Cardiac Sympathetic Dysfunction Correlates With Abnormal Myocardial Contractile Reserve in Dilated Cardiomyopathy Patients

Journal of the American College of Cardiology © 2005 by the American College of Cardiology Foundation Published by Elsevier Inc.

Vol. 46, No. 11, 2005 ISSN 0735-1097/05/$30.00 doi:10.1016/j.jacc.2005.08.046

Cardiac Sympathetic Dysfunction Correlates With Abnormal Myocardial Contractile Reserve in Dilated Cardiomyopathy Patients Satoru Ohshima, MD,* Satoshi Isobe, MD, PHD,* Hideo Izawa, MD, PHD,* Mamoru Nanasato, MD, PHD,* Akitada Ando, MD, PHD,* Akira Yamada, MD,* Kiyoyasu Yamada, MD, PHD,* Tomoko S. Kato, MD, PHD,* Koji Obata, PHD,† Akiko Noda, PHD,‡ Takao Nishizawa, MD,† Katsuhiko Kato, MD, PHD,§ Kohzo Nagata, MD, PHD,‡ Kenji Okumura, MD, PHD,* Toyoaki Murohara, MD, PHD,* Mitsuhiro Yokota, MD, PHD, FACC† Nagoya, Japan We investigated the relationship between iodine-123-metaiodobenzylguanidine (123IMIBG) findings and myocardial contractile reserve in patients with mild to moderate dilated cardiomyopathy (DCM). BACKGROUND Little is known regarding the relationship between cardiac sympathetic nervous function and myocardial contractile reserve in DCM. METHODS Twenty-four DCM patients who showed sinus rhythm underwent echocardiography, biventricular catheterization, and myocardial 123I-MIBG scintigraphy. Left ventricular (LV) pressures were measured using a micromanometer-tipped catheter. The myocardial contractile function (LV dP/dtmax) was determined at rest and during atrial pacing. The messenger ribonucleic acid (mRNA) expressions of intracellular Ca2⫹-regulatory proteins were analyzed by real-time quantitative reverse transcription-polymerase chain reaction. Myocardial 123IMIBG accumulation was quantified as a heart-mediastinum ratio (HMR). RESULTS A significant correlation was observed between the delayed 123I-MIBG HMR and the percentage change in LV dP/dtmax from the baseline to the peak or critical heart rate (r ⫽ 0.64; p ⬍ 0.001). The delayed 123I-MIBG HMR was significantly lower in patients showing a worsening change in LV dP/dtmax than in those showing a favorable change (p ⬍ 0.005). The maximum LV dP/dtmax during pacing and the sarcoplasmic reticulum Ca2⫹-ATPase (SERCA2) mRNA levels were significantly more reduced in patients with a delayed HMR ⱕ1.8 than in those with a delayed HMR ⬎1.8 (p ⬍ 0.05, respectively). CONCLUSIONS Abnormal myocardial 123I-MIBG accumulation is related to an impaired myocardial contractile reserve and down-regulation of SERCA2 mRNA in DCM. Myocardial 123IMIBG scintigraphy can be useful in noninvasively evaluating myocardial contractile reserve in patients with mild to moderate DCM. (J Am Coll Cardiol 2005;46:2061– 8) © 2005 by the American College of Cardiology Foundation OBJECTIVES

Previous clinical studies have demonstrated the diminished myocardial contractile reserve in response to pacing-induced tachycardia in patients with dilated cardiomyopathy (DCM) (1,2). Some studies have shown that myocardial contractile reserve reflects the severity of DCM and is a prognostic determinant in patients with idiopathic DCM (3,4). In general, myocardial contractile function is thought to be determined by myocardial intracellular Ca2⫹ handling, which consists of Ca2⫹ releasing factors from sarcoplasmic reticulum such as ryanodine receptor-2 and intracellular Ca2⫹-regulating factors such as sarcoplasmic reticulum Ca2⫹-ATPase (SERCA2) and phospholamban (5– 8). We previously demonstrated the relationship between an abnormal myocardial contractile reserve and a reduced messenger ribonucleic acid (mRNA) expression of SERCA2 in patients with hypertrophic cardiomyopathy (9). Therefore, it From the Departments of *Cardiology and †Cardiovascular Genome Science, Nagoya University School of Medicine, Nagoya, Japan; ‡Department of Medical Technology, Nagoya University School of Health Science, Nagoya, Japan; and the §Department of Radiology, Nagoya University Hospital, Nagoya, Japan. Manuscript received January 21, 2005; revised manuscript received June 30, 2005, accepted August 1, 2005.

is of interest to assess the relation of myocardial contractile reserve to Ca2⫹-handling proteins in DCM. Iodine-123-metaiodobenzylguanidine (123I-MIBG) is a useful imaging tracer that shares similar myocardial uptake, storage, and release mechanisms as norepinephrine (NE) in sympathetic nerve terminals. Measurements of a 123IMIBG heart-mediastinum ratio (HMR) and washout rate have enabled more detailed assessment of the function and integrity of myocardial sympathetic innervation. It is well known that myocardial 123I-MIBG accumulation is reduced in patients with heart failure by enhanced NE spillover from cardiomyocyte (10). It has been reported that reduced myocardial 123I-MIBG accumulation is correlated with diminished left ventricular (LV) function in patients with heart failure (11,12). However, the relation between cardiac sympathetic function and myocardial contractile reserve in patients with DCM still remains to be established. Accordingly, in the present study we determined the relationship between cardiac sympathetic function, contractile reserve, and myocardial cellular Ca2⫹ handling, and investigated whether myocardial 123I-MIBG scintigraphy

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Abbreviations and Acronyms DCM ⫽ dilated cardiomyopathy HMR ⫽ heart-mediastinum ratio 123 I-MIBG ⫽ iodine-123-metaiodobenzylguanidine LV ⫽ left ventricular LV dP/dtmax ⫽ maximum first derivative of left ventricular pressure LVEF ⫽ left ventricular ejection fraction mRNA ⫽ messenger ribonucleic acid NE ⫽ norepinephrine SERCA2 ⫽ sarcoplasmic reticulum Ca2⫹-ATPase T1/2 ⫽ pressure half-time

could be useful in noninvasively evaluating myocardial contractile reserve in patients with mild to moderate DCM.

MATERIALS AND METHODS Study population. Twenty-four patients with mild to moderate DCM, who showed sinus rhythm on electrocardiogram, were enrolled in this study. A detailed history was obtained and a physical examination was performed for all patients before inclusion in this study. According to the definition of the World Health Organization/International Society and Federation of Cardiology, DCM is a heart muscle disease of unknown origin with predominant impairment of the systolic function (13). Criteria for enrollment in this study were normal coronary artery and no evidence of specific cardiomyopathy such as ischemic, valvular, hypertensive, diabetic, alcoholic, inflammatory, or systemic cardiomyopathy. Patients were excluded if they had atrial fibrillation, neuromuscular diseases, or parkinsonism. No patients had received reserpine, tricyclic antidepressant, or other drugs that could interfere with NE kinetics. All patients were hospitalized for examinations and underwent echocardiography, cardiac catheterization, and resting myocardial 123I-MIBG scintigraphy. Endomyocardial biopsy was performed to analyze real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). Sixteen patients had been treated with angiotensin-converting enzyme inhibitors, thirteen with diuretics, eight with digitalis, six with angiotensin receptor blockades, and three with beta-blockers. All medications were withdrawn at least 72 h before the study. The study protocol was approved by our institutional review committee. Written informed consent was obtained from all patients. 123 I-MIBG imaging. Myocardial 123I-MIBG scintigraphy was performed after an overnight fast. One hundred fortyeight MBq (4 mCi) of 123I-MIBG was injected intravenously through the antecubital vein at rest. The planar view was obtained approximately 15 min and 4 h after the tracer injection. A two-head gamma camera (ECAM; Toshiba, Tokyo, Japan) equipped with a low-energy high-resolution collimator was rotated over a 180° arc with an acquisition time of 20 s per image at 4° intervals for each view. Energy

