Transaortic gradient is pressure-dependent in a pulsatile model of the circulation.
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Abstract:
Although the transvalvular gradient is described as flow-dependent, pressure-dependence of the gradient, irrespective of flow, has not been demonstrated.The Sheffield pulse duplicator equipped with a X-Cell 21 porcine valve mounted in the aortic position was used. Transaortic gradient was measured at a constant rate of 80 beats/min, while flow was kept at 2, 5 or 8 l/min, and systemic pressure was increased up to 200 mmHg by adjusting peripheral resistance manually. Valve area was computed with the Gorlin formula. A total of 87 measurements was carried out.For each flow, transvalvular gradient increased linearly with pressure, and computed area decreased. The slope of the pressure-gradient relationship was independent of flow.Transaortic gradient depends not only on flow, but also shows pressure-dependency that should be taken into account when evaluating aortic stenosis, especially in hypertensive and hypotensive states.Keywords:
Pulsatile flow
Pressure gradient
Peripheral resistance
Aortic pressure
Adverse pressure gradient
Pulse pressure
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Aortic stenosis is a heterogeneous disorder. Variations in the pathological and physiological responses to pressure overload are incompletely understood and generate a range of flow and pressure gradient patterns, which ultimately cause varying microvascular effects. The impact of cardiac-coronary coupling depends on these pressure and flow effects. In this article, we explore important concepts concerning cardiac physiology and the coronary microcirculation in aortic stenosis and their impact on myocardial remodeling, aortic valve flow patterns, and clinical progression.
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Introduction: Aortic stenosis induces a hemodynamic burden on the left ventricle (LV) that leads to geometric changes. Yet the additional impact of the arterial system on the LV is often ignored.
Hypothesis: We hypothesized that arterial load is associated with LV mass in subjects with aortic stenosis, independently of aortic valve area (AVA).
Methods: We studied 40 subjects with aortic stenosis. We measured LV mass and cardiac output with SSFP MRI cine imaging, and determined MRI AVA using planimetry. Central pressures were obtained using carotid tonometry, and ascending aortic flow was quantified with through-plane phase-contrast MRI. We assessed the following indices of pulsatile load via pressure-flow analyses: total arterial compliance (TAC), proximal aortic characteristic impedance (Zc), and forward (Pf) and reflected wave (Pb) amplitude. We assessed the relationship between arterial load and LV mass.
Results: Among 40 subjects with AS, 16 subjects had mild AS, 20 subjects had moderate AS, and 4 subjects had severe AS. In models that adjusted for AVA and resistive load (SVR), only reflected wave amplitude (Pb, standardized β=0.52, P=0.007) was significantly associated with LV mass (Table).
Conclusion: Pulsatile load is an important and often overlooked determinant of LV mass in aortic stenosis. After adjustment for SVR and aortic valve area, reflected waves were significantly associated with LV mass, implicating late systolic load in LV hypertrophy in this condition.
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Severe aortic stenosis induces abnormalities in central aortic pressure, with consequent impaired organ and tissue perfusion. Relief of aortic stenosis by transcatheter aortic valve replacement (TAVR) is associated with both a short- and long-term hypertensive response. Counterintuitively, patients who are long-term normotensive post-TAVR have a worsened prognosis compared with patients with hypertension, yet the underlying mechanisms are not understood. We investigated immediate changes in invasively measured left ventricular and central aortic pressure post-TAVR in patients with severe aortic stenosis using aortic reservoir pressure, wave intensity analysis, and indices of aortic function. Fifty-four patients (mean age 83.6±6.2 years, 50.0% female) undergoing TAVR were included. We performed reservoir pressure and wave intensity analysis on invasively acquired pressure waveforms from the ascending aorta and left ventricle immediately pre- and post-TAVR. Following TAVR, there were increases in systolic, diastolic, mean, and pulse aortic pressures (all P <0.05). Post-TAVR reservoir pressure was unchanged (54.5±12.4 versus 56.6±14.0 mm Hg, P =0.30) whereas excess pressure increased 47% (29.0±10.9 versus 42.6±15.5 mm Hg, P <0.001). Wave intensity analysis (arbitrary units, au) demonstrated increased forward compression wave (64.9±35.5 versus 124.4±58.9, ×10 3 au, P <0.001), backward compression wave (11.6±5.5 versus 14.4±6.9, ×10 3 au, P =0.01) and forward expansion wave energies (43.2±27.3 versus 82.8±53.1, ×10 3 au, P <0.001). Subendocardial viability ratio improved with aortic function effectively unchanged post-TAVR. Increased central aortic pressure following TAVR relates to increased transmitted power and energy to the proximal aorta with increased excess pressure but unchanged reservoir pressure. These changes provide a potential mechanism for the improved prognosis associated with relative hypertension post-TAVR.
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Although the transvalvular gradient is described as flow-dependent, pressure-dependence of the gradient, irrespective of flow, has not been demonstrated.The Sheffield pulse duplicator equipped with a X-Cell 21 porcine valve mounted in the aortic position was used. Transaortic gradient was measured at a constant rate of 80 beats/min, while flow was kept at 2, 5 or 8 l/min, and systemic pressure was increased up to 200 mmHg by adjusting peripheral resistance manually. Valve area was computed with the Gorlin formula. A total of 87 measurements was carried out.For each flow, transvalvular gradient increased linearly with pressure, and computed area decreased. The slope of the pressure-gradient relationship was independent of flow.Transaortic gradient depends not only on flow, but also shows pressure-dependency that should be taken into account when evaluating aortic stenosis, especially in hypertensive and hypotensive states.
Pulsatile flow
Pressure gradient
Peripheral resistance
Aortic pressure
Adverse pressure gradient
Pulse pressure
Cite
Citations (23)
Pressure gradient
Aortic pressure
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Citations (6)
Aortic pressure
Ventricular pressure
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Citations (12)