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`RED CELLS
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`Longitudinal analysis of heart and liver iron in thalassemia major
`Leila J. Noetzli,1 Susan M. Carson,2 Anne S. Nord,2 Thomas D. Coates,2 and John C. Wood1,3
`
`1Department of Pediatrics, Division of Cardiology, 2Division of Hematology-Oncology, and 3Department of Radiology, Childrens Hospital Los Angeles, CA
`
`High hepatic iron concentration (HIC) is
`associated with cardiac iron overload.
`However, simultaneous measurements of
`heart and liver iron often demonstrate no
`significant linear association. We postu-
`lated that slower rates of cardiac iron accu-
`mulation and clearance could reconcile
`these differences. To test this hypothesis,
`we examined the longitudinal evolution of
`cardiac and liver iron in 38 thalassemia ma-
`jor patients, using previously validated mag-
`Introduction
`
`netic resonance imaging (MRI) techniques.
`On cross-sectional evaluation, cardiac iron
`was uncorrelated with liver iron, similar to
`previous studies. However, relative changes
`in heart and liver iron were compared with
`one another using a metric representing the
`temporal delay between them. Cardiac iron
`significantly lagged liver iron changes in
`almost half of the patients, implying a func-
`tional but delayed association. The degree
`of
`time lag correlated with initial HIC
`
`(r ⴝ 0.47, P < .003) and initial cardiac R2*
`(r ⴝ 0.57, P < .001), but not with patient age.
`Thus, longitudinal analysis confirms a lag in
`the loading and unloading of cardiac iron
`with respect to liver iron, and partially ex-
`plains the weak cross-sectional association
`between these parameters. These data rec-
`oncile several prior studies and provide
`both mechanical and clinical insight into
`cardiac iron accumulation. (Blood. 2008;
`112:2973-2978)
`
`Despite availability of iron chelation, iron-mediated cardiac
`toxicity remains the leading cause of death in thalassemia major
`patients.1 Cardiac dysfunction, whether detected by radionu-
`clide angiography, echocardiography, or magnetic resonance
`imaging (MRI), is often a late finding and carries an ominous
`prognosis.2,3 Although intense chelation can rescue many pa-
`tients, depleting cardiac iron burden often takes years and
`mortality is high with incomplete compliance.3 Thus, prevention
`of cardiac iron accumulation and dysfunction is imperative.
`Initial studies in this area examined hepatic iron concentration
`(HIC), as measured by liver biopsy, and serum ferritin levels as
`potential predictors of cardiac toxicity.4-6 This hypothesis was
`logical because HIC is an excellent indicator of iron balance and
`total body iron stores.6,7 These early studies concluded that
`elevated liver iron and serum ferritin trends raise prospective
`risk of cardiac dysfunction, implying a correlation between
`cardiac and liver iron deposition.4-6 Based upon this work,
`treatment algorithms for iron removal therapy based primarily
`on HIC and ferritin levels8,9 were developed with the goal of
`minimizing cardiac and endocrine toxicities.
`However, the use of HIC and ferritin to infer cardiac iron has
`been challenged by recent MRI studies.10-13 MRI allows organ
`iron concentrations to be easily and noninvasively measured and
`has been validated on both animals and humans.14-16 Cross-
`sectional analysis has demonstrated poor correlation between
`HIC or ferritin and cardiac iron.10-12,13 In addition, some patients
`develop cardiac deposition and symptoms with relatively minor
`somatic iron overload.17-19 These findings have produced a
`backlash against the use of conventional markers of iron stores
`to predict cardiac risk.20,21
`Reconciliation of the disparity between longitudinal and cross-
`sectional studies requires knowledge of the temporal association of
`
`cardiac and liver iron stores. MRI data suggest that the kinetics of
`iron loading and unloading differ markedly in the 2 organs.11,22
`These kinetic differences may introduce lag between changes in
`liver and cardiac iron, destroying the cross-sectional correlations
`between these observations, while preserving a causal relationship.
`To test the hypothesis that cardiac iron lags changes in liver iron,
`we evaluated longitudinal heart and liver iron time courses in
`38 thalassemia major patients using an objective metric of time
`delay. We also compared whether patient liver iron was higher at
`the onset of detectable cardiac iron accumulation (T2* ⬍ 20 ms)
`than at the moment of cardiac iron clearance (T2* ⬎ 20 ms).
`
`Methods
`
`We performed a retrospective review of medical records from more than
`100 patients with thalassemia major who had MRI examinations for cardiac
`and liver iron performed at Childrens Hospital Los Angeles (CHLA).
`Approximately 60% of the patients received thalassemia care at outside
`institutions, but had their noninvasive iron assessments at CHLA. Permis-
`sion for medical review and waiver of informed consent according to the
`Declaration of Helsinki were approved by the IRB Committee on Clinical
`Investigation at CHLA. There were 38 eligible subjects who underwent 3 or
`more MRIs within 2002 to 2007 to estimate their heart and liver iron
`concentration. The mean age of the patients was 20.6 plus or minus
`8.9 years (range: 5.4-43.8 years). The average cardiac R2* at first MRI was
`80.1 plus or minus 94.5 Hz (median was 37.1 Hz) and the average HIC was
`14.7 plus or minus 11.9 mg/g dry weight liver. The average time between a
`patient’s first and last MRI was 3.1 plus or minus 1.2 years (range:
`0.9-4.9 years). All patients were on chronic transfusions every 2 to 4 weeks
`to maintain a pretransfusion hemoglobin level greater than 95 g/L. All of
`these patients had used deferoxamine for most of their chelation history. At
`the time of the last MRI reviewed for this study, 8 patients remained on
`deferoxamine therapy, 28 patients were using deferasirox for an average of
`
`Submitted April 8, 2008; accepted July 3, 2008. Prepublished online as Blood
`First Edition paper, July 23, 2008; DOI 10.1182/blood-2008-04-148767.
`
`The publication costs of this article were defrayed in part by page charge
`payment. Therefore, and solely to indicate this fact, this article is hereby
`marked ‘‘advertisement’’ in accordance with 18 USC section 1734.
`
`The online version of this article contains a data supplement.
`
`© 2008 by The American Society of Hematology
`
`BLOOD, 1 OCTOBER 2008 䡠 VOLUME 112, NUMBER 7
`
`2973
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`Ex. 2006
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`2974
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`NOETZLI et al
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`BLOOD, 1 OCTOBER 2008 䡠 VOLUME 112, NUMBER 7
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`Figure 2. Distribution of area under the curve measured for each of the
`38 trajectories. Area under the curve (AUC) represents the magnitude of time lag;
`the italicized numbers above each bar represent the number of patients having a
`given AUC. The distribution is badly skewed toward positive trajectories, revealing
`that cardiac iron significantly lags liver iron in many patients.
`
`Applying this approach to the top example, we can observe that the
`subtended triangles have zero total area, corresponding to the lack of delay
`between the parameters. The bottom example illustrates the metric from a
`time course where liver iron lags cardiac iron. Now, the time points rotate
`clockwise about the center of mass, instead of counterclockwise; the
`subtended area again reflects the relative magnitude of the delay. Arbi-
`trarily, we designated counterclockwise rotation (heart lagging liver) to
`have a positive sign, and clockwise rotation (liver lagging heart) was given
`a negative sign.
`The relative frequency of time courses having positive and negative
`rotation was compared using Fisher exact test. The relative magnitude of
`positive and negative AUCs was compared using Wilcoxin signed rank test.
`AUCs were compared with patient age, initial HIC, and initial cardiac R2*
`using simple linear regression. HIC values preceding the transitions from
`undetectable to detectable cardiac iron (T2* ⬎ 20 ms to T2* ⬍ 20 ms)
`were compared with HIC values preceding clearance of detectable cardiac
`iron (T2* ⬍ 20 ms to T2* ⬎ 20 ms) by Wilcoxin signed rank test.
`A P value of .05 was deemed significant for all analyses.
`
`Results
`
`Figure 2 is a histogram showing the AUC distribution calculated
`for 38 time courses; 26 (68.4%) had an overall positive area and
`12 (31.6%) had an overall negative area (P ⫽ .16). However, the
`distribution was positively skewed (mean ⫽ 51.0; median ⫽ 25.9)
`and large areas were observed only in the counterclockwise
`direction. The magnitude of the positive areas averaged 84.0 (range:
`7.4-449), and the magnitude of the negative areas averaged
`⫺20.6 (range: ⫺37.2-⫺6.8); P value less than .006. In fact,
`18 (47.3%) of 38 patients had a positive area greater than the
`largest observed negative area, representing time lags detectable
`above measurement uncertainties. The magnitude of all of the
`positive areas represented 89.8% of the total and the magnitude of
`all of the negative areas represented 10.2% of the total.
