested and who had “passed” several health tests himself (DM clear, SAS clear & Thyroid normal), but had not yet been Holtered. The two prospective breeding partners complemented each other perfectly, so I threw a Holter monitor on the young dog and sent it off to one of the commercial Holter reading services, asking that they return the tape to me after reading it.  I usually send my Holter tapes to a cardiologist for interpretation due to a friend’s sad experience with one of the “quickie” services, but I wanted a faster turnaround than the cardiologist provided for a pre-breeding clearance.

In only a few days, I had a report that showed 5 VPCs and zero (0) supraventricular ectopics (also called APCs, or Atrial Premature Contractions). The tape was returned shortly thereafter. Because the early days of my breeding program were haunted by Boxer Cardiomyopathy (before anyone knew what it was), I wasn’t completely happy with 5 VPCs in such a young dog, but it was now or never for my bitch, so I proceeded with the breeding. Then I mailed the tape to the cardiologist to whom I usually send Holter recordings for interpretation, hoping that some of those 5 VPCs were just artifacts.

The cardiologist’s report was sent to me within two weeks and read, in part:

 “There were a total of 4, Ventricular Premature Beats (VPC’s or PVC’s) during the monitoring period. There were frequent singular atrial premature beats during the recording period. There were runs of supraventricular tachycardia during the monitoring period. The singular APCs are not as concerning as the runs of SVT at fast rates. The longest run of SVT was 9 beats duration…”

“Diagnosis: Abnormal 24 hour holter study”

“Recommendations: I recommend treatment of these arrhythmias specifically to try to slow down or abolish the runs of fast SVT. I suggest we begin Atenolol 25 mg tabs --1/2 tab by mouth twice daily....This type of arrhythmia is not the classic arrhythmia noted in Boxers affected with Arrhythmogenic Right Ventricular Cardiomyopathy in that they are usually ventricular in origin. Some Boxers will have this rhythm as the first sign of ARVC and follow up holter studies may show the development of ventricular arrhythmias. Alternatively this can be an arrhythmia problem noted in Boxers or other breeds which is not associated with ARVC.”

Whoa! Only 4 VPCs – fewer than on the report from the commercial service – but runs of supraventricular tachycardia and a cardiologist’s recommendation of treatment with Atenolol?  Where did that come from?!  The first report said there were zero supraventricular ectopics!

A Third Holter Report + an Echo

I immediately called my own cardiologist to discuss the second Holter report, and to arrange for rental of a digital Holter monitor (my own monitor is analog, and my cardiologist no longer processes analog recordings or tapes). Shortly after the monitor was returned to the second cardiologist, the doctor called personally to give me the bad news: Although interpretation of the recording wasn’t yet complete, the third Holter report looked very much like the second. At that point, I made an appointment for a face-to-face consult at the cardiologist’s clinic, which included an echo to rule out structural heart disease.

After reviewing the third Holter report at my cardiologist’s clinic a week or so later, it became obvious that there was something very, very wrong with the first Holter reading done by the commercial service. Remember the zero (0) Supraventricular Ectopics noted on the first report? My cardiologist recorded 23,689 isolated (single) supraventricular events plus 5 Couplets and 20 Runs. That’s 23,825 supraventricular ectopics, or 18% of the dog’s total heartbeats!  Cardiologist # 2 also suggested that we consider medication (sotalol) to slow the fast heart rate.

Frankly, I was blown away. How could that first Holter have been so completely out of the ballpark? Had the Holter service sent some other dog’s report?  But that couldn’t be, because the same tape had been returned to me and sent on to the first cardiologist; and the second cardiologist had produced a similar report from a different (digital) recording!

As soon as I got home, I fired off an email to the commercial Holter reading service to which I had originally sent the tape.  I attached a copy of their Holter report showing 5 VPCs and zero supraventricular ectopics and excerpts from the reports generated by the cardiologists. A company rep answered in short order, and said he was going to look into what had happened and would get back to me.

The next morning, I received a phone call from the manager of the Holter service. We talked for about 30 minutes.  His attitude was both apologetic and defensive. At the end of our conversation, I understood what had happened but was – there’s no other word for it – incredulous.

Apparently, because a few supraventricular ectopics (Atrial Premature Contractions) are no big deal (both cardiologists had said much the same thing), and because part of the canine side of the business came from individual owners who were primarily concerned about VPCs and ARVC and didn’t know what supraventricular ectopics were (I certainly hadn’t known), those concerned owners tended to call the service for an explanation when they saw numbers in the “Supraventricular Ectopics” column of the report. So the people who dealt with dog owners (rather than with the human and veterinary cardiologists who used the service, presumably) decided that they would stop confusing their customers with irrelevant information and simply stopped collecting and reporting ANY supraventricular activity to individual dog owners.

As noted, the representative I spoke with was both defensive and apologetic. He repeatedly made the point that a little atrial arrhythmia was usually nothing to be worried about, but admitted that there was nothing usual about nearly twenty-four thousand atrial ectopics. He also admitted that the report generated by his company had, in effect, given my young dog a “pass,” when the dog clearly had a condition that needed to be addressed by a cardiologist and that would have been immediately obvious if the “Supraventricular Ectopics” column had not shown zeros across the board.

By the end of our conversation, the Holter company representative had assured me that in the future, their reports would include supraventricular ectopics; and I was left of two minds about the whole experience: On the one hand, I believe that in the absence of a reliable gene test, all North American Boxer breeders and owners should Holter their breeding animals at least once a year and that these fast, inexpensive Holter services make it possible for everyone to do that – no excuses!  And I understand that my dog presented an unusual situation that I may never encounter again. I still don’t know exactly what’s wrong with him, or whether the problem is hereditary or might be atrial myocarditis caused by something like Lyme disease.

On the other hand, it was unsettling to find that the management of a Holter reading service had felt their customers were incapable of understanding all the information the service had been paid to provide and so decided not to provide some of it; and it’s only human nature to ask, what else did they miss? 

The fact is, while some veterinary cardiologists are prohibitively expensive, some are quite reasonable and are willing to work with breeders. My inclination at this point is to say, if you really care about Boxer heart disease, find one of those “reasonable” cardiologists. Or at the very least, the next time you send a Holter recording to one of the fast, cheap Holter reading services, ask that their in-house cardiologist read and interpret your tape, even if it costs a little extra.