Variable interatrial conduction illustrated in a hypertrophic cardiomyopathy population

Deciphering hypertrophic cardiomyopathy with electrocardiography

The comprehensive assessment of patients with hypertrophic cardiomyopathy is a complex process, with each step concurrently focusing on confirmation of the diagnosis, differentiation between sarcomeric and non-sarcomeric disease (phenocopy), and prognostication. Novel modalities such as genetic testing and advanced imaging have allowed for substantial advancements in the understanding of this condition and facilitate patient management. However, their availability is at present not universal, and interpretation requires a high level of expertise. In this setting, electrocardiography, a fast and widely available method, still retains a significant role in everyday clinical assessment of this population. In our review, we follow a stepwise approach for the interpretation of each electrocardiographic segment, discussing clinical implications of electrocardiographic patterns in sarcomeric disease, their value in the differential diagnosis from phenocopies, and impact on patient management. Outlining the substantial amount of information to be obtained from a simple tracing, we exhibit how electrocardiography is likely to remain an integral diagnostic tool in the future as well.

Electrocardiographic and Echocardiographic predictors of paroxysmal atrial fibrillation detected after ischemic stroke

BACKGROUND

Detection of atrial fibrillation after ischemic stroke is challenging due to its paroxysmal nature. We aimed to assess predictors of paroxysmal atrial fibrillation using non-invasive surface ECG and transthoracic echocardiography to select candidates for atrial fibrillation screening.

METHODS

Ischemic stroke patients without documented atrial fibrillation (n = 110, 67 ± 10 years, 40 female) and a control group of age- and gender-matched patients with history of paroxysmal atrial fibrillation prior to stroke (n = 55, 67 ± 10 years, 19 female) comprised the study sample. Using non-invasive ECG monitoring for three weeks, short episodes of paroxysmal atrial fibrillation were detected in 24 of 110 patients (22 %). The standard 12-lead ECG with sinus rhythm at stroke onset was digitally processed and analyzed. Transthoracic echocardiography data were reviewed for these patients.

RESULTS

Atrial fibrillation history was independently associated with P terminal force in lead V 1 > 40 mm*ms (OR 4.04 95 % CI 1.34-12.14, p = 0.013) and left atrial volume index (OR 1.08 95 % CI 1.03-1.13, p = 0.002; for LAVI > 40 mL/m² OR 6.40 95 % CL 1.47-27.91, p = 0.013). Among patients without atrial fibrillation history, no ECG characteristics were predictive of atrial fibrillation detected after stroke. Left atrial volume index remained an independent predictor of atrial fibrillation detected after stroke (OR 1.09 95 % CI 1.02-1.16, p = 0.017). A cutoff of <40 mL/m² had an 84 % negative predictive value for ruling out atrial fibrillation on ambulatory monitoring with a sensitivity of 50 % and a specificity of 86 %.

CONCLUSION

In a post hoc analysis, left atrial dilatation assessed by left atrial volume index independently predicted atrial fibrillation after stroke in patients without prior atrial fibrillation history, while the other clinical or ECG markers were not predictive of atrial fibrillation detected early after ischemic stroke.

TRIAL REGISTRATION

This study is a post hoc analysis from the prospective case-control study registered in December 2011, ClinicalTrials.gov ID: NCT01325545 .

Progressive interatrial block associated with atrial fibrillation in a patient with hypertrophic cardiomyopathy

Progressive interatrial block is a clinically significant condition that has previously been reported in various patient populations. It is a manifestation of progressive fibrosis affecting the Bachmann region. This report presents a case of progressive interatrial block associated with atrial fibrillation in the context of hypertrophic cardiomyopathy.

