Simple Heart Ultrasound Measure Flags Hidden Atrial Fibrillation After Mysterious Strokes

Every year, hundreds of thousands of people worldwide suffer a stroke or transient ischemic attack that leaves doctors puzzled. The clot that cut off blood flow to the brain clearly came from somewhere, yet no obvious culprit—a blocked neck artery, a large-vessel occlusion, or a documented heart rhythm disorder—can be found. Cardiologists call these events embolic strokes of undetermined source, or ESUS, and they have long suspected that many of them are actually caused by silent, intermittent episodes of atrial fibrillation that no monitor happened to catch. The problem is knowing which patients deserve the invasive, expensive, and prolonged rhythm surveillance needed to unmask that hidden arrhythmia. A new study published in Clinical Research in Cardiology suggests that a routine echocardiogram, interpreted through a novel index, may hold the answer.

The research, led by Chiara Giordano and Giacomo Gamberini of the University of Milan together with senior author Stefano Carugo and a team spanning the Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, focused on a measurement called the Left Atrial Volumetric–Mechanical Coupling Index, abbreviated LACI-VM. The index is elegantly simple: it is calculated by dividing the left atrial volume index—the size of the heart’s upper left chamber adjusted for body surface area—by a′, the late diastolic mitral annular velocity measured with Doppler tissue imaging. That denominator reflects how well the atrium contracts during its mechanical squeeze. A large atrium that still contracts vigorously produces a modest ratio; a large, sluggish atrium produces a high one. In other words, LACI-VM fuses two complementary dimensions of atrial disease into a single number obtainable from any standard transthoracic echo.

The rationale is rooted in the biology of atrial cardiomyopathy. When the left atrium is chronically exposed to high filling pressures, hypertension, or aging-related fibrosis, it enlarges and its muscle fibers are progressively replaced by scar tissue. Electrical conduction through this remodeled chamber becomes slow and heterogeneous, creating the substrate for the reentrant circuits that drive atrial fibrillation. Structural dilation alone, captured by the left atrial volume index, has long been known to predict AF detection after cryptogenic stroke. Mechanical dysfunction, assessable through atrial strain or annular velocities, adds independent information. By combining both, LACI-VM aims to capture the full anatomical and functional footprint of an atrium that is primed to fibrillate.

The Milanese team applied this concept to 285 consecutive patients admitted with an embolic stroke or transient ischemic attack of undetermined source. All underwent transthoracic echocardiography during the index hospitalization, including measurement of LACI-VM and of the related Left Atrioventricular Coupling Index, or LACI, which is defined as the ratio of left atrial end-diastolic volume to left ventricular end-diastolic volume and reflects atrioventricular uncoupling. The patients, whose median age was 71 years and of whom 43 percent were women, were then followed for new-onset atrial fibrillation. Over a median follow-up of 10.9 months, AF appeared in 24 patients, or 8.4 percent of the cohort—and, critically, 62 percent of those events occurred within the first year, underscoring how early the arrhythmia tends to declare itself after a cerebral embolic event.

The statistical results were striking. LACI-VM was significantly higher in patients who went on to develop atrial fibrillation, and after multivariable adjustment for confounders it remained independently associated with incident AF, with a hazard ratio of 6.64 and a confidence interval of 1.34 to 59.88, reaching a p-value of 0.041. A hazard ratio approaching seven means that patients with an impaired coupling index faced roughly a six- to seven-fold higher rate of AF detection than their counterparts with preserved values, a magnitude of effect rarely seen for a single echocardiographic parameter. By contrast, the purely volumetric LACI showed only a non-significant overall association, with a hazard ratio of 2.28 and a p-value of 0.09, and its predictive power appeared confined to events occurring within the first twelve months. The comparison suggests that atrial mechanical performance, not merely chamber size, carries the prognostic signal that matters for unmasking occult AF.

Perhaps the most clinically actionable finding emerged when the researchers combined LACI-VM with an assessment of left ventricular filling pressures, expressed as the E/e′ ratio—the ratio of early transmitral flow velocity to early diastolic mitral annular velocity. Patients whose LACI-VM remained below 2.5 and whose E/e′ was 10 or lower experienced an AF incidence of only about 2 percent, identifying a genuinely low-risk subgroup in whom intensive, invasive rhythm monitoring may be safely deferred. At the opposite extreme, when both the coupling index was elevated at 2.5 or above and filling pressures were elevated above 10, the AF risk climbed to roughly 20 percent—a tenfold difference between the two phenotypes. This layered approach transforms a single ultrasound number into a practical decision tool: one echo study, performed during the index admission, can separate stroke survivors who need implantable loop recorders from those who can be managed with conventional, less burdensome surveillance.

