Determinants of stroke volume response to exercise in patients with mitral stenosis: a Doppler echocardiographic study

Hemodynamics and Prognostic Impact of Concomitant Mitral Stenosis in Patients Undergoing Surgical or Transcatheter Aortic Valve Replacement for Aortic Stenosis

BACKGROUND

Mitral stenosis frequently coexists in patients with severe aortic stenosis. Mitral stenosis severity evaluation is challenging in the setting of combined aortic stenosis and mitral stenosis because of hemodynamic interactions between the 2 valve lesions. The impact of aortic valve replacement (AVR) for severe aortic stenosis on mitral stenosis is unknown. This study aimed to assess the effect of AVR on mitral stenosis hemodynamics and the clinical outcomes of patients with severe aortic stenosis with and without mitral stenosis.

METHODS

We retrospectively investigated patients who underwent surgical AVR or transcatheter AVR for severe aortic stenosis from 2008 to 2015. Mean transmitral gradient by Doppler echocardiography ≥4 mm Hg was identified as mitral stenosis; patients were then stratified according to mitral valve area (MVA, by continuity equation) as >2.0 cm² or ≤2.0 cm². MVA before and after AVR in patients with mitral stenosis were evaluated. Clinical outcomes of patients with and without mitral stenosis were compared using 1:2 matching for age, sex, left ventricular ejection fraction, method of AVR (surgical AVR versus transcatheter AVR) and year of AVR.

RESULTS

Of 190 patients with severe aortic stenosis and mitral stenosis (age 76±9 years, 42% men), 184 were matched with 362 with severe aortic stenosis without mitral stenosis. Among all mitral stenosis patients, the mean MVA increased after AVR by 0.26±0.59 cm² (from 2.00±0.50 to 2.26±0.62 cm², P<0.01). MVA increased in 105 (55%) and remained unchanged in 34 (18%). Indexed stroke volume ≤45 mL/m² (odds ratio [OR] 2.40; 95% CI, 1.15-5.01; P=0.020) and transcatheter AVR (OR, 2.36; 95% CI, 1.17-4.77; P=0.017) were independently associated with increase in MVA. Of 107 with significant mitral stenosis (MVA ≤2.0 cm²), MVA increased to >2.0 cm² after AVR in 52 (49%, pseudo mitral stenosis) and remained ≤2.0 cm² in 55 (51%, true mitral stenosis). During follow-up of median 2.9 (0.7-4.9) years, true mitral stenosis was an independent predictor of all-cause mortality (adjusted hazard ratio, 1.88; 95% CI, 1.20-2.94; P<0.01).

CONCLUSIONS

MVA improved after AVR in nearly half of patients with severe aortic stenosis and mitral stenosis. MVA remained ≤2.0 cm² (true mitral stenosis) in nearly half of patients with severe aortic stenosis and significant mitral stenosis; this was associated with worse survival among patients undergoing AVR for severe aortic stenosis.

Degenerative Mitral Stenosis: From Pathophysiology to Challenging Interventional Treatment

Mitral stenosis (MS) is characterized by obstruction of left ventricular inflow as a result of narrowing of the mitral valve orifice. Although its prevalence has declined over the last decade, especially in developed countries, it remains an important cause of morbidity and mortality.  The most often cause of MS worldwide is still postrheumatic mitral valve disease. However, in developed countries, degenerative or calcific changes cause MS in a siginificant proportion of patients. Although the range of treatment for mitral valve disease has grown over the years in parallel with transcatheter therapies for aortic valve disease, these improvements in mitral valve disease therapy have experienced slower development. This is mainly due to the more complex anatomy of the mitral valve and entire mitral apparatus, and the interplay of the mitral valve with the left ventricle which hinders the development of effective implantable mitral valve devices. This is especially the case with degenerative MS where percutaneous or surgical comissurotomy is rarely employed due to the presence of extensive annular calcification and at the base of leaflets, without associated commissural fusion. However, the last few years have witnessed innovations in transcatheter interventional procedures for degenerative MS which consequently hinted that in the future, transcatheter mitral valve replacement could be the treatment of choice for these patients.

