Anticoagulation Without Atrial Fibrillation: What Amyloid Does to the Atria Directly
Her heart has never gone into atrial fibrillation. The disease infiltrating her atria may not need to cause that arrhythmia to put her at real risk of a clot forming there anyway.
G.T., a 74-year-old woman, spent decades building custom furniture in a small workshop behind her house, work she only recently scaled back after her hands started giving her trouble — unrelated, as it turned out, to the diagnosis that brought her to cardiology. She was found to have wild-type transthyretin cardiac amyloidosis eighteen months ago after a workup for unexplained heart failure symptoms, confirmed by nuclear scintigraphy, and has been followed since with serial echocardiograms tracking progressive wall thickening and declining strain. She has never had documented atrial fibrillation on any of her monitoring, including a recent two-week patch monitor obtained specifically to look for it.
Her most recent echocardiogram shows a severely dilated left atrium with markedly reduced strain and near-absent mechanical contraction on Doppler assessment, despite an electrically normal sinus rhythm throughout. That distinction matters directly to her risk: cardiac amyloidosis causes atrial myopathy that can produce mechanical standstill even while the atrium's electrical rhythm looks entirely normal, and multiple cohort studies have found intracardiac thrombi and arterial thromboembolic events occurring in amyloidosis patients who were in sinus rhythm throughout, with no atrial fibrillation ever documented. The largest series bearing on this — roughly 1,200 transthyretin amyloidosis patients across four amyloid centers — put the embolic rate in sinus rhythm at 1.3 events per 100 patient-years without anticoagulation and at none among those anticoagulated, while patients with atrial fibrillation still had events at 1.7 per 100 patient-years despite anticoagulation. It also found the CHA2DS2-VASc score did not predict events at all in the sinus-rhythm group and concluded it should not be used to gauge risk in this disease — which leaves a genuine gray zone: retrospective, non-randomized evidence, no trial, and no validated way to score her.
At the amyloidosis cardiology follow-up
I want to name this directly rather than default to 'no AF, no anticoagulation.' Her atrium isn't contracting mechanically, regardless of what the electrical rhythm shows, and multiple cohort studies have found thromboembolic events in amyloidosis patients in sinus rhythm with no AF ever documented. I think her near-absent atrial strain is a real, independent risk marker here.
I agree the mechanism is real, but I want to flag that the literature itself calls this a gray zone, not a settled indication. The signal is retrospective and the tool we normally reach for is no help — the largest series found CHA2DS2-VASc simply doesn't predict embolic events in these patients when they're in sinus rhythm, and explicitly said not to use it here. So we're acting on a mechanism and an imaging finding, with no score to anchor it.
That's not an argument against anticoagulating her, since the alternative is doing nothing about a documented mechanical-standstill pattern — it's an argument for being honest with her that this isn't as clean a decision as anticoagulating a patient with confirmed AF.
Agreed, and I'll frame it that way with her directly. Given her severely reduced atrial mechanical function on imaging and the real, if imperfect, evidence that this predicts thromboembolic risk independent of rhythm, I'd start apixaban at standard dose given her preserved-enough renal function, while being explicit that this is extrapolated from observational data, not a randomized trial in patients who look exactly like her.
Apixaban 5 mg twice daily started. Continued routine rhythm monitoring in case atrial fibrillation eventually develops, though the anticoagulation decision itself was not contingent on that.
Explicitly acknowledged as extrapolated rather than definitively evidence-based, and left that way rather than overstated:
Both physicians agreed the decision rested on a real but imperfectly validated risk marker — her near-absent atrial strain — and that the field's own literature calls anticoagulation in sinus-rhythm cardiac amyloidosis a genuine gray zone, not a settled recommendation her case simply confirms.