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discrimination was provided by a 20% window centered at 159 keV. Biventricular cardiac catheterization and echocardiography. All patients underwent biventricular catheterization using brachial approach in fasting state. A 20-gauge catheter was placed in the left brachial artery to measure arterial pressures. A 6-F fluid-filled pigtail catheter with a high-fidelity micromanometer (model SPC-464D; Millar Instruments, Houston, Texas) was advanced into the LV cavity through a 6-F sheath in the right brachial artery to measure LV pressures. A 7-F triple-lumen Swan-Ganz thermodilution catheter (Baxter Healthcare, Deerfield, Illinois) was positioned in the right pulmonary artery through the right brachial vein to measure pulmonary artery wedge pressure (PAWP) and cardiac index (CI). A 6-F bipolar pacing catheter was introduced through the right subclavian vein and positioned in the high right atrium. After baseline data were obtained, right atrial pacing was initiated at 80 beats/min and increased in increments of 10 beats/min up to the maximum value of 140 beats/min. All patients underwent two-dimensional echocardiography with a Hewlett-Packard ultrasound system (Sonos 2500; Andover, Massachusetts) equipped with a 2.5- to 3.5-MHz transducer to measure wall thickness, cardiac chamber size, and fractional shortening (FS) at rest. 123 I-MIBG analysis. Myocardial 123I-MIBG uptake was quantified in anterior planar views at 15 min (early image) and 4 h (delayed image) after tracer injection. After regions of interest over the whole heart (H) and over the upper mediastinum (M) were set, an HMR was calculated. In our laboratory, the normal 123I-MIBG HMR values of the early and delayed images obtained from other age-matched controls (9 male and 1 female, mean age 53 ⫾ 9 years) were 1.9 to 2.8 and 1.8 to 2.7, respectively. Cardiac hemodynamic analysis. Micromanometer pressure signals and standard electrocardiograms were recorded with a multichannel recorder (MR-40, TEAC, Tokyo, Japan) throughout the study. Left ventricular pressure signals were digitized at 3-ms intervals and analyzed with software developed in our laboratory with a 32-bit microcomputer system (PC-9821-ST20; NEC, Tokyo, Japan). Hemodynamic data were analyzed by two independent observers who were unaware of the clinical, echocardiographic, and scintigraphic data. We selected steady-state LV pressure data at baseline and at each pacing rate for analysis, then measured LV end-diastolic pressure (LVEDP), the maximum first derivative of LV pressure (LV dP/dtmax) as an index of contractility, and the pressure half-time (T1/2) to evaluate LV isovolumic relaxation according to Mirsky’s method (14). A biphasic pattern of change, with an initially positive and subsequently negative slope in the force-frequency relation, and a flat pattern of change without initial increasing in the force-frequency relation (e.g., the percent change in LV dP/dtmax from the baseline to the maximum value is ⬍10%) are considered to be worsening changes. Both patterns of changes indicate

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impairment in myocardial contractile reserve (15). We defined the critical heart rate (HR) as the HR at which LV dP/dtmax reached the maximum value during a progressive increase in HR. Thus, the value beyond which LV dP/dtmax declined by 5% was the critical HR for isovolumic contraction (16,17). The peak pacing rates were defined as the HR at which either second-degree atrioventricular block or pulsus alternans occurred (17). After completion of the pacing study, selective coronary angiography, left ventriculography, and endomyocardial biopsy were performed. Left ventricular end-diastolic volume, LV end-systolic volume, and stroke volume were measured by contrast-enhanced left ventriculography. Left ventricular end-diastolic volume index (LVEDVI), LV end-systolic volume index (LVESVI), stroke volume index (SI), and LV ejection fraction (LVEF) were calculated according to the Sandler and Dodge method (18). In right cardiac catheterization, PAWP and CI were measured using a Swan-Ganz thermodilution catheter. Several biopsy specimens were obtained from the left side of the interventricular septum. Biopsy specimens for mRNA analysis were frozen immediately in liquid nitrogen and stored at ⫺80°C until use. Echocardiographic data were analyzed by two independent observers who were unaware of the clinical, hemodynamic, and scintigraphic data. In two-dimensional echocardiography, the LV end-diastolic dimension (LVEDD), LV end-systolic dimension (LVESD), interventricular septal thickness (IVST), posterior wall thickness (PWT), and FS were measured on the M-mode of the long-axis image according to standard criteria (19). Measurement of neurohumoral factors. The blood sample was immediately placed on ice and centrifuged at 4°C. The plasma NE levels were measured using highperformance liquid chromatography. The plasma brain natriuretic peptide (BNP) levels were measured with a specific radioimmunoassay for human BNP using a commercially available kit. RT-PCR analysis. The total ribonucleic acid was isolated from 1 to 2.5 mg of the frozen samples of LV biopsy specimens and subjected to real-time quantitative RT-PCR analysis as previously described (20). The mRNA expressions of intracellular Ca2⫹-regulatory proteins, including SERCA2, ryanodine receptor-2, phospholamban, calsequestrin, and Na⫹/Ca2⫹ exchanger, were analyzed by a fluorogenic 5=-nuclease PCR assay using an ABI PRISM 7700 sequence detector (Perkin-Elmer, Wellesley, Massachusetts). All PCR assays were performed in triplicate. TaqMan glyceraldehyde-3-phosphate dehydrogenase (GAPDH) control reagents (Perkin-Elmer) were used for the detection of human GAPDH transcript as an internal standard. Statistical analysis. Data were expressed as mean values ⫾ SD. An unpaired Student t test was performed to determine differences between mean values for continuous variables when appropriate. Neurohumoral factors (BNP, NE) were not normally distributed. Therefore, the nonparametric

