Low Flow Aortic Stenosis Outcomes Driven by Hemodynamics Rather Than Cause

Clinical outcomes in individuals diagnosed with severe low-flow aortic stenosis are governed predominantly by the underlying low-flow hemodynamic state and concurrent atrioventricular valve regurgitation rather than by the specific anatomical or physiological etiology responsible for reduced transvalvular flow, according to a comprehensive observational cohort study published in the journal Cardiovascular Ultrasound. The clinical investigation, conducted by an academic research team led by Giorgio Fiore and Eustachio Agricola, systematically evaluated the distinct causes, relative prevalence, and prognostic implications of reduced flow across a well-characterized cohort of patients presenting with severe aortic stenosis. Aortic stenosis represents the most common valvular heart disease and the primary indication for surgical or transcatheter valvular interventions in aging global populations, placing substantial operational and financial demands on modern healthcare infrastructures. Although many affected individuals maintain preserved left ventricular ejection fraction and normal transvalvular flow rates, a substantial and clinically vulnerable subset presents with low-flow hemodynamics, a condition historically associated with elevated peri-procedural mortality, advanced disease staging, impaired ventricular-arterial coupling, and heightened susceptibility to elevated cardiac afterload.

To evaluate these complex pathophysiological relationships, the researchers executed a single-center retrospective observational cohort investigation involving four hundred and eight consecutive adult patients aged eighteen years or older who received an echocardiographic diagnosis of severe low-flow aortic stenosis at San Raffaele University Hospital in Milan, Italy, between November 1, 2016, and October 31, 2022. Severe low-flow aortic stenosis was strictly defined in accordance with standardized international clinical consensus recommendations, requiring both an aortic valve area of no more than one square centimeter (or an indexed aortic valve area of no more than 0.6 square centimeters per square meter of body surface area) and a stroke volume index of no more than thirty-five milliliters per square meter. The investigators deliberately excluded individuals who had undergone previous aortic valve replacement or repair procedures. Clinical variables, historical medical records, laboratory parameters, and comprehensive transthoracic echocardiographic examinations were systematically extracted from institutional electronic medical software archives and consolidated within an audited clinical repository approved by the local institutional review board.

Standardized diagnostic echocardiography across the study population was conducted utilizing commercial high-resolution ultrasound platforms, specifically GE Vivid E9, GE Vivid E95, and Philips EPIQ 7 systems, adhering strictly to established clinical practice guidelines. The severity of aortic stenosis was confirmed through a multiparametric diagnostic evaluation incorporating peak transaortic velocity, mean transvalvular pressure gradient, and continuity equation calculations of aortic valve area. Stroke volume indexed to body surface area was derived from velocity-time integral calculations obtained within the left ventricular outflow tract alongside direct planar diameter measurements acquired from the parasternal long-axis acoustic window. Concomitant mitral and tricuspid valve regurgitation were categorized into five discrete ordinal tiers: absent or trivial (grade 0), mild (grade 1+), moderate (grade 2+), moderate-to-severe (grade 3+), and severe (grade 4+). Right ventricular systolic function was determined through tricuspid annular plane systolic excursion, tissue Doppler imaging of the lateral tricuspid annulus, and fractional area change, with overt right ventricular dysfunction formally defined by the concurrent presence of at least two abnormal diagnostic parameters.

The study cohort exhibited advanced demographic maturity and an extensive burden of cardiovascular comorbidities, characterized by an overall mean age of eighty plus or minus eight years and a female representation of 47.5 percent. At initial presentation, nearly all patients reported significant functional limitations, with 42 percent classified as New York Heart Association functional class II and 45 percent presenting in functional class III. The underlying pathophysiological drivers of low transvalvular flow separated the cohort into two broad diagnostic categories: classical low flow, characterized by reduced left ventricular ejection fraction below 50 percent, and paradoxical low flow, characterized by preserved left ventricular ejection fraction of 50 percent or greater. Reduced left ventricular ejection fraction constituted the primary cause of low flow across the overall population, accounting for two hundred and twenty-eight patients, or 55.9 percent, who demonstrated an average ejection fraction of thirty-four plus or minus eight percent. Patients presenting with preserved ejection fraction numbered one hundred and eighty, representing 44.1 percent of the total cohort with an average ejection fraction of sixty plus or minus six percent.

