Letters to the Editor

497

“Optimal” cutoff value of heart rate; appraisal based on heart rate variability and C-reactive protein Yoon-Jung Choi a, Kyu-Hwan Park a, Chan-Hee Lee a, Sang-Hee Lee a, Jong-Seon Park a, Ung Kim a, Jang-Won Son a, Jeon Lee b, Jae-Ryong Kim c, Dong-Gu Shin a,⁎ a b c

Cardiovascular Division, Internal Medicine, Yeungnam University Hospital, Daegu 705-717, South Korea Department of Biomedical Engineering, Yonsei University, 1 Yonseidae-gil, Wonju, Gangwon-do 220-710, South Korea Department of Biochemistry and Molecular Biology, Aging-associated Vascular Disease Research Center, Yeungnam University, Daegu 705-717, South Korea

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Article history: Received 19 May 2014 Accepted 5 July 2014 Available online 12 July 2014 Keywords: Heart rate Heart rate variability C-reactive protein

The evidences from the last 3 decades have emphasized the role of elevated resting heart rate (HR) as an independent predictor of allcause and cardiovascular mortality in the general population and in several pathological conditions [1,2]. Although the importance of resting HR is reflected in the guideline [3], no cutoff HR can be offered presently to increase the accuracy of total cardiovascular risk stratification because of the wide range of suggested resting HR normality values (60 to 90 beats/min). It has been known that enhanced parasympathetic activity has a cardioprotective effect via cholinergic anti-inflammatory pathway [4]. The C-reactive protein (CRP), a circulating marker of inflammation, has been identified as an independent predictor of both short- and long-term risks of cardiovascular events including sudden cardiac death or stroke in healthy populations [5]. The aim of this study is to determine the HR cutoff value by assessing its relationship with HR variability as an index of cardiac vagal modulation, and high-sensitivity C-reactive protein (hs-CRP). The study protocol conformed to the ethical guidelines of the 1975 Declaration of Helsinki and approved by the Institutional Review Board. Informed consent was obtained from all subjects prior to enrollment. ECGs were recorded for 10 min in a dimly lit room during spontaneous breathing (AcqKnowledge ver 3.5, Biopac Systems, Santa Barbara, CA, USA). Resting HR as a mean of 10-min HR and frequency domain measure of RR interval variability were computed (Kubios HRV software, ver 2.0, Kuopio, Finland). The low frequency (LFP, 0.04– 0.15 Hz) and the high frequency spectral power (HFP, 0.15–0.4 Hz) were computed and normalized the distribution with a natural logarithmic transformation (lnLFP and lnHFP, respectively) [6]. The hs-CRP was measured using ultra-high-sensitivity latex turbidimetric immunoassay (Beckman Coulter UniCel DxC 800, Beckman Coulter, Fullerton, CA, USA). Blood samples were collected simultaneously with ECG recording and analyzed for white blood cell count (WBC), hemoglobin (Hgb), serum creatinine, free tetraiodothyronine (FT4) and thyroid stimulating hormone (TSH), serum sodium and potassium levels, fasting blood sugar (FBS), and lipid profile including total and high-density lipoprotein (HDL) cholesterol, and triglyceride. All tests were performed between 07:00 and 09:00 after abstaining from

⁎ Corresponding author at: Cardiovascular Division, Internal Medicine, Yeungnam University Hospital, Aging-associated Vascular Disease Research Center, 170, Hyeonchungno, Nam-Gu, Daegu 705-717, South Korea. Tel.: + 82 53 620 3313; fax: + 82 53 621 3310. E-mail address: [email protected] (D.-G. Shin).