The impact of cardiac rhythm on the mitral valve area and gradient in patients with mitral stenosis

OBJECTIVE

The aim of this study was to evaluate the effect of cardiac rhythm on the echocardiographic mitral valve area (MVA) and transmitral gradient calculation in relation to net atrioventricular compliance (Cn).

METHODS

Patients (n=22) with mild or moderate pure rheumatic mitral stenosis (MS) (MVA <2 cm2 and MVA >1 cm2) and atrial fibrillation (AF) were evaluated. All patients underwent transthoracic electrical DC cardioversion under amiodarone treatment. Nineteen of the 22 patients were successfully converted to sinus rhythm (SR). The patients were evaluated with transthoracic echocardiography before and two to three days after DC cardioversion. In order to deal with variable R-R intervals, the measurements were averaged on five to eight consecutive beats in AF. Cn was calculated with a previously validated equation [Cn (mL/mm Hg)=1.270 x MVA/E-wave downslope]. The Cn difference between AF and SR was calculated as follows: [(AF Cn-SR Cn)/AF Cn] x 100. The percentage gradient (mean or maximal) difference between AF and SR was calculated as follows: [AF gradient (mean or maximal) - SR gradient (mean or maximal)]/[AF gradient (mean or maximal)] x 100.

RESULTS

The MVA was lower (MVA planimetric; 1.62±0.29 vs. 1.54±0.27; p=.003, MVA PHT; 1.66±0.30 vs. 1.59±0.26; p=0.01) but transmitral gradient (mean gradient; 6.49±2.51 vs. 8.89±3.52; p=0.001, maximal gradient: 16.94±5.11 vs. 18.57±4.54; p=0.01) and Cn values (5.37±0.77 vs. 6.26±0.64; p<0.001) were higher in the AF than SR. There was a significant correlation between Cn difference and transmitral gradient difference (mean and maximal) (Cn difference-mean gradient difference; r=0.46; p=0.05; Cn difference-maximal gradient difference; r=0.72; p=0.001).

CONCLUSION

Cardiac rhythm has a significant impact on echocardiographic evaluation of MVA, transmitral gradient, and Cn in patients with MS.

The Use of Stress Echocardiography in the Assessment of Mitral Valvular Disease

Stress echocardiography plays an important role in evaluating asymptomatic patients with significant mitral stenosis and symptomatic patients with only mild disease at rest, as it correlates the exercise-induced symptoms with changes in transmitral gradients, pulmonary pressures, and mitral valve area. In patients with mitral regurgitation (MR), exercise or dobutamine protocols assess for the change in the degree of regurgitation and the pulmonary artery pressure (PAP) in response to high flow states, and detect underlying left ventricular (LV) dysfunction prior to valvular surgery. Exercise echocardiography also helps in the prognostic assessment of patients with mitral valve prolapse as new MR, or latent LV dysfunction may be provoked to identify a group of high risk individuals with normal resting echocardiographic parameters. Finally, it evaluates the proper functioning of prosthetic mitral valves and helps on the monitoring of transmitral gradients and PAPs after mitral valve surgery.

Dobutamine stress echocardiography for noninvasive assessment and risk stratification of patients with rheumatic mitral stenosis

OBJECTIVES

We sought to evaluate the impact of dobutamine stress echocardiography (DSE) in patients with known rheumatic mitral stenosis (MS) in order to assess its safety, feasibility, and prognostic correlation to well-known clinical outcomes.

BACKGROUND

Noninvasive prognostic assessment of MS still represents an unresolved task in patients with clinically challenging disease.

METHODS

Dobutamine stress echocardiography was performed in 53 patients with MS (8 males; age 37.4 +/- 11.3 years) with no major complications.

RESULTS

During follow-up (60.5 +/- 11.0 months), 29 patients presented with clinical events: 16 hospitalizations, seven cases of acute pulmonary edema, and six symptomatic supraventricular arrhythmias. On multivariate analysis, the diastolic mitral valve mean gradient at peak DSE (DSE-MG) was the best predictor of clinical events (p < 0.008), especially in patients with moderate disease (p < 0.001). The best performance of DSE for the detection of clinical events was obtained at a cut-off value of 18 mm Hg DSE-MG (sensitivity 90%, specificity 87%, and accuracy 90%). The addition of DSE to the conventional cardiology work-up would allow a 17% increment for the detection of high-risk patients in the entire population and a 40% increment in patients with presumed moderate disease.