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Table 1. Patient Demographics Gender (M/F) Age (yrs) NYHA functional class (n) I II CTR (%) Echocardiography IVST (mm) PWT (mm) LVEDD (mm) LVESD (mm) LAD (mm) FS (%) Cardiac catheterization LVEDVI (ml/m2) LVESVI (ml/m2) SI (ml/m2) LVEF (%) LVEDP (mm Hg) PAWP (mm Hg) CI (l/mim/m2)

20/4 53 ⫾ 10 19 5 52 ⫾ 7 8.3 ⫾ 1.3 8.3 ⫾ 1.3 59 ⫾ 10 47 ⫾ 9 42 ⫾ 8 21 ⫾ 5.0 90 ⫾ 55 55 ⫾ 25 35 ⫾ 10 41 ⫾ 7.0 17 ⫾ 8.9 12 ⫾ 7.2 3.6 ⫾ 1.1

Data are expressed as mean values ⫾ SD. CI ⫽ cardiac index; CTR ⫽ cardiothoracic ratio; FS ⫽ fractional shortening; IVST ⫽ interventricular septal thickness; LAD ⫽ left atrial dimension; LVEDD ⫽ left ventricular end-diastolic dimension; LVEDP ⫽ left ventricular end-diastolic pressure; LVEDVI ⫽ left ventricular end-diastolic volume index; LVEF ⫽ left ventricular ejection fraction; LVESD ⫽ left ventricular end-systolic dimension; LVESVI ⫽ left ventricular end-systolic volume index; NYHA ⫽ New York Heart Association; PAWP ⫽ pulmonary artery wedge pressure; PWT ⫽ posterior wall thickness; SI ⫽ stroke index.

Mann-Whitney U test was used to assess differences. Correlations between scintigraphic and hemodynamic parameters were performed by linear regression analysis. A multiple linear regression analysis was performed using the percentage change in LV dP/dtmax as dependent parameter. Age, LV wall thickness, LV volume index, LVEF, neurohumoral factors, and delayed 123I-MIBG HMR were used as independent parameters. The partial regression coefficient (␤) was calculated to assess significant independent parameters. A threshold value of a delayed MIBG HMR for detecting an abnormal contractile response was defined by receiver-operating characteristic analysis. A p value ⬍0.05 was considered statistically significant.

RESULTS Patient demographics. The demographics of the patients enrolled in this study are summarized in Table 1. The mean age of the 24 patients (20 men, 4 women) was 53 ⫾ 10 years. Nineteen patients were classified as New York Heart Association (NYHA) functional class I, and five patients as NYHA class II. The mean cardiothoracic ratio was 52 ⫾ 7%. The LVEDD and LVESD derived from echocardiography were 59 ⫾ 10 mm and 47 ⫾ 9 mm, respectively, and the LVEDVI and LVESVI derived from contrast ventriculography were 90 ⫾ 55 ml/m2 and 55 ⫾ 25 ml/m2, respectively, suggesting LV dilatation. The IVST and PWT were 8.3 ⫾ 1.3 mm and 8.3 ⫾ 1.3 mm, respectively, suggesting a tendency to wall thinning. The LVEF and FS were reduced, with mean values of 41 ⫾ 7.0% and 21 ⫾

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5.0%, respectively. The mean values of early HMR and delayed HMR were 1.97 ⫾ 0.34 and 1.83 ⫾ 0.30, respectively. Eleven patients showed a debilitating pattern of changes in LV dP/dtmax, and 13 showed a favorable pattern. Relationship between 123I-MIBG findings and hemodynamic parameters. No adverse complications were observed in the hemodynamic study. A significant correlation was observed between the delayed 123I-MIBG HMR and the percentage change in LV dP/dtmaxfrom the baseline to the peak or critical HR (r ⫽ 0.64; p ⬍ 0.001) (Fig. 1). A positive linear correlation was observed between the delayed 123 I-MIBG HMR and the percentage shortening in T1/2 from the baseline to the peak HR, but it did not reach statistical significance (r ⫽ 0.35; p ⫽ 0.08). No significant correlation was observed between the delayed HMR and other hemodynamic parameters (LV dimensions, LVEF, LV volume indexes, LVEDP, PAWP, or CI) derived from echocardiography or biventricular catheterization. No significant correlation was observed between the early 123IMIBG HMR and any hemodynamic parameters. A multiple regression analysis revealed that the delayed 123I-MIBG HMR was a significant independent parameter for the percentage change in LV dP/dtmax (␤ ⫽ 0.47; p ⫽ 0.03). Comparison of patients with and without worsening changes in LV dP/dtmax. When we divided the DCM patients based on the rate-dependent changes in LV dP/ dtmax, the delayed 123I-MIBG HMR was significantly lower in patients with worsening changes than in those showing non-worsening changes (p ⬍ 0.005) (Table 2). In the echocardiographic study, the LVEDD and LVESD were significantly greater in patients showing worsening changes than in those showing non-worsening changes in LV dP/dtmax (p ⬍ 0.05) (Table 2). In the hemodynamic study, no significant difference was observed in the percentage change in HR during the pacing study in the two groups. No significant difference was observed in the baseline systolic blood pressure, the baseline diastolic blood pressure, the peak systolic blood pressure, or the peak diastolic blood

