Hemodynamic effects of exercise in isolated valvular aortic stenosis

Normative values of the aortic valve area and Doppler measurements using two-dimensional transthoracic echocardiography: results from the Multicentre World Alliance of Societies of Echocardiography Study

AIMS

Aortic valve area (AVA) used for echocardiographic assessment of aortic stenosis (AS) has been traditionally interpreted independently of sex, age and race. As differences in normal values might impact clinical decision-making, we aimed to establish sex-, age- and race-specific normative values for AVA and Doppler parameters using data from the World Alliance Societies of Echocardiography (WASE) Study.

METHODS AND RESULTS

Two-dimensional transthoracic echocardiographic studies were obtained from 1903 healthy adult subjects (48% women). Measurements of the left ventricular outflow tract (LVOT) diameter and Doppler parameters, including AV and LVOT velocity time integrals (VTIs), AV mean pressure gradient, peak velocity, were obtained according to ASE/EACVI guidelines. AVA was calculated using the continuity equation. Compared with men, women had smaller LVOT diameters and AVA values, and higher AV peak velocities and mean gradients (all P < 0.05). LVOT and AV VTI were significantly higher in women (P < 0.05), and both parameters increased with age in both sexes. AVA differences persisted after indexing to body surface area. According to the current diagnostic criteria, 13.5% of women would have been considered to have mild AS and 1.4% moderate AS. LVOT diameter and AVA were lower in older subjects, both men and women, and were lower in Asians, compared with whites and blacks.

CONCLUSION

WASE data provide clinically relevant information about significant differences in normal AVA and Doppler parameters according to sex, age, and race. The implementation of this information into clinical practice should involve development of specific normative values for each ethnic group using standardized methodology.

Pressure gradient vs. flow relationships to characterize the physiology of a severely stenotic aortic valve before and after transcatheter valve implantation

Aims

Echocardiography and tomographic imaging have documented dynamic changes in aortic stenosis (AS) geometry and severity during both the cardiac cycle and stress-induced increases in cardiac output. However, corresponding pressure gradient vs. flow relationships have not been described.

Methods and results

We recruited 16 routine transcatheter aortic valve implantations (TAVI’s) for graded dobutamine infusions both before and after implantation; 0.014″ pressure wires in the aorta and left ventricle (LV) continuously measured the transvalvular pressure gradient (ΔP) while a pulmonary artery catheter regularly assessed cardiac output by thermodilution. Before TAVI, ΔP did not display a consistent relationship with transvalvular flow (Q). Neither linear resistor (median R² 0.16) nor quadratic orifice (median R² < 0.01) models at rest predicted stress observations; the severely stenotic valve behaved like a combination. The unitless ratio of aortic to left ventricular pressures during systolic ejection under stress conditions correlated best with post-TAVI flow improvement. After TAVI, a highly linear relationship (median R² 0.96) indicated a valid valve resistance.

Conclusion

Pressure loss vs. flow curves offer a fundamental fluid dynamic synthesis for describing aortic valve pathophysiology. Severe AS does not consistently behave like an orifice (as suggested by Gorlin) or a resistor, whereas TAVI devices behave like a pure resistor. During peak dobutamine, the ratio of aortic to left ventricular pressures during systolic ejection provides a ‘fractional flow reserve’ of the aortic valve that closely approximates the complex, changing fluid dynamics. Because resting assessment cannot reliably predict stress haemodynamics, ‘valvular fractional flow’ warrants study to explain exertional symptoms in patients with only moderate AS at rest.

Effect of late sodium current inhibition on MRI measured diastolic dysfunction in aortic stenosis: a pilot study

Background

Ranolazine is a new anti-anginal drug that acts via late sodium current inhibition, and has been shown to improve diastolic dysfunction in isolated myocytes. Diastolic dysfuntion is common in patients with aortic stenosis (AS), and precedes symptom development and systolic dysfunction. The purpose of this study was to assess the effects of ranolazine on peak early diastolic strain rate (PEDSR) and exercise capacity in patients with AS.

Methods

Patients with asymptomatic moderate to severe AS and diastolic dysfunction underwent trans-thoracic echocardiography, exercise testing and cardiac magnetic resonance (CMR) imaging at baseline, 6 weeks after commencing ranolazine and at 10 weeks (4 weeks after discontinuation). Diastolic function was assessed using PEDSR measured on tagged CMR images.

Results

Fifteen patients (peak pressure gradient 48.8 ± 12.4 mmHg, mean pressure gradient 27.1 ± 7.5 mmHg, aortic valve area 1.26 ± 0.31 cm²) completed the week-6 visit and 13 completed the final visit. Global PEDSR did not significantly increase from baseline (0.79 ± 0.15) to week-6 (0.86 ± 0.18, p = 0.198). There was a borderline significant increase in total exercise duration from 10.47 ± 3.68 min to 11.60 ± 3.25 min (p = 0.06).

Conclusion

This small pilot study did not show a significant improvement in diastolic function with the use of ranolazine in asymptomatic patients with moderate-severe AS. Further studies with a larger population may be indicated.

EduraCT number 2011-000111-26

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-1874-0) contains supplementary material, which is available to authorized users.

Aortic valve and ascending aorta guidelines for management and quality measures: executive summary

The Society of Thoracic Surgeons Clinical Practice Guidelines are intended to assist physicians and other health care providers in clinical decision making by describing a range of generally acceptable approaches for the diagnosis, management, or prevention of specific diseases or conditions. These guidelines should not be considered inclusive of all proper methods of care or exclusive of other methods of care reasonably directed at obtaining the same results. Moreover, these guidelines are subject to change over time, without notice. The ultimate judgment regarding the care of a particular patient must be made by the physician in light of the individual circumstances presented by the patient.

Stress echocardiography expert consensus statement: European Association of Echocardiography (EAE) (a registered branch of the ESC)

Stress echocardiography is the combination of 2D echocardiography with a physical, pharmacological or electrical stress. The diagnostic end point for the detection of myocardial ischemia is the induction of a transient worsening in regional function during stress. Stress echocardiography provides similar diagnostic and prognostic accuracy as radionuclide stress perfusion imaging, but at a substantially lower cost, without environmental impact, and with no biohazards for the patient and the physician. Among different stresses of comparable diagnostic and prognostic accuracy, semisupine exercise is the most used, dobutamine the best test for viability, and dipyridamole the safest and simplest pharmacological stress and the most suitable for combined wall motion coronary flow reserve assessment. The additional clinical benefit of myocardial perfusion contrast echocardiography and myocardial velocity imaging has been inconsistent to date, whereas the potential of adding - coronary flow reserve evaluation of left anterior descending coronary artery by transthoracic Doppler echocardiography adds another potentially important dimension to stress echocardiography. New emerging fields of application taking advantage from the versatility of the technique are Doppler stress echo in valvular heart disease and in dilated cardiomyopathy. In spite of its dependence upon operator's training, stress echocardiography is today the best (most cost-effective and risk-effective) possible imaging choice to achieve the still elusive target of sustainable cardiac imaging in the field of noninvasive diagnosis of coronary artery disease.

Analog simulation of two clinical conditions: (1) Acute left ventricle failure; (2) exercise in patient with aortic stenosis

A computer analysis of an equivalent electronic circuit is developed. Thus it is possible to simulate the human cardiovascular system, its negative feedback loops (including the control of venous tone, of myocardial contractility, and of heart rate) and negative intrathoracic pressure. If the simulated cardiovascular system is acted upon by various disturbances their consequences can be studied in detail. The consequences of two disturbances are studied by simulation: (i) acute left ventricular failure and (ii) exercise (decreased peripheral resistance) in aortic stenosis. However, prior to the simulation of the latter, a relatively complex condition, two additional procedures are implemented, i.e. simulations of (iii) increased sympathetic tone and of (iv) aortic stenosis are performed. Simulation of exercise (decreased peripheral resistance) in aortic stenosis is also compared with data observed in patients. Results show that, by using the present equivalent circuit, conditions described above can be qualitatively and to some extent quantitatively well simulated.

Exercise Testing in Aortic Stenosis

Physician-supervised exercise testing in asymptomatic patients with aortic stenosis allows an objective assessment of the hemodynamic response to exercise and it provides a measure of exercise capacity. Exercise testing cannot be used to determine the presence or absence of coronary artery disease, but limited data indicate that exercise testing can provide prognostic information. The results of such testing can be used to provide an exercise prescription and to reassure the patient who might otherwise excessively limit his or her activity.

Hemodynamic stability of valve area, valve resistance, and stroke work loss in aortic stenosis: a comparative analysis

BACKGROUND

Although aortic valve area (AVA) has provided the standard index for assessing aortic stenosis severity, valve resistance and percent left ventricular stroke work (%LVSW) loss have been proposed as alternative flow independent indices of stenosis severity that may provide a more stable measure under diverse hemodynamic conditions. In 30 patients with moderate or severe aortic stenosis (AVA < or = 1.2 cm(2)), Doppler echocardiography indices of AVA, valve resistance, and %LVSW loss were measured at multiple transvalvular flow rates during dobutamine infusions (0-10 microg/kg/min) to compare their hemodynamic stability.

RESULTS

From baseline to maximum dobutamine dose in the 30 patients, transvalvular flow rate increased 43% and resulted in a 42% increase in mean transvalvular pressure gradient, a 15% increase in Doppler AVA, and a 26% increase in %LVSW loss. Group mean valve resistance did not change for the total cohort. For individual patients, AVA and %LVSW loss demonstrated a linear relationship with transvalvular flow (median r = 0.74 and 0.84, respectively). In contrast, both flow-mediated increases and decreases in valve resistance were observed in individual patients, resulting in the apparent stability of the group mean valve resistance in the total cohort. For individual patients, Doppler AVA and valve resistance demonstrated comparable stability in response to changes in hemodynamic conditions and were significantly more stable than mean transvalvular pressure gradient and %LVSW loss.

CONCLUSION

Doppler AVA and valve resistance provide stenotic indices of equivalent hemodynamic stability. However, transvalvular flow has a predictable directional effect on AVA and an unpredictable directional effect on valve resistance, potentially limiting valve resistance as a measure of hemodynamic severity.

Dobutamine echocardiography in patients with aortic stenosis and left ventricular dysfunction: predicting outcome as a function of management strategy

STUDY OBJECTIVE

To prospectively address the question whether the assessment of valvular hemodynamics and myocardial function during low-dose dobutamine infusion can guide decision making in patients with aortic stenosis and left ventricular (LV) dysfunction.

PATIENTS AND MEASUREMENTS

Twenty-four patients with aortic stenosis and LV dysfunction (mean ejection fraction, 28%; New York Heart Association class, II to IV) were studied by dobutamine echocardiography assessing mean pressure gradient, aortic valve area, and aortic valve resistance. Patients were prospectively divided into severe and nonsevere aortic stenosis groups according to the response of the valve area to the augmentation of systolic flow. The clinical decision was considered to be concordant with the results of dobutamine echocardiography, when patients with severe aortic stenosis and preserved contractile function were referred by a specialist for aortic valve replacement and when patients with nonsevere aortic stenosis were not. Patients were observed for up to 3 years.

RESULTS

All eight patients with severe aortic stenosis who were referred for surgery survived and had good cardiovascular outcomes, and six of eight patients who were not initially referred for surgery had poor outcomes, including heart failure and sudden cardiac death. The eight patients with nonsevere aortic stenosis did comparatively well without valve replacement. Cardiac death or pulmonary edema occurred in 4 of 16 patients (25%) when the clinical decision was concordant with the results of the dobutamine echocardiogram and occurred in 6 of 8 patients (75%) when the clinical decision was discordant (p = 0.019 [chi(2) test]).

CONCLUSION

Patients with aortic stenosis, LV dysfunction, and relatively low gradients have better outcomes when management decisions are based on the results of dobutamine echocardiograms. Those patients identified as having severe aortic stenosis and preserved contractile reserve by dobutamine echocardiography should undergo surgery, while patients identified as having nonsevere aortic stenosis can be managed conservatively.

Stress Echocardiography in Aortic Stenosis: Insights into Valve Mechanics and Hemodynamics

Stress interventions have been classically combined with cardiac catheterization recordings to understand the hemodynamic principles of valvular stenosis. Indices of aortic stenosis such as pressure gradient and valve area were based on simple hydraulic principles and have proved to be clinically useful for patient management during a number of decades. With the advent of Doppler echocardiography, these hemodynamic indices can be readily obtained noninvasively. Abundant evidence obtained using exercise and pharmacological stress echocardiography has demonstrated that the assumptions of classic hemodynamic models of aortic stenosis were wrong. Consequently, it is recognized that conventional indices may be misleading indicators of aortic stenosis significance in particular clinical situations. To improve diagnostic accuracy, several alternative hemodynamic models have been developed in the past few years, including valve resistance and left ventricular stroke work loss, among others. Nevertheless, these more-accurate indices should be obtainable noninvasively and need to demonstrate greater diagnostic and prognostic power than conventional indices; preliminary data suggest such superiority. Stress echocardiography is well established as the tool of choice for testing hypothesis and physical models of cardiac valve function. Although the final role of alternative indices is not yet well established, the new insights into valvular hemodynamics provided by this technique may change the clinical assessment of aortic stenosis.

Variation of anatomic valve area during ejection in patients with valvular aortic stenosis evaluated by two-dimensional echocardiographic planimetry: comparison with traditional Doppler data

OBJECTIVES

Flow variations can affect valve-area calculation in aortic stenosis and lead to inaccuracies in the evaluation of the stenosis. Knowing that transvalvular flow varies normally within one beat, we designed this study to assess the response of the valve to intrabeat variation of flow during systole. Results were compared with flow-derived measurements.

BACKGROUND

Technological improvements now allow us to evaluate aortic valve area directly by short axis planimetry. This offers the possibility to perform serial planimetries during one ejection phase and analyze the intrabeat dynamic behavior of the stenotic-aortic valve and compare these measurements with flow-derived measurements.

METHODS

Forty echocardiograms displaying different degrees of aortic stenosis were analyzed by frame-by-frame planimetry of the valve area from onset of opening to complete closure. Maximal-mean area, opening and closing rates and ejection times were obtained and compared with Doppler-derived data.

RESULTS

Valve area varied during ejection. Stenotic valves opened and closed more slowly than normals and remained maximally open for a shorter period. Mean area by Doppler data corresponded more closely to maximal than to mean-planimetered area. Duration of flow was shorter than valve opening in severely stenotic valves. Discrepancies between Doppler-derived and two-dimensional (2D) measurements decreased in less stenotic valves.

CONCLUSIONS

Our observations reveal striking differences between the dynamics of normal and stenotic valves. Surprisingly, Doppler-derived mean-valve area correlated better with maximal-anatomic area than with mean-anatomic area in patients with aortic stenosis. Discrepancies between duration of flow and valve opening could explain this phenomenon.

Aortic stenosis. Clinical evaluation and optimal timing of surgery

Aortic valve disease is common in the elderly with recent data suggesting that aortic sclerosis and stenosis are the end-stage of an active disease process. Aortic atenosis may be diagnosed at symptom onset (angina, heart failure or syncope) but often the diagnosis is suspected in an asymptomatic patient with a systolic murmur. The diagnosis can be confirmed and disease severity evaluated reliably using Doppler echocardiography. Symptomatic severe aortic stenosis is treated with valve replacement, even in the elderly, due to the extremely poor prognosis without relief of outflow obstruction. Management is controversial when there is coexisting moderate aortic stenosis and left ventricular systolic dysfunction.

Flow dependence of valve area in aortic stenosis: relation to valve morphology

OBJECTIVES

We sought to develop an index of flow dependence of valve area in aortic valve (AoV) stenosis and to determine whether this index is related to structural characteristics of the diseased valve.

BACKGROUND

Many studies of AoV stenosis using Gorlin or continuity equation methods have demonstrated flow dependence (an increase in valve area with increased flow). Variation in flow dependence between patients despite similar flow rates remains unexplained.

METHODS

Dobutamine Doppler echocardiography was used to calculate flow rate and valve area by the continuity equation in 27 patients with aortic stenosis. For each patient the slope of the regression line of valve area to flow rate was determined (slope of flow dependence). Transesophageal echocardiography was used to evaluate features of valve morphology potentially related to the etiology of AoV stenosis and the mechanism of flow dependence.

RESULTS

Mean slope of flow dependence was 0.28 cm2/100 ml per s (range -0.06 to 0.53); flow dependence was significantly >0 in 21 patients and was lower for bicuspid valves (slope 0.21 cm2/100 ml per s) than for tricuspid valves with <10% commissural fusion (slope 0.35, p < 0.01). Off-center/ovoid orifices demonstrated the least flow dependence (slope 0.19), whereas star-shaped orifices showed the most (slope 0.36, p < 0.01). Greater flow dependence was related to a lower percentage of commissural fusion (r = -0.46, p = 0.02) as well as diffuse sclerosis, primarily involving the cusp bodies, rather than localized sclerosis, with involvement of cusp margins.

CONCLUSIONS

The slope of flow dependence of valve area in AoV stenosis differs markedly between patients. More flow dependence was associated with tricuspid valves and the morphologic features characteristic of calcific AoV stenosis, whereas less flow dependence was associated with bicuspid valves and the features of rheumatic disease.

Assessment of the Björk-Shiley prosthetic valve orifice area in the aortic position

The actual orifice area of a valve is still considered to be a valuable index for assessing prosthetic valve function. Valve orifice area as calculated by Gorlin's formula is, however, not constant but changes in proportion to the transvalvular flow rate. The purpose of the present study was to examine the relationship between orifice area and flow rate across the Björk-Shiley prosthetic valve as calculated by Gorlin's formula, and to modify the formula in a series of patients with the Björk-Shiley prosthetic valve in the aortic position. Fifty-six patients who had received aortic valve replacement with a Björk-Shiley prosthetic valve underwent cardiac catheterization. Prosthetic valve orifice area was calculated by Gorlin's formula and then plotted against flow rate across the valve with respect to valve size. The relationship between orifice area and flow was linear. The discharge coefficient of Gorlin's formula was plotted against flow rate, and a linear correlation was obtained. By substituting Gorlin's formula for an empiric coefficient into the function for transvalvular flow rate, a modified formula that can predict the actual orifice area of the prosthetic valve is obtained.

Planimetry and transthoracic two-dimensional echocardiography in noninvasive assessment of aortic valve area in patients with valvular aortic stenosis

OBJECTIVES

The aim of this study was to evaluate the reliability of transthoracic two-dimensional echocardiography in measuring aortic valve area (AVA) by planimetry.

BACKGROUND

Planimetry of AVA using two-dimensional transesophageal echocardiographic images has been reported to be a reliable method for measuring AVA in patients with aortic stenosis. Recent advances in resolution of two-dimensional echocardiography permit direct visualization of an aortic valve orifice from the transthoracic approach more easily than before.

METHODS

Forty-two adult patients with valvular aortic stenosis were examined. A parasternal short-axis view of the aortic valve was obtained with transthoracic two-dimensional echocardiography. AVA was measured directly by planimetry of the inner leaflet edges at the time of maximal opening in early systole. AVA was also measured by planimetry using transesophageal echocardiography, by the continuity equation and by cardiac catheterization (Gorlin formula).