food or caffeine and drinking prior to the test. Statistical analyses were performed at the level of significance b 0.05 using PASW, Statistics 18 (SPSS Inc., Chicago, IL, USA). To analyze HR as categorical variables, HR value was divided into ten groups on the basis of deciles in men and women separately. A total of 1831 healthy subjects (49 ± 12 years, 1187 male) were studied. Subjects who are metabolically unstable, or who have had a recent illness, or infection, and who have other any acute or chronic inflammation were excluded. Age and gender distribution, and their clinical characteristics are described in Supplementary Tables 1 and 2, respectively. Significant gender differences are found in multiple variables including HR, hs-CRP and lnHFP (Supplementary Table 2). The correlation of HR with clinical variables is summarized in Table 1. The gender, WBC, FBS, triglyceride, serum potassium, FT4, hs-CRP, lnHFP and lnLFP are related to the HR on multivariate analysis (Table 1). Among them, gender, hs-CRP and lnHFP are variables having strong influences on HR (standardized β coefficients; 0.167, 0.105 and −0.167, respectively, p b 0.0001 for all). The HR showed an inverse correlation with lnHFP (γ = − 0.448, p b 0.0001). The lnHFP decreased gradually with increasing HR deciles in men and women (p for linear trend b 0.0001) as shown in Fig. 1A. However, there was a sharp drop-off of the lnHFP value above the 9th decile (71–75 bpm) in men (4.74 ± 1.10 vs. 4.07 ± 1.32 of the highest decile (N75 bpm), p b 0.0001). No significant differences of the lnHFP value between any 2 groups from deciles 1–9 were found. As is the case with men, a sharp decrease of the lnHFP value above the 9th decile (74–79 bpm) was found in women (4.36 ± 1.20 vs. 3.85 ± 1.13 of the highest decile (N79 bpm), p = 0.008, Fig. 1A). The correlation of HR with hs-CRP was weak but significant (γ = 0.057, p b 0.05). The hs-CRP value increased steeply above the 8th decile (68–70 bpm) in men and the 9th decile in women. The hs-CRP values of the 9th and the highest decile for men were 2.72 ± 5.27 and 2.94 ± 7.69 mg/L, respectively, which were significantly higher than those of HR deciles 1–8 (p b 0.05, Fig. 1B). Similar to the change of hs-CRP in men, the hsCRP value (3.52 ± 10.03 mg/L) of the highest HR decile of women was significantly higher than those of HR deciles 1–9 (p b 0.01, Fig. 1B). No significant differences of the hs-CRP values between any 2 groups from HR deciles 1–8 of men and from HR deciles 1–9 of women were found. The hs-CRP ≥ 3.0 mg/L is the cutpoint of highrisk category, in which about 2-fold increase in relative risk compared with the low-risk tertile is shown [7]. Recent studies have reported that high hs-CRP levels (generally ≥2 mg/L) are associated with increased risk independent of conventional cardiovascular risk factors and recommended 2 mg/L as a hs-CRP cutoff for intervention [8]. Also, the level of hs-CRP ≥ 2.0 mg/L is an expert opinion threshold above which revising risk assessment upward is recommended [9]. Finally, in terms of relation of HF power with hs-CRP, an inverse correlation between lnHFP and hs-CRP was found (γ = −0.136, p b 0.0001). This study demonstrated the cholinergic modulation of inflammatory responses via the so-called inflammatory reflex [4] and consistent with previous finding in which a strong inverse correlation between HR variability and levels of inflammatory cytokines was reported [10]. It would be reasonable to set the HR of the highest decile as cutoff HR value in which HF power at it's nadir in conjunction with the increase of hs-CRP beyond the threshold of high risk category is present. Therefore,

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Letters to the Editor

Table 1 The determinants of heart rate on multivariate linear regression analysis and it's correlation coefficients. Correlation coefficienta

Multivariate linear regression analysis Standardized β

Age, years Gender SBP, mm Hg DBP, mm Hg WBC, K/uL Hemoglobin, gm/dL FBS, mg/dL Total-chol, mg/dL Triglyceride, mg/dL HDL-chol, mg/dL Creatinine, mg/dL Sodium, mEq/L Potassium, mEq/L TSH, mμ/L FT4, pmol/L hs-CRP, mg/L lnHFP lnLFP LF/HF ratio

−0.040 0.147† 0.079⁎⁎ 0.079⁎⁎ 0.107† 0.013 0.129† 0.033 0.090† 0.005 − 0.114† −0.075⁎⁎

−0.116† −0.010 0.053⁎ 0.057⁎ − 0.448† −0.278† 0.189

t

95% CI

p value b0.0001 0.691 0.210 0.001

0.167 0.018 0.057 0.073

5.324 0.398 1.030 3.185

2.097, 4.543 − 0.049, 0.074 −0.032, 0.145 0.170, 0.715

0.076

3.424

0.012, 0.046

0.001

0.092

3.909

0.005, 0.014

b0.0001

− 0.048 − 0.026 − 0.116

− 1.491 −1.185 − 5.358

− 6.133, 0.835 − 0.262, 0.065 − 4.861, − 2.256

0.136 0.236 b0.0001

0.172 0.105 − 0.167 − 0.117 0.119

8.038 4.797 − 6.002 − 4.074 4.819

4.223, 6.950 0.157, 0.373 − 0.004, − 0.002 − 0.001, 0.000 0.124, 0.295

b0.0001 b0.0001 b0.0001 b0.0001 b0.0001

SBP: systolic blood pressure; WBC: white blood cell; TSH: thyroid stimulating hormone; FT4: free tetraiodothyronine; HDL: high density lipoprotein; lnHFP: log-transformed highfrequency power; lnLFP: log-transformed low-frequency power. a Spearman's rho. † p b 0.0001. ⁎⁎ p = 0.001. ⁎ p b 0.05.