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pressure in the two groups (Table 2). The LVEDVI and LVESVI were also significantly greater in patients showing worsening changes than in those showing non-worsening changes (p ⬍ 0.05, respectively) (Table 2). The peak T1/2 was significantly less prolonged in patients with worsening changes than in those showing non-worsening changes (p ⬍ 0.05) (Table 2). The calsequestrin mRNA levels were significantly lower in patients with worsening changes than in those showing non-worsening changes (p ⬍ 0.05) (Table 2). Comparison of patients with and without a low HMR. At the threshold value of a delayed 123I-MIBG HMR of ⱕ1.8, the sensitivity, specificity, and accuracy for detecting patients showing worsening changes in LV dP/dtmaxwere 81.8%, 84.6%, and 83.3%, respectively, using receiveroperating characteristic analysis. According to the quantitative 123I-MIBG findings, we divided the DCM patients into two groups as follows: 10 patients with a low delayed HMR (delayed HMR ⱕ1.8) and 14 without it (delayed HMR ⬎1.8). The maximum LV dP/dtmax during pacing was significantly more reduced in patients with a low HMR than in those without it (1,337 ⫾ 275 mm Hg/s vs. 1,705 ⫾ 349 mm Hg/s; p ⫽ 0.011). The percentage change in LV dP/dtmax from the baseline to the peak or critical HR was less in patients with a low HMR than in those without it (11 ⫾ 5.4% vs. 20 ⫾ 8.3%; p ⫽ 0.0079). The worsening change in LV dP/dtmax was more frequently observed in patients with a low HMR than in those without it (8 of 10 patients [80%] vs. 2 of 14 patients [14%]; p ⫽ 0.0008). The percentage shortening in T1/2 from the baseline to the peak HR was significantly less in patients with a low HMR than in those without it (⫺21 ⫾ 7.2% vs. ⫺30 ⫾ 5.8%; p ⫽ 0.047). The plasma NE levels were higher in patients with a low HMR than in those without it (671 ⫾ 266 pg/ml vs. 460 ⫾ 173 pg/ml; p ⫽ 0.0091). The SERCA2 mRNA levels were significantly lower in patients with a low HMR than in those without it (SERCA2/GAPDH ratio: 0.335 ⫾ 0.053 vs. 0.453 ⫾ 0.053; p ⬍ 0.01). Myocardial 123I-MIBG scintigraphy and the changes in LV dP/dtmax of two typical cases are presented in Figures 2 and 3.

DISCUSSION

Figure 1. Relationship between the delayed iodine-123-metaiodobenzylguanidine heart-mediastinum ratio (HMR) and the percentage change in LV dP/dtmax from the baseline to the peak or critical heart rate. LV dP/dtmax ⫽ maximum first derivative of left ventricular pressure.

In this study, a significant correlation was observed between the change in the acceleration of contractility (percentage change in LV dP/dtmax from the baseline to the peak or critical HR) during atrial pacing and the quantitative myocardial 123 I-MIBG uptake (delayed 123 I-MIBG HMR). Patients with an inability to increase LV dP/dtmax exhibited lower 123I-MIBG HMR than those without it. In addition, the SERCA2 mRNA levels were lower in patients with impaired sympathetic nervous function than in those with relatively preserved function. These results suggest that abnormal 123I-MIBG findings may be related to the im-