Substantial demographic and clinical divergences emerged when comparing individuals presenting with preserved versus reduced left ventricular ejection fraction across the study cohort. Patients with preserved left ventricular function were significantly older, had a smaller mean body surface area (1.71 plus or minus 0.20 square meters compared to 1.80 plus or minus 0.20 square meters, p less than 0.001), were predominantly female (67.2 percent versus 32.0 percent, p less than 0.001), and demonstrated a significantly higher baseline prevalence of advanced atrioventricular valve regurgitation of grade 3+ or greater. Conversely, patients presenting with reduced ejection fraction exhibited significantly higher baseline rates of ischemic heart disease, including diagnosed coronary artery disease (61 percent versus 41.1 percent, p less than 0.001), prior documented myocardial infarction (31.6 percent versus 12.8 percent, p equals 0.03), diabetes mellitus (43 percent versus 29.4 percent, p greater than 0.01), and arterial hypertension (87.3 percent versus 76.7 percent, p equals 0.015).

In the paradoxical low-flow subgroup of one hundred and eighty individuals with preserved left ventricular ejection fraction, two experienced echocardiographers independently adjudicated the dominant underlying etiology into five predefined pathophysiological categories. Discrepancies were resolved through unblinded consensus review, yielding an unweighted Cohen’s kappa of 0.94 (95 percent confidence interval, 0.91 to 0.98, p less than 0.001) and an absolute inter-observer diagnostic agreement of 95.6 percent. Mixed etiologies represented the single most prevalent mechanism, identified in sixty-five patients (36.1 percent), reflecting complex multifactorial combinations such as coexisting atrial fibrillation, moderate valvular lesions, or right ventricular dysfunction where no single pathological feature predominated. A small left ventricular cavity—defined by relative wall thickness exceeding 0.43 alongside an indexed end-diastolic volume of forty milliliters per square meter or less—constituted the second most frequent cause, identified in fifty-eight patients (32.2 percent). Isolated significant mitral regurgitation accounted for thirty-nine cases (21.7 percent), isolated significant tricuspid regurgitation accounted for thirteen cases (7.2 percent), and isolated hemodynamically significant mitral stenosis accounted for five cases (2.8 percent).

Definitive therapeutic management following baseline evaluation was established via multidisciplinary Heart Team consensus, leading to invasive aortic valve replacement in three hundred and two patients, representing 74 percent of the total study population. Transcatheter aortic valve replacement, executed entirely via transfemoral vascular access, was performed in two hundred and forty-five patients (60 percent), whereas surgical aortic valve replacement was completed in fifty-seven individuals (14 percent). Ninety-one patients (22.3 percent) were managed non-invasively through conservative medical therapy, while post-evaluation procedural records were unavailable for fifteen individuals (3.7 percent). Notably, patients presenting with a baseline mean transvalvular gradient of forty millimeters of mercury or greater were substantially more likely to undergo invasive valve replacement, with only 5.1 percent of these individuals managed conservatively compared to 29.2 percent of patients presenting with lower transvalvular gradients (p less than 0.001).

Long-term clinical follow-up extending beyond six months was successfully completed for three hundred and two patients (70.6 percent), encompassing two hundred and thirty individuals who received invasive aortic valve replacement and seventy-two managed conservatively (p equals 0.3). Over a median observational follow-up duration of fifteen months (interquartile range, 6 to 36 months), one hundred and fifty-nine patients, or 52.6 percent, met the primary composite endpoint of all-cause mortality and heart failure hospitalization. Overall, one hundred and eight patients died (35.8 percent), with sixty-seven deaths classified as cardiovascular and forty-one attributed to non-cardiovascular causes, while ninety-one individuals experienced hospital admissions for decompensated heart failure. Time-to-event survival curves revealed no statistically significant differences in primary endpoint occurrence between classical reduced ejection fraction and paradoxical preserved ejection fraction groups (hazard ratio, 1.16; 95 percent confidence interval, 0.84 to 1.59; log-rank p equals 0.4). Similarly, among individuals with preserved ejection fraction, cumulative event-free survival demonstrated no significant divergence across the specific underlying low-flow etiologies (log-rank p equals 0.95).

