YANNICK ALLANORE, CHRISTOPHE MEUNE, OLIVIER VIGNAUX, SIMON WEBER, PAUL LEGMANN, and ANDRE KAHAN

ABSTRACT.

Objective. To evaluate the short-term effects of bosentan on myocardial perfusion and function assessed by cardiac magnetic resonance imaging (MRI) and Tissue-Doppler echography (TDE) respectively in patients with systemic sclerosis (SSc).

Methods. We prospectively evaluated 18 SSc patients without clinical heart failure and with normal pulmonary arterial pressure. MRI perfusion index and systolic and diastolic strain rates (SR) determined by TDE were assessed at baseline for comparison with healthy controls (after a 72-hour vasodilator washout period), and repeated after 4 weeks of bosentan treatment (62.5 mg bid for 2 weeks titrated to 125 mg bid for 2 weeks).

Results. Patients with SSc had decreased MRI perfusion index and TDE SR in comparison with healthy controls. Bosentan treatment led to a significant increase in median (range) global MRI perfusion index [from 0.17 (0.09–0.23) at Day 0 to 0.22 (0.13–0.30) after bosentan treatment; p = 0.0004], systolic SR [from 2.1 (1.3–3.1) s–1 to 2.8 (2.1–4.8) s–1; p = 0.0002), and diastolic SR [from 2.6 (1.4–6.7) to 3.6 (2.0–7.6) s–1; p = 0.0003].

Conclusion. Short-term treatment with bosentan simultaneously improves myocardial perfusion and function, as evaluated by highly sensitive and quantitative methods, in patients with SSc. Whether additional remodeling effect may be observed after longterm treatment with bosentan remains to be determined. (First Release Oct 15 2006; J Rheumatol 2006;33:2464-9)

Key Indexing Terms:

SYSTEMIC SCLEROSIS
BOSENTAN
MYOCARDIUM
MAGNETIC RESONANCE IMAGING
TISSUE DOPPLER ECHOCARDIOGRAPHY

Dr. Kahan has received consulting fees or honoraria from Actelion Pharmaceuticals.

Y. Allanore, MD, PhD; A. Kahan, MD, PhD, Service de Rhumatologie A; C. Meune, MD; S. Weber, MD, PhD, Service de Cardiologie; O. Vignaux, MD, PhD; P. Legmann, MD, PhD, Service de Radiologie A, Université Paris-Descartes, Faculté de Médecine, Hôpital Cochin.

Dr. Allanore and Dr. Meune contributed equally to the study.

Address reprint requests to Dr. Y. Allanore, Hôpital Cochin, Service de Rhumatologie A, 27 rue du faubourg Saint-Jacques, 75014 Paris, France. E-mail: yannick.allanore@cch.aphp.fr

Accepted for publication July 31, 2006.

Single-photon emission computed tomography (SPECT), positron emission tomography, and radionuclide ventriculography have been previously used for myocardial perfusion and contractility assessment; various vasodilator agents such as nifedipine, nicardipine, and captopril were shown to mitigate both myocardial perfusion and function abnormalities^5-8. Recent advances in cardiology imaging include the development of magnetic resonance imaging (MRI), a quantitative, highly sensitive method of assessing myocardial perfusion^9,10. Tissue-Doppler echocardiography (TDE) is a recent method allowing direct measurement of myocardial velocities and strain rate, a good index of contractility, independent of myocardial translation¹¹, less dependent on loading conditions, and far more sensitive than conventional methods¹².

Endothelial injury in SSc leads to increased release of endothelin 1 (ET); this 21-amino acid peptide is the most potent naturally occurring vasoconstrictive mediator, and is suspected to play a key role in pathogenesis of SSc vascular disease^13,14. Endothelin has 2 known receptor subtypes. ETA, found predominately on vascular smooth muscle cells (VSMC), induces a vasoconstrictor effect, while ETB, found on endothelial cells and VSMC, has both a vasoconstrictor and vasodilator effect¹⁵. Bosentan is the first endothelin receptor antagonist with an affinity for the 2 endothelin receptors (ETA and ETB). Bosentan has demonstrated significant efficacy on primary pulmonary hypertension and pulmonary hypertension related to collagen vascular diseases such as SSc¹⁶; more recently, bosentan showed effectivity in preventing new digital ulcers and improving hand function in patients with SSc¹⁷. Based on these results, we investigated the myocardial effects of bosentan using cardiac MRI and TDE.

