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European Journal of Heart Failure 2007 9(4):403-408; doi:10.1016/j.ejheart.2006.10.018
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© 2007 European Society of Cardiology

Myocardial viability estimation during the recovery phase of stress echocardiography after acute beta-blocker administration

Stefanos E. Karagiannisa, Harm H.H. Feringaa, Jeroen J. Baxb, Abdu Elhendyc, Martin Dunkelgruna, Radosav Vidakovica, S.E. Hoeksa, Ron van Domburga, Roelf Valhemad, Dennis V. Cokkinose and Don Poldermansa,*

a Department of Cardiology Erasmus MC, Rotterdam, The Netherlands
b Department of Cardiology, Leiden University Leiden, The Netherlands
c Department of Cardiology, University of Omaha Nebraska, USA
d Department of Nuclear Medicine Erasmus MC, Rotterdam, The Netherlands
e 1st Department of Cardiology, Onassis Cardiac Surgery Centre Athens, Greece

* Corresponding author. Department of Cardiology, Room H 921, Erasmus MC, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands. Tel.: +31 104639222; fax: +31 104634957. E-mail address: d.poldermans{at}erasmusmc.nl


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 
Background: Myocardial viability assessment in severely dysfunctional segments by dobutamine stress echocardiography (DSE) is less sensitive than nuclear scanning.

Aim: To assess the additional value of using the recovery phase of DSE after acute beta-blocker administration for identifying viable myocardium.

Methods: The study included 49 consecutive patients with ejection fraction (LVEF) ≤35%. All patients underwent DSE evaluation at low–high dose and during recovery phase, and dual-isotope single photon emission tomography (DISA-SPECT) evaluation for viability of severely dysfunctional segments. Patients with ≥4 viable segments were considered viable. Coronary revascularization followed within 3 months in all patients. Radionuclide evaluation of LVEF was performed before and 12 months after revascularization.

Results: Viability with DISA-SPECT was detected in 463 (59%) segments, while 154 (19.7%) segments presented as scar. The number of viable segments increased from 415 (53%) at DSE to 463 (59%) at DSE and recovery, and the number of viable patients increased from 43 to 49 respectively. LVEF improved by ≥5% in 27 patients. Multivariate regression analysis showed that, DSE with recovery phase was the only independent predictor of ≥5% LVEF improvement after revascularization (OR 14.6, CI 1.4–133.7).

Conclusion: In this study, we demonstrate that the recovery phase of DSE has an increased sensitivity for viability estimation compared to low–high dose DSE.

Key Words: Dobutamine Stress Echocardiography • Recovery phase • Viability

Received May 30, 2006; Revised October 1, 2006; Accepted October 19, 2006


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 References
 
Coronary artery disease (CAD) is one of the major causes of left ventricular (LV) dysfunction and is one of the leading causes of mortality and morbidity. The predictive value of dobutamine stress echocardiography (DSE) for the recovery of LV function after revascularization is less than for nuclear scan techniques. Nuclear scan techniques mainly focus on finding islands of viable tissue; however, DSE focuses on segmental LV function; a feature that explains the lower sensitivity of the test compared to other imaging techniques, with a slightly better specificity [1]. The studies published to date on the use and importance of DSE in the evaluation of myocardial viability, combine various subgroups of patients [1,2]. A complete test (low-high dose), compared with only low-dose images, is more accurate in predicting LV functional recovery after revascularization. This is ascribed to the ability of full-dose dobutamine to recognize more accurately the biphasic and ischaemic response [1]. These ischaemic responses may be missed if only a low-dose dobutamine protocol is performed. Furthermore, it has been shown [3] that the recovery phase of DSE, in patients receiving acute beta-blockade after peak images have been obtained, is important in identifying further ischaemia. It has been demonstrated that injection of beta-blockers at the peak dose of DSE might enhance regional wall abnormalities and increase the sensitivity of the combined peak plus metoprolol images [3]. In order to identify heart failure patients suitable for revascularization, it is important to clearly identify patients with dysfunctional but viable myocardium. However, the evaluation of the recovery phase of DSE for viability estimation has not been studied previously. The aim of this study was therefore to assess the additional value of viability estimation during the recovery phase of DSE after administering acute beta-blockade, compared to findings at low-high dose DSE. Dual-isotope single photon emission tomography (DISA-SPECT) was used as reference.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 References
 
2.1. Patient population
The study population included 49 consecutive patients with known or suspected CAD who were referred at the Thoraxcenter (Rotterdam, The Netherlands) between January 2004 and January 2005. Patients with an ejection fraction ≤35% were enrolled. All patients underwent DSE and DISA-SPECT examination for evaluation of viability. A revascularization procedure followed within 3 months, at the discretion of the referring physician, who was aware of the tests results.

Radionuclide ventriculography was also performed within 1 month before and 12 months after the revascularization procedure. The local medical ethics committee approved the study protocol. All patients gave informed consent to participate in the study.

2.2. Radionuclide ventriculography
Radionuclide ventriculography was performed at rest with the patient in supine position after administration of 740 MBq of Tc-99 m. Images were acquired with a small field of view gamma camera (Orbiter, Siemens Corp., Erlangen, Germany) oriented in the 45° left anterior oblique position with a 5° to 10° caudal tilt. LV ejection fraction was calculated by standard methods (Odyssey VP, Picker, Cleveland, Ohio).

2.3. Dobutamine stress echocardiography
The DSE protocol was approved by the Hospital Ethics Committee and was performed in accordance with well-established protocols [4,5]. Studies were performed using a Sonos 5500 imaging system (Phillips Medical Systems, Eindhoven, The Netherlands). Patients underwent a resting two-dimensional echocardiographic examination from the standard apical and parasternal views. Images were recorded on videotape and also digitized for comparison of different stages. Dobutamine was then administered intravenously by infusion pump, starting at 5 µg/kg/min for 3 min, followed by 10 µg/kg/min for 5 min and increasing by 10 µg/kg/min every 3 min to a maximum of 40 µg/kg/min (stage 5), and continued for 6 min. The dobutamine infusion was stopped if a target heart rate (85% of the theoretical maximal heart rate (men: (220–age)x85%; women: (200–age)x85%) was achieved. If the target heart rate was not achieved and patients had no symptoms or signs of ischaemia, atropine (starting with 0.25 mg, increased to a maximum of 2.0 mg) was given intravenously at the end of stage 5 while the dobutamine administration was continued. During the test, a 12-lead ECG was recorded every minute. Blood pressure was measured every 3 min. Metoprolol was administered (1,0 to 5,0 mg) intravenously after peak stress images were acquired and according to heart rate response and systolic blood pressure, to achieve a recovery phase, defined as heart rate within 10% range of resting heart rate.

The criteria for stopping the test were: (1) achievement of the target heart rate (2) severe and extensive NWMA, (3) horizontal or down-sloping ST depression of ≥0.2 mV measured 80 ms after the J point, or ST-segment elevation of ≥0.2 mV in the absence of Q waves, (4) symptomatic decline in systolic blood pressure of more than 40 mm Hg, or a systolic blood pressure ≤90 mm Hg, (5) hypertension (blood pressure >240/140 mm Hg), (6) the occurrence of sustained cardiac arrhythmias, (7) severe angina pectoris, and (8) intolerable adverse effects considered to be the result of dobutamine or atropine. Two experienced investigators performed off-line assessment of the echocardiographic images without knowledge of the patient's clinical and coronary angiography data, but with knowledge of the doses of dobutamine and atropine used. Inter-observer and intra-observer agreement for analysis of DSE studies have been reported previously (92% and 94%, respectively) [6]. Regional function was scored according to a 16 segment, five point scoring model: 1, normal; 2, mildly hypokinetic; 3, severely hypokinetic; 4, akinetic; and 5, dyskinetic. Wall-motion score index (WMSI) (total score divided by the number of segments scored) was calculated, at rest, low dose, during peak stress, and during the recovery phase.

Myocardial viability was assessed only in severely dysfunctional segments; 4 types of wall motion responses were observed: (1) biphasic pattern: improvement of wall motion at 5, 10, or 20 mg/kg/min dobutamine with worsening at higher dosages; (2) worsening; (3) sustained improvement; and (4) no change. Severely dysfunctional segments exhibiting a biphasic, sustained improvement, or ischaemic response were considered viable, whereas segments with unchanged wall motion were considered scarred. The same criteria were applied when recovery phase images were added to the evaluation.

A patient was considered to have viable myocardium in the presence of ≥4 viable segments and as non-viable in the presence of ≤4 viable segments [7]. This definition is based on previous work with receiver operator characteristic curve analysis that showed that recovery of function may be predicted in the presence of ≥4 viable segments [7].

Digital screen format was used to compare images. When there was disagreement between the two assessors, a third investigator viewed the images without knowledge of the previous assessments, and a majority decision was reached.

2.4. Dual-isotope single photon emission tomography
DISA-SPECT imaging using technetium-99 m tetrofosmin (perfusion) and fluorine-18 fluorodeoxyglucose (metabolism) tracers was performed as previously described [8]. The left ventricle was divided into 16 segments (6 basal-anterior, anterolateral, inferolateral, inferior, inferoseptal, and anteroseptal), 6 distal, and 4 apical segments, corresponding to the echocardiographic segments. Segmental tetrofosmin and FDG uptake were scored by an experienced observer (blinded to echo data) using a 4-point grading system (0, normal; 1, mildly-moderately reduced; 2, severely reduced; and 4, absent). According to this scoring model, criteria of viability were (1) normal perfusion and FDG uptake, (2) concordantly mildly-moderately reduced perfusion and FDG uptake, or (3) reduced perfusion with preserved or increased FDG uptake (mismatch). Segments with severely reduced or absent perfusion and concordantly reduced (or absent) FDG uptake was considered scar tissue.

2.5. Statistics
Results are expressed as mean value±SD. The t-test was used for continuous variable and the chi-square test was used for categorical variables. A two-tailed p<0.05 was considered significant. Kappa statistics were used for agreement between DISA-SPECT and DSE. On the basis of Fleiss's classification [9] k values <0.4, between 0.4 and 0.75, and >0.75 were considered to indicate poor, fair to good, and excellent agreement respectively. A McNemar test was applied to study the difference in DSE results with and without recovery phase evaluation, controlled by nuclear testing results.

Multivariate logistic regression was used to investigate the predictive value of viability in DSE+recovery phase, versus low-high DSE, for global left ventricular improvement after revascularization, adjusting for age, gender, previous MI, and heart failure [10].

Sensitivity, specificity, diagnostic accuracy and predictive values were calculated according to standard definitions.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 References
 
The patients' clinical characteristics are presented in Table 1. Medications were not discontinued during the study. All patients underwent revascularization; 40 underwent percutaneous transluminal coronary angioplasty and 9 coronary artery by-pass grafting. In total 27 patients showed a ≥5% increase in left ventricular ejection fraction 12 months after revascularization.


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  		Table 1 Study population characteristics

 
3.1. Patient characteristics and haemodynamic response
During DSE heart rate increased significantly from rest to peak stress. Test end point (target heart rate) was reached in 94% of patients. Atropine was added at peak stress in 31 patients as the majority of patients were on chronic beta-blockade which was not stopped prior to the study. The mean maximal dobutamine dose was 38±8 mcg/kg/min. All patients received metoprolol (1.0 to 5.0 mg) intravenously after peak stress images were acquired and according to heart rate response and systolic blood pressure. Side effects included haemodynamically stable sustained ventricular tachycardia (>10 complexes) in 1 (2%) patients, non-sustained ventricular tachycardia (<10 complexes) in 2 (3%) patients, atrial fibrillation in 2 (3%) patients and severe hypotension (decrease of systolic blood pressure >40 mm Hg) in 1 (2%) patients. No myocardial infarction or ventricular fibrillation was recorded during or attributed to DSE.

The rate-pressure product values at rest, low, peak and recovery were 8694±286, 13910±546, 17028±351 and 10648±299 respectively. WMSI at rest was 2.05±0.91, at low dose 1.83±0.79, at peak dose 1.90±0.83 and at recovery phase 2.15±0.94.

The number of viable segments increased from 415 (53%) at DSE to 463 (59%) at DSE+recovery. 295 segments developed an ischaemic response at peak and another 48 only during recovery phase.

During DSE 43 patients had ≥4 viable segments. During the recovery phase another 6 patients were considered as viable (Fig. 1). These were patients that changed from non-viable i.e. unchanged response to dobutamine at peak, to ischaemic indicating a prolonged ischaemic effect of dobutamine during the recovery phase, after acute beta-blocker injection. Only 3 of these patients had a ≥5% increase in left ventricular ejection fraction 12 months after revascularization.


Figure 01
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  		Fig. 1 Patients with viability at DSE versus DSE+recovery (p<0.03 after controlling for DISA-SPECT results).

 
3.2. DISA-SPECT and radionuclide ventriculography
Viability was detected in 463 (59%) segments, while 154 (19.7%) segments presented as scar. The rest of the segments had normal or mildly reduced function and metabolism. Mean left ventricular ejection fraction as assessed by radionuclide ventriculography was 28%±7% prior to revascularization and 37%±6% post revascularization.

3.3. DSE in viability estimation
Table 2 shows the respective changes of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the detection of viability at DSE and DSE+recovery and by using DISA-SPECT as reference. The sensitivity at low-high DSE for viability estimation was 72% (95% CI 68% to 76%) and specificity 74% (95% CI 72% to 76%). When recovery images were also analyzed the sensitivity for viability estimation increased to 85% (95% CI 81% to 89%), while specificity remained unchanged.


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  		Table 2 Sensitivity, specificity, accuracy, positive predictive value and negative predictive value for viability evaluation at DSE and DSE+recovery

 
Patients on chronic beta-blockade did not show any difference in sensitivity compared to the group that did not receive chronic beta-blocker therapy.

Using k-statistics, the detection of agreement between DISA-SPECT results and DSE results increased from 0.55 at low-high DSE to 0.68 at DSE+recovery, indicating a good agreement of DSE with the nuclear findings when the recovery phase was also scored.

Multivariate regression analysis showed that, DSE+recovery phase results in total were the only independent predictors of improved left ventricular function (ejection fraction improvement ≥5%) after revascularization(p=0.04, odds ratio [OR] 14.65, 95% CI 1.34 to 133.7). Furthermore the number of scarred segments as shown by DISA-SPECT, was the only independent predictor of deterioration of left ventricular function after revascularization, in multivariate analysis (p=0.03, OR 0.78, 95% CI 0.62 to 0.98).


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
References
 
Dobutamine stress echocardiography is widely used for viability detection in patients with CAD [11-14]. However the sensitivity of the test is less than for other imaging techniques, with a slightly better specificity [11-14]. In this study, we demonstrated that sensitivity increased from 72% to 85% (p<0.001) when the recovery phase was also scored and more importantly it was not accompanied by a decrease in specificity. Furthermore the negative predictive value of the test was also significantly improved.

Previously, Tsoukas et al. [15] studied the presence of myocardial ischaemia during the recovery phase of DSE. Their results showed that patients with extensive coronary artery disease have more prolonged ischaemia. Furthermore, Mathias et al. [3] demonstrated that injection of beta-blockers at the peak dose of DSE enhanced regional wall abnormalities and increased the sensitivity of the recovery images for detecting ischemia. We similarly found an enhanced sensitivity in our study. Moreover, as no myocardial infarction or ventricular fibrillation was recorded during or attributed to DSE our data support the safety of the use of acute beta-blockade during DSE. Concerning viability, a study by Zaglavara et al. [16] suggested that beta-blocker withdrawal is not necessary before DSE studies if a complete DSE protocol is performed. A complete protocol is required as some viability can be detected at higher doses than the traditional low dose stages. Our protocol also included recovery phase evaluation as part of standard DSE.

In our study, during the recovery phase the status in six patients changed from "non-viable" at peak (i.e. unchanged response to dobutamine), to "viable" (i.e. ischaemic), indicating a prolonged ischaemic effect of dobutamine during the recovery phase, after acute beta-blocker injection. This is also indicated by the value of rate-pressure product during the recovery phase, as a measure of oxygen consumption rate, which was less than the value at peak stress, but more than the value at rest. Dobutamine stimulates β1, β2, and {alpha}1-adrenergic receptors [17]. Acute β-blockade interacts with β1 and β2 receptors leaving unopposed {alpha}1-adrenergic vasoconstriction [18] and therefore leading to a reduction in coronary flow reserve [19]. This means that increased vasoconstriction can cause myocardial ischaemia which could also explain the paradoxical enhancement of ischaemic response in the recovery phase.

Our findings also demonstrate that viability estimation by the combination of low, peak, and recovery phase scoring was the only independent predictor of improved left ventricular function after revascularization. Indeed this finding was similar to that of a previous study which showed that DSE is both sensitive and specific in predicting improved myocardial function after revascularization [16]. Furthermore, Afridi et al. [20] demonstrated that myocardial viability was the only multivariable predictor of good outcome after revascularization.

We also found a good correlation between the two imaging techniques for detecting myocardial viability when recovery phase was also scored, and irrespectively of resting left ventricular ejection fraction; a finding that is in concordance with previous studies [1,14,16,20-22].

To our knowledge this is the first study demonstrating the additional value of the recovery phase of DSE in the estimation of viability in patients with CAD. This observed increased sensitivity of the test, could add to the clinical usage of DSE in this respect.

Possible limitations of our study include the fact that the study population consisted of patients with chronic ischaemic LV dysfunction, thus findings may not apply to patients with acute or recent myocardial infarction. Another limitation is the subjectivity of DSE interpretation. This potential limitation may be reduced by the introduction of automatic quantitative scoring systems. A third limitation was the large number of scarred non-viable segments. In addition, the specificity of the reference method was expected to be low and there was no follow-up echo 12 months after revascularization. Global left ventricular function improvement as estimated by radionuclide ventriculography was selected for evaluation post-revascularization over the actual recovery on a segmental level, as it is an acceptable and important clinical surrogate which is easily understood by most general physicians.

In conclusion, the assessment of myocardial viability by DSE in patients with coronary artery disease has improved sensitivity when scoring of individual segments in the recovery phase becomes an integral part of the regular DSE scoring.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 

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