Fig. 1. A. The relation of log-transformed HF power (lnHFP) with HR deciles in both men and women. An inverse correlation between HR and lnHFP is noted. A significant drop-off of the lnHFP value is seen in the highest HR decile in both genders. B. The relation of hs-CRP with HR deciles. A significant increase up to 3 mg/L of the hs-CRP is noted in the 9th and highest HR decile in men, and beyond 3 mg/L in the highest HR decile in women. Dotted line of (a) denotes the hs-CRP cutpoint of high-risk category (N 3.0 mg/L) according to the AHA/CDC scientific statement on markers on inflammation and cardiovascular disease [7], and (b) denotes the expert opinion thresholds of hs-CRP (≥2.0 mg/L) above which revising risk assessment upward is recommended in the 2013 ACC/AHA Guideline on the Assessment of Cardiovascular Risk [9].

we conclude that 75 bpm for men and 79 bpm for women would be an optimal cutoff value in terms of resting HR. This work was supported by the 2009 Yeungnam University Research Grant. Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.ijcard.2014.07.061. All authors have no conflict of interest to disclosure. References [1] Kristal-Boneh E, Silber H, Harari G, Froom P. The association of resting heart rate with cardiovascular, cancer and all-cause mortality: eight year follow-up of 3527 male Israeli employees (the CORDIS study). Eur Heart J 2000;21:116–24.

[2] Fox K, Borer JS, Camm AJ, et al. For the Heart Rate Working Group. Resting heart rate in cardiovascular disease. J Am Coll Cardiol 2007;50:823–30. [3] Mancia G, De Backer G, Dominiczak A. Guidelines for the management of arterial hypertension: The Task Force for the Management of Arterial Hypertension of the European Society of Hypertension (ESH) and of the European Society of Cardiology (ESC). Eur Heart J 2007;28(12):1462–536. [4] Tracey KJ. Physiology and immunology of the cholinergic anti-inflammatory pathway. J Clin Invest 2007;117:289–96. [5] Koenig W, Sund M, Frohlich M, et al. C-reactive protein, a sensitive marker of inflammation, predicts future risk of coronary heart disease in initially healthy middle-aged men. Results from the MONICA (Monitoring Trends and Determinants in Cardiovascular Disease) Augsburg Cohort Study, 1984 to 1992. Circulation 1999;99:237–42. [6] Malik M, et al. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology

Letters to the Editor and the North American Society of Pacing and Electrophysiology. Circulation 1996;93(5):1043–65. [7] Pearson TA, Mensah GA, Alexander RW, et al. Markers of inflammation and cardiovascular disease: application to clinical and public health practice: a statement for healthcare professionals from the Centers for Disease Control and Prevention and the American Heart Association. Circulation 2003;107(3):499–511. [8] Ridker PM, Danielson E, Fonseca FA, et al. Rosuvastatin to prevent vascular events in men and women with elevated C-reactive protein. N Engl J Med 2008;359(21):2195–207.

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[9] Goff Jr DC, Lloyd-Jones DM, Bennett G, et al. 2013 ACC/AHA Guideline on the Assessment of Cardiovascular Risk: a report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2014;63:2935–59. [10] Sloan RP, McCreath H, Tracey KJ, Sidney S, Liu K, Seeman T. RR interval variability is inversely related to inflammatory markers: the CARDIA study. Mol Med 2007;13(3–4):178–84.

http://dx.doi.org/10.1016/j.ijcard.2014.07.061 0167-5273/© 2014 Elsevier Ireland Ltd. All rights reserved.