MATERIALS AND METHODS

Patients. Consecutive patients fulfilling the LeRoy classification criteria for SSc¹⁸ were included. The clinical features of their disease were assessed as recommended¹⁹. The exclusion criteria were pregnancy, symptoms of heart failure, venous distension and/or recent major lower limb edema, systolic blood pressure < 85 mm Hg, heart rate < 50 or > 130 bpm, pulmonary arterial hypertension (systolic arterial pressure > 40 mm Hg determined by echocardiography), severe pulmonary involvement (forced vital capacity or carbon monoxide diffusing capacity < 50% of the predicted value), or severe disease complications such as cancer or gangrene. No patient was allowed in the study if they had renal involvement with serum creatinine concentration > 106 µmol/l, hemoglobin or leukocytes > 30% out of normal range, or hepatic transaminases > 3 times the upper limit of normal. Three months of stable current treatment was necessary for inclusion, and prednisone at a dose less than 10 mg/day was authorized. Vasodilators, including calcium channel blockers and angiotensin-converting enzyme (ACE) inhibitors, had to be withdrawn at least 3 days before inclusion, a time-interval superior to 5 drug half-lives. All patients gave informed consent for all procedures and the study was approved by the local ethics committee.

Apart from clinical examination, MRI, and TDE, the following investigations were carried out for all patients: laboratory tests including blood cell counts, Westergren erythrocyte sedimentation rate, C-reactive protein levels, serum creatinine concentration, and anticentromere and antitopoisomerase I antibody assays. Pulmonary involvement was assessed by computed tomography (CT) scan, forced vital capacity (FVC), and the ratio of carbon monoxide diffusion capacity to hemoglobin concentration (DLCOc/Hb). Pulmonary arterial systolic pressure was determined by echocardiography at rest, based on the tricuspid and/or pulmonary regurgitation, adding 10 mm Hg, as an estimation of right atrial pressure.

Myocardial evaluations were performed in patients at rest, at room temperature, with MRI performed first, followed by TDE 1 hour later. Patients were then treated by bosentan 62.5 mg bid for 14 days and by 125 mg bid for 14 days; all measurements were reinvestigated in similar conditions by the predefined cardiac tests 2 hours after the last intake. Transaminase values were determined after the 14 days of treatment by bosentan 62.5 mg bid and reevaluated after the 14 days of treatment by bosentan 125 mg bid.

In addition, MRI was performed twice in a 6-month period in 6 matched healthy controls in order to ensure stability of measurements and for comparison with SSc patients. Baseline TDE measurements were compared to those of 15 matched healthy controls¹².

Magnetic resonance imaging. All patients were examined in the supine position (1.5 T Echospeed GEMS; Milwaukee, WI, USA) using a phased-array cardiac dedicated coil. After determination of the axis and length of the left ventricular (LV) cavity, 3 short-axis planes were imaged. The distance between each plane was individually set as one-third of the end-systolic length of the LV cavity (one basal slice, one midventricular slice, and one apical slice). A interleaved notched saturation segmented k-space turbo-gradient-echo/echo-planar-imaging-hybrid technique with notched saturation prepulse and T1 preparation (echo time = min full, R-R interval = 2, flip = 25, inversion time = 160 ms; matrix 128 ´ 128; slice thickness 8 mm) was used. Multislice acquisitions were performed during the first pass of 0.025 mmol gadolinium-DTPA/kg body weight (Schering) flushed with 10 ml 0.9% NaCl (flow rate 5 ml/s; Medrad, Spectris). Images were acquired during breath-holding for 10 heartbeats before and 60 heartbeats during the injection (instruction was to breathe freely but very slowly at the end of the acquisition when breath-holding was too long for the patient). All acquisitions were stored on a hard disk; myocardial perfusion index was then determined by an examiner blinded to any information as follows: (1) The endocardial and epicardial contours were traced and corrected manually for displacements (e.g., breathing). The outer 50% of the myocardium was excluded to get stronger weighting of the subendocardium. (2) Left ventricular signal intensity of the cavitary and myocardial signal intensity was determined for all timepoints. The myocardial signal intensity time curves and the maximum myocardial upslope were determined automatically by computer software (MASS, Medical Imaging Solutions, Leiden, The Netherlands).