Atrial and ventricular arrhythmias in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease caused by mutations in genes coding for cardiac sarcomeres. HCM is the most common inherited heart disease, with a prevalence of 0.2%. There are multiple genetic variants that cause pleomorphic clinical attributes and disease characterized by myocardial disarray and myocardial hypertrophy. Patients are at an increased risk of atrial and ventricular arrhythmias. Management of these arrhythmias is complex. Atrial fibrillation is associated with increased mortality and thromboembolism. Ventricular arrhythmias are life threatening and best treated with an implantable defibrillator.

Variability of P-wave morphology predicts the outcome of circumferential pulmonary vein isolation in patients with recurrent atrial fibrillation

INTRODUCTION

Severe atrial structural remodeling may reflect irreversible damage of the atrial tissue in patients with atrial fibrillation (AF) and is associated with changes of P-wave duration and morphology. Our aim was to study whether variability of P-wave morphology (PMV) is associated with outcome in patients with AF after circumferential PV isolation (CPVI).

METHODS AND RESULTS

70 consecutive patients (aged 60±9years, 46 men) undergoing CPVI due to symptomatic AF were studied. After cessation of antiarrhythmic therapy, standard 12-lead ECG during sinus rhythm was recorded for 10min at baseline and transformed to orthogonal leads. Beat-to-beat P-wave morphology was subsequently defined using a pre-defined classification algorithm. The most commonly observed P-wave morphology in a patient was defined as the dominant morphology. PMV was defined as the percentage of P waves with non-dominant morphology in the 10-min sample. At the end of follow-up, 53 of 70 patients had no arrhythmia recurrence. PMV was greater in patients without recurrence (19.5±17.1% vs. 8.2±6.7%, p<0.001). In the multivariate logistic regression model, PMV≥20% (upper tertile) was the only independent predictor of ablation success (OR=11.4, 95% CI 1.4-92.1, p=0.023). A PMV≥20% demonstrated a sensitivity of 41.5%, a specificity of 94.1%, a PPV of 96.7%, and an NPV of 34.0% for free of AF after CPVI.

CONCLUSIONS

We report a significant association between increased PMV and 6-month CPVI success. PMV may help to identify patients with very high likelihood of freedom of AF 6-months after CPVI.

P-wave morphology is associated with echocardiographic response to cardiac resynchronization therapy in MADIT-CRT patients

BACKGROUND

In this study we hypothesized that signs of atypical atrial activation would be associated with cardiac resynchronization therapy (CRT) response in patients with mildly symptomatic heart failure (CHF), left ventricular dysfunction, and wide QRS complex.

METHODS

Patients included in the CRT-D arm in MADIT-CRT were studied (n = 892). Unfiltered signal-averaged P waves were analyzed to determine orthogonal P-wave morphology (typical morphologies were predefined as having positive signals in Leads X and Y and a negative or negative-positive signal in Lead Z. All other patterns were classified as atypical). The association between P-wave morphology and data on echocardiographic response at 1 year was analyzed.

RESULTS

Atypical P-wave morphology was found in 21% (n = 186) of the patients at baseline. Patients with atypical P-wave morphology were more often female (31% vs. 24%, P = 0.025), had lower BMI (28 ± 5 kg/m(2) vs. 29 ± 5 kg/m(2) , P = 0.008), had more ischemic CHF (60% vs. 52%, P = 0.026) and had smaller left atrial volumes (90 ± 20 mL vs. 94 ± 22 mL, P = 0.034). Atypical P-wave morphology at baseline was associated with superior response to CRT at 1 year with a larger reduction in left ventricular end-diastolic volume (-23 ± 12% vs. -20 ± 11%, P = 0.009), left ventricular end-systolic volume (-36 ± 16% vs. -31 ± 16%, P = 0.006), and left atrial volume (-31 ± 12% vs. -27 ± 12%, P = 0.005), with a slightly larger absolute increase in left ventricular ejection fraction (LVEF) (12 ± 5% vs. 11 ± 5%, P = 0.009). These associations were found to be independent of traditional predictors.

CONCLUSION

The presence of atypical P-wave morphology recorded is independently associated with a favorable echocardiographic cardiac remodeling response to CRT.