`To investigate potential predictors of this time lag, AUCs were
`compared with initial HIC, initial cardiac R2*, and patient age.
`Greater time lags were observed with greater initial HIC (r ⫽ 0.47,
`P ⬍ .003) and initial cardiac R2* (r ⫽ 0.57, P ⬍ .001); no correla-
`tion was seen with patient age.
`Not only did the time courses rotate counterclockwise individu-
`ally, they formed loops in the aggregate as well. Figure 3 shows the
`longitudinal relationship between HIC and cardiac R2* for the
`entire population. In each time course, the circle represents the
`initial HIC and R2* measurement and each following point
`
`Figure 1. Schematic illustrating time lag detection and quantification. Center of
`mass is calculated for each time course by finding the average liver iron and cardiac
`R2* for all of the consecutive time points (T1-T5), and the magnitude (area under
`the curve) and direction of the time course “rotation” is determined. (Top) No rotation,
`area ⫽ 0: HIC and cardiac R2* have a linear relationship with no delays. (Middle) Coun-
`terclockwise (positive) rotation indicates that cardiac R2* lags liver iron changes.
`(Bottom) Clockwise (negative) rotation indicates that HIC lags cardiac R2*.
`
`1.4 years, 1 patient was using deferiprone for 2.2 years, and 1 patient was
`on combination therapy of deferiprone and deferoxamine for 5.1 years
`(Document S1, available on the Blood website; see the Supplemental
`Materials link at the top of the online article). HIC was estimated at
`intervals ranging from 3 to 18 months using liver R2 and R2* measure-
`ments as previously described.23 Cardiac R2* (equal to 1000/T2*) was also
`determined by previously validated methods.24 Although an absolute
`calibration curve does not exist, in vivo, cardiac R2* has been shown to be
`directly proportional to iron in animal and autopsy studies.14,16
`Figure 1 demonstrates the metric used to detect lag between cardiac and
`liver iron levels. In the top example, heart and liver iron levels at
`consecutive observations (labeled T1-T5) form a straight line, indicating no
`temporal delay between these changes. To establish a reproducible refer-
`ence point, we calculated the center of mass for each time course; the center
`of mass represents the average liver iron and cardiac R2* for all of the
`points (T1-T5). Note that the time course passes through the center of mass
`if there is no time lag between the heart and liver iron.
`In the second example, cardiac iron levels lag behind changes in liver
`iron. To quantify this lag, we can draw segments from each time point to the
`center of mass. This forms a series of triangles that rotate counterclockwise
`about the center of mass. The greater the time lag between heart and liver
`iron, the greater the total triangular area or area under the curve (AUC).
`
`

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`BLOOD, 1 OCTOBER 2008 䡠 VOLUME 112, NUMBER 7
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`HEART AND LIVER IRON ANALYSIS IN THALASSEMIA MAJOR
`
`2975
`
`Figure 3. Aggregate of positive (top) and negative (bottom) time courses
`formed by plotting chronologic HIC and cardiac R2* measurements for
`38 subjects. Cardiac R2* (equal to 1000/T2*) is on the vertical axis in log scale; HIC
`(calculated using liver R2 and R2*) is on the horizontal axis. First and last MRI
`measurements are denoted by a filled circle and an “x,” respectively. In the plot of
`positive time courses, the time courses having AUCs more than 37.2 (the largest
`negative AUC) are indicated by dark lines and the smaller AUCs, by light gray lines.
`The time course indicated by a thick, black line is representative of the counterclock-
`wise movement of these time courses as a whole. The inset in the top left corner
`shows the numbered “limbs.” In the plot of negative time courses, all time courses are
`shown in light gray except one. The time course indicated by a thick, black line is a
`representative of the clockwise movement of these time courses as a whole.