CONCLUSIONS

In patients with MS, DSE is a safe and highly feasible stress test. A DSE-MG > or =18 mm Hg identifies a subgroup of high-risk patients in whom a more aggressive approach may be warranted; on the other hand, patients with a DSE-MG <18 mm Hg predicts an uneventful clinical course and may justify a more conservative strategy.

Does balloon mitral valvuloplasty improve cardiac function? A mechanistic investigation into impact on exercise capacity

Procedural technical success of balloon mitral valvuloplasty (BMV) is indicated by an increase in valve area and a reduction in transvalvar gradient, but there are conflicting results regarding whether these indicators correlate with subsequent improvements in exercise capacity. We conducted a study to explore the effects of valvuloplasty on cardiac function to gain insight into the mechanisms responsible for the impact on exercise ability. Sixteen patients with mitral stenosis participated in the study and the five who did not proceed to valvuloplasty served as the control group. All patients performed maximal cardiopulmonary exercise tests before and 6 weeks after valvuloplasty (without valvuloplasty in controls). Central haemodynamics including cardiac output were measured non-invasively at rest and peak exercise. At baseline, the cardiopulmonary exercise test results were similar in the two groups. Following valvuloplasty, cardiac output did not alter at rest, but increased significantly at peak exercise (8.7+/-1.7 to 10.5+/-2.1 l min(-1), P<0.01), as did peak cardiac power output (1.88+/-0.55 to 2.28+/-0.74, P<0.05) and cardiac reserve (1.07+/-0.33 to 1.45+/-0.55 watts, P<0.05). Aerobic exercise capacity improved (13.9+/-4.2 to 16.4+/-4.3 ml kg(-1) min(-1), P<0.01) as did exercise duration (354+/-270 to 500+/-266 s, P<0.01). There were no significant changes in the controls. There was a significant correlation between the changes in peak VO(2) and changes in cardiac reserve (r=0.62, P<0.01) but not with changes in resting haemodynamics. These changes did not correlate with changes in peri-procedural mitral valve haemodynamics, despite increases in mitral valve area from 1.05+/-0.16 to 1.74+/-0.4 cm(2) (P<0.0001), accompanied by falls in the transvalvar gradient and pulmonary artery pressure (12.4+/-4.7 to 4.5+/-3 mmHg, and 26.8+/-8.4 to 17.4+/-5.2 mmHg, respectively, all P<0.0001). In conclusion, we found that successful mitral valvuloplasty in our patient cohort led to improved cardiac and physical functional capacity but not resting haemodynamics. Neither indicators of technical success nor resting haemodynamics were very reliable in predicting functional improvement.

Is the mitral valve area flow-dependent in mitral stenosis? A dobutamine stress echocardiographic study

OBJECTIVES

The purpose of this study was to compare the effect of changes in flow rate on the mitral valve area (MVA) derived from two-dimensional echocardiographic planimetry and Doppler pressure half-time (PHT) methods in patients with mitral stenosis (MS).

BACKGROUND

Dobutamine stress echocardiography has been proposed as a means of assessing the severity of MS. However, data regarding the effect of an increase in flow rate on MVA are limited. If MVA is indeed flow-dependent, this has important implications for the assessment of the severity of MS, particularly in the setting of reduced cardiac output (CO).

METHODS

Dobutamine echocardiography was performed in 57 patients with isolated MS who were in sinus rhythm. The MVA was determined by planimetry and Doppler PHT methods.

RESULTS

Cardiac output increased by > or =50% in 27 patients (group I) and by <50% in 30 patients (group II). In group I, the MVA by planimetry increased by only 10.6 +/- 2% and the MVA by PHT increased by 21.9 +/- 4.8%. These changes were similar to those observed in group II (10.7 +/- 3% and 14.8 +/- 4%, respectively; p = NS), despite a much smaller increase in CO. A clinically important change (from the severe to mild category) occurred in only one patient when using the PHT method and in none by planimetry.

CONCLUSIONS

Changes in flow rate result in small but clinically insignificant changes in echocardiographic MVA measurement. These methods provide an accurate assessment of MS severity in a majority of patients, independent of changes in flow rate.

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.

Overview of stress echocardiography: uses, advantages, and limitations

Responses of the heart to changes in our environment are probably even more important than how the heart functions at rest. Accordingly, stress testing with noninvasive imaging has become important for diagnosis, prognosis, and monitoring the effects of therapy. Echocardiography at rest and with stress permits characterization of global and segmental left ventricular function as well as valvular structure and function. Moreover, echocardiography can be performed during or after a number of different physical or even mental stressors. Advantages of stress echocardiography include its ready availability, relatively low capital cost, and incremental value in that it allows characterization of cardiac anatomy as well as the myocardial response to a potentially ischemic stimulus. Moreover, echocardiography has the potential to image myocardial perfusion along with wall motion and wall thickening. Substantial literature has now been accumulated on the value of stress echocardiography for the diagnosis of ischemic disease, preoperative risk assessment, and assessment of myocardial viability. Echocardiography has compared generally well with nuclear imaging techniques for the detection of angiographic coronary artery disease. Overall sensitivity, however, has been slightly less, particularly for the detection of single-vessel coronary disease, although specificity has been on average somewhat higher than nuclear cardiology techniques. Because of the potential for variability in study acquisition as well as interpretation, careful safeguards need to be employed. Specifically, meticulous technique needs to be applied to obtain high-quality images and to assure that those images are obtained promptly after treadmill exercise stress. Only readers with specific interest and expertise should interpret stress echocardiography studies. Continuing efforts need to be made to assess and minimize variability and to assure continuing quality improvement. Advances in instrumentation, including evolving technology for real-time 3-dimensional imaging, and echocardiography contrast assessment of myocardial perfusion will likely improve the sensitivity of echocardiography and further extend its usefulness.

Impact of atrioventricular compliance on pulmonary artery pressure in mitral stenosis: an exercise echocardiographic study

BACKGROUND

The decay of the pressure gradient across a stenotic mitral valve is determined by the size of the orifice and net AV compliance (C(n)). We have observed a group of symptomatic patients, usually in sinus rhythm, characterized by pulmonary hypertension (particularly during exercise) despite a relatively large mitral valve area by pressure half-time. We speculated that this discrepancy was due to low atrial compliance causing both pulmonary hypertension and a steep decay of the transmitral pressure gradient despite significant stenosis. We therefore tested the hypothesis that C(n) is an important physiological determinant of pulmonary artery pressure at rest and during exercise in mitral stenosis.

METHODS AND RESULTS

Twenty patients with mitral stenosis were examined by Doppler echocardiography. C(n), calculated from the ratio of effective mitral valve area (continuity equation) and the E-wave downslope, ranged from 1.7 to 8.1 mL/mm Hg. Systolic pulmonary artery pressure (PAP) increased from 43+/-12 mm Hg at rest to 71+/-23 mm Hg (range, 40 to 110 mm Hg) during exercise. There was a particularly close correlation between C(n) and exercise PAP (r=-0.85). Patients with a low compliance were more symptomatic (P<0.025). Catheter- and Doppler-derived values for C(n), determined in 10 cases, correlated well (r=0.79).

CONCLUSIONS

C(n), which can be noninvasively assessed, is an important physiological determinant of PAP in mitral stenosis. Patients with low C(n) represent an important clinical entity, with symptoms corresponding to severe increases in PAP during stress echocardiography.

Estimation of cardiac reserve by peak power: validation and initial application of a simplified index

OBJECTIVES

To validate a simplified estimate of peak power (SPP) against true (invasively measured) peak instantaneous power (TPP), to assess the feasibility of measuring SPP during exercise and to correlate this with functional capacity.

DESIGN

Development of a simplified method of measurement and observational study.

SETTING

Tertiary referral centre for cardiothoracic disease.

SUBJECTS

For validation of SPP with TPP, seven normal dogs and four dogs with dilated cardiomyopathy were studied. To assess feasibility and clinical significance in humans, 40 subjects were studied (26 patients; 14 normal controls).

METHODS

In the animal validation study, TPP was derived from ascending aortic pressure and flow probe, and from Doppler measurements of flow. SPP, calculated using the different flow measures, was compared with peak instantaneous power under different loading conditions. For the assessment in humans, SPP was measured at rest and during maximum exercise. Peak aortic flow was measured with transthoracic continuous wave Doppler, and systolic and diastolic blood pressures were derived from brachial sphygmomanometry. The difference between exercise and rest simplified peak power (Delta SPP) was compared with maximum oxygen uptake (VO(2)max), measured from expired gas analysis.

RESULTS

SPP estimates using peak flow measures correlated well with true peak instantaneous power (r = 0.89 to 0.97), despite marked changes in systemic pressure and flow induced by manipulation of loading conditions. In the human study, VO(2)max correlated with Delta SPP (r = 0.78) better than Delta ejection fraction (r = 0.18) and Delta rate-pressure product (r = 0.59).

CONCLUSIONS

The simple product of mean arterial pressure and peak aortic flow (simplified peak power, SPP) correlates with peak instantaneous power over a range of loading conditions in dogs. In humans, it can be estimated during exercise echocardiography, and correlates with maximum oxygen uptake better than ejection fraction or rate-pressure product.

Stress echocardiography in valvular heart disease

Stress echocardiography has been widely accepted as an important diagnostic and prognostic tool in the assessment of known or suspected coronary artery disease. Its use in valvular heart disease, to date, has been more limited, but is continuing to grow as the technology and the understanding of valvular disorders progress. In this article, we will review the current literature regarding the use of both exercise and pharmacological stress testing in conjunction with echocardiography in the settings of native and prosthetic mitral and aortic valve disease. We will also discuss the limitations of this modality and touch upon possible future areas of investigation.

Valve Resistance in Mitral Stenosis: Its Determinants and its Role in the Evaluation of the Disease

To evaluate the value and the determinants of valve resistance in mitral stenosis, 95 patients with pure mitral stenosis were examined by Doppler echocardiography during their clinical follow-up, measuring cavity dimensions, left ventricular function, mitral area (by planimetry and pressure half time), mean transmitral pressure gradient, aortic flow, and pulmonary artery systolic pressure. The mitral resistance was calculated as mean transmitral pressure gradient/aortic flow ratio. To graduate the severity of the morphological abnormalities in valvular structure, we used a point score system with evaluation of leaflet and subvalvular thickness, calcification, and valvular mobility. The functional class was determined according to NYHA classification. In this study, both mitral area (r = -0.79, P < 0.001 and r(p) = -0.60, P < 0.001) and mitral score (r = 0.68, P < 0.001 and r(p) = 0.25, P = 0.013) were independent determinants of mitral resistance. In multivariate analysis, mitral resistance and female gender were selected by multiple linear regression analysis as determinants of pulmonary artery systolic pressure, and mitral area and pulmonary artery systolic pressure were selected by logistic linear regression analysis as determinants of NYHA functional class. In patients with moderate or severe mitral stenosis, the estimated probability for III and IV NYHA functional class considering mitral area 1 cm(2) or below went from 51.1-86.4% when mitral resistance below or above 130 dynes.sec.cm(-5), respectively, was considered together. Thus, mitral valve resistance should be used as a complement to the mitral area method in assessment of mitral stenosis, adding the effects of the reduction in mitral area and the damage in mitral valve apparatus.

Comparison of exercise and dobutamine stress echocardiography in assessing mitral stenosis

Dobutamine elicited similar hemodynamic response to exercise in 20 consecutive patients with mitral stenosis, and significantly altered management in 6 of them (30%). Dobutamine stress echocardiography is a safe and feasible alternative to exercise in patients with mitral stenosis of mild-to-moderate severity and ambiguous symptoms.

Effect of inadequate cardiac output reserve on exercise tolerance in patients with moderate mitral stenosis

Twenty-nine patients with moderate mitral stenosis and 29 age-matched normal controls underwent symptom-limited upright bicycle exercise testing with simultaneous hemodynamic monitoring. Exercise tolerance in the mitral stenosis group was found to be limited by inadequate cardiac output reserve and not by resting mitral valve area or exercise pulmonary capillary wedge pressure.

[Usefulness of exercise Doppler in the diagnosis of severe mitral stenosis]

BACKGROUND

Exercise in mitral stenosis produces an increase in cardiac output and heart rate which determines the increment in the transmitral gradient. However, it has not yet been established what level is reached by the gradients on exercise in severe mitral stenosis nor whether the rise in the gradient during such exercise is different to that occurring in non-severe stenosis.