P-wave morphology is unaffected by atrial size: a study in healthy athletes

BACKGROUND

Orthogonal P-wave morphology has previously been described in different populations, but its relation to atrial size has not been studied in detail. In this study, we investigated whether atrial size affects P-wave morphology in athletes, who are known to have different degrees of atrial enlargement.

METHODS

A total of 504 healthy, male, professional soccer players were included (median age 25 years). All underwent echocardiographic and 12-lead electrocardiographic (ECG) recordings. The ECG was transformed into orthogonal leads, using the inverse Dower transform. The association between echocardiographic parameters and standard P-wave measures (i.e., orthogonal morphology, left atrial abnormality assessed as negative P-wave terminal force [PTF] in lead V1 > 0.04 mm × s, and duration) was analyzed.

RESULTS

The vast majority had either type 1 P-wave morphology (75%) (positive leads X and Y and negative lead Z) or type 2 P-wave morphology (22%) (positive leads X and Y and biphasic lead Z [negative/positive]). Left atrial enlargement (≥29 mL/m(2) ) was found in 79% on echocardiography. There was no significant difference in left atrial end-systolic volume, left or right atrial diameters, or right atrial area between individuals with different P-wave morphologies. ECG signs of left atrial abnormality were found in eight subjects, who did not have significantly larger left atrial dimensions than the rest.

CONCLUSIONS

We demonstrated that P-wave morphology does not depend on the size of the atria in young, healthy athletes, and that PTF is not a reliable marker of left atrial enlargement in the current population.

Detection of hypertrophic cardiomyopathy is improved when using advanced rather than strictly conventional 12-lead electrocardiogram

INTRODUCTION

Twelve-lead electrocardiogram (ECG) is used to screen for hypertrophic cardiomyopathy (HCM), but up to 25% of HCM patients do not have distinctly abnormal ECGs, whereas up to 5% to 15% of healthy athletes do. We hypothesized that an approximately 5-minute resting advanced 12-lead ECG test ("A-ECG score") could detect HCM with greater sensitivity than pooled conventional ECG criteria and distinguish healthy athletes from HCM with greater specificity.

MATERIALS AND METHODS

Five-minute 12-lead ECGs were obtained from 56 HCM patients, 56 age/sex-matched healthy controls, and 69 younger endurance-trained athletes. Electrocardiograms were analyzed using recently suggested pooled conventional ECG criteria and also A-ECG scoring techniques that considered results from multiple advanced and conventional ECG parameters.

RESULTS

Compared with pooled criteria from the strictly conventional ECG, an A-ECG logistic score incorporating results from just 3 advanced ECG parameters (spatial QRS-T angle, unexplained portion of QT variability, and T-wave principal component analysis ratio) increased the sensitivity of ECG for identifying HCM from 89% (78%-96%) to 98% (89%-100%; P = .025), while increasing specificity from 90% (83%-94%) to 95% (92%-99%; P = .020).

CONCLUSIONS

Resting 12-lead A-ECG scores that are simultaneously more sensitive than pooled conventional ECG criteria for detecting HCM and more specific for distinguishing healthy athletes and other healthy controls from HCM can be constructed. Pending further prospective validation, such scores may lead to improved ECG-based screening for HCM.

Diagnostic utility of the spatial versus individual planar QRS-T angles in cardiac disease detection

INTRODUCTION

We compared the diagnostic utility of various planar QRS-T angles to that of the spatial QRS-T angle in detecting various cardiac diseases.

MATERIALS AND METHODS

Electrocardiographic (ECG) and derived vectorcardiographic (VCG) data were analyzed from 370 patients with imaging-proven cardiac disease (coronary artery disease, hypertrophic cardiomyopathy, or left ventricular systolic dysfunction) and 210 apparently healthy controls. The areas under the curve (AUC) of the Receiver Operating Characteristic (ROC) for distinguishing cardiac health from disease for each disease condition were statistically compared for the spatial mean QRS-T angle versus the ECG-derived frontal and VCG-derived frontal, left sagittal and horizontal planar QRS-T angles.