`
`represents a chronologic measurement. The x represents the last
`measurement for that time course. Positive time courses are shown
`in the top panel and negative time courses in the bottom panel. The
`18 positive time courses having AUCs more than 37.2 (the largest
`negative AUC) are indicated by dark lines and the smaller AUCs in
`gray. Macroscopically, it is quite apparent that larger positive time
`courses trace a counterclockwise loop or rectangle, consisting of
`4 “limbs,” numbered 1 through 4. Limb 1 demonstrates increasing
`or decreasing HIC with little change in R2*;
`limb 2 showed
`increasing R2* with little change in HIC; limb 3 exhibits decreas-
`ing HIC with little change in R2*; and limb 4 reveals decreasing
`R2* with little change in HIC. Notably, there are no time courses
`going through the middle of the loop, highlighting the nonlinearity
`of the liver-heart iron relationship. The 53% of trajectories showing
`weak time lags (AUC ⬍ 37.2) either did not have cardiac iron
`overload or exhibited extremely small changes in cardiac
`iron, leaving AUC calculation vulnerable to the inherent MRI
`measurement errors.
`
`Figure 4. Time courses of patients who transitioned above or below a cardiac
`R2* of 50 Hz. The time courses of the patients with increasing and decreasing
`cardiac R2* are shown in the top and bottom panels, respectively. Cardiac R2* (equal
`to 1000/T2*) is on the vertical axis in log scale; HIC (calculated using liver R2 and
`R2*) is on the horizontal axis. First and last MRI measurements are denoted by a filled
`circle and an “x,” respectively. These graphs represent 8 patients with 9 transitions.
`The patient who transitioned above and below an R2* of 50 Hz during the given time
`is shown in both panels (*). In each panel, only the relevant part of this time course is
`colored black; the unrelated portion is gray. The arrows indicate the direction of
`cardiac iron (increasing R2* or decreasing R2*).
`
`If cardiac iron does lag liver iron in both somatic iron loading
`and unloading, one would expect that the liver iron at which cardiac
`iron accumulates will be significantly higher than the liver iron
`level at which the heart clears. To test this hypothesis, we looked at
`HIC values of patients who transitioned above or below a cardiac
`R2* of 50 Hz (a T2* of 20 ms, the lower limit of normal). Of the
`38 patients analyzed, there were 9 transitions about the critical
`value (Figure 4). The 5 patients with onset of detectable cardiac
`iron loading (top panel) had an HIC between 2.3 and 48.4 (median:
`15.2) at the time of the transition, whereas the 4 patients who
`showed clearance of detectable cardiac iron (bottom panel) had an
`HIC between 1.1 and 9.9 (median: 3.5) at the time of the transition;
`P ⫽ .14. One patient transitioned above and below an R2* of
`50 Hz during the given time. Although this difference was not
`statistically significant, perhaps because of small sample size, it
`suggests that cardiac iron clearance may not occur until liver iron is
`quite low. In contrast, primary cardiac iron accumulation occurs
`over an extremely broad range of liver iron concentrations.
`
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`2976
`
`NOETZLI et al
`
`Discussion
`
`Although HIC measurements are an excellent gauge of body iron
`stores and iron balance, the ability of HIC to predict target organ
`iron toxicity is limited. On cross-sectional evaluation, there is a
`marked disconnect between liver and heart iron values. This can be
`easily appreciated in Figure 3, and has been described in several
`prior studies.10-13 One reason for this disconnect is organ-specific
`mechanisms of iron uptake/release. Liver, bone marrow, and spleen
`are the natural reservoirs for iron, and transferrin-bound iron is
`shuttled among these stores in a tightly regulated manner. The heart
`and endocrine glands also have well-regulated transferrin-mediated
`uptake, but pathologic iron deposition in these organs occurs
`through unregulated influx of NTBI.25-27 NTBI levels rise once
`transferrin is fully saturated and are modulated by the type and
`duration of chelator exposure.28
`The different iron uptake mechanisms of heart and liver result in
`uneven rate of organ iron loading. Transfusional
`iron burden
`initially fills the liver through transferrin-mediated uptake; positive
`and negative iron balance at this stage leads to leftward and
`rightward movement in limb 1 of Figure 3. Interestingly, some of
`the patient time courses in this limb still form shallow counterclock-
`wise loops, suggesting fluctuations of cardiac iron within the
`“normal” range. The physiologic factors responsible for delaying
`cardiac iron uptake relative to liver iron uptake are unknown. It
`may be that NTBI levels are initially well controlled through
`chelation despite high somatic iron burdens. Alternatively, there
`may be as yet uncharacterized maturational, endocrine, genetic, or
`metabolic comodulators of cardiac iron uptake.29-31
`Despite an apparent “delay” in cardiac iron uptake, some
`patients rapidly increase their cardiac iron at high liver iron
`concentration (Figure 3 limb 2). Several patients continued to
`accumulate cardiac iron despite negative liver iron balance, suggest-
`ing some degree of momentum or memory to the cardiac iron
`uptake process. Previous studies have demonstrated a HIC thresh-
`old at which chelatable iron and cardiac iron accumulation increase
`drastically.32 One possible explanation is that elevated liver iron
`may damage the liver, inhibiting hepatic NTBI uptake and increas-
`ing cardiac NTBI exposure.33 Alternatively, cell culture work
`suggests that cardiac iron accumulation up-regulates cardiac iron
`transport, creating a mechanism for precipitous cardiac iron uptake
`and uptake memory.25
`Although these observations suggest that high HIC prospec-
`tively predicts cardiac iron loading, low HIC does not necessarily
`imply low risk for cardiac iron. According to Figure 4, 2 of
`5 patients who developed de novo cardiac iron deposition did so
`with liver iron concentrations less than 6 mg/g. Others have also
`described primary cardiac iron accumulation in otherwise “low-
`risk” patients.17-19 Because most adult thalassemia major patients
`have fully saturated transferrin, regardless of their liver iron, they
`remain at risk for cardiac iron accumulation whenever they do not
`have circulating free chelator.