OBJECTIVE

To evaluate the effect of exercise in patients with severe mitral stenosis on the mitral valve gradients in absolute values and on the increment with respect to base values.

METHODS

Forty-eight mitral stenosis patients (mean age: 48.8 +/- 11 years) underwent 50 exercise Doppler echocardiographic studies using supine bicycle ergometry in two stages with increases of 25 W every 3 minutes; from each of these we obtained the peak and mean mitral gradient using a non-imaging continuous-wave Doppler probe. We also conducted this procedure on 14 patients with a mean age of 50 +/- 6 who had Bjork mitral prostheses which were functioning normally.

RESULTS

We defined a hemodynamic profile of severity based on the data from 18 patients whose basal mitral valve areas was < 1.2 cm2 (group I), and compared them with the data from the 32 studies of mitral stenosis patients with an area > 1.1 cm2 (group II) and with the patients with mitral prostheses (group III). The mean mitral gradient (mmHg) in group I was greater than in group II at rest (9.3 +/- 3.2 and 6.6 +/- 2.7; p < 0.001), at 25 W (20.6 +/- 4.8 and 14.1 +/- 5; p < 0.001) and at 50 W (25.9 +/- 5.4 and 17.3 +/- 5.8; p < 0.001). The increase in mean mitral gradient from the baseline to 50 watts was 16.7 +/- 4.5 mmHg in group I, which was greater than in group II and III (11.1 +/- 4.1 and 6.8 +/- 2.6 mmHg; p < 0.001).

CONCLUSIONS

Exercise Doppler echocardiography enabled us to define a differential hemodynamic profile in patients with severe mitral stenosis which can be used in isolation as an indicator of severity in this condition.

Prognostic value of noninvasively obtained left ventricular contractile reserve in patients with severe heart failure

OBJECTIVES

The present study sought to evaluate the prognostic value of contractile reserve measured noninvasively during dobutamine infusion in patients with severe heart failure.

BACKGROUND

In patients with severe heart failure there is a great need for objective criteria to define candidates for heart transplantation or intensive medical treatment. Cardiac pumping performance reserve has been shown to have excellent prognostic value in patients with cardiogenic shock.

METHODS

Cardiac peak power, an afterload-independent contractility index, was measured noninvasively at rest and at peak dobutamine inotropic stimulation. Contractile reserve was defined as the difference between maximal cardiac power at peak dobutamine dose and baseline value. Maximal cardiac power was calculated from the maximal product of validated central arterial pressure and aortic flow.

RESULTS

Results were obtained from 52 subjects (42 patients, 10 control subjects). Twenty-two patients were in New York Heart Association functional classes III and IV. Of nine patients with a contractile reserve < 1.5 W/ml, eight died during the 3-year follow-up period. In contrast, all survivors had a contractile reserve > 1.5 W/ml. Using multiple logistic regression analysis, contractile reserve was shown to be the only predictor of survival.

CONCLUSIONS

Contractile reserve measured noninvasively during dobutamine infusion is a valuable prognostic indicator in patients with severe heart failure, with added value to ejection fraction.

Evaluation of contractile reserve by dobutamine echocardiography: noninvasive estimation of the severity of heart failure

Functional status in chronic heart failure is evaluated in general by subjective means, such as the New York Heart Association class, or by invasive techniques difficult to use routinely. The aim of this study was to evaluate noninvasively the contractile reserve in cases of heart failure as a means to define the functional status of the patients. Cardiac peak power, a new noninvasively obtained afterload-independent index of contractility, was calculated from online Doppler and central arterial blood pressure estimated noninvasively in 35 patients with heart failure and 10 healthy subjects during dobutamine infusion. Cardiac output increased in all patients to the same extent, without differentiation among the functional classes. Contractile reserve, as assessed by peak power, was found to be a good marker of functional class: it was significantly higher in functional class 1 than in functional classes 2 through 4. A correlation of r = 0.99 and probability of p < 0.001 was found with the functional status. This new, noninvasive contractility index, peak power, allows an objective evaluation of the severity of heart failure.

Factors determining the exercise capacity in mitral stenosis

In mitral stenosis, peak pulmonary pressure after exercise rather than valve area at rest or mitral gradient, was found to be an important factor in determining the exercise capacity.

Determination of mitral valve area in patients with mitral stenosis by the flow-convergence-region method during changing hemodynamic conditions

Twenty-eight patients with mitral stenosis underwent Doppler echocardiography at rest and during exercise to determine the accuracy of mitral valve area determination by the flow-convergence-region method during exercise-induced changing hemodynamic conditions. The mitral valve area calculated by using the flow-convergence-region method correlated strongly with that measured by the Gorlin formula both at rest (r = 0.85) and during exercise (r = 0.92) for all 28 patients studied. Although mitral valve area obtained by the flow-convergence-region method did not change (p = 0.1) in 16 patients with echocardiographic mitral scores > or = 12, it increased significantly during exercise (p = 0.0001) in 12 patients with echocardiographic mitral scores < 12. This study suggests that in mitral stenosis, the mitral valve area can be accurately estimated by the flow-convergence-region method both at rest and during changing hemodynamic conditions induced by supine bicycle exercise.

Can dobutamine echocardiography distinguish necrotic from ischemic myocardium, early after myocardial infarction?

The aim of this study was to evaluate the usefulness of dobutamine echocardiography (DE) in distinguishing necrotic from ischemic myocardium in infarct zones. We performed DE in 39 patients, 3 to 5 days after admission for a first, acute myocardial infarction, treated with thrombolysis. DE was considered positive if wall motion in the infarct zone worsened progressively during increasing dose of dobutamine or if wall motion in the infarct zone initially improved at low dose of dobutamine and deteriorated at higher dose. The results of DE were correlated to the evolution of wall motion in the infarct zone after 3 months and to the need for supplementary balloon dilatation. In 15 of the 39 patients, there was evidence of residual ischemia in the infarct zone. Twenty of the 39 patients had a positive dobutamine echocardiogram. Eleven of these 20 patients had evidence of residual ischemia in the infarct zone. They showed generalized changes of wall motion in the total infarct territory during DE. The other 9 patients demonstrated only localized changes of wall motion in isolated segments of the infarct zone during DE. None of these patients had evidence of residual ischemia.

IN CONCLUSION

DE seems worthwhile in the detection of residual ischemia in the region of infarction. To reduce the number of false positive DE early after myocardial infarction, only extensive changes of wall motion in the total infarct territory should be accepted as indicative of residual ischemia in the infarct zone.

Influence of preload reserve on stroke volume response to exercise in patients with left ventricular systolic dysfunction: a Doppler echocardiographic study

OBJECTIVES

This study evaluated the role of preload reserve in the stroke volume response to exercise in patients with left ventricular systolic dysfunction by assessing the relation between stroke volume and late left ventricular diastolic filling during exercise.

BACKGROUND

In patients with left ventricular diastolic dysfunction, the absence of left ventricular distension is the fundamental mechanism explaining the nonaugmentation of stroke volume during exercise.

METHODS

In 32 patients with left ventricular systolic dysfunction and 16 healthy control subjects, mitral and aortic velocities were recorded by Doppler echocardiography at rest and during submaximal supine bicycle exercise. Stroke volume, peak early (E) and late (A) mitral velocities, A/E ratio and end-diastolic filling were measured at rest and during exercise.

RESULTS

Stroke volume increased significantly in control subjects but did not change in patients. Peak early mitral velocity increased significantly and to the same extent in both groups, whereas peak late mitral velocity and end-diastolic filling increased significantly in both groups but more so in control subjects; the A/E ratio increased significantly in control subjects but did not change in patients. In addition, stroke volume correlated significantly with peak late mitral velocity during exercise in patients (r = 0.72, p < 0.001).

CONCLUSIONS

Compared with control subjects, patients with left ventricular systolic dysfunction exhibited limited increases in both stroke volume and late left ventricular filling during exercise. Furthermore, their stroke volume response correlated with the capacity of the left ventricle to increase late diastolic filling, that is, preload reserve.

Observations suggesting a high incidence of exercise-induced severe mitral regurgitation in patients with mild rheumatic mitral valve disease at rest

OBJECTIVES

The aim of this study was to determine the hemodynamic effects of upright bicycle ergometry in symptomatic patients with mild, mixed mitral stenosis and regurgitation.