The division of the myocardial upslope through the left ventricular upslope, determining thereby a myocardial perfusion index, was corrected for differences of the speed and compactness of the contrast agent bolus due to potential variations of loading measures after bosentan.

Tissue Doppler echocardiography. TDE was performed with an ATL HDI5000 system (Diagnostic Ultrasound, Bothell, WA, USA) equipped with tissue Doppler, second harmonic imaging technologies and a 2–3.5 MHz phased array transducer. Myocardial velocities were measured and strain rate determined in the posterior wall from a parasternal short axis view at the level of the papillary muscle on M-mode TDE recordings, as described^10,12. Special attention was paid to the proper alignment of the beam perpendicular to the LV wall. The Doppler receive gain was adjusted to provide optimal color-coded filling of the myocardial wall, and the grayscale receive gain for precise detection of the endocardial and epicardial boundaries. The Doppler velocity range was set as low as possible to avoid aliasing (aliasing velocity corresponding to systolic and early-diastolic times, respectively) and 2 M-mode recordings were stored. Offline TDE measurements were made with the HDI Lab software package installed in a standard PC workstation. (1) Myocardial wall motion velocities were extracted along lines drawn manually in the subendocardium and subepicardium to determine endocardial and epicardial velocity patterns over time. (2) Peak systolic velocity, defined as maximal velocity during LV ejection, was determined from endocardial (EndoVSYS) and epicardial (EpiVSYS) velocity patterns. Peak early diastolic velocity was determined from endocardial (EndoVDIA) and epicardial (EpiVDIA) patterns. (3) Peak systolic and early diastolic strain rate (SR) was defined as the maximal transmural velocity gradient during systolic (SRSYS) and early diastolic (SRDIA) times and was calculated as: SR (s-1) = (EndoV – EpiV)/d (where d is the distance between endocardium and epicardium).

TDE measurements were performed by 2 experienced practitioners, according to a blind protocol, and the mean value between both measurements was used for further analysis.

Statistical analysis. In order to detect a Δ/SD = 1 increase in perfusion index¹⁰, with a unilateral a value of 0.05 and a ß value of 0.1, 18 patients had to be enrolled. Data, expressed as mean ± SD or median (range) according to the normality of distribution of the values, were analyzed using Mann-Whitney (unpaired data) and Wilcoxon (paired data) tests for the comparison of groups, and Spearman's rank correlation test for assessment of the relationship between quantitative variables. P values less than 0.05 were considered significant (Statview Software, Abacus Concepts, Berkeley, CA, USA).

RESULTS

Clinical findings. Eighteen patients were included (14 women; 10 with the diffuse cutaneous subtype). The clinical and biological characteristics of the population are shown in Table 1.

Table 1. Clinical and biological characteristics of 18 patients with SSc.

MRI. Patients with SSc had lower median (range) myocardial perfusion index compared to control subjects: 0.17 (0.09–0.23) versus 0.23 (0.21–0.24; p = 0.0023).

Myocardial perfusion index significantly increased after 4 weeks of treatment with bosentan from a median (range) of 0.17 (0.09–0.23) at baseline to 0.22 (0.13–0.30; p = 0.0004, Table 2). Individual data are presented in Figure 1. There was a significant correlation between individual baseline levels and changes after treatment (r = 0.77; p = 0.001). Age, disease duration, cutaneous subtype of the disease, pulmonary artery pressure, pulmonary fibrosis, carbon monoxide diffusion, and autoantibody status were not associated with baseline MRI results or changes after treatment.

Table 2. Hemodynamic, myocardial perfusion, and strain rate (SR) values. Data are mean ± SD or median (range).

[click, then close, image]

Figure 1. Myocardial perfusion index measured by MRI, after 4 weeks of treatment with bosentan in 18 patients with SSc. The median (range) value increased from 0.17 (0.09–0.23) per s at baseline to 0.22 (0.13–0.30) after treatment (p = 0.0004).

In order to ensure the stability of the method and reproducibility of measurements, the 6 healthy controls were reinvestigated 6 months after the initial examination. Myocardial perfusion index at baseline and at 6 months was, respectively, 0.23 (0.21–0.24) and 0.24 (0.22–0.25) (data not shown).

Tissue Doppler echocardiography. The interobserver variability was 0.13 for systolic SR and 0.17 for diastolic SR, which is consistent with previous studies¹⁰.

As expected, patients with SSc had lower systolic SR than controls [2.1 (1.3–3.1) vs 3.7 (1.7–7.9), per s; p < 0.0001], and lower diastolic SR [2.6 (1.4–6.4) vs 5.4 (4.2–8.1) per s; p = 0.0004]¹².

Median (range) peak systolic SR was markedly improved after bosentan treatment, from 2.1 (1.3–3.1) at baseline to 2.8 (2.1–4.8) s-1 after treatment (p = 0.0002; individual data are shown in Figure 2), and there was a trend for a correlation between individual baseline values and changes (r = 0.44, p = 0.07). Bosentan also significantly increased the median (range) peak early diastolic SR from 2.6 (1.4–6.7) to 3.6 (2.0–7.6) per s (p = 0.0003), and a correlation between baseline measurements and individual improvement (r = 0.53, p = 0.03) was demonstrated.

[click, then close, image]

Figure 2. Individual measurements of peak systolic strain rate determined by TDE at baseline and after 4 weeks of treatment with bosentan in 18 patients with SSc. The median (range) value increased from 2.1 (1.3–3.1) per s at baseline to 2.8 (2.1–4.8) after treatment (p = 0.0002).

Neither demographic criteria nor biological measures were associated with significant differences in SR measurements or changes.

Safety. Overall, there were no clinically important changes in systolic blood pressure or heart rate (Table 2) and no patients experienced serious adverse events during the study. There was no notable increase in transaminase values for any patient during this study; no patient had liver enzyme elevation of up to 3-fold the upper limit of normal during the study.

DISCUSSION

Our main finding was that in SSc, 4 weeks of treatment with bosentan simultaneously increases myocardial perfusion and function, as evaluated by MRI and TDE, respectively.

Primary myocardial involvement is common in SSc and a general vasospastic mechanism is thought to play a key role in this disease, especially in the onset and progression of myocardial involvement. Vasospasm would initially impair perfusion and function, but with reversible involvement. This would be followed by structural arteriolar lesion leading to irreversible lesions. This hypothesis is consistent with the beneficial effects demonstrated on myocardial perfusion, metabolism, and function with various vasodilators such as calcium channel blockers and ACE inhibitors^2,5-8. Our study, showing both reduced myocardial perfusion and contractility compared with controls, is in accord with previous ones and reinforces the necessity of prompt detection of infraclinical alterations^2,5-8,12.

In SSc, the microvascular bed is the target of an immune-inflammatory injury that leads to dysregulation of vascular tone control; the endothelial hypothesis suggests a production of endothelin that has unanimously been reported to be elevated²⁰. This is also supported by recent demonstration of the efficacy of bosentan, an oral endothelin dual receptor antagonist, in the treatment of pulmonary hypertension and for reduction in the number of new digital ulcers in patients with SSc^16,17. Our study showed that 4 weeks of bosentan therapy concomitantly improves myocardial perfusion and function as evaluated by modern and accurate methods. Indeed, myocardial perfusion was assessed by cardiac MRI, a noninvasive quantitative method of assessment of myocardial perfusion²¹ capable of detecting subendocardial perfusion abnormalities in patients with cardiac syndrome X. This suggests it has higher sensitivity than conventional perfusion techniques²². Further, we documented the stability of MRI measurements in a control group over a 6-month period; this suggests that the observed differences in patients with SSc are consecutive to bosentan treatment.

We investigated cardiac function using TDE, a modern and accurate method to determine contractility and diastolic function, and far more sensitive than conventional echocardiography or radionuclide ventriculography^12,23,24. Indeed, peak systolic and peak early diastolic SR are respective markers of contractility and diastolic function; our results therefore suggest that bosentan increases both measures. Our results may also suggest a greater improvement in diastolic function. As well, diastolic function is altered earlier in the course of SSc and is more prevalent in patients with SSc⁵; as a direct consequence the effect of bosentan may be more pronounced upon diastolic function. However, diastolic function is also more dependent than contractility on hemodynamic condition; we did not document any significant effect on loading conditions as estimated by blood pressure and the systolic blood pressure-heart rate product, and cannot affirm that a minimal variation in loading condition may contribute to this apparent discrepancy between improvement of both functions.

Bosentan has previously been investigated in patients with chronic severe heart failure mostly resulting from coronary atherosclerosis, and did not demonstrate any clinical benefit²⁵. Indeed, endothelin is elevated in congestive heart failure (CHF) but may be a simple marker of endothelium dysfunction and/or increased vasoconstrictor tone and shear stress. Moreover, it has been suggested that in failing hearts, endothelin loses its ability to enhance cardiac contraction and furthermore may act to depress contractility²⁶. Thus, therapies that target endothelin receptor may fail to be able to improve cardiac function in advanced CHF. In contrast, we investigated cardiac-asymptomatic patients with SSc for whom the hallmark is vasospastic propensity. Moreover elevated endothelin concentrations have been demonstrated in such patients, at an early stage of the disease, which suggests a crucial role in the onset and progression of the disease. Lastly, we evaluated myocardial perfusion and function using very sensitive methods, which could also account, at least in part, for our observed differences. Using the same methods, we previously showed nifedipine concomitantly improved myocardial perfusion and function¹⁰; it is noteworthy that, although the 2 drugs were not directly compared, bosentan and nifedipine improved myocardial measures to the same extent. The main hypothesis is that, although acting through different mechanisms, they both target the reversible component of the vascular abnormalities, improving vasodilation and allowing better cardiac perfusion and function.

In our study we included a majority of patients with the diffuse cutaneous subtype, whereas the limited subtype is the more prevalent. Although cardiac involvement could be more prevalent and more severe in the diffuse cutaneous subtype of the disease, there is increasing evidence to suggest that the limited form is not free of cardiac involvement. In a large epidemiological Italian study, heart symptoms were not found to be significantly different between patients with the diffuse subtype and those with the limited form²⁷. Some data based on echocardiography have even suggested a more prevalent involvement in the limited subtype of the disease²⁸. In our experience of patients with recent onset of disease, no significant difference between the 2 cutaneous subgroups of patients could be demonstrated⁵.

Our study was not designed as a randomized, controlled, double-blind protocol. However, based on the low variability of TDE in our laboratory and in others, and the reproducibility of MRI measurements in controls, we assume that the observed difference in myocardial perfusion and contractility was a direct consequence of bosentan treatment. Bosentan may induce some hemodynamic changes that could have influenced myocardial measures; however, SR determined by TDE is less load-dependent than other methods¹¹ and we did not observe any significant difference in the systolic blood pressure-heart rate product, an index of afterload evaluation (Table 2).

The exact mechanism of bosentan's efficacy cannot be derived from our study. Endothelin has been shown to act as a vasoconstrictor, but also stimulates fibroblast and smooth muscle cell proliferation and fibroblast matrix biosynthesis¹³. Endothelin may thereby also play a key role in the genesis of the structural vascular lesion in SSc, and longterm studies are warranted to determine if this drug may have sustained beneficial effects on heart involvement, together with improvement and prevention in other organ systems affected by vascular disease. The limited number of patients included in our series and the global properties of MRI evaluation in contrast to the segmental evaluation by TDE may account for the absence of correlations between measurements. Moreover, myocardial perfusion may increase in segments with various degrees of fibrotic lesions, resulting in different effects on measures of function.

Finally, we assessed the effects of bosentan treatment on myocardial perfusion and segmental function after only 4 weeks; thus, no formal conclusion can be drawn from this study about the possible sustained therapeutic benefits of this drug.

Four weeks of treatment with bosentan simultaneously improved myocardial perfusion and regional function, determined by 2 quantitative, accurate, and highly sensitive methods, MRI and TDE, respectively. Our data demonstrate the beneficial short-term myocardial effects of bosentan in patients with SSc. Longterm investigations are warranted.

ACKNOWLEDGMENT

We thank Dr. Virginie Gressin from Actelion Pharmaceuticals for helpful discussion and manuscript preparation and Actelion Pharmaceuticals, France, who provided the drug.

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