Grzegorz Raczak

Bio: Grzegorz Raczak is an academic researcher from Gdańsk Medical University. The author has contributed to research in topics: Atrial fibrillation & Medicine. The author has an hindex of 16, co-authored 161 publications receiving 1279 citations.

Heart rate variability measures: a fresh look at reliability.

Abstract: Despite its extensive use in physiological and clinical research, the analysis of HRV (heart rate variability) is still poorly supported by rigorous reliability studies. The main aim of the present study was to perform an in-depth assessment of absolute and relative reliability of standard indexes of HRV from short-term laboratory recordings. In 39 healthy subjects [mean age (min-max): 38 (26-56) years; 18 men and 21 women] we recorded 5 min of supine ECG during spontaneous and paced (15 breaths/min) breathing. The test was repeated on the next day under the same conditions. From the RR intervals we computed standard indexes of HRV: SDNN (S.D. of RR interval values), RMSSD (root-mean-square of successive RR interval differences), LF (low frequency) and HF (high frequency) power (absolute and normalized units) and LF/HF. Absolute reliability was assessed by 95% limits of random variation; relative reliability was assessed by the ICC (intraclass correlation coefficient). The sample size needed to detect a mean difference > or =30% of the between-subject S.D. was also estimated. Although there was no significant mean change between the two tests, we found that in individual subjects the second measurement was as high/low as 1.9/0.5 times (SDNN, best case) and 3.5/0.3 times (LF/HF, worst case) the first measurement, due to pure random variation. For most parameters the ICC was >0.8 (range 0.65-0.88). The estimated sample size ranged from 24-98 subjects. Reliability indexes tended to improve during paced breathing. We conclude that short-term HRV parameters are subject to large day-to-day random variations. Random error, however, represents a limited part of the between-subject variability; therefore observed differences between individuals mostly reflect differences in the subjects' error-free value rather than random error. Overall, paced breathing improves reliability.

Measuring baroreflex sensitivity from the gain function between arterial pressure and heart period.

Abstract: We tested an innovative approach for estimating baroreflex sensitivity (BRS) from the gain function between spontaneous oscillations of systolic arterial pressure (SAP) and heart period (HP). The major goal was to assess the practical implications of abandoning the classical coherence criterion (& 0.5) as regards measurability of BRS, and agreement with values of BRS obtained using the phenylephrine test (Phe-BRS). We studied 19 normal subjects, 44 patients with a history of previous myocardial infarction (MI) and 45 patients with chronic heart failure (CHF). The experimental protocol included recording of SAP and HP for 10 min of supine rest, and evaluation of Phe-BRS. From resting SAP and HP, the gain and coherence functions were computed. The new BRS index was obtained in all subjects by averaging the gain function over the whole low-frequency band (0.04‐0.15 Hz) (whole-band average BRS, WBA-BRS). WBA-BRS was 7.4 (5.8‐10.8) ms/mmHg [median (25th‐75th percentile)] in normal controls, 3.1 (1.4‐ 5.4) ms/mmHg in MI patients (P ! 0.001 compared with normals) and 5.0 (3.2‐6.9) ms/mmHg in CHF patients (P ! 0.01 compared with normals). Using the coherence criterion, BRS could be measured in only 43% and 49% of MI and CHF patients respectively, and the proportion of the low-frequency band contributing to the measurement was 21% (14‐47%) and 29% (16‐35%) respectively. The correlation between WBA-BRS and Phe-BRS was 0.47, 0.63 and 0.36 in the normal, MI and CHF groups respectively (all P ! 0.001). The relative bias of WBA-BRS was fi5.2 ms/mmHg (P ! 0.001) in normals, fi1.4 ms/mmHg (P fl 0.004) in MI patients and fi1.0 ms/mmHg (P fl 0.11) in CHF patients. The limits of agreement were fi13 to 2.6, fi7.4 to 4.6 and fi9.3 to 7.3 ms/mmHg in the normal, MI and CHF groups respectively. Thus the WBABRS method standardizes the computation of BRS among subjects, and dramatically increases its measurability in subjects with pathology compared with the classical spectral technique based on the coherence criterion. Compared with Phe-BRS, WBA-BRS tends to give negatively biased results. The correlation and the magnitude of the limits of agreement between the two methods are similar to those observed previously using coherence-based spectral methods.

Assessing nonlinear properties of heart rate variability from short-term recordings: are these measurements reliable?

Abstract: Several parameters assessing nonlinear properties of heart rate variability (HRV) from short-term ( 140%. Relative reliability was substantial (0.6 < ICC < 0.8) in half of the indices, moderate in one and poor in the remaining. Compared to classical linear indices, nonlinear HRV parameters seem more suitable for individual test–retest evaluations but, due to a reduced ICC, they need increased sample size in comparative studies involving two groups of subjects.

Lone Atrial Fibrillation - What Do We Know?

