Who's at High Risk for ICD, Pacemaker Infection? PADIT Risk Score Could Help

May 13, 2019

SAN FRANCISCO — A scoring system for predicting infection risk in patients considered for pacemaker or defibrillator procedures could help, case by case, with clinical decision-making, such as choice of antibiotic prophylaxis or whether it's wise even to proceed at all, say researchers from the PADIT trial.

The "clinician- and patient-friendly risk score" is based on weightings assigned to five characteristics of a proposed procedure, such as whether it involves an implantable cardioverter defibrillator (ICD) versus a pacemaker, and whether it's the patient's first such device or only the latest, explained David H. Birnie, MD, Ottawa Heart Institute, Ontario, Canada, for theheart.org | Medscape Cardiology.

"I think it will be important for selecting patients in whom you might want to do additional anti-infective measures up front," he said.

"We've already instituted this in our own hospitals," he added. For example, "everybody with an infection risk score of 5 or more gets additional antibiotics."

Some centers that are well off in terms of resources, Birnie said, may decide that patients with scores indicating high risk should have their new device implanted inside an antibiotic-laced absorbable pouch or envelope like the TYRX (Medtronic).

Also, the PADIT infection-risk scoring system should be useful for shared decision-making, he said, such as when weighing the pros and cons of device replacement in some patients.

"If you're an 85-year-old patient with a little bit of renal dysfunction and you've got a primary prevention ICD, it's never gone off, and you're waiting for your third battery change, your risk of infection is 4% and your potential benefit from the defibrillator is virtually zero."

Such a patient's PADIT risk score would be at least 7, and might suggest the likelihood of harm from a new device would be greater than the benefit, he said. "It's going to be very translatable to clinical practice for these types of decisions."

Birnie unveiled the infection-risk scoring system, developed and validated based on the nearly 20,000 patients who participated in the PADIT trial comparing antibiotic strategies with pacemaker or defibrillator procedures, here at the Heart Rhythm Society (HRS) 2019 Scientific Sessions.

The randomized PADIT trial, presented a year ago at these sessions, compared a conventional single-drug antibiotic approach with an "incremental" dosing strategy involving several antibiotics with different pharmacologic half-lives in 19,559 patients undergoing device procedures, mostly pulse-generator replacements but also lead or pocket revisions and upgrades to ICDs or biventricular pacemakers.

The trial did not show a significant difference in infection events between the groups — probably, observers said, because the population's overall infection rate scraped bottom at less than 1% over a year, far below expected.

PADIT investigators later developed and validated their proposed infection risk scoring system based on all of the trial's patients.

"I do think it will change practice," said Fred M. Kusumoto, MD, not a PADIT investigator, who agreed that different centers are likely to interpret and apply the scoring system according to their own practices and means.

"When you're resource-poorer, for example, for someone with a PADIT score of 1, is there really a reason to put one of these antibacterial pouches, even in light of WRAP-IT?" Kusumoto, from Mayo Clinic, Jacksonville, Florida, told theheart.org | Medscape Cardiology. Such pouches, he said, "do add to the cost of device procedures."

The WRAP-IT trial, presented at the March American College of Cardiology 2019 Scientific Session and seemingly on the minds of many here at the HRS meeting, saw a significant 61% drop in infection rate in those of its nearly 7000 patients randomized to receive the TYRX envelope with their device replacement or upgrade or step-up to an ICD with biventricular pacing.

Perhaps the PADIT risk score will be useful in patients such as those treated in WRAP-IT, agreed Ulrika Birgersdotter-Green, MD, University of California, San Diego, as invited discussant after Birnie's presentation of the PADIT risk score data.

That's especially because WRAP-IT suggested that 200 patients would need to be treated with TYRX to prevent one infection, she said, which is "quite high" given the device's added cost.

Birgersdotter-Green said she is not sanguine about risk scores in general "because I sometimes think that they take away from independent thinking. Sometimes we're stating the obvious in numbers that may not be needed. But it's not bad to have this at hand when you have discussions about the patients."

The risk score "I think will be important for shared decision making" if it reliably risk stratifies patients according to their predicted risk of infection from device procedures, Richard I. Fogel, MD, Vincent Medical Group, Indianapolis, told theheart.org | Medscape Cardiology.

It could guide clinicians to intensify anti-infection measures when proceeding with a planned device procedure, "although there are no data to support it," Fogel said. He seemed more impressed by the prospect of using the PADIT score to cancel a proposed device procedure in patients with a predicted infection risk that overwhelms any likely benefit from the device.

Whereas the acronym PADIT is the name of the Prevention of Arrhythmia Device Infection Trial, PADIT as a risk score combines the initials of the underlying individual risk predictors.

The first is "previous procedures," that is, whether or not the patient has already received at least two ICD or pacemaker implantations. The second, "age," refers to whether the patient is younger than 60, 60 to 69, or at least 70 years of age.

Age relates to infection risk in a manner opposite to what most might expect, in that younger patients had more infections in PADIT, Birnie said.

"Decreased renal function" as a score contributor was defined as an estimated glomerular filtration rate (eGFR) <30 mL/min.

"Immunocompromised" refers to being immunosuppressed because of disease or drug therapy.

The last is "type of procedure," or whether the device procedure is for a first or replacement pacemaker, which carry the lowest infection risk; a first or generator-change ICD; a first or generator-change biventricular pacemaker for cardiac resynchronization therapy (CRT); or a pocket and/or system upgrade with addition of new leads, which posed the highest risk.

Odds Ratios (OR) for Hospitalization due to Device Infection by Risk Factors and Assigned Weightings Contributing to Overall PADIT Score
Risk Factor OR (95% CI) P Value PADIT Points
Previous Procedures, ≥2 vs none 3.37 (2.11–5.39) <.001 4
Previous Procedures, 1 vs none 1.51 (0.98–2.31) .059 1
Age <60 vs ≥70 years 1.63 (1.10–2.41) .015 2
Age 60–69 vs ≥70 years 1.43 (0.99–2.05) .54 1
eGFR <30 mL/min 1.48 (1.02–2.13) .037 1
Immunocompromised state 2.24 (1.03–4.86) .042 3
Device revision or upgrade 4.16 (2.74–6.32) <.001 5
CRT vs pacemaker 2.87 (1.83–4.51) <.001 4
ICD vs pacemaker 1.83 (1.14–2.93) .013 2

Based on the PADIT cohort, a total PADIT score of 7 or greater corresponded to a high infection risk, that is 3.5%. About 7.3% of the study population had a total score of at least 7, Birnie said.

At the other end, about 27% had a PADIT score of 0, which corresponded to an infection risk of 0.51%.

Indeed, scores ranging up to 4 were classified as low risk. A total score of 5 or 6, with an infection risk of 1.42%, was considered intermediate.

The scoring system based on easily available predictors is open to further validation and even modification, Birnie said. One of its big limitations is that there may be other potentially useful risk predictors to be gleaned from other datasets. In particular, the PADIT system currently does not account for any antiplatelet therapy or perioperative oral anticoagulation.

"Both of these have been shown to increase the risk of pocket hematoma, which in turn has been shown to increase the risk of subsequent device infection," Birnie cautioned during his presentation.

Birnie, Kusumoto, and Fogel report that they have no relevant disclosures. Birgersdotter-Green discloses receiving honoraria or speaking or consulting fees from Abbott Laboratories, Biotronik, and Medtronic.

Heart Rhythm Society (HRS) 2019 Scientific Sessions: Abstract  S-LBCT02. Presented May 10, 2019.

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