15.2 RV Systolic Function: TAPSE, S-prime, FAC, and Coupling

Acquire the RV-focused view first

Right ventricular systolic function reflects longitudinal shortening, radial inward motion, anteroposterior shortening, and interaction with the septum. The RV's crescent geometry prevents one 2-D plane or one surrogate from representing all components. From a conventional apical four-chamber view, move laterally and rotate until the entire free wall is visible throughout the cycle, the RV basal diameter is maximized, and neither LVOT nor coronary sinus creates an oblique plane. Keep the apex and both tricuspid annuli in view. Foreshortening, a different rib space, and inconsistent rotation change TAPSE alignment and FAC area, so save landmarks for serial studies.

Record rhythm, respiration, blood pressure, oxygen or ventilation state, and recent loading treatment. RV function is highly afterload sensitive: acute pulmonary pressure elevation may abruptly reduce output, while severe TR can unload systolic ejection into the RA and make some motion indices appear better than effective forward performance. Preload, positive-pressure ventilation, pericardial constraint, LV function, and septal mechanics also change the result. Assess RV size, wall thickness, septal shape, TR severity, pulmonary hemodynamics, and IVC findings with function.

Measure three complementary mechanics

TAPSE measures distance, whereas S′ measures peak velocity; they are related but not interchangeable. For TAPSE, do not angle-correct a poorly aligned M-mode cursor. Verify that the annulus, not a lead or adjacent tissue, is tracked. For S′, place a small sample in the basal free-wall myocardium at the annulus, lower wall filters appropriately, and trace the peak systolic tissue signal rather than a valve click or isovolumic spike. Both measures sample one basal region and can miss apical or RVOT dysfunction.

For FAC, use [(RV end-diastolic area − RV end-systolic area) / RV end-diastolic area] × 100. Trace from lateral annulus around the free wall and apex to the septal annulus; include trabeculations, papillary muscles, and moderator band within the cavity. Use maximum and minimum cavity frames and the same plane for both. Endocardial dropout, heavy trabeculation, and foreshortening change both areas. FAC includes longitudinal and radial change but excludes the RVOT, so it is broader than TAPSE without becoming a full-volume RVEF.

Add 3-D RVEF and RV free-wall strain when feasible. A current normal 3-D RVEF is greater than 45%, and normal free-wall strain is more negative than approximately −20%, using the laboratory's convention. Three-dimensional data require the entire inflow, body, apex, and outflow without dropout or stitching and may underestimate volume compared with CMR. Strain requires adequate frame rate and tracking and varies with vendor and load. Visual free-wall thickening remains important, especially when regional infarction or postoperative geometry makes annular surrogates discordant.

Use discordance as a prompt to investigate

A normal TAPSE cannot overrule abnormal FAC, 3-D RVEF, strain, and visual motion when those acquisitions are valid. Conversely, low TAPSE or S′ immediately after cardiac surgery or pericardiotomy may reflect altered annular translation more than proportional global RVEF loss. Severe TR, a trans-tricuspid lead, pacing, pericardial disease, RV pressure overload, and LV tethering can separate the metrics. Recheck plane, alignment, border, timing, and representative beats before explaining the physiology. Report each valid value rather than averaging unlike percentages, centimeters, and velocities into a synthetic grade.

Relate contraction to pulmonary afterload

RV-pulmonary artery coupling describes whether RV contractile response is adequate for pulmonary afterload. The noninvasive TAPSE/PASP ratio divides TAPSE in millimeters by estimated pulmonary artery systolic pressure in mm Hg. Healthy cohorts generally fall around 0.5–0.7 mm/mm Hg; values around 0.3–0.4 mm/mm Hg in pulmonary hypertension are associated with uncoupling and increased risk. These are physiologic and prognostic ranges, not a universal diagnostic switch. Age, sex, body habitus, disease, and method change the optimal threshold.

The ratio is meaningful only when both inputs are valid and acquired under the same loading state. PASP requires a complete, aligned TR CW envelope plus a defensible RAP estimate and approximates pulmonary artery pressure only without pulmonic or RVOT obstruction. Severe free TR, an incomplete envelope, uncertain IVC response, or outflow obstruction can make the denominator misleading. TAPSE carries its own basal and angle limitations. FAC/PASP or strain/PASP may add information in specialized practice, but no coupling surrogate directly replaces pressure-volume loops or right-heart catheterization.

Conclude with an integrated statement: RV size and remodeling, visual function, TAPSE, S′, FAC, 3-D RVEF or strain when available, TR, estimated pressure, coupling confidence, rhythm, loading, and image limitations. Serial change is strongest when the focused plane, software, respiratory state, and treatment context match. A defensible examination identifies concordance, explains credible disagreement, and avoids diagnosing or prognosticating from one metric.

A coupling ratio inherits two sets of error

TAPSE/PASP is unreliable if annular tracking is off-axis or if PASP is based on an incomplete TR envelope, uncertain RAP, severe free TR, or RV outflow obstruction. Validate both inputs before interpreting the ratio.