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Table 2. Comparison of Patients Showing Non-Worsening With Those Showing Worsening Changes in LV dP/dtmax Parameters Gender (M/F) Age (yrs) NYHA functional class (n) I II CTR (%) Echocardiography IVST (mm) PWT (mm) LVEDD (mm) LVESD (mm) LAD (mm) FS (%) Cardiac catheterization Baseline HR (beats/min) Peak HR (beats/min) Baseline SBP (mm Hg) Peak SBP (mm Hg) Baseline DBP (mm Hg) Peak DBP (mm Hg) LVEDVI (ml/m2) LVESVI (ml/m2) SI (ml/m2) LVEF (%) Baseline LVEDP (mm Hg) Peak LVEDP (mm Hg) ⌬LVEDP (mm Hg) Baseline LV dP/dtmax (mm Hg/s) Peak LV dP/dtmax (mm Hg/s) %LV dP/dtmax (%) Baseline T1/2 (ms) Peak T1/2 (ms) %T1/2 (%) PAWP (mm Hg) CI (l/min/m2) Neurohumoral factors NE (pg/ml) BNP (pg/ml) mRNA expression of intracellular Ca2⫹-regulatory proteins SERCA2/GAPDH RyR/GAPDH PLB/GAPDH CQ/GAPDH Na⫹/Ca2⫹ exchanger/GAPDH MIBG scintigraphy Early HMR Delayed HMR

Non-Worsening Pattern (n ⴝ 13)

Worsening Pattern (n ⴝ 11)

10/3 54 ⫾ 9

10/1 52 ⫾ 11

0.74

11 2 52 ⫾ 3

8 3 52 ⫾ 4

0.80

8.5 ⫾ 1.3 8.5 ⫾ 1.4 55 ⫾ 5 42 ⫾ 3 42 ⫾ 8 22 ⫾ 6.7

8.0 ⫾ 1.3 8.1 ⫾ 1.3 64 ⫾ 12 52 ⫾ 10 45 ⫾ 8 19 ⫾ 3.3

0.60 0.43 0.013 0.0054 0.18 0.21

77 ⫾ 16 137 ⫾ 9 144 ⫾ 27 143 ⫾ 22 84 ⫾ 18 81 ⫾ 10 147 ⫾ 27 82 ⫾ 15 63 ⫾ 20 42 ⫾ 5 17 ⫾ 7 8⫾7 ⫺9 ⫾ 6 1431 ⫾ 237 1701 ⫾ 336 19 ⫾ 15 42 ⫾ 8.3 34 ⫾ 8.0 ⫺22 ⫾ 7.4 11 ⫾ 5.2 4.0 ⫾ 1.3

73 ⫾ 15 132 ⫾ 10 128 ⫾ 20 147 ⫾ 24 77 ⫾ 11 86 ⫾ 14 220 ⫾ 96 144 ⫾ 76 76 ⫾ 35 39 ⫾ 6 18 ⫾ 11 5⫾6 ⫺13 ⫾ 9 1425 ⫾ 257 1661 ⫾ 343 16 ⫾ 11 38 ⫾ 6.5 28 ⫾ 5.4 ⫺33 ⫾ 14.3 13 ⫾ 9.3 3.2 ⫾ 0.7

0.71 0.17 0.12 0.70 0.29 0.37 0.015 0.0089 0.25 0.21 0.89 0.34 0.24 0.95 0.78 0.57 0.22 0.047 0.13 0.57 0.11

439 ⫾ 179 117 ⫾ 178

648 ⫾ 349 94 ⫾ 148

0.13 0.76

0.39 ⫾ 0.51 1.28 ⫾ 0.51 0.36 ⫾ 0.13 1.51 ⫾ 0.55 2.17 ⫾ 0.82

0.40 ⫾ 0.12 0.90 ⫾ 0.29 0.53 ⫾ 0.37 0.67 ⫾ 0.033 1.82 ⫾ 0.78

0.98 0.30 0.29 0.037 0.52

2.0 ⫾ 0.3 1.9 ⫾ 0.2

1.8 ⫾ 0.3 1.6 ⫾ 0.3

0.054 0.0038

p Value

Data are expressed as mean values ⫾ SD. BNP ⫽ brain natriuretic peptide; CQ ⫽ calsequestrin; DBP ⫽ diastolic blood pressure; GAPDH ⫽ glyceraldehyde-3phosphate dehydrogenase; HR ⫽ heart rate; HMR ⫽ heart to mediastinum ratio; LV dP/dtmax ⫽ maximum first derivative of left ventricular pressure; NE ⫽ norepinephrine; PAWP ⫽ pulmonary artery wedge pressure; PLB ⫽ phospholamban; RyR ⫽ ryanodine receptor-2; SBP ⫽ systolic blood pressure; SERCA2 ⫽ sarcoplasmic reticulum Ca2⫹-ATPase; T1/2 ⫽ pressure half-time; % ⫽ percentage change in parameters from the baseline to the peak or critical heart rate; ⌬ ⫽ absolute change in parameters from the baseline to the peak or critical heart rate; other abbreviations as in Table 1.