RESULTS

The AUC ROC of the spatial mean QRS-T angle, which ranged from 0.801 ± 0.035 to 0.987 ± 0.007 depending on the specific comparison, was always significantly greater than that of the ECG frontal planar QRS-T angle (range from 0.680 ± 0.043 to 0.796 ± 0.045) and usually significantly greater than that of all other QRS-T angles for the diseases studied.

DISCUSSION

The spatial mean QRS-T angle is statistically significantly more diagnostically powerful than the ECG-derived frontal planar QRS-T angle and also generally more diagnostically powerful than all VCG-derived planar QRS-T angles in detecting cardiac disease. The ECG frontal planar QRS-T angle should not be considered an adequate diagnostic substitute for the spatial QRS-T angle.

Paradoxical effects of interatrial conduction delay in a hypertrophic cardiomyopathy patient in the long-term: time is a great healer

We present a unique case where early proarrhythmic and late antiarrhythmic characteristics of interatrial conduction delay were observed during the long-term progression of HCM. Occurrence of AT constantly increased as the interatrial conduction delay became more prominent, while the P-wave width in sinus rhythm and the AT cycle length both showed an instantaneous increase in parallel. As the interatrial delay reached a critical point, the right and left atrial P-wave became virtually separated, as demonstrated by the findings of ECGs and echocardiography. This phenomenon resulted in the complete cessation of tachycardias.

Abnormal P-wave morphology is a predictor of atrial fibrillation development and cardiac death in MADIT II patients

BACKGROUND

Several ECG-based approaches have been shown to add value when risk-stratifying patients with congestive heart failure, but little attention has been paid to the prognostic value of abnormal atrial depolarization in this context. The aim of this study was to noninvasively analyze the atrial depolarization phase to identify markers associated with increased risk of mortality, deterioration of heart failure, and development of atrial fibrillation (AF) in a high-risk population with advanced congestive heart failure and a history of acute myocardial infarction.

METHODS

Patients included in the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) with sinus rhythm at baseline were studied (n = 802). Unfiltered and band-pass filtered signal-averaged P waves were analyzed to determine orthogonal P-wave morphology (prespecified types 1, 2, and 3/atypical), P-wave duration, and RMS20. The association between P-wave parameters and data on the clinical course and cardiac events during a mean follow-up of 20 months was analyzed.

RESULTS

P-wave duration was 139 + or - 23 ms and the RMS20 was 1.9 + or - 1.1 microV. None of these parameters was significantly associated with poor cardiac outcome or AF development. After adjustment for clinical covariates, abnormal P-wave morphology was found to be independently predictive of nonsudden cardiac death (HR 2.66; 95% CI 1.41-5.04, P = 0.0027) and AF development (HR 1.75; 95% CI 1.10-2.79, P = 0.019).

CONCLUSION

Abnormalities in P-wave morphology recorded from orthogonal leads in surface ECG are independently predictive of increased risk of nonsudden cardiac death and AF development in MADIT II patients.

Prevalence of interatrial block in healthy school-aged children: definition by P-wave duration or morphological analysis

BACKGROUND

P waves > or = 110 ms in adults and > or = 90 ms in children are considered abnormal, signifying interatrial block, particularly in the first case.

METHODS

To evaluate the prevalence of interatrial block in healthy school-aged children, we obtained 12-lead digital ECGs (Cardioperfect 1.1, CardioControl NV, Delft, The Netherlands) of 664 healthy children (349 males/315 females, age range 6-14 years old). P-wave analysis indices [mean, maximum and minimum (in the 12 leads) P-wave duration, P-wave dispersion, P-wave morphology in the derived orthogonal (X, Y, Z) leads, as well the amplitude of the maