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

Pathophysiologic and prognostic importance of cardiac power output reserve in heart failure with preserved ejection fraction

AIMS

Heart failure with preserved ejection fraction (HFpEF) is a syndrome characterized by multiple cardiac reserve limitations during exercise. Cardiac power output (CPO) is an index of global cardiac performance and can be estimated non-invasively by echocardiography. We hypothesized that CPO reserve during exercise would be associated with impaired cardiovascular reserve, exercise intolerance, and adverse outcomes in HFpEF.

METHODS AND RESULTS

Exercise stress echocardiography was performed in 425 dyspnoeic patients [217 HFpEF and 208 non-heart failure (HF) controls] to estimate CPO at rest and during exercise. We classified patients with HFpEF based on the median value of changes in CPO from rest to peak exercise (ΔCPO >0.49 W/100 g). Patients with HFpEF and a lower CPO reserve had poorer biventricular systolic function, impaired chronotropic response during exercise, and worse aerobic capacity than controls and those with a higher CPO reserve. During a median follow-up of 358 days, a composite outcome of all-cause mortality or HF events occurred in 30 patients. Patients with a lower CPO reserve had four-fold and nearly 10-fold increased risks of the outcomes compared with those with a higher CPO reserve and controls, respectively [hazard ratio (HR) 4.05, 95% confidence interval (CI) 1.16-10.1, P = 0.003 and HR 9.61, 95% CI 3.58-25.8, P < 0.0001]. We further found that a lower CPO reserve had an incremental prognostic value over the H2FPEF score and exercise duration. In contrast, resting CPO did not predict clinical outcomes in patients with HFpEF.

CONCLUSION

A lower CPO reserve was associated with biventricular systolic dysfunction, chronotropic incompetence, exercise intolerance, and adverse outcomes in patients with HFpEF.

Assessment of cardiac dynamics during stress echocardiography by the peak power output-to-left ventricular mass ratio

Peak cardiac power-to-mass and peak mass-to-power are variables that couple cardiac power output with left ventricular (LV) mass at peak exercise or during maximal inotropic stimulation. Quantitative stress echocardiography enables the calculation of power output according to the formula: 133 × 10–6 × stroke volume per second (ml) × mean blood pressure (BP; mmHg) × heart rate. Power-to-mass may be calculated as LV power output per 100 g of LV mass: 100 g × LV power output divided by LV mass (W/100 g). Conversely, mass-to-power may be estimated by dividing LV mass index by LV power output (g/m2/W). With a little rearrangement of the formulas we can write: power-to-mass (W/100 g) = 0.222 × cardiac output (l/min) × mean BP (mmHg)/LV mass (g) and mass-to-power (g/m2/W) = LV mass index/0.00222 × cardiac output (l/min) × mean BP (mmHg). These parameters reflect the energy delivery of ventricular myocardium with respect to potential energy that is stored in LV mass. The assessment of peak power-to-mass and peak mass-to-power indices may be useful to distinguish compensatory versus maladaptive remodeling in patients with LV dysfunction. When the integrity of myocardial structure is compromised, a disproportion becomes apparent between maximal cardiac power output and LV mass and this leads to either a reduction of peak power-to-mass or an increase of peak mass-to-power. Preliminary reports have demonstrated the usefulness and the prognostic value of peak power-to-mass and peak mass-to-power in patients with LV systolic dysfunction and coronary artery disease.

Peak power output to left ventricular mass: an index to predict ventricular pumping performance and morbidity in advanced heart failure

BACKGROUND

Similar to power-to-weight ratio and weight-to-power ratio, which are measurements of the actual performance of any engine, the ratios of peak power output to left ventricular (LV) mass (peak power/mass) and of peak LV mass to power output (peak mass/power) are indices of LV performance potentially useful in heart failure (HF). This Doppler echocardiographic study was designed to evaluate peak power/mass and peak mass/power in patients with advanced HF compared with healthy subjects and to assess their prognostic value.

METHODS

Power output was measured at rest and at peak exercise in 75 subjects, 60 patients with advanced HF (LV ejection fraction ≤ 35%) and 15 controls. Peak LV power output (W) was calculated as the maximal product of (133 × 10⁻⁶) × stroke volume (mL) × mean arterial pressure (mm Hg) × heart rate (beats/min). LV mass was assessed using a standard M-mode echocardiographic method.

RESULTS

Peak power/mass was 1.84 ± 0.46 W/100 g and 0.76 ± 0.31 W/100 g, and peak mass/power was 32 ± 10 g/m²/W and 84 ± 38 g/m²/W in controls and in patients with HF, respectively (both P values < .0001). Peak power/mass was a powerful predictor of outcome on multivariate logistic regression analysis (hazard ratio, 0.907; P = .009). On receiver operating characteristic curve analysis, the areas under the curve for HF-related events were greater for peak power/mass (P = .002) and peak mass/power (P = .011) with respect to resting ejection fraction. Comparisons of Cox models showed that peak power/mass added prognostic value to a model that included age, New York Heart Association class, etiology, ejection fraction, and diastolic dysfunction (P < .0001).

CONCLUSION

Peak power/mass is useful to discriminate and risk stratify patients with advanced HF with additional power with respect to ejection fraction.

Resting measures and physiological responses to exercise for the determination of prognosis in patients with chronic heart failure: useful tools for clinical decision-making

Despite recent advances in the management of chronic heart failure (CHF), the prognosis of many of these patients remains dire. The need for an accurate prognosis in these patients has led to the identification of several indicators purported to represent the impact of the disease. Such indicators often are obtained at rest and are not always accurate at determining the clinical status of CHF patients. As a result, the relationship between prognostic indicators and clinical outcomes is frequently weak. On the other hand, physiological responses to acute exercise may unmask patients with the worst clinical status and identify those at increased risk of poor outcomes. Therefore, the present review appraises the value of several prognostic indicators for patients with CHF collected at rest and in response to exercise. In particular, it contrasts the value and accuracy of predictors of mortality widely used in clinical settings, such as oxygen uptake, ventilatory efficiency, and left ventricular ejection fraction, with new and more direct indicators of ventricular systolic and diastolic function.

Modulation of catecholamine responsiveness and beta-adrenergic receptor/adenylyl cyclase pathway during cardiac allograft rejection1 2

BACKGROUND

This study investigated the changes of catecholamine responsiveness and beta-adrenergic receptor/adenylyl cyclase pathway during acute cardiac transplant rejection.

METHODS

Isogeneic Lewis to Lewis and allogeneic Dark Agouti (DA) to Lewis rat cardiac transplants were studied 3 and 5 days after heterotopic intraabdominal transplantation (n=6/group). Myocardial blood flow (MBF), left ventricular systolic pressure (LVSP), maximum pressure development (+dP/dt), and end-diastolic pressure (LVEDP) were measured using an intraventricular balloon. Contractile response to dobutamine (5 microg/kg/min) was also assessed. In separate groups beta-adrenergic receptor density and adenylyl cyclase activity were measured in the grafts, in the recipients' native hearts and in native hearts of sham-operated controls.

RESULTS

During mild to moderate rejection cardiac function indices remained unchanged, although MBF and contractile response to dobutamine decreased significantly (P<0.05) in the allogeneic group. The beta-adrenergic receptor density was significantly (P<0.05) increased in both isografts and allografts and in the native hearts of allografted recipients in comparison to native hearts of controls. Adenylyl cyclase activity showed a significant decrease (P<0.05) only in allografts. During severe rejection, LVSP and +dP/dt decreased and LVEDP increased in allografts in comparison to isografts (P<0.05). This was accompanied by a significant decrease in MBF, contractile response to dobutamine, beta-adrenergic receptor density, and adenylyl cyclase activity (P<0.05).

CONCLUSIONS

Both microcirculatory disturbances and primary alteration in adenylyl cyclase activity may contribute to decreased contractile reserve in mild to moderate cardiac allograft rejection, whereas beta-adrenergic receptor density seems to be also influenced by cardiac denervation. Severe rejection leads to systolic and diastolic heart failure with complex dysregulation of the beta-adrenergic receptor/adenylyl cyclase pathway and impaired microcirculation.

Dobutamine echocardiography in idiopathic dilated cardiomyopathy: clinical and prognostic implications

The dobutamine echocardiographic test (DET) is frequently used in coronary artery disease to detect viable myocardium, but few data are available about its role in idiopathic dilated cardiomyopathy (IDCM). The aims of this study were to evaluate the clinical role of DET and the prognostic implications of the 'contractile reserve' in patients with IDCM treated with optimal medical therapy, including beta-blockade (BB). A total of 51 patients with IDCM underwent DET at diagnosis. A positive response to DET (DET+) was judged to be a significant increase (> or =10 points) in left ventricular ejection fraction (LVEF) with a peak value > or =40%, and a reversed restrictive left ventricular filling pattern (RFP) if present at baseline study. Improvement at follow-up was defined according to combined clinical and echo-Doppler criteria. In all, 22 patients (43%) were classified as DET+. DET+ patients were less symptomatic (P<0.001), with lower heart rate (P<0.01), less enlarged left and right ventricles (P<0.0001 and P<0.05), higher LVEF (P=0.0001), less frequent RFP (P=0.01), and lower pulmonary pressure (P<0.01). At follow-up (34+/-16 months), 21 patients had improved, while four had died and seven had received a transplant. Among clinical data, NYHA classes I-II (OR=0.25, P=0.07) and BB dosage (OR=0.97, P<0.005) were significantly associated with higher transplant-free survival at multivariate analysis. The addition of DET+ (OR=0.34, P<0.05) showed a moderate but significant improvement of sensitivity, but the predictive power of the model remained low (sensitivity, 0.67; specificity, 0.55). Absence of left bundle branch block (OR=0.27, P<0.01) and BB dosage (OR=1.03, P<0.005), but not DET+, were predictive of improvement. In patients with IDCM, DET response is associated with a more favourable outcome, since it suggests an earlier stage of the disease. However, in the light of our data, the incremental prognostic power of DET response compared to clinical evaluation at enrollment, despite being significant, seems to be of limited clinical value. Further studies should be carried out in order to clarify the prognostic value of DET in IDCM patients.

Examination of left ventricular contractile reserve by Doppler myocardial imaging in patients with dilated cardiomyopathy

Detection of left ventricular contractile reserve by means of dobutamine stress echocardiography is a well known technique. The aim of the present study was to detect velocity changes during the administration of dobutamine, to establish if Doppler myocardial imaging is a suitable method for determining left ventricular contractile reserve, and to determine if the technique provides more information than traditional stress echocardiography. Twenty-five patients (all males; mean age, 53.4 years) were examined for a clinical diagnosis of idiopathic dilated cardiomyopathy with a poor left ventricular systolic function (ejection fraction less than 30%). Doses of 5-10 and 20 mg/kg/min dobutamine were administered and elevated at 4-minute intervals. Ejection fraction was calculated using the Simpson rule. The peak systolic and the early and late diastolic velocities were measured in the basal segment of the septum and the inferior wall at baseline and at full dose of dobutamine. Results indicated that peak systolic velocity increased significantly, both in the septum (0.11±0.03 vs. 0.20±0.05 m/sec; p=0.001) and in the inferior wall (0.10±0.05 vs. 0.17±0.06 m/sec; p=0.03). Late diastolic velocities also increased significantly, both in the septum (0.17±0.05 vs. 0.22±0.07 m/sec; p=0.01) and in the inferior wall (0.18±0.08 vs.0.21±0.02 m/sec; p=0.01). There was a significant linear correlation between the relative increases in basal ejection fraction value and in peak systolic velocity upon dobutamine stimulation. Patients were divided into responders and nonresponders based on responses in either ejection fraction (25% relative increase) or peak systolic velocity (5 cm/s increase). This study concludes that 1) Doppler myocardial imaging is an adequate and simple technique to examine left ventricular contractile reserve; and 2) measurement of peak systolic velocity during dobutamine stimulation seems to be a simple and good indicator of left ventricular contractile reserve. (c)2001 CHF, Inc.

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.

The role of exercise testing in the evaluation and management of heart failure

The clinical syndrome of heart failure has been investigated so extensively that it may now almost be regarded as a metabolic disorder. Although an initial insult reduces cardiac pump efficacy, the resultant physiological response culminates in complex neurohormonal dysfunction. This has created confusion and prevented the acceptance of a universal definition of cardiac failure. With much current research concentrating on the pharmacological modification of neuroendocrine imbalance, it is easy to lose sight of the fundamental principles behind heart failure management, namely, to improve cardiac function. In attempting to achieve this, the issues of morbidity and mortality must be addressed jointly; they are not mutually exclusive entities. Discrepant results between mortality studies and changes in exercise capacity have undermined the value of exercise testing. Because a treatment enhances longevity we should not ignore its effect on symptomatic status, and likewise we should not discard a therapy, which improves function because adverse events result in occasional premature deaths. Informed patient choice must exist. Historically, exercise testing has been quintessential in our understanding and evaluation of heart failure. Peak oxygen consumption remains the best overall indicator of symptomatic status, exercise capacity, prognosis and hospitalisation. Unfortunately, muddling of surrogate and true end-points has confused many of these issues. Improved comprehension may be gained by applying the concept of cardiac reserve which has been described in a variety of heart conditions and used in cardiac failure patients to provide an indication of prognosis and functional capacity.

Optimal preload adjustment of maximal ventricular power index varies with cardiac chamber size

BACKGROUND

Maximal left ventricular power (PWRmax) can index contractile function and reserve; however, its marked preload dependence mandates load adjustment to yield a more cardiac-specific measurement. Prior studies have used varying methods, but supporting data have generally been lacking. We hypothesized that the optimal approach for preload adjustment varies with ventricular volume (particularly end-systolic volume) and is significantly different for dilated hearts with reduced left ventricular function compared with small to normal-sized hearts with normal systolic function.

METHODS

Left ventricular pressure-volume relations were measured by the conductance catheter method in 36 patients, with preload altered by inferior vena cava obstruction. Patients with normal ventricles (n = 16), hypertrophy or mitral stenosis (n = 12), and dilated cardiomyopathy (n = 8) were divided into three groups based on resting end-diastolic volume: group 1, 66.3 +/- 12; group 2, 118.1 +/- 20; and group 3, 218.2 +/- 48 ml. PWRmax was the maximal product of simultaneous left ventricular pressure and rate of volume change. PWRmax end-diastolic volume (EDV) data were fit to a power function, PWRmax = alphaEDVbeta (where alpha is a scaling factor and beta is the power coefficient), and the preload sensitivity of beta and PWRmax/EDVbeta ratios (beta = 1, 2, or best fit) were compared.

RESULTS

Beta varied directly with chamber size: 0 = 0.004 x (EDV + 0.56), r = 0.65, p < 0.0001. However, it was equally well approximated by 1.0 in groups 1 and 2 (ESV <75 ml, EF >40%), whereas beta = 2 was more appropriate in group 3.

CONCLUSION

PWRmax/EDV provides adequate preload independence in all but dilated hearts with reduced LV function, whereas PWRmax/EDV2 is required in the latter. These data should help clinical application of a noninvasive PWRmax index for assessing chamber contractility and contractile reserve in human beings.

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.