paired myocardial contractile reserve in response to atrial pacing in patients with mild to moderate DCM. Abnormal myocardial contractile reserve in DCM. In this study, impaired cardiac sympathetic function was related to an impaired force-frequency relation during atrial pacing. In general, myocardial contractile function is af-

fected by intramyocardial Ca2⫹ concentration, which is regulated by Ca2⫹-handling and Ca2⫹-releasing factors (5– 8). We previously demonstrated that an abnormal contractile reserve is caused by a reduced mRNA expression of SERCA2 in patients with hypertrophic cardiomyopathy (9). In this study, patients with impaired contractile reserve

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Figure 2. A representative case of a 50-year-old woman. Left ventricular ejection fraction (LVEF) is 35%, and this patient is in New York Heart Association (NYHA) functional class II. (A) Increased lung uptake and severely reduced myocardial uptake are observed on the delayed 123I-MIBG planar image. The delayed HMR is 1.4. (B) The relationship between heart rate (HR) and LV dP/dtmax of this patient is shown. The baseline LV dP/dtmax and maximum LV dP/dtmax are 1,107 mm Hg/s and 1,284 mm Hg/s, respectively. The percentage change in LV dP/dtmax from the baseline to the critical HR is 10%. A biphasic pattern of change in LV dP/dtmax is observed. bpm ⫽ beats per minute; other abbreviations as in Figure 1.

showed reduced mRNA expression of calsequestrin, and no significant difference in mRNA abundance for SERCA2 was observed between the subgroups. However, SERCA2/ GAPDH ratio was significantly lower in DCM patients with a low HMR than in those without it, probably indicating that reduced expression of SERCA2 is associated with impaired cardiac sympathetic activity. Previous studies have mentioned that expression of SERCA2 increases after beta-blocker treatment, suggesting a causal link between beta-blocker therapy and expression of Ca2⫹-regulatory proteins in patients with mild to moderate heart failure (21,22). Our results may support the demonstrations of

these previous studies. Abnormal quantitative 123I-MIBG findings may reflect the abnormal myocardial contractile reserve, which is associated with abnormal Ca2⫹ handlings. We found that some DCM patients show worsening changes in LV dP/dtmax. Previous clinical studies have demonstrated diminished myocardial contractile reserve during pacing-induced tachycardia in patients with DCM (1,2). Some studies have also indicated that potentiation of the force of contraction is attenuated or absent in the failing myocardium (15,23,24). These results are in accord with our results. In DCM patients with worsening changes in LV dP/dtmax, the delayed 123I-MIBG HMR was significantly

Figure 3. A case of a 60-year-old man. LVEF is 45%, and this patient is in NYHA functional class I. (A) Mildly reduced myocardial uptake is observed in the inferior wall on the delayed 123I-MIBG planar image. The delayed HMR is 2.0. (B) The relationship between HR and LV dP/dtmax of this patient is shown. The baseline LV dP/dtmax and maximum LV dP/dtmax are 1,224 mm Hg/s and 1,509 mm Hg/s, respectively. The percentage change in LV dP/dtmax from the baseline to the peak HR is 27%. A progressively increasing pattern of change in LV dP/dtmax is observed. Abbreviations as in Figures 1 and 2.

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lower compared with those showing non-worsening changes. The plasma NE levels were higher in patients with a low HMR than in those without it. In the failing myocardium, a reduced intramyocardial NE content and downregulation of beta-receptors have been reported (25–27). Moreover, another study demonstrated that reduced contractile reserve in the papillary muscle is yielded by the depletion of intramyocardial NE contents in the failing human heart (28). Accordingly, we assume that the abnormal myocardial contractile reserve may be at least in part caused by the depletion of intramyocardial NE contents. Actually, we could not address the mechanism by which cardiac sympathetic nervous dysfunction is involved in a reduced contractile reserve in response to atrial pacing stimulation. However, our result, which demonstrated a significant correlation between cardiac sympathetic function and myocardial contractile function, may suggest that cardiac adrenergic nervous integrity, at least in part, plays a role in regulating myocardial contractile function. Quantitative 123I-MIBG parameters. A previous study reported that an increase in NE turnover at cardiac sympathetic nerve endings led to a decrease in uptake in the delayed image, so that the increase in turnover, that is, an increase in washout rate, depended on the severity of the impaired sympathetic function (29). Moreover, another study reported that because the neuronal accumulation of 131I-MIBG reaches a peak value 4 h after tracer administration, the neuronal uptake of NE can be evaluated accurately if the 131I-MIBG imaging is performed 4 h after tracer administration (30). Furthermore, it is reported that the early 125I-MIBG uptake reflects only the integrity of presynaptic nerve terminals and uptake-1 function, whereas the delayed 125I-MIBG uptake includes overall information regarding neuronal function from uptake to release through the storage system at nerve terminals (31). The delayed image can reflect the severity of heart diseases more accurately than the early image. Given these advantages of using the delayed HMR, we used it to classify the DCM patients in this study. A significant correlation was observed between the delayed 123I-MIBG HMR and myocardial contractile reserve. In contrast, no significant correlations were observed between the early HMR and myocardial contractile reserve. Our results may be supported by the rationale given in two previous studies (30,31). Clinical implications. In this study, the delayed 123I-MIBG HMR correlated with myocardial contractile reserve (percentage change in LV dP/dtmax). In addition, the maximum LV dP/dtmax was more reduced, and the percentage change in LV dP/dtmax and T1/2 (relaxation-frequency relation) was less in DCM patients with severely impaired sympathetic nervous function than in those with mild impairment. However, no significant correlation was observed between the 123I-MIBG HMR and other functional parameters derived from echocardiography or cardiac catheterization. In general, it is well known that LVEF and LV volumes are associated with the clinical outcome or prognosis of patients with heart failure. However, they are more operator-dependent factors and tend