Abstract: Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Despite the common association of AF with cardiovascular disease, some patients can be classified as 'lone AF'. The latter is essentially a diagnosis of exclusion, and should be preceded by careful evaluation, including thorough collection of medical history, physical examination, blood pressure measurement, laboratory tests, ECG, echocardiography and, possibly, chest x-ray and exercise testing. Lone AF patients were initially thought to have a good prognosis with respect to thromboembolism and mortality, compared with the general AF population, but more recent data suggest otherwise. This review focuses on the clinical epidemiology and management aspects of lone AF, as well as various associated novel risk factors, such as familial, genetic and socioeconomic factors, alcohol, sports activity and biochemical markers.

Cardiovagal Response to Acute Mild Exercise in Young Healthy Subjects

Abstract: Background The aim of the present study was to investigate the effect of a single bout of mild exercise on autonomic nervous system activity in healthy subjects Methods and Results The study group comprised 18 healthy males, aged between 20 and 24 years, who had not been training regularly for the last 3 months A supine recording of systolic arterial pressure (SAP) and RR interval and the administration of the phenylephrine test were performed at baseline and repeated after a 60-min recovery period following treadmill exercise training for 30 min at 65% of maximal heart rate Mean SAP and RR interval, heart rate variability (HRV) indices (the standard deviation of normal-to-normal RR intervals (SDNN), the square root of the mean of squared differences between successive intervals and the percentage of adjacent RR intervals differing more than 50 ms), noninvasive spectral baroreflex sensitivity (Spe-BRS) and phenylephrine baroreflex sensitivity (Phe-BRS) were assessed before and after training Mean SAP measured after exercise was lower than baseline (120±12 mmHg vs 128±12 mmHg, p=005) Spe-BRS and Phe-BRS increased significantly after exercise, from 118±61 ms/mmHg to 160±78 ms/mmHg (p=0034), and from 160±88 ms/mmHg to 219±93 ms/mmHg (p=0022), respectively A parallel increase was also observed in SDNN (from 81±44 ms to 96±53 ms, p=002), but the other HRV indices showed no significant differences between pre- and post-exercise Conclusions A single session of mild exercise performed by sedentary young men leads to significant autonomic nervous system improvement, which suggests that even mild physical activity is beneficial for neural cardiac regulation and should be recommended to sedentary healthy subjects (Circ J 2005; 69: 976 - 980)

Esc guidelines for the diagnosis and treatment of acute and chronic heart failure 2008 (ending)

Abstract: ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure 2008 (ending).

Atrial Fibrillation Pathophysiology Implications for Management

Abstract: Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, is an important contributor to population morbidity and mortality. An arrhythmia that is particularly common in the elderly, AF is growing in prevalence with the aging of the population. Our understanding of the basic mechanisms that govern AF occurrence and persistence has been increasing rapidly. This article reviews the basic pathophysiology of AF over a broad range of levels, touching on the tissue mechanisms that maintain the arrhythmia, the relationship between clinical presentation and basic mechanisms, ion channel and transporter abnormalities that lead to ectopic impulse formation, basic models and tissue determinants of reentry, ion channel determinants of reentry, the nature and roles of electric and structural remodeling, autonomic neural components, anatomic factors, interactions between atrial and ventricular functional consequences of AF, and the basic determinants of atrial thromboembolism. We then review the potential implications of the basic pathophysiology of the arrhythmia for its management. We first discuss consequences for improved rhythm control pharmacotherapy: targeting underlying conditions, new atrium-selective drug targets, new targets for focal ectopic source suppression, and upstream therapy aiming to prevent remodeling. We then review the implications of basic mechanistic considerations for rate control therapy, AF ablation, and the prevention of thromboembolic events. We conclude with some thoughts about the future of translational research related to AF mechanisms.

A quantitative systematic review of normal values for short-term heart rate variability in healthy adults

Abstract: Heart rate variability (HRV) is a known risk factor for mortality in both healthy and patient populations. There are currently no normative data for short-term measures of HRV. A thorough review of short-term HRV data published since 1996 was therefore performed. Data from studies published after the 1996 Task Force report (i.e., between January 1997 and September 2008) and reporting short-term measures of HRV obtained in normally healthy individuals were collated and factors underlying discrepant values were identified. Forty-four studies met the pre-set inclusion criteria involving 21,438 participants. Values for short-term HRV measures from the literature were lower than Task Force norms. A degree of homogeneity for common measures of HRV in healthy adults was shown across studies. A number of studies demonstrate large interindividual variations (up to 260,000%), particularly for spectral measures. A number of methodological discrepancies underlined disparate values. These include a systematic failure within the literature (a) to recognize the importance of RR data recognition/editing procedures and (b) to question disparate HRV values observed in normally healthy individuals. A need for large-scale population studies and a review of the Task Force recommendations for short-term HRV that covers the full-age spectrum were identified. Data presented should be used to quantify reference ranges for short-term measures of HRV in healthy adult populations but should be undertaken with reference to methodological factors underlying disparate values. Recommendations for the measurement of HRV require updating to include current technologies.