RESULTS

In 32 (76%) of the 42 study patients, AVA could be detected by using the transthoracic planimetry method. There were good correlations between results of transthoracic two-dimensional echocardiographic planimetry and the continuity equation (y = 0.90x + 0.09, r = 0.90, p < 0.001, SEE = 0.09 cm2), transesophageal echocardiographic planimetry (y = 1.05x - 0.02, r = 0.98, p < 0.001, SEE = 0.04 cm2) and the Gorlin formula (y = 1.02x + 0.05, r = 0.89, p < 0.001, SEE = 0.10 cm2).

CONCLUSIONS

Transthoracic two-dimensional echocardiography provides a feasible and reliable method in measuring AVA in patients with aortic stenosis.

Percutaneous transvenous mitral balloon valvuloplasty alone in patients with combined aortic and mitral stenosis

To investigate the feasibility of percutaneous transvenous balloon dilatation of the mitral valve in patients with combined aortic and mitral stenosis, 12 patients were studied by echocardiography and catheterization before and after mitral valvuloplasty. Aortic stenosis was defined from prevalvuloplasty catheterization study as a transaortic pressure gradient of more than 25 mm Hg. All 12 patients underwent transvenous balloon mitral valvuloplasty successfully. Immediately after the procedure, all patients experienced improvement in clinical symptoms and in hemodynamic variables. Mitral valve areas were significantly increased from 0.78 +/- 0.18 to 1.73 +/- 0.21 cm2 (P < 0.0001) by planimetry method. Cardiac output was significantly increased from 3.6 +/- 0.1 to 4.2 +/- 0.5 L/min (P = 0.01). Mean transaortic flow rate increased 33% (from 198 +/- 68 to 254 +/- 41 mL/s, P = 0.002). Mean pressure gradient across the aortic valve after mitral valvuloplasty was not significantly increased, from 34 +/- 7 to 37 +/- 13 mm Hg. Aortic valve areas, derived from the Gorlin formula, were significantly increased from 0.57 +/- 0.12 to 0.73 +/- 0.14 cm2 (P = 0.006) after mitral valvuloplasty. However, continuity equation-derived aortic valve area was independent of increasing flow rate after mitral valvuloplasty from 1.29 +/- 0.35 to 1.30 +/- 0.29 cm2. During follow-up with a mean of twenty four +/- fourteen months, 8 patients were in New York Heart association functional class I, 3 in class II, and 1 in class IV who received pericardiotomy owing to constrictive pericarditis without aortic valve replacement. In conclusion, mitral valvuloplasty alone may be safe and effective in alleviating symptoms in mitral stenosis patients with transaortic pressure gradient > 25 mm Hg. Continuity equation-derived aortic valve areas seem to be flow independent in evaluation of aortic stenosis and are important for decision making.

Simultaneous determination of aortic valve area by the Gorlin formula and by transesophageal echocardiography under different transvalvular flow conditions. Evidence that anatomic aortic valve area does not change with variations in flow in aortic stenosis

OBJECTIVES

The purpose of this study was to determine the impact of changes in flow on aortic valve area (AVA) as measured by the Gorlin formula and transesophageal echocardiographic (TEE) planimetry.

BACKGROUND

The meaning of flow-related changes in AVA calculations using the Gorlin formula in patients with aortic stenosis remains controversial. It has been suggested that flow dependence of the calculated area could be due to a true widening of the orifice as flow increases or to a disproportionate flow dependence of the formula itself. Alternatively, anatomic AVA can be measured by direct planimetry of the valve orifice with TEE.

METHODS

Simultaneous measurement of the planimetered and Gorlin valve area was performed intraoperatively under different hemodynamic conditions in 11 patients. Left ventricular and ascending aortic pressures were measured simultaneously after transventricular and aortic punctures. Changes in flow were induced by dobutamine infusion. Using multiplane TEE, AVA was planimetered at the level of the leaflet tips in the short-axis view.

RESULTS

Overall, cardiac output, stroke volume and transvalvular volume flow rate ranged from 2.5 to 7.3 liters/min, from 43 to 86 ml and from 102 to 306 ml/min, respectively. During dobutamine infusion, cardiac-output increased by 42% and mean aortic valve gradient by 54%. When minimal flow was compared with maximal flow, the Gorlin area varied from (mean +/- SD) 0.44 +/- 0.12 to 0.60 +/- 0.14 cm2 (p < 0.005). The mean change in Gorlin area under different flow rates was 36 +/- 32%. Despite these changes, there was no significant change in the planimetered area when minimal flow was compared with maximal flow. The mean difference in planimetered area under different flow rates was 0.002 +/- 0.01 cm2 (p = 0.86).

CONCLUSIONS

By simultaneous determination of Gorlin formula and TEE planimetry valve areas, we showed that acute changes in transvalvular volume flow substantially altered valve area calculated by the Gorlin formula but did not result in significant alterations of the anatomic valve area in aortic stenosis. These results suggest that the flow-related variation in the Gorlin AVA is due to a disproportionate flow dependence of the formula itself and not a true change in valve area.

Effects of increasing flow rate on aortic stenotic indices: evidence from percutaneous transvenous balloon dilatation of the mitral valve in patients with combined aortic and mitral stenosis

OBJECTIVES

To investigate the effects of transvalvar flow rate on aortic valve resistance and valve area after percutaneous transvenous balloon dilatation of the mitral valve in a homogeneous group of patients with rheumatic heart disease.

DESIGN

Retrospective analysis of 12 patients with combined aortic and mitral stenosis who had undergone balloon dilatation of the mitral valve over a period of 9 years.

SETTING

Tertiary referral centre.

PATIENTS

Twelve (8 women, 4 men; mean (SD) age 37 (9) of 227 consecutive patients with critical mitral stenosis undergoing transvenous balloon dilation of the mitral valve in the centre also had aortic stenosis, defined as a transaortic pressure gradient of more than 25 mm Hg measured at a catheterisation study before valvuloplasty.

INTERVENTIONS

Echocardiographic variables (mitral valve area measured by the pressure half-time method and planimetry, and the aortic valve area derived from the continuity equation) and haemodynamic measurements (cardiac output, left ventricular mean systolic pressure, aortic mean pressure, transaortic valve pressure gradient, mitral valve and aortic valve areas derived from the Gorlin formula, and aortic valve resistance) were assessed before and after transvenous balloon dilatation of the mitral valve. Follow up catheterisation to measure haemodynamic variables was performed one week after mitral valvuloplasty.

RESULTS

Mean transaortic flow rate increased 33% after mitral valvuloplasty (from 198 (68) to 254 (41) ml/s, P = 0.002). Aortic valve areas derived from the Gorlin formula were significantly increased from 0.57 (0.12) to 0.73 (0.14) cm2 (P = 0.006) after mitral valvuloplasty. However, aortic valve area and valve resistance derived from the continuity equation were independent of the increase in flow rate after mitral valvuloplasty (from 1.29 (0.35) to 1.30 (0.29) cm2 and from 317 (65) to 259 (75) dyn.s.cm-5, both P = NS).