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to be more affected by pre- and afterload than myocardial properties derived from catheterization. On the other hand, it has been reported that increased cardiac NE spillover in congestive heart failure, which reflects an increased sympathetic nervous activity, is associated with both malignant ventricular arrhythmias and poor prognosis (32,33). Our results, in which plasma NE levels were significantly higher in DCM patients with severely reduced MIBG uptake than in those with mildly reduced MIBG uptake, may indicate that DCM patients with reduced 123I-MIBG uptake show increased NE spillover. It is well known that the prognosis of DCM patients with severely impaired LV function is very poor. Conversely, it is important to assess which factors are predictive for clinical outcome in DCM patients with mildly to moderately impaired LV function. Myocardial contractile reserve is reported to be an important prognostic determinant in patients with idiopathic DCM without overt heart failure (3). Accordingly, from the viewpoint of our results, the delayed 123 I-MIBG HMR may be better than other functional parameters to indicate mild to moderate DCM patients with an impaired contractile reserve who will show a poor clinical outcome. Myocardial 123I-MIBG scintigraphy may be useful not only in noninvasively evaluating the degree of impaired myocardial reserve but in reflecting clinical outcome in mild to moderate DCM patients. However, further studies will be needed to elucidate the relationship among the cardiac sympathetic function, myocardial function, and prognosis in a larger patient population. It has been reported that beta-blockers provide long-term benefits in patients with severe heart failure (34,35). To clarify the impacts of a beta-blocker on delayed 123I-MIBG accumulation and decreased contractile reserve, further investigations must be made. Study limitations. Clinically stable and ambulatory patients with sinus rhythm were enrolled in this study. Moreover, our patients were in NYHA functional classes I and II, indicating DCM patients at relatively early stages. Therefore, our results may not be widely extrapolated to patients with more severe LV dysfunction. However, in this study we aimed to clarify the correlation between sympathetic nervous activity and myocardial function in DCM patients at the early stage. It would have been preferable to measure the protein abundance of these proteins and/or their degree of phosphorylation to gain insight into the basis for the differences in physiologic responses between the subgroups of patients defined by differences in their 123I-MIBG HMR. However, it is difficult to analyze protein abundance and its function in the small amount of tissues generated by percutaneous LV biopsies. Accordingly, we assessed the Ca2⫹-handling proteins by RT-PCR only. We defined the delayed 123I-MIBG cutoff value of 1.8 on the basis of receiver-operating characteristic analysis. We believe that this value is useful in predicting DCM patients showing an abnormal contractile reserve. However, this cutoff value may not be extrapolated as predictive of the

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differences observed in a different study population, and the validation of this value would be needed in future studies.

CONCLUSIONS Myocardial 123I-MIBG accumulation is related to myocardial contractile reserve in patients with DCM. In addition, reduced myocardial 123I-MIBG accumulation may be related to the down-regulation of SERCA2 mRNA expression, which indicates an altered Ca2⫹ handling. The myocardial 123I-MIBG scintigraphy may reflect myocardial contractile reserve, and may be useful in noninvasively detecting DCM patients with moderately impaired LV function who will progress to an advanced stage. However, further studies including prognostic evaluation will be needed to clarify this issue in a larger population. Reprint requests and correspondence: Dr. Satoshi Isobe, Department of Cardiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi 466-8550, Japan. E-mail: [email protected].

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