The implications reach into one of the most contested corners of stroke medicine. Randomized trials such as CRYSTAL-AF and FIND-AF, which used implantable or prolonged monitoring, established that occult atrial fibrillation is common after cryptogenic stroke, detecting it in a meaningful fraction of patients over months to years. Yet prolonged monitoring is costly, and debates persist about how intensively every ESUS patient should be screened, whether oral anticoagulation benefits all detected subgroups, and how to weigh the burden of devices against the risk of recurrent embolism. European Society of Cardiology consensus statements have repeatedly called for better tools to stratify patients. An index that costs nothing beyond an echocardiogram already being performed fits that need precisely, potentially concentrating expensive monitoring resources on the patients most likely to benefit.

The study also builds on a growing literature. LACI-VM was first proposed as a predictor of outcomes in heart failure with reduced ejection fraction, and subsequent work has linked atrioventricular coupling indices to cardiovascular events in the Multi-Ethnic Study of Atherosclerosis, to new-onset AF in hypertrophic cardiomyopathy, and to heart failure and AF in the general population. Earlier investigations specifically in ESUS populations reported that the volumetric-mechanical coupling index associated with AF detection, and the Milan group itself had previously shown that peak atrial longitudinal strain can catch atrial fibrillation in sinus-rhythm patients admitted for cerebral ischemic events. The present analysis extends this line by demonstrating independent prediction in a dedicated ESUS and TIA cohort and by pairing the index with filling pressures to define a truly low-risk stratum.

Certain caveats temper the enthusiasm. The investigation was retrospective and conducted at a single center, and the confidence interval around the hazard ratio is wide, reflecting the modest number of endpoint events; larger, prospective, multicenter validation will be needed before the index enters guidelines. The follow-up duration of roughly eleven months captures the early window in which most events occurred but may miss later arrhythmia emergence. Still, the direction of the evidence is coherent with atrial physiology, the measurement is reproducible with standard techniques endorsed by the American Society of Echocardiography and the European Association of Cardiovascular Imaging, and the effect sizes are large enough to be clinically meaningful even in a small cohort.

For patients and clinicians alike, the message is compelling. A stroke whose cause remains invisible may not be invisible to the heart itself: the left atrium often carries the fingerprints of the arrhythmia that launched the clot. By reading those fingerprints through a simple ratio of atrial size to atrial squeeze, obtained from an ultrasound exam already part of routine care, physicians may soon be able to tailor rhythm monitoring with far greater precision—intensifying surveillance for the one in five patients at highest risk while sparing the many at genuinely low risk from unnecessary devices and prolonged uncertainty. In a field where every undetected episode of atrial fibrillation represents a potential second, potentially devastating stroke, a cheap, fast, and widely available predictor is exactly the kind of advance that could change practice.

Subject of Research: Prediction of early new-onset atrial fibrillation after embolic stroke or TIA of undetermined source using echocardiographic left atrial volumetric–mechanical coupling indices

Article Title: Echocardiography-derived Left Atrial Volumetric–Mechanical Coupling Index predicts early new-onset atrial fibrillation after embolic stroke/transient ischemic attack of undetermined source

Article References: Giordano, C., Gamberini, G., Faggiano, A., Garau, L., Conti, G., D’Andria, P. F., Moda, F., Mallardi, G., Saviano, M., Bonato, S., Ghione, I., Lanfranconi, S., Gherbesi, E., Santangelo, G., Ruscica, M., Bursi, F., & Carugo, S. (2026). Echocardiography-derived Left Atrial Volumetric–Mechanical Coupling Index predicts early new-onset atrial fibrillation after embolic stroke/transient ischemic attack of undetermined source. Clinical Research in Cardiology. https://doi.org/10.1007/s00392-026-03041-y

Image Credits: AI Generated

DOI: 10.1007/s00392-026-03041-y

Keywords: atrial fibrillation, embolic stroke of undetermined source, echocardiography, left atrium, LACI-VM, left atrioventricular coupling index, transient ischemic attack, rhythm monitoring, implantable loop recorder, atrial cardiomyopathy, E/e′ ratio, stroke prevention