CONCLUSION

The Gorlin-derived aortic valve area tends to be flow-dependent, and continuity equation-derived aortic valve area and catheterisation-derived valve resistance seem to be less flow-dependent. In patients with combined mitral and aortic stenosis, these flow-independent indices are important for decision-making.

Changes in effective aortic valve area during ejection in adults with aortic stenosis

Measurements of valve orifice area in aortic stenosis are based on the assumption that orifice area remains constant throughout ejection and is independent of transvalvular gradients and flow. Recent studies, however, have suggested that the calculated valve area of calcific aortic stenosis may change in different flow conditions. Therefore, we tested the hypothesis that in vivo effective orifice area of a stenotic aortic valve changes continuously during ejection, which would make a single area measurement a potentially inadequate indicator of the severity of the stenosis. Doppler measurements of flow velocity in the ascending aorta and in the left ventricular outflow tract at peak velocity, at half-peak velocity during acceleration (midacceleration), and at half-peak velocity during deceleration (mid-deceleration) were obtained in 26 patients with aortic stenosis (mean gradient 50 +/- 19 mm Hg and effective aortic orifice are 0.7 +/- 0.3 dcm2) and in 14 normal subjects of similar age and gender, to calculate instantaneous effective aortic orifice area at midacceleration, at peak velocity and at mid-deceleration. In the 26 patients with aortic stenosis, aortic valve area at midacceleration was 84 +/- 15% of valve area at peak velocity (p < 0.0001), and valve area at mid-deceleration was 113 +/- 17% of that measured at peak velocity (p < 0.01). Conversely, in normal subjects, aortic valve area remained constant during ejection and was 97 +/- 5% and 99 +/- 6% of valve area at peak velocity, respectively, at midacceleration and mid-deceleration (p > 0.05). In addition, in patients with aortic stenosis the percentage of change in effective aortic valve area from midacceleration to mid-deceleration varied widely, from -17% to +49% (mean change +26 +/- 14%). There was no relation between percentage of change in effective valve area and mean transaortic gradient (r = 0.05; p = 0.30) or effective valve area at peak velocity (r = -0.11; p = 0.14). Our results indicate that effective aortic valve area continues to change during ejection in patients with aortic stenosis, and that the magnitude of this change is independent of the usual indexes of severity of the stenosis. Conversely, effective aortic valve area remains constant during ejection in normal subjects.

Hemodynamic assessment of patients with low-flow, low-gradient valvular aortic stenosis

In aortic stenosis (AS), conventional indexes of severity vary with changes in transvalvular flow. It is important to determine the true severity of obstruction because AS in the presence of low cardiac output and low gradient is associated with high mortality during aortic valve replacement. This study compares 3 indexes of stenosis severity at different transvalvular flow rates in patients with low-flow, low-gradient critical AS. Eight patients with critical AS (valve area < or = 0.7 cm2), low cardiac output (< 4.0 L/min), and low mean transvalvular gradient (< or = 40 mm Hg) underwent hemodynamic assessment at baseline, after transvalvular flow was augmented with dobutamine, and after the valve opening was increased with percutaneous balloon aortic valvuloplasty. Severity of obstruction was assessed using 3 different measures: Gorlin formula calculated valve area, valvular resistance, and percentage left ventricular stroke work loss. Dobutamine infusion increased cardiac output by 35% and mean transvalvular gradient by 27%. The mean Gorlin formula calculated aortic valve area increased from 0.5 to 0.6 cm2 (p = 0.002). Percentage left ventricular stroke work loss increased from 23% to 28% (p = 0.03). Valve resistance was unchanged by dobutamine (350 to 310 dynes X sec X cm(-5); p = NS). Balloon valvuloplasty increased cardiac output 13% and decreased the gradient 31%; this resulted in an increase in the calculated valve area from 0.6 to 0.9 cm2 (p = 0.001). Percentage left ventricular stroke work loss decreased from 28% to 20% (p = 0.002), and valve resistance decreased from 310 to 181 dynes X sec X cm(-5) (p = 0.001) after valvuloplasty. We conclude that in patients with low-flow, low-gradient critical AS, valve resistance is the most flow-independent measure of severity of stenosis. All measures improve with percutaneous balloon aortic valvuloplasty.

Flow dependence of the aortic valve area in patients with aortic stenosis: assessment by application of the continuity equation

It has been argued that the aortic valve area (AVA) in patients with aortic stenosis increases with flow. Others, however, have attributed the apparent increase to flow dependence of the empiric constant in the Gorlin formula. We examined the changes in AVA during changes in transvalvular flow induced by dipyridamole infusion in 34 patients with aortic stenosis. Two-dimensional and Doppler echocardiography was used and AVA was calculated according to the continuity equation, which does not include empiric constants. Flow increased in 29, decreased in four, and was unchanged in one patient. There was a linear correlation between percent change in flow and percent change in AVA: delta AVA% = 1.1 + delta flow%. 0.56 (r = 0.72; p < 0.001) In conclusion, AVA was found to be flow dependent. The magnitude of change in AVA observed by noninvasive recordings agrees with previous invasive studies according to the Gorlin formula.

Effects of variations in flow on aortic valve area in aortic stenosis based on in vivo planimetry of aortic valve area by multiplane transesophageal echocardiography

This study provides evidence that acute changes in stroke volume and cardiac output do not result in significant alterations in the anatomic AVA measured with multiplane TEE in patients with AS of moderate or severe degree. Thus, TEE could be useful in the assessment of severity of AS in both low- and high-output states.

Comparison of valvular resistance, stroke work loss, and Gorlin valve area for quantification of aortic stenosis. An in vitro study in a pulsatile aortic flow model

BACKGROUND

Valvular resistance and stroke work loss have been proposed as alternative measures of stenotic valvular lesions that may be less flow dependent and, thus, superior over valve area calculations for the quantification of aortic stenosis. The present in vitro study was designed to compare the impacts of valvular resistance, stroke work loss, and Gorlin valve area as hemodynamic indexes of aortic stenosis.

METHODS AND RESULTS

In a pulsatile aortic flow model, rigid stenotic orifices in varying sizes (0.5, 1.0, 1.5 and 2.0 cm2) and geometry were studied under different hemodynamic conditions. Ventricular and aortic pressures were measured to determine the mean systolic ventricular pressure (LVSPm) and the transstenotic pressure gradient (delta Pm). Transvalvular flow (Fm) was assessed with an electromagnetic flowmeter. Valvular resistance [VR = 1333.(delta Pm/Fm)] and stroke work loss [SWL = 100.(delta Pm/LVSPm)] were calculated and compared with aortic valve area [AVA = Fm/(50 square root of delta Pm)]. The measurements were performed for a large range of transvalvular flows. At low-flow states, flow augmentation (100-->200 mL/s) increased calculated valvular resistance between 21% (2.0 cm2 orifice) and 66% (0.5-cm2 orifice). Stroke work loss demonstrated an increase from 43% (2.0 cm2) to 100% (1.0 cm2). In contrast, Gorlin valve area revealed only a moderate change from 29% (2.0 cm2) to 5% (0.5 cm2). At physiological flow rates, increase in transvalvular flow (200-->300 mL/s) did not alter calculated Gorlin valve area, whereas valvular resistance and stroke work loss demonstrated a continuing increase. Our experimental results were adopted to interpret the results of three clinical studies in aortic stenosis. The flow-dependent increase of Gorlin valve area, which was found in the cited clinical studies, can be elucidated as true further opening of the stenotic valve but not as a calculation error due to the Gorlin formula.

CONCLUSIONS

Within the physiological range of flow, calculated aortic valve area was less dependent on hemodynamic conditions than were valvular resistance and stroke work loss, which varied as a function of flow. Thus, for the assessment of the severity of aortic stenosis, the Gorlin valve area is superior over valvular resistance and stroke work loss, which must be indexed for flow to adequately quantify the hemodynamic severity of the obstruction.

Flow dependence of measures of aortic stenosis severity during exercise

OBJECTIVES

This study was designed to investigate the effect of altering transvalvular volume flow rate on indexes of aortic stenosis severity (valve area, valve resistance, percent left ventricular stroke work loss) derived by using Doppler echocardiography.

BACKGROUND

Assessment of hemodynamic severity in aortic stenosis has been limited by the absence of an index that is independent of transvalvular flow rate. The traditional measurement of valve area by the Gorlin equation has been shown to vary with alterations in transvalvular flow. Recently, valve resistance and percent stroke work loss have been proposed as indexes that are relatively independent of flow. Although typically derived with invasive measurements, valve resistance and percent stroke work loss (in addition to continuity equation valve area) can be determined noninvasively with Doppler echocardiography.

METHODS

We performed 110 symptom-limited exercise studies in 66 asymptomatic patients with valvular aortic stenosis. Continuity equation valve area, valve resistance (the ratio between mean transvalvular pressure gradient and mean flow rate) and the steady component of percent stroke work loss (the ratio between mean transvalvular pressure gradient and left ventricular systolic pressure) were assessed by Doppler echocardiography at rest and immediately after exercise.

RESULTS

Mean transvalvular volume flow rate increased 24% (from [mean +/- SD] 319 +/- 80 to 400 +/- 140 ml/s, p < 0.0001); mean pressure gradient increased 36% (from 30 +/- 14 to 41 +/- 18 mm Hg, p < 0.0001); continuity equation aortic valve area increased 14% (from 1.38 +/- 0.50 to 1.58 +/- 0.69 cm2, p < 0.0001); valve resistance increased 13% (from 137 +/- 81 to 155 +/- 97 dynes.s.cm-5, p < 0.0001); and percent stroke work loss increased 17% (from 17.4 +/- 6.9% to 20.3 +/- 8.5%, p < 0.0001). The effects of flow on valve area, valve resistance and percent stroke work loss were independent of the presence of an aortic valve area < or = or > 1.0 cm2 or reduced transvalvular flow rate (rest cardiac output < 4.5 liters/min).

CONCLUSIONS

In patients with asymptomatic aortic stenosis, Doppler echocardiographic measures of valve area, valve resistance and percent stroke work loss are flow dependent. Flow dependence is observed with valve area < or = or > 1.0 cm2 and in the presence of both normal and low transvalvular flow states. The potential effects of transvalvular flow should be considered when interpreting Doppler measures of aortic stenosis severity.

Dependence of Gorlin formula and continuity equation valve areas on transvalvular volume flow rate in valvular aortic stenosis

BACKGROUND

Valve areas derived by the Gorlin formula have been observed to vary with transvalvular volume flow rate. Continuity equation valve areas calculated from Doppler-echo data have become a widely used alternate index of stenosis severity, but it is unclear whether continuity equation valve areas also vary with volume flow rate. This study was designed to investigate the effects of changing transvalvular volume flow rate on aortic valve areas calculated using both the Gorlin formula and the continuity equation in a model of chronic valvular aortic stenosis.

METHODS AND RESULTS

Using a canine model of chronic valvular aortic stenosis in which anatomy and hemodynamics are similar to those of degenerative aortic stenosis, each subject (n = 8) underwent three studies at 2-week intervals. In each study, transvalvular volume flow rates were altered with saline or dobutamine infusion (mean, 10.3 +/- 5.1 flow rates per study). Simultaneous measurements were made of hemodynamics using micromanometer-tipped catheters, of ascending aortic instantaneous volume flow rate using a transit-time flowmeter, and of left ventricular outflow and aortic jet velocity curves using Doppler echocardiography. Valve areas were calculated from the invasive data by the Gorlin equation and from the Doppler-echo data by the continuity equation. In the 24 studies, mean transit-time transvalvular volume flow rate ranged from 80 +/- 33 to 153 +/- 49 mL/min (P < .0001). Comparing minimum to maximum mean volume flow rates, the Gorlin valve area changed from 0.54 +/- 0.22 cm2 to 0.68 +/- 0.21 cm2 (P < .0001), and the continuity equation valve area changed from 0.57 +/- 0.18 cm2 to 0.70 +/- 0.20 cm2 (P < .0001). A strong linear relation was observed between Gorlin valve area and mean transit-time volume flow rate for each study (median, r = .88), but the slope of this relation varied between studies. The Doppler-echo continuity equation valve area had a weaker linear relation with transit-time volume flow rate for each study (median, r = .51).

CONCLUSIONS

In this model of chronic valvular aortic stenosis, both Gorlin and continuity equation valve areas were flow-dependent indices of stenosis severity and demonstrated linear relations with transvalvular volume flow rate. The changes in calculated valve area that occur with changes in transvalvular volume flow should be considered when measures of valve area are used to assess the hemodynamic severity of valvular aortic stenosis.

Effect of exercise on valvular resistance in patients with mitral stenosis

OBJECTIVES

This exercise study assessed the relation between valvular resistance and flow in patients with mitral stenosis.

BACKGROUND

Valvular resistance has been proposed as an alternative measure of stenotic valvular lesions, which is speculated to remain stable under changing hemodynamic conditions.

METHODS

In 35 of 40 patients with pure or predominant mitral stenosis, continuous wave Doppler measurements of the mitral stenotic jet were possible at rest and during supine bicycle ergometry. Simultaneously, transvalvular flow was assessed by thermodilution technique. For calculation of valvular resistance, the mean mitral valve pressure gradient was determined according to the simplified Bernoulli equation and divided by transvalvular flow. Additionally, effective mitral valve area was calculated according to the continuity equation method, dividing flow by the mean diastolic flow velocity.

RESULTS

Valvular resistance was 65 +/- 32 dynes.s.cm-5 at rest and increased to 82 +/- 43 dynes.s.cm-5 at 25 W (p < 0.001). The most prominent increase in valvular resistance (rest to 25 W 63 +/- 28 to 95 +/- 48 dynes.s.cm-5, p < 0.001) was found in those patients who had no or only a moderate (< 20%) change in effective mitral valve area. In contrast, valvular resistance remained constant (67 +/- 36 vs. 70 +/- 32 dynes.s.cm-5) in patients with a significant (> or = 20%) increase in mitral valve area with exercise.

CONCLUSIONS

In patients with mitral stenosis, the exercise-induced changes in valvular resistance are heterogeneous. This is the result of the variable response of mitral valve area to an increase in flow. In the individual patient, mitral valve area can significantly increase, a factor that has to be taken into account when interpreting the hemodynamic relevance of the obstruction. Calculated valvular resistance is flow dependent and has no advantage over valve area calculations for quantifying mitral stenosis.

Simplified method for calculating aortic valve resistance: correlation with valve area and standard formula

Aortic valve resistance (AVR) is a useful index to assess the severity of aortic stenosis. This study compared the standard method to calculate AVR with a simplified method based on the conventional approach for measuring vascular resistance: AVR = (peak-to-peak transaortic pressure gradient/(cardiac output*2.5))*80, where 80 is a conversion factor and 2.5 assumes that the systolic ejection period comprises 40% of the R-R cycle. We compared the standard AVR, the simplified AVR, and the Gorlin-derived value area in 118 patients with pure or dominant aortic stenosis. There was a strong linear correlation between the standard and simplified AVR (r = 0.96, p < .0001). There was a curvilinear relation between the aortic valve area and AVR (r = 0.92, p < .001). In 48 patients with aortic valve area > or = 0.7 cm2, the AVR was < 300 dynes-sec-cm-5 in 45 patients (94%) by the standard method and in 42 patients (88%) by the simplified method (p = NS). In conclusion, our method for measuring AVR is accurate and simpler than the standard method.

Aortic valve resistance as an adjunct to the Gorlin formula in assessing the severity of aortic stenosis in symptomatic patients

OBJECTIVES

This study was conducted to determine the utility of aortic valve resistance in assessing the severity of aortic stenosis.

BACKGROUND

Assessment of the severity of aortic stenosis has traditionally employed hemodynamic data and the Gorlin formula to calculate the area of the aortic valve. Recently, flow dependence of the Gorlin formula has been identified and the accuracy of the formula challenged. Aortic valve resistance, the quotient of gradient and cardiac output, has been advanced as potentially useful in assessing the severity of valve stenosis.

METHODS

We studied 48 symptomatic patients with an initial diagnosis of severe aortic stenosis based on a calculated aortic valve area of less than or equal to 0.8 cm2 by the Gorlin formula. Forty of these patients (Group I) were confirmed to have severe aortic stenosis, whereas 8 (Group II) were subsequently proved not to have severe aortic stenosis. The 18 patients in Group I with a valve area of 0.6 to 0.8 cm2 (Group IA) were directly compared with Group II patients who had a similar valve area.

RESULTS

Aortic valve area was nearly identical in Group IA and Group II patients (0.69 +/- 0.05 and 0.71 +/- 0.06 cm2, respectively, p = NS). However, aortic valve resistance was much less in Group II patients (212 +/- 6 vs. 316 +/- 11 dynes.s.cm-5, p less than 0.0001). In this small cohort, aortic valve resistance achieved nearly complete separation of patients in Groups IA and II.

CONCLUSIONS

In some patients with relatively mild aortic stenosis, the calculated valve area may indicate that the stenosis is severe. The use of aortic valve resistance in conjunction with the Gorlin formula helps separate patients with truly severe aortic stenosis from those with milder disease.

Physiologic changes with maximal exercise in asymptomatic valvular aortic stenosis assessed by Doppler echocardiography

OBJECTIVES

We hypothesized that the physiologic response to exercise in valvular aortic stenosis could be measured by Doppler echocardiography.

BACKGROUND

Data on exercise hemodynamics in patients with aortic stenosis are limited, yet Doppler echocardiography provides accurate, noninvasive measures of stenosis severity.

METHODS

In 28 asymptomatic subjects with aortic stenosis maximal treadmill exercise testing was performed with Doppler recordings of left ventricular outflow tract and aortic jet velocities immediately before and after exercise. Maximal and mean volume flow rate (Qmax and Qmean), stroke volume, cardiac output, maximal and mean aortic jet velocity (Vmax, Vmean), mean pressure gradient (delta P) and continuity equation aortic valve area were calculated at rest and after exercise. The actual change from rest to exercise in Qmax and Vmax was compared with the predicted relation between these variables for a given orifice area. Subjects were classified into two groups: Group I (rest-exercise Vmax/Qmax slope > 0, n = 19) and Group II (slope < or = 0, n = 9).

RESULTS

Mean exercise duration was 6.7 +/- 4.3 min. With exercise, Vmax increased from 3.99 +/- 0.93 to 4.61 +/- 1.12 m/s (p < 0.0001) and mean delta P increased from 39 +/- 20 to 52 +/- 26 mm Hg (p < 0.0001). Qmax rose with exercise (422 +/- 117 to 523 +/- 209 ml/s, p < 0.0001), but the systolic ejection period decreased (0.33 +/- 0.04 to 0.24 +/- 0.04, p < 0.0001), so that stroke volume decreased slightly (98 +/- 29 to 89 +/- 32 ml, p = 0.01). The increase in cardiac output with exercise (6.5 +/- 1.7 to 10.2 +/- 4.4 liters/min, p < 0.0001) was mediated by increased heart rate (71 +/- 17 to 147 +/- 28 beats/min, p < 0.0001). There was no significant change in the mean aortic valve area with exercise (1.17 +/- 0.45 to 1.28 +/- 0.65, p = 0.06). Compared with Group I patients, patients with a rest-exercise slope < or = 0 (Group II) tended to be older (69 +/- 12 vs. 58 +/- 19 years, p = 0.07) and had a trend toward a shorter exercise duration (5.3 +/- 2.9 vs. 7.3 +/- 4.9 min, p = 0.20). There was no difference between groups for heart rate at rest, blood pressure, stroke volume, cardiac output, Vmax, mean delta P or aortic valve area. With exercise, Group II subjects had a lower cardiac output (7.4 +/- 2.4 vs. 11.5 +/- 4.6 liters/min, p = 0.005) and a smaller percent increase in Vmax (3 +/- 9% vs. 22 +/- 14%, p < 0.0001).

