Elevated LV filling pressure is a major determinant of cardiac symptoms and prognosis in patients with chronic heart failure, regardless of LVEF. The invasive estimation of LV filling pressure may be done either by right heart catheterization, which allows PCWP to be measured as an indirect, though accurate, estimate of left atrial pressure, or by direct sampling of the LV cavity during left heart catheterization. In clinical practice, measuring PCWP with right heart catheterization has been established as a surrogate measurement that has largely replaced direct measurements of LVEDP, However, a recent patient series showed a poor agreement between the two methods. In patients with HFPEF and elevated left atrial pressure, it has been shown that there is a relevant pressure drop between PCWP and the left atrium due to an increase in pulmonary venous resistance. In a recent study on patients with HFPEF, it was reported that PCWP measurements were more closely related to outcome than those of LVEDP., It was then speculated that both the low diffusion capacity of carbon monoxide and the pressure gradient between PCWP and LVEDP reflect the thickening of the alveolocapillary membrane due to chronic congestion., Both parameters are associated with disease severity and should be addressed in future large-scale studies.

A noninvasive estimation of LV filling pressure may be obtained using Doppler echocardiography Mitral inflow, tissue Doppler annular velocities, tricuspid regurgitation velocity, and left atrial volume are the cornerstones of diastolic function evaluation. However, the fact that the various parameters used are subject to fundamental limitations and reflect different physiological aspects of diastole has led to substantial ambiguity in the diagnosis of LV diastolic dysfunction. Current recommendations encourage the use of pulsed tissue Doppler for calculating the ratio between the preload-dependent transmitral E velocity and the average of septal and lateral velocities of the earliest diastolic motion (e') of the mitral annulus for the estimation of LV filling pressure. This average velocity may reflect the rate of myocardial relaxation, not depending on pressure flow gradients. In addition to being very feasible and widely available, the prognostic significance of the E/e ratio is widely recognized in various cardiovascular diseases (eg, heart failure, myocardial infarction, arterial hypertension).

Despite its wide use, the real utility of the E/e' ratio has been recently challenged in several studies, which led to a revision of the 2009 recommendations for the assessment of LV diastolic function and LV filling pressure., To examine and validate the accuracy of these new recommendations, the European Association of Cardiovascular Imaging (EACVI) Research Committee performed the EURO-FILLING study, a large multicenter prospective project with simultaneous assessment of invasive measurements and noninvasive estimates of LV filling pressure. A total of 159 patients were enrolled in 9 EACVI centers; 39 (25%) patients had a reduced LVEF (<50%), 77 (64%) had an NYHA class ell, 85 (53%) had coronary artery disease, and 64 (40%) had elevated LVEDP (215 mm Hg). Taken individually, all echocar- diographic Doppler estimates of LV filling pressure (E/A, E/e', left atrial volume, tricuspid regurgitation jet velocity) were marginally correlated with LVEDP., By using the 2016 recommendations, 65% of patients with a normal noninvasive estimate of LV filling pressure had a normal LVEDP, while 79% of those with an elevated noninvasive LV filling pressure had an elevated invasive LVEDP.

By using the 2009 recommendations, 68% of the patients with a normal noninvasive LV filling pressure had a normal LVEDP, while 55% of those with an elevated noninvasive LV filling pressure had an elevated LVEDP. The 2016 recommendations (sensitivity, 75%; specificity, 74%; positive predictive value, 39%; negative predictive value, 93%; AUC, 0.78) identified patients with an elevated invasive LVEDP (215 mm Hg) slightly better than the 2009 recommendations (sensitivity, 43%; specificity, 75%; positive predictive value, 49%; negative predictive value, 71%; AUC, 0.68). The authors of the EURO-FILLING study concluded that the new 2016 recommendations for noninvasively assessing LV filling pressure are fairly reliable, clinically useful, and superior to the 2009 recommendations in estimating invasive LVEDP. In a more recent study, Andersen et al showed a good correlation between the 2016 echocardiographic algorithm for the estimation of LV filling pressure and the invasive assessment of PCWP.6

Although previous works have considered changes in echocardiographically derived indexes as a function of HR, no HR-adjusting index has been proposed that incorporates the smooth and continuous increase in the rate of cardiac output as HR increases.7-9 Changes in HR in the context of shortening the R-R interval are primarily modulated by the duration of diastasis. The duration of the E wave and the A wave are roughly HR-independent. Each shows a <15% to 20% decrease in duration for a 100% increase in HR. Mitral deceleration time shows a mere 20% decrease for a 100% increase in HR. Moreover, HR is positively associated with peak velocity A and atrial filling fraction and inversely associated with peak velocity E, peak velocity E/A, and time velocity E/A., The relationship between relaxation and frequency shortens in response to increasing HR, however, the slope of this relationship is significantly steeper in patients with heart failure compared with patients with normal LV function. 

In heart failure, changes in HR affect early relaxation and diastolic compliance more than in control subjects. However, with sinus tachycardia, various degrees of merging of mitral E and A velocities are observed secondary to the shortening of the diastolic filling period, adding complexity to the evaluation of filling dynamics and pressure.10 Nevertheless, the E/e' ratio can still be used to estimate PCWP with reasonable accuracy in sinus tachycardia, even with a complete merging of E and A velocities. Exercise-induced elevation of filling pressures límits exercise capacity, which may indicate diastolic dysfunction. In subjects with normal myocardial relaxation, E and e' velocities increase proportionally, and the Ele' ratio remains either unchanged or reduced. However, in patients with impaired myocardial re-laxation, the increase in e' with exercise is much less than that of the mitral E velocity, such that the Ele' ratio increases... In this regard, the E/e' ratio was shown to relate significantly to LV filling pressure during exercise, when Doppler echocardiography was acquired simultaneously with cardiac catheterization.12

Exertional dyspnea is a nonspecific symptom; therefore, concern is often expressed over the frequency of diastolic dysfunction leading to the overdiagnosis of HFPEF. In the early stages of HFPEF, while the primary problem relates to im- paired LV relaxation (rather than impaired LV compliance or increased filling pressure at rest), a high HR during exercise may be particularly detrimental by reducing the time for diastolic filling and promoting an increased LV filling pressure, and exercise intolerance and dyspnea. The patients can be identified by assessing the increments of E/e ratio with exercise. Therapeutic measures prolonging the LV filling phase may optimize transmitral flow, thereby reducing increased filling pressures and the resultant dyspnea.

During exercise, the marked increase in LV filling rate in early diastole mainly depends on the ability of the LV to relax rapidly and completely. The physiological mechanisms allowing this adaptation involve an increase in both heart rate and contractility through adrenergic stimulation. As a consequence, B-blockers strongly alter the relaxation process as a result of the combination of their negative chronotropic and inotropic properties, both at rest and during exercise. For instance, atenolol alleviates the acceleration of LV pressure falls during exercise manner. In contrast to atenolol, ivabradine, an inhibitor of the pacemaker If current, for a similar reduction in heart rate at rest and during exercise, does not exert any negative lusitropic effect. Ivabradine induces dose-dependent reductions in heart rate, is devoid of an intrinsic negative inotropic effect, and does not alter either global LV systolic function or coronary vasomotion.

Patients with HFPEF have inappropriate tachycardia during exercise, with higher heart rates at constant workloads than in subjects with normal LV filling, based on impaired stroke volume reserve and reliance on increasing heart rate to augment
cardiac output. Interestingly, a selective HR reduction by ivabradine improves vascular stiffness, LV contractility, and diastolic function in patients with HFPEF. The mechanisms behind the favorable effect of ivabradine on LV diastolic function are not confined to a simple lengthening of diastolic filling time. Other benefits include acceleration of myocardial relaxation by enhancing the phosphorylation of phospholamban and subsequent stimulation of sarcoplasmic reticulum Ca2+ adenosine triphosphatase, increase in myocardial compliance by reducing the expression of the titin N2B isoform and myocardial collagen content, and improving arterial stiffness and endothelial function. Clinically, short-term treatment with ivabradine increases exercise capacity, with a contribution from improved LV filling pressure response to exercise as reflected by a better E/e´ ratio at exercise.