Multivariable Cox proportional hazards modeling, adjusted for age, sex, and univariable predictors with aortic valve replacement entered as a time-dependent covariate, identified several independent clinical determinants of the primary composite endpoint. Severe grade 4+ mitral regurgitation (adjusted hazard ratio, 1.71; p equals 0.04), severe grade 4+ tricuspid regurgitation (adjusted hazard ratio, 1.47; p equals 0.04), and baseline New York Heart Association functional class greater than II maintained robust independent associations with adverse clinical outcomes. In contrast, undergoing invasive aortic valve intervention (adjusted hazard ratio, 0.76; p less than 0.001) and displaying a baseline mean transvalvular pressure gradient of forty millimeters of mercury or greater (adjusted hazard ratio, 0.39; p less than 0.001) functioned as substantial, independent protective factors. When evaluating secondary clinical endpoints separately, invasive intervention conferred marked protection against all-cause mortality (hazard ratio, 0.32; 95 percent confidence interval, 0.24 to 0.42; p less than 0.001) and cardiovascular mortality (hazard ratio, 0.34; 95 percent confidence interval, 0.24 to 0.47; p less than 0.001). Under Fine-Gray competing-risks analysis accounting for death, severe mitral regurgitation markedly increased the risk of heart failure hospitalization (subdistribution hazard ratio, 1.97; 95 percent confidence interval, 1.68 to 2.30), while severe tricuspid regurgitation reached statistical significance exclusively in the subdistribution model (subdistribution hazard ratio, 1.61; 95 percent confidence interval, 1.30 to 2.00).

To rigorously explore the independent prognostic contributions of stroke volume index and pressure gradients, the investigators compared the study population against a one-to-one age-matched control cohort of three hundred and two patients presenting with normal-flow, high-gradient severe aortic stenosis from the same medical institution. Kaplan-Meier survival analyses demonstrated a distinct gradient of clinical risk across three progressive hemodynamic groups: individuals with normal-flow, high-gradient aortic stenosis experienced the most favorable prognosis; patients with low-flow, high-gradient severe aortic stenosis exhibited intermediate clinical risk; and individuals presenting with low-flow, low-gradient aortic stenosis suffered the worst long-term outcomes (all comparisons p less than 0.001). The age-matched normal-flow cohort exhibited significantly lower rates of coronary artery disease, less atrioventricular valve disease, lower degrees of right ventricular systolic dysfunction, and markedly fewer subjective clinical symptoms, suggesting that the adverse trajectory of low-flow aortic stenosis is driven primarily by extensive underlying myocardial and extravalvular damage.

The study authors highlighted several methodological limitations inherent to their research design that warrant careful consideration when interpreting these conclusions. The investigation was retrospective in nature and conducted within a single specialized tertiary referral hospital for valvular heart disease, introducing potential institutional selection biases that may constrain the direct generalizability of the findings to broader community populations. A considerable proportion of patients were excluded from the survival analysis due to follow-up intervals under six months or loss to contact, although baseline profiles between retained and excluded patients remained broadly comparable. Furthermore, quantitative computed tomography aortic valve calcium scoring and dobutamine stress echocardiography data were unavailable for a substantial number of patients who had undergone initial diagnostic testing at external referring centers. The cohort lacked systematic documentation regarding underlying cardiac amyloidosis, recurrent hospital admissions were not tracked to permit recurrent-event modeling, specific etiologies underlying systolic impairment in the reduced ejection fraction cohort were not characterized, and the control comparison was matched strictly on age rather than comprehensive propensity matching. Nevertheless, the authors concluded that low-flow severe aortic stenosis represents an advanced systemic disease state where clinical prognosis is driven by low flow and atrioventricular valve dysfunction rather than the specific low-flow etiology.

Subject of Research: Prevalence, etiologies, and clinical outcomes of severe low-flow aortic stenosis

Article Title: Prevalence and prognostic implications of different aetiologies of low flow aortic stenosis

Article References: Fiore, G., Biondi, F., Fabris, M., Cunsolo, P., Morosato, M., Gamardella, M., Ingallina, G., Stella, S., Ancona, F., Tavernese, A., Margonato, D., Belli, M., Castiglioni, A., Montorfano, M., Maisano, F., & Agricola, E. (2025). Prevalence and prognostic implications of different aetiologies of low flow aortic stenosis. Cardiovascular Ultrasound, 24(1), Article 3. https://doi.org/10.1186/s12947-025-00363-1

Image Credits: AI Generated

DOI: 10.1186/s12947-025-00363-1

Keywords: Aortic Stenosis, Cardiovascular Ultrasound, Low-Flow Aortic Stenosis, Echocardiography, Heart Failure, Transcatheter Aortic Valve Replacement, Surgical Aortic Valve Replacement, Mitral Regurgitation, Tricuspid Regurgitation, Prevalence, prognostic, implications