CONCLUSIONS

Doppler echocardiography allows assessment of physiologic changes with exercise in adults with asymptomatic aortic stenosis. A majority of subjects show a rest-exercise response that closely parallels the predicted relation between Vmax and Qmax for a given orifice area. The potential utility of this approach for elucidating the relation between hemodynamic severity and clinical symptoms deserves further study.

Effects of dobutamine on Gorlin and continuity equation valve areas and valve resistance in valvular aortic stenosis

Previous studies demonstrated changes in aortic valve area calculated by the Gorlin equation under conditions of varying transvalvular flow in patients with valvular aortic stenosis (AS). To distinguish between flow-dependence of the Gorlin formula and changes in actual orifice area, the Gorlin valve area and 2 other measures of severity of AS, continuity equation valve area and valve resistance, were calculated under 2 flow conditions in 12 patients with AS. Transvalvular flow rate was varied by administration of dobutamine. During dobutamine infusion, right atrial and left ventricular end-diastolic pressures decreased, left ventricular peak systolic pressure and stroke volume increased, and systolic arterial pressure did not change. Heart rate increased by 19%, cardiac output by 38% and mean aortic valve gradient by 25%. The Gorlin valve area increased in all 12 patients by 0.03 to 0.30 cm2. The average Gorlin valve area increased from 0.67 +/- 0.05 to 0.79 +/- 0.06 cm2 (p < 0.001). In contrast, the continuity equation valve area (calculated in a subset of 6 patients) and valve resistance did not change with dobutamine. The data support the conclusion that flow-dependence of the Gorlin aortic valve area, rather than an increase in actual orifice area, is responsible for the finding that greater valve areas are calculated at greater transvalvular flow rates. Valve resistance is a less flow-dependent means of assessing severity of AS.

Beat-by-beat aortic valve area measurements indicate constant orifice area in aortic stenosis: analysis of Doppler data with varying RR intervals

Gorlin formula calculation of aortic valve area suggests that orifice area increases in patients with aortic stenosis with rising cardiac output. Evidence that aortic orifice area varies was sought in patients with aortic stenosis by analyzing Doppler data beat by beat versus RR interval in 22 patients with spontaneous RR variability. Stroke volume increased in all patients from minimum to maximum RR interval by 129% +/- 19%. Over the same range of RR intervals, assessment of aortic valve area by (A) simultaneous inner and outer continuous wave Doppler signals, or (B) nonsimultaneous RR-matched pulsed wave Doppler from the left ventricular outflow tract and continuous wave Doppler from the aortic valve failed to suggest an increase in aortic valve area. A positive relationship between aortic valve area and RR interval was not consistently observed with the exception of seven out of eight patients with mild to moderate (pulsed wave Doppler/continuous wave Doppler time velocity integral ratio of 0.3 to 0.7) aortic stenosis (p less than 0.05). Beat-by-beat measurements of aortic valve orifice area using Doppler techniques do not suggest that the aortic stenosis orifice varies over a wide range of RR intervals and stroke volumes.

Hemodynamic assessment of aortic stenosis

The decision to operate in patients with aortic stenosis is based on the presence of symptoms and hemodynamically significant valvular obstruction. The strengths and limitations of cardiac catheterization and Doppler echocardiography are compared, and the concept of "critical" aortic stenosis is discussed. The recommendation of aortic valve replacement must take into account the symptom status, the hemodynamic significance of the lesion, and the size and type of valve to be implanted.

Effect of exercise on indices of valvular aortic stenosis

Changes in the physiologic state of the patient may affect indices of valvular aortic stenosis. We determined the effects of supine exercise on the Gorlin valve area, Cannon valve area, aortic valve resistance, and a modified stroke work loss index in 80 patients with aortic stenosis. Exercise caused a significant increase in the Gorlin and Cannon valve area, while work loss and valve resistance decreased significantly. The average percent change in work loss, 12.2%, was lower than the other indices (P less than 0.02), i.e., 15.3% for valve resistance, 18.6% for the Gorlin area, and 19.3% for the Cannon area. The correlation between the rest and exercise measurements was highest for work loss (r = 0.94), compared to 0.93, 0.88, and 0.89 for the other 3 indices, respectively. In patients with a Gorlin area below 1 cm2, exercise caused a significant decrease in work loss, but not Cannon area or valve resistance. However, the percent change was significantly lower and the correlation was better with the work loss index. We conclude that the work loss index is less affected by supine exercise than other indices of aortic stenosis.

Mitral valve resistance as a hemodynamic indicator in mitral stenosis

Variability of the valve area calculated by the Gorlin formula has been noted in bioprosthetic and aortic valves, but few data are available for native stenotic mitral valves. Valve resistance has been proposed as an alternative hemodynamic indicator; however, its value in mitral stenosis has not been assessed. Thirty-four patients had simultaneous recordings of left atrial and ventricular pressures, 26 after percutaneous balloon mitral dilatation (PBMD). Patients with shunt or mitral regurgitation were excluded. Mitral valve resistance correlated exponentially with Gorlin mitral area (y = 133*[area]-1.5; p less than 0.0001). Both Gorlin mitral area and mitral resistance improved after PBMD (0.89 +/- 0.07 cm2 to 2.22 +/- 0.15 cm2; p less than 0.001; and 166 +/- 20 to 40 +/- 8 dynes.s.cm-5; p less than 0.001). Gorlin area and mitral resistance correlated with New York Heart Association functional class. After infusion of isoproterenol in 17 patients, there was an increase in Gorlin area (baseline 1.77 +/- 0.22 cm2, change 0.23 +/- 0.10; p less than 0.03), whereas mitral resistance did not change (baseline 96 +/- 16 dynes.s.cm-5, change 2 +/- 5; p = not significant). Mitral resistance is valuable in the assessment of mitral stenosis. It varies less than Gorlin mitral area under changing hemodynamic conditions.