Preserved adrenal function in fully PCSK9-deficient subject Bertrand Cariou a,b,c,⁎, Isabelle Benoit d, Cédric Le May a a

INSERM, UMR1087, CNRS UMR6291, l'Institut du Thorax, F-44000 Nantes, France Université de Nantes, Faculté de Médecine, l'Institut du Thorax, F-44000 Nantes, France Department of Endocrinology, University Hospital of Nantes, F-44000 Nantes, France d Department of Endocrinology, District Hospital Center, F-85000 La Roche sur Yon, France b c

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Article history: Received 19 May 2014 Accepted 5 July 2014 Available online 12 July 2014 Keywords: PCSK9 inhibitors steroidogenesis genetics safety

PCSK9 (Proprotein Convertase Subtilisin Kexin type 9) is the ninth member of the proprotein convertase family. PCSK9 is secreted by the liver and acts as a natural inhibitor of the LDL receptor pathway, by targeting the receptor to lysosomes for degradation [1]. While PCSK9 gain-of-function mutations are associated to autosomal dominant hypercholesterolemia and premature atherosclerosis, PCSK9 loss-offunction (LOF) mutations lead to low concentrations of plasma LDLcholesterol (LDL-C) and protection against cardiovascular disease [1]. Thus, PCSK9 inhibition is thought to be a promising pharmacological approach to achieve low levels of LDL-C in combination with statins [2]. In recent phase 2 trials conducted in patients with familial or primary hypercholesterolemia, treatment with human monoclonal antibodies directed against PCSK9 has led to a drastic reduction of LDL-C baseline levels up to 60%, on top of statins, without altering HDL-C levels [3]. Safety data appeared reassuring, but the duration of treatment exposure remains short. One theoretical safety concern about PCSK9 inhibition is the delivery of lipoprotein-derived cholesterol to the adrenals for steroidogenesis, especially in patients in whom LDL-C reached extremely low levels (i.e. b25 mg/dl). Cholesterol is essential for adrenal steroidogenesis that regulates stress responses, blood pressure, electrolyte homeostasis and secondary sexual characteristics. Cholesterol is synthesized de novo in the adrenals or taken up by the glands from circulating lipoproteins and stored as cholesterol esters [4].

⁎ Corresponding author at: Clinique d'Endocrinologie, l'Institut du Thorax, Hôpital Guillaume & René Laennec, Boulevard Jacques Monod, 44093 Nantes cedex, France. Tel.: +33 2 53 48 27 07; fax: +33 2 53 48 27 08. E-mail address: [email protected] (B. Cariou).

Here, we assessed the consequences of PCSK9-deficiency on adrenal function in a subject bearing PCSK9 LOF mutation with no detectable plasma PCSK9 [5]. A 54 year-old man carries a heterozygous LOF mutation in PCSK9 (R104C-V114A) [5]. He underwent a standard acute ACTH-(1–24) stimulation test. The test started after an overnight fast, at 08:00 am. Baseline blood samples were obtained 1 min before administration of an iv bolus of 1 μg of cosyntropin (0.25 mg; Organon, East Orange, NJ). Plasma cortisol and aldosterone were measured at baseline as well as 30 and 60 min after cosyntropin administration. The other hormones were measured at baseline only. The patients provided written informed consent for the constitution of plasma biocollection, which was declared and approved by the French regulatory authorities (DC2011-1399; CPP Ouest IV). As described previously [5], this subject has no detectable plasma PCSK9 and very low LDL-C levels (24 mg/dl), with normal HDL-C concentration (66 mg/dl) (Table 1). He has a type 2 diabetes mellitus that is well controlled by the combination of metformin (2 g/day) and sitagliptin (100 mg/day) with HbA1C at 6.4% (46 mmol/mol). As shown in Table 1, the patient had a normal adrenal function in basal conditions, with normal values of cortisol, aldosterone and androgens (DHEA-S and Δ4-androstenedione). In addition, his plasma level of ACTH was also in the normal range. Finally, the cortisol response to ACTH stimulation was preserved with plasma cortisol value higher than 30 μg/dl 1 h after cosyntropin injection. One of the proband's daughter, who also carried the PCSK9 dominant negative mutant, has a less severe phenotype with reduced, but detectable, plasma PCSK9 concentrations [5]. Her adrenal cortical function was also found to be normal (Table 1). Patients fully deficient for PCSK9 are extremely rare with only 3 cases reported in the literature [6,7]. Here, we demonstrate for the first time that genetic PCSK9-deficiency does not alter adrenal function in human. However this study addressed chronic, life-long deficiency in PCSK9 and therefore does not directly translate into acute, late-in-life removal of PCSK9 with monoclonal antibodies. The assessment of adrenal function in patients treated with anti-PCSK9 monoclonal antibodies in the ongoing large-scale studies will help to clarify this issue. Nevertheless, our results are in accordance with previous studies suggesting a role for HDL rather than LDL derived cholesterol in adrenal steroidogenesis in humans. For instance, patients with familial hypobetalipoproteinemia do not have any