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J Am Coll Cardiol, 2001; 37:818-824
© 2001 by the American College of Cardiology Foundation
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CLINICAL STUDY: HEART FAILURE

Left ventricular inotropic reserve and right ventricular function predict increase of left ventricular ejection fraction after beta-blocker therapy in nonischemic cardiomyopathy

Tarik M. Ramahi, MD, FACC*, Marcella D. Longo, MD{dagger}, Arina R. Cadariu, MD*, Kate Rohlfs, RN*, Stella A. Carolan, RN*, Kathryn M. Engle, RN*, Habib Samady, MD* and Frans J. Th Wackers, MD, PhD, FACC*

* Section of Cardiovascular Medicine, Yale School of Medicine, New Haven, Connecticut, USA
{dagger} Division of Cardiology, University of Turin, Molinette Hospital, Turin, Italy

Manuscript received February 28, 2000; revised manuscript received September 29, 2000, accepted November 3, 2000.

Reprint requests and correspondence: Dr. Tarik M. Ramahi, 135 College Street, Suite 301, New Haven, Connecticut 06510-2483
ramahi{at}aya.yale.edu


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
OBJECTIVES

The purpose of this study was to determine whether higher left ventricular inotropic reserve, defined as the increase in left ventricular ejection fraction (LVEF) in response to intravenous dobutamine infusion, or other ventriculographic variables predict the increase in LVEF after beta-blocker therapy in patients with nonischemic cardiomyopathy (NICM).

BACKGROUND

Long-term beta-blocker therapy increases LVEF in some patients with NICM. Other than dose, there are no definite predictors of LVEF increase.

METHODS

Thirty patients with LVEF ≤0.35 and NICM underwent assessment of LVEF at rest and after a 10-min intravenous infusion of dobutamine at 10 µg/kg/min, using equilibrium radionuclide ventriculography. Age was 49 ± 11 years, 33% women, functional class 2.6 ± 0.5, duration of chronic heart failure 3.2 ± 2.9 years, LVEF 0.21 ± 0.07, left ventricular end-diastolic volume index 180 ± 64 ml/m2. Right ventricular ejection fraction (RVEF) was abnormal in 37%. Mean dobutamine-induced augmentation of LVEF (Do{Delta}LVEF) was 0.12 ± 0.08. Patients were started on one of three beta-blockers (carvedilol, bucindolol or metoprolol) and the dose was advanced to the maximum tolerated.

RESULTS

Left ventricular ejection fraction, reassessed 7.4 ± 5.9 months after maximum beta-blocker dose was reached, increased to 0.34 ± 0.13 (p = 0.0006). The following baseline variables correlated with improvement of LVEF: Do{Delta}LVEF (p = 0.001), RVEF (p = 0.005), systolic blood pressure at end of dobutamine infusion (p = 0.02) and dose of beta-blocker (p = 0.07). In a multivariate analysis, only Do{Delta}LVEF (p = 0.0003) and RVEF (p = 0.002) were predictive of the increase in LVEF.

CONCLUSIONS

Patients with nonischemic cardiomyopathy who have higher left ventricular inotropic reserve and normal RVEF derive higher increase in LVEF from beta-blocker therapy.

Abbreviations and Acronyms
  CHF = chronic heart failure
  DBP = diastolic blood pressure
  {Delta}LVEF = change in left ventricular ejection fraction after beta-blocker treatment
  Do{Delta}LVEF = dobutamine-induced increase in left ventricular ejection fraction
  ECG = electrocardiogram
  HR = heart rate
  LVEDVI = left ventricular end-diastolic volume index
  LVEF = left ventricular ejection fraction
  NICM = nonischemic cardiomyopathy
  RVEF = right ventricular ejection fraction
  SBP = systolic blood pressure

Recent clinical trials have demonstrated the beneficial effects of several beta-adrenergic receptor blockers on survival in large groups of patients with chronic heart failure (CHF) (1–4). Although concordant in their overall results, these studies have several unexplained inconsistencies (1–7) and the effect of beta-blockers on survival appears heterogeneous. Not all patients with heart failure benefit from beta-blocker therapy, and there are no good means to predict who will derive a benefit. With the expanding medical regimen and cost of care, the ability to identify patients with high likelihood of improvement is desirable.

The same clinical trials, and several smaller earlier studies, have also demonstrated a consistent increase in the mean left ventricular ejection fraction (LVEF) after beta-blocker therapy (1–16). This sustained noninotrope-induced improvement of left ventricular systolic function appears to be a marker for decreased risk of death and reduced morbidity (16–18). Other than dose, no definite predictors of beta-blocker-induced increase in LVEF have been identified (16). The identification of patients who are most likely to derive an increase in LVEF with beta-blocker therapy might therefore allow for the identification of patients who are highly likely to derive a survival benefit.

Ventricular systolic dysfunction is associated with decrease in the density of the ß1 and sensitivity of the ß2 adrenergic receptors that lead to heterogeneous decrease in contractile response to adrenergic stimulation (19–22). This variably diminished inotropic reserve appears to be an independent predictor of survival (23–26). Although higher inotropic reserve predicts better survival, it is associated with higher relative risk of sudden cardiac death (26). It identifies ventricles more responsive to adrenergic stimulation and therefore likely more susceptible to the harmful effects of chronic sympathetic activation (27). Because beta-blocker therapy reduces the risk of sudden and progressive heart failure death (1–4), higher inotropic reserve might identify patients who are most likely to benefit from such therapy. The purpose of this study is to determine whether higher left ventricular inotropic reserve, defined as the increase in LVEF in response to intravenous dobutamine infusion (Do{Delta}LVEF), predicts the increase in LVEF ({Delta}LVEF) after long-term beta-blocker therapy in CHF patients with nonischemic dilated cardiomyopathy (NICM).


   Methods
Top
 Abstract
 Methods
Results
 Discussion
 References
 
Patients.   The study subjects were 30 consecutive ambulatory patients with stable chronic heart failure and nonischemic cardiomyopathy, LVEF ≤ 0.35, who were started on beta-blockers at the Yale Heart Failure Clinic. There were 20 men and 10 women. Mean age was 49 ± 11 years (range 22 to 75 years), and mean duration of CHF was 3.2 ± 2.9 years. Mean functional class (NYHA classification) was 2.6 ± 0.5. All patients were in normal sinus rhythm except for one with atrial fibrillation. Coronary artery disease was excluded by coronary angiography. The etiology of cardiomyopathy was either hypertensive or idiopathic. The study was performed under an Institutional Review Board-approved protocol, and informed written consent was obtained. Patient characteristics are summarized in Table 1.


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  		Table 1 Patient Characteristics

 
Radionuclide ventriculography.   All study subjects underwent gated equilibrium radionuclide angiocardiography at rest and during the last 5 min of a 15-min peripheral intravenous infusion of dobutamine (Dobutrex, Eli Lilly & Co., Indianapolis, Indiana) at a dose of 10 µg/kg/min. Right and left ventricular ejection fractions were measured after modified in vivo red blood cell labeling (25–30 mCi Technetium-99m pertechnetate) according to standardized techniques (28). Data were acquired in electrocardiographic-synchronized frame mode (16 frames/RR cycle) in 64 x 64 computer matrix. Global LVEF was computed from the left anterior oblique image using validated and standardized software (29). A varying left ventricular region of interest and a cycle-dependent background region were used. The computer software automatically determines left ventricular edges and background, but also allows for operator interaction as may be necessary in patients with intense radiotracer accumulation adjacent to the left ventricle. Left ventricular ejection fraction was determined from the fitted curve in the usual manner: end-diastolic counts minus end-systolic counts, divided by end-diastolic counts. Using this software the lower limit of normal LVEF is 0.50. The reproducibility of LVEF measurement using this software is excellent (30).

Right ventricular ejection fraction (RVEF) was computed in 21 patients using the electrocardiogram (ECG)-gated first pass technique (31). Using this method, the injection of the patient’s Tc-99m-labeled red blood cells was used to acquire ECG-gated right anterior oblique images of the transit of radioactive bolus through the right ventricle. Data acquisition was stopped when the bolus entered the pulmonary artery. In this manner there was no overlap with other cardiac structures. Two regions of interest were then drawn manually over the end-diastolic and end-systolic contours of the right ventricle. No background subtraction was applied. Right ventricular ejection fraction was calculated from right ventricular end-diastolic and end-systolic counts in the usual manner. Using this method the lower limit of normal RVEF is 0.40 (31). A qualitative assessment of RVEF was performed in all 30 patients by visual inspection of the morphology and contraction of the right ventricle on the cine display in the anterior and left anterior oblique equilibrium views. Using this visual approach, global right ventricular function was categorized as either normal or abnormal. Left ventricular end-diastolic volume (LVEDV) was determined using the Massardo count ratio method (32) and was indexed to the body surface area. Under this method, normal patients have LVEDV 100–150 ml.

Beta-blocker therapy.   All patients were on standard medical therapy before initiation of beta-blocker therapy (Table 1). None were on intermittent or chronic intravenous inotropic infusion therapy. Patients were started on one of three beta-blockers: 22 on carvedilol, seven on bucindolol and one on metoprolol succinate. The median period from baseline ventriculographic study until start of beta-blocker therapy was one month. The dose was increased as tolerated every one to two weeks up to the target or maximally tolerated dose. Target dose for carvedilol was 25 mg twice daily for patients weighing ≤85 kg, otherwise 50 mg twice daily; for bucindolol 50 mg twice daily for patients weighing ≤75 kg, otherwise 100 mg twice daily; and for metoprolol 200 mg daily. Left ventricular ejection fraction was reassessed at least three months after the initiation of beta-blocker therapy.

Statistical analysis.   Data were expressed as mean ± standard deviation. The paired t test was used for comparison of continuous variables within groups and the nonpaired t test for comparison between groups. Fisher exact probability test was used for comparison of noncontinuous variables. Simple linear regression and correlation analysis were used to examine the relation between the increase in LVEF ({Delta}LVEF) and baseline clinical and ventriculographic variables. The Shapiro-Wilk statistic tested the null hypothesis that the sample data were derived from a normally distributed population. Two-sided p value <0.05 was considered statistically significant.

Multivariate analysis was performed to determine which of the following baseline clinical and ventriculographic variables were associated with the increase in LVEF after beta-blocker therapy: LVEF, RVEF, Do{Delta}LVEF, left ventricular end-diastolic volume index (LVEDVI), systolic blood pressure (SBP) at end of dobutamine infusion, duration of CHF, duration of treatment and dose. A stepwise multiple regression procedure was used, with an entry significance level of p < 0.10 and an exit significance level of p > 0.20. All analyses were performed using PC-SAS 6.12 (SAS Institute Inc., Cary, North Carolina).


   Results
Top
 Abstract
 Methods
 Results
Discussion
 References
 
Beta-blocker dose and duration of therapy.   The attained daily dose of beta-blocker was 66 ± 30 mg of carvedilol, 75 ± 32 mg of bucindolol, and 50 mg of metoprolol. The period from initiation of beta-blocker therapy until attainment of final dose was 2 ± 1 months (median 2 months). Left ventricular ejection fraction was reassessed 7.4 ± 5.9 months after maximal beta-blocker dose was reached (median 6.5 months).

Ventriculographic findings.   Before beta-blocker therapy, LVEF was 0.21 ± 0.07 (range 0.08 to 0.35). Right ventricular ejection fraction was abnormal in 11 patients (37%). Quantitative RVEF, obtained in 21 patients, was 0.43 ± 0.12. LVEDVI was 180 ± 64 ml/m2. Before dobutamine infusion, heart rate (HR) was 80 ± 11 and SBP was 123 ± 17 mm Hg. At end of infusion HR was 106 ± 18 and SBP 133 ± 24 mm Hg. With dobutamine infusion, LVEF increased to 0.33 ± 0.13. Mean dobutamine-induced increase of LVEF (Do{Delta}LVEF) was 0.12 ± 0.08 (median 0.10, range 0.02 to 0.35)

After beta-blocker therapy LVEF increased to 0.34 ± 0.13 ({Delta}LVEF 0.14 ± 0.09, p = 0.0006) (Table 1). There was significant linear correlation between Do{Delta}LVEF and each of RVEF (r = 0.66, p = 0.001), LVEF (r = 0.52, p = 0.003), SBP on dobutamine (r = 0.47, p = 0.008) and LVEDVI (r = –0.47, p = 0.01). The linear correlation between Do{Delta}LVEF and other baseline variables (duration of CHF, peak HR and change in HR on dobutamine) was not significant.

Table 2 compares the clinical and ventriculographic characteristics of patients with high versus low dobutamine-induced increase in LVEF, and Table 3 compares the characteristics of patients on the basis of the increase in LVEF after beta-blocker therapy.


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  		Table 2 Clinical and Ventriculographic Characteristics of Patients with Low versus High Response to Dobutamine

 

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  		Table 3 Clinical and Ventriculographic Characteristics of Patients Based on the Increase in LVEF after Beta-blocker Therapy

 
Predictors of LVEF improvement.   The increase in LVEF ({Delta}LVEF) after beta-blocker therapy was significantly correlated to baseline inotropic reserve, Do{Delta}LVEF (r = 0.57, p = 0.001), RVEF (r = 0.50, p = 0.005), SBP at end of dobutamine infusion (r = 0.43, p = 0.02) and dose of beta-blocker (r = 0.33, p = 0.07) (Figs. 1 and 2). There was no significant correlation between {Delta}LVEF and the rest of baseline ventriculographic and clinical variables. In multivariate analysis only Do{Delta}LVEF (p = 0.0003), and RVEF (p = 0.002) were significantly associated with the increase in LVEF after beta-blocker therapy. The positive predictive value of Do{Delta}LVEF was 100% and its negative predictive value was 67%. The positive and negative predictive values of RVEF were 89% and 73%, respectively (Table 4).



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  		Figure 1 Change in left ventricular ejection fraction (LVEF) after beta-blocker therapy versus baseline dobutamine-induced increase in LVEF.

 


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  		Figure 2 Change in left ventricular ejection fraction (LVEF) after beta-blocker therapy versus baseline right ventricular function. RVEF = right ventricular ejection fraction.

 

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  		Table 4 Predictive Values for Beta-Blocker-Induced Increase in LVEF

 

   Discussion
Top
 Abstract
 Methods
 Results
 Discussion
References
 
This study shows that left ventricular inotropic reserve and right ventricular function are independent predictors of the increase in LVEF after beta-blocker therapy in a well-defined cohort with severe nonischemic left ventricular systolic dysfunction. Specifically, patients with the highest dobutamine-induced augmentation of LVEF and normal RVEF derived the highest increase in LVEF after long-term beta-blocker therapy. This relation was independent of resting LVEF, dose of beta-blocker, duration of disease and duration of treatment. These findings could help identify patients with NICM who are most likely to derive significant benefit from beta-blocker therapy. Patients who derive the highest increase in LVEF are likely to be at lower risk for progressive heart failure death, and because beta-blocker therapy also reduces the risk of sudden cardiac death (1–4), these patients also incur a lower risk of sudden death. Although proven for large patient populations, the benefit of beta-blockade has not yet been conclusively established for all subgroups, and not all CHF patients benefit from it (1–7). An increased sophistication in the identification of patients who are most likely to derive a benefit should allow for the extension of this potentially highly beneficial therapy to a large segment of the CHF population.

Significance of higher inotropic reserve.   Inotropic reserve, as measured in this study, is a reflection of the contractile response to the stimulation of the myocardial adrenergic signaling pathways. Although it is not a true measure of myocardial contractile reserve, an entity that is difficult to define, inotropic reserve provides a measure of the responsiveness of the myocardial adrenergic signaling pathways as well as that of the myocardial contractile apparatus. Higher inotropic reserve identifies ventricles with less downregulation of beta-adrenergic receptors. These ventricles are probably more susceptible to the arrhythmogenic and myotoxic effects of chronic sympathetic activation (27). Higher inotropic reserve is also a marker of the overall health of the ventricle and is an independent predictor of survival (23–26). These ventricles tend to have better left and right ventricular function, smaller size and shorter duration of disease (Table 2). These seem to be the ventricles that are more likely to derive a significant and sustained increase in LVEF from beta-blocker therapy (Table 3). Although the positive predictive value of higher inotropic reserve was perfect, its negative predictive value was only 67%. Therefore, even patients with low inotropic reserve might derive a significant increase in LVEF from beta-blocker therapy. Of course, these patients and others might derive a clinical benefit from beta-blockade in the absence of increase in LVEF.

Increase in LVEF and survival.   An increase in the mean LVEF was the most consistent effect of beta-blocker therapy in multiple studies (1–16). The exact mechanism of this increase remains uncertain (17). Despite the large database of heart failure patients treated with beta-blockers, other than dose there are no definitively established predictors of the increase in LVEF. Furthermore, there are no well-established clinical markers of higher likelihood of survival after beta-blocker therapy. Given that the improvement of survival has been adopted as the most important therapeutic goal, such markers would be quite useful in several ways. They would allow for the identification of patients most likely to benefit from treatment. They would also provide surrogate endpoints in the evaluation of newer therapeutic agents. Recent data suggest that the sustained long-term increase in LVEF after beta-blocker therapy might predict lower likelihood of death, at least from progressive heart failure, and better clinical outcomes (16–18). Although patients with higher LVEF have lower risk of all-cause mortality (33), they have higher relative risk of sudden cardiac death (34–36). Higher inotropic reserve could be a consequence of more responsive adrenergic signaling pathways. These pathways are involved in the mediation of ventricular tachyarrhythmia (37), a common cause of sudden death in nonischemic cardiomyopathy (38–41). Higher inotropic reserve might therefore identify patients who are at highest relative risk for sudden arrhythmic death and those of higher likelihood to derive an increase in LVEF after beta-blocker therapy.

RVEF and increase in LVEF.   In this study normal right ventricular function was also associated with increase in LVEF after beta-blocker therapy. Normal RVEF is another marker of healthier hearts and an independent predictor of better survival (42,43). Ventricles with higher Do{Delta}LVEF tend to have higher RVEF (26). Although this could in part be due to the hemodynamic coupling of right and left ventricular function, it is more likely a reflection of the extent of ventricular contractile impairment. Because RVEF is easy to assess, it might serve as a practical means to identify candidates for beta-blocker therapy. It should not, however, be the sole criterion, as many patients with impaired right ventricular function also derive benefit from beta-blockade in the form of increase in LVEF and RVEF and better survival (44). In this study, a normal RVEF had a lower positive predictive value than did inotropic reserve, but its negative predictive value was higher.

Patients with ischemic cardiomyopathy.   This study aimed to examine the predictive value of adrenergic inotropic reserve on the increase in LVEF after beta-blocker therapy. The exclusion of patients with coronary artery disease eliminated the complicating effects of myocardial ischemia and prior infarction on the evaluation of adrenergic inotropic reserve. The presence and extent of coronary artery disease, ischemic burden and old myocardial infarction all make the assessment of inotropic reserve imprecise. The viable dysfunctional myocardium has the same downregulation of adrenergic receptors and diminished inotropic reserve. The response of the entire ventricle to adrenergic agents, however, depends on the extent of infarcted myocardium and the presence of hemodynamically important coronary artery disease. If there is extensive ischemic burden, adrenergic stimulation might increase oxygen demand and worsen ischemia. This might blunt the contractile response or even diminish the ejection fraction, rendering the assessment of inotropic reserve imprecise. The results of this study therefore cannot be extended to patients with ischemic cardiomyopathy.

Study limitations.   This observational study in a small, albeit well-defined, cohort of young nonischemic cardiomyopathy patients was designed to test a specific hypothesis. It should not serve as a means for selecting patients for beta-blocker therapy. Now that the benefit of beta-blockade has been established in large and heterogeneous populations of heart failure, further studies are needed to define the patients who are most likely to benefit from this therapy. This study is a step in that direction. It employed the three beta-blockers most extensively studied in heart failure, and which were all shown to increase LVEF in multiple previous studies. Because of the small number of patients involved in this study, it is not certain whether the findings apply to all three beta-blockers. Also, because of the small number of patients, it is not possible to adjust for any confounders. Although qualitative right ventricular function assessment was performed in all patients and used in the analysis, quantitative RVEF was not obtained in 30% of the subjects.

Peripheral dobutamine infusion has multiple effects on the heart. In addition to increasing force of contraction, it can increase HR and change pulmonary and systemic vascular resistance. The sum effect of these hemodynamic changes could contribute to the change in LVEF with dobutamine infusion. In this study, there was no correlation between the dobutamine-induced increase in LVEF and peak HR, change in HR or change in SBP at peak dobutamine infusion. Furthermore, a weak positive correlation existed between Do{Delta}LVEF and SBP at peak dobutamine infusion. Although intracoronary infusion of dobutamine minimizes peripheral effects on cardiac loading and is therefore a more precise method for the assessment of inotropic reserve (22,25), intravenous dobutamine infusion is less invasive, safer and clinically practicable. The dose of dobutamine used in this study was chosen based on previous experience (26). It was intended to maximize inotropic response while minimizing chronotropic response, risk of dysrhythmia and the peripheral effects of dobutamine. Infusion duration of 10 min prior to repeat imaging allows for the attainment of steady state.

Conclusions.   This study showed that NICM patients with normal right ventricular function and higher left ventricular inotropic reserve are most likely to derive an increase in LVEF after long-term treatment with beta-blockers. Further studies are needed to determine whether this finding would identify patients more likely to derive survival benefit from beta-blockade.


   References
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 Abstract
 Methods
 Results
 Discussion
 References
 

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