`In addition to differences in iron uptake, there are differences in
`iron elimination that weaken the cross-sectional relationship be-
`tween heart and liver iron. Cardiac iron is relatively more difficult
`to remove than liver iron; the cardiac iron removal rate with
`deferoxamine is 5 times slower than the liver during intensive
`chelation.22 Patients on intensive chelation therapy can move from
`a state of heavy heart and liver iron burdens to a state of heavy
`cardiac iron and minimal liver iron burden. Patients in limbs
`3 and 4 of Figure 3 demonstrate this type of behavior. Cardiac iron
`
`BLOOD, 1 OCTOBER 2008 䡠 VOLUME 112, NUMBER 7
`
`may not significantly decrease until liver iron is quite low; in fact,
`patients who managed to clear the heart had a median liver iron of
`3.5 (Figure 4).
`Slow cardiac iron clearance is a major contributor to the curved
`time course observed macroscopically (Figure 3) and for individual
`patients (Figure 2). Not surprisingly, time lag was more profound
`in patients with initially elevated cardiac and liver iron. Many of
`these high-risk patients receive intense chelation, unmasking the
`kinetic differences between the heart and the liver because there is
`less time for equilibration. There is also evidence that cardiac iron
`is chemically less accessible at higher cardiac iron concentrations.34
`Although cardiac iron levels seem to lag with respect to HIC
`during both somatic iron loading and unloading, cardiac iron levels
`cannot be viewed as passively following liver iron levels. The type
`and pattern of chelation can affect the heart and liver differently
`and are vital in influencing the relationship between cardiac and
`liver iron. For example, it has been demonstrated that the number
`of deferoxamine doses per year is the strongest predictor of
`survival, regardless of ferritin levels.35 The success of continuous
`deferoxamine lies in its ability to continuously suppress NTBI, not
`in the delivery of greater amount of drug.36,37 The pattern of drug
`administration is important for oral chelation as well. In the gerbil,
`dividing deferasirox into 2 doses per day instead of the same dose
`once per day significantly increased cardiac iron removal relative to
`the liver.38 The data presented in this paper predominantly reflect
`subcutaneous, intermittent deferoxamine chelation therapy (61% of
`chelation-years), compared with deferasirox (33% of chelation-
`years) and deferiprone (6% of chelation-years). Deferiprone, in
`particular, may lower cardiac iron with less change in hepatic iron
`concentration, but our study was too small and unbalanced among
`the chelators to make any comparison in this regard.39,40
`This present work suffered from several other limitations as
`well. The study was observational and patients had wide ranges of
`ages, iron loading, and chelation compliance. MRI study intervals
`varied among individual patients. The relatively small sample size
`limited the number of patients in a given cardiac iron and liver iron
`range, as well as the number of patients who crossed the R2* of
`50-Hz threshold. Because some of the patients had comprehensive
`care elsewhere, we had incomplete data regarding transfusional
`burden, past medical care, and chelation compliance. Referral
`patterns may have also biased the study population toward greater
`iron burdens. Despite the variability introduced by these shortcom-
`ings, clear and statistically significant patterns were identified in
`cardiac and liver iron parameters. Another limitation is the choice
`of the T2* threshold to designate presence or absence of cardiac
`iron. Cardiac iron is never actually cleared from the heart; it is
`necessary for normal heart function, but varies continuously with
`cardiac 1/T2* in all subjects. Because pathologic amounts of iron
`must be distinguished from physiologic fluctuations in iron levels
`and weak noniron modulators of cardiac T2*, a cutoff of 20 ms is
`the generally accepted threshold for “detectable” cardiac iron. Like
`any threshold, it is imperfect, and a certain percentage of patients in
`the range 20 to 25 ms will have mild cardiac iron overload; we
`typically report these patients as having borderline T2* values.1,33
`We used the 20-ms threshold to demarcate the onset of MRI-
`recognizable cardiac iron accumulation and clearance, but the
`concepts would have been similar for a different threshold choice.