BACKGROUND

Patients with seemingly mild rheumatic mitral valve disease often complain of exertional dyspnea or fatigue. These symptoms are usually ascribed to flow-dependent increases in the gradient across the stenotic mitral valve. Although catheterization studies in these patients may demonstrate an increase in mitral valve gradient proportional to an increase in cardiac output, this approach does not specifically address the underlying mechanism of any observed increases in mitral gradient or left atrial (i.e., pulmonary capillary wedge) pressure. Exercise echocardiography is uniquely suited to the dynamic assessment of exercise-induced hemodynamic changes.

METHODS

Fourteen symptomatic patients with exertional dyspnea and mild mitral stenosis and regurgitation at rest performed symptom-limited upright bicycle ergometry with quantitative two-dimensional, Doppler and color Doppler echocardiographic analysis.

RESULTS

Average pulmonary artery systolic pressure in the 13 patients with adequate spectral signals of tricuspid regurgitation increased from 36 +/- 5 mm Hg (mean +/- SD) at rest to 63 +/- 14 mm Hg at peak exercise (p < 0.001). The mean transmitral pressure gradient in all patients increased from 4.5 +/- 1.4 mm Hg at rest to 12.7 +/- 2.7 mm Hg at peak exercise (p < 0.001). Five patients developed severe mitral regurgitation during exercise.

CONCLUSIONS

Patients with exertional dyspnea and mild mitral stenosis and regurgitation at rest demonstrate a marked increase in pulmonary artery systolic pressure and mean transmitral pressure gradient during dynamic exercise. In a subset of these patients, marked worsening of mitral regurgitation appears to be the underlying mechanism of this hemodynamic deterioration. Because of the small sample size, this novel observation must be considered preliminary with respect to the true prevalence of exercise-related development of severe mitral regurgitation. If additional studies confirm the importance of this phenomenon, it has important implications for the management of patients with rheumatic mitral valve disease.

Contribution of mitral valve reserve capacity to sustained symptomatic improvement after balloon valvulotomy in mitral stenosis: implications for restenosis

OBJECTIVES

To explain the discrepancy between the symptomatic status of patients and the hemodynamically calculated mitral valve area during long-term follow-up after mitral balloon valvulotomy, mitral valve orifice variability after dobutamine infusion was investigated in two groups of patients.

BACKGROUND

A significant increase in aortic valve area with increased aortic transvalvular flow has been reported in patients with calcific aortic stenosis after aortic balloon valvulotomy. A similar phenomenon with regard to the mitral valve has not been studied in detail.

METHODS

Group 1 comprised 10 patients (mean age 33 +/- 9 years) with untreated mitral stenosis. Group 2 comprised 29 consecutive patients (mean age 32 +/- 7 years) who underwent successful percutaneous mitral balloon valvulotomy 13 +/- 2 months before the study.

RESULTS

After dobutamine infusion, heart rate and cardiac index increased significantly in both groups. The mean pulmonary artery pressure, mitral valve gradient and pulmonary capillary pressure remained unchanged in Group 2 but increased significantly in Group 1. The mean mitral valve area was significantly larger in Group 2 after dobutamine infusion than at baseline (1.9 +/- 0.5 vs. 2.4 +/- 0.6 cm2, p < 0.0001) but was unchanged in Group 1 (1.2 +/- 0.2 vs. 1.3 +/- 0.3 cm2, p = NS). The mean mitral valve area in seven patients in Group 2 (24%) was < or = 1.5 cm2 before dobutamine infusion (1.3 +/- 0.4 cm2), which was defined as restenosis. In five of these seven patients who had minimal or no symptoms, the mitral valve area increased significantly after dobutamine infusion (1.3 +/- 0.1 vs. 1.9 +/- 0.1 cm2). In the other two patients who were symptomatic, the mitral valve area did not change after dobutamine infusion. These two patients were identified as having "true" restenosis, and redilation of the mitral valve was performed in both.

CONCLUSIONS

In patients who underwent mitral balloon valvulotomy, increased mitral valve reserve capacity contributed to symptomatic improvement on long-term follow-up. Dobutamine infusion may be helpful in detecting clinically significant restenosis.