`Lastly, the AUC metric that we used to detect the lag between
`cardiac and liver iron loading is ad hoc and cannot be used to derive
`pharmacokinetic information regarding organ iron loading or
`removal. Because liver iron can respond with a half-life of 2 to
`3 months, our clinical practice of annual MRI examinations may
`
`

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`BLOOD, 1 OCTOBER 2008 䡠 VOLUME 112, NUMBER 7
`
`HEART AND LIVER IRON ANALYSIS IN THALASSEMIA MAJOR
`
`2977
`
`undersample the true time course of heart and liver iron, underesti-
`mating the time lag severity.
`Despite these limitations, the present data have clinical implica-
`tions in addition to offering mechanistic insight. For example,
`although high liver iron levels appear to increase the risk of severe
`cardiac iron accumulation, there is simply no safe lower liver iron
`concentration that guarantees cardiac protection. As a result,
`regular cardiac MRI screening is a vital component in chelation
`monitoring. The present data also reinforce that cardiac iron
`clearance is slow, emphasizing the need for primary prevention of
`cardiac iron overload. Adequate protection depends on the type and
`pattern of iron chelation just as much as the total chelator dose and
`liver iron levels. Most importantly, regular clinical monitoring of
`hepatic and cardiac iron is essential for primary prevention. Better
`understanding of these contributing factors will lead to improved
`clinical guidelines for cardioprotection.
`
`Acknowledgments
`
`We are grateful to Debbie Harris, Trish Peterson, Paola Pederzoli,
`Colleen McCarthy, Janelle Miller, Thomas Hofstra, and Susan
`Claster for their support of the MRI program. We would also like to
`thank Nancy Sweeters, Ellen Butensky, Paul Harmatz, and Elliot
`Vichinsky from Childrens Hospital Oakland for their help with subject
`recruitment. We would also like to acknowledge Dr Michael Tyszka at
`
`the California Institute of Technology for his helpful discussions on the
`mathematical formalism used in this paper.
`This work was supported by the National Heart, Lung, and
`Blood Institute (Bethesda, MD; 1 RO1 HL075592-01A1), General
`Clinical Research Center at the Children’s Hospital Los Angeles
`(RR000043-43), Centers for Disease Control (Thalassemia Center
`Grant U27/CCU922106; Atlanta, GA), Novartis Pharma (East
`Hanover, NJ), and the Department of Pediatrics, Childrens Hospital
`Los Angeles (Los Angeles, CA).
`
`Authorship
`
`Contribution: L.J.N. performed research, analyzed data, and wrote
`the paper. S.M.C., A.S.N., and T.D.C. collected data and assisted in
`writing; and J.C.W. designed and performed research, analyzed
`data, and wrote the paper.
`is a member of the
`Conflict-of-interest disclosure: S.M.C.
`Novartis speaker’s bureau for deferasirox. T.D.C. has received
`research funding and honoraria from Novartis and has received
`honoraria from Apotex (Weston, ON). J.C.W. is a consultant to and
`has received research funding and honoraria from Novartis, and has
`received honoraria from Apotex (Weston, ON). All other authors
`declare no competing financial interests.
`Correspondence: John C. Wood, Childrens Hospital Los Ange-
`les, Division of Cardiology, 4650 Sunset Boulevard, Los Angeles,
`CA 90027; e-mail: jwood@chla.usc.edu.
`
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`

`

`From
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`on September 7, 2017. by guest
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`For personal use only.
`
`2978
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`NOETZLI et al
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`BLOOD, 1 OCTOBER 2008 䡠 VOLUME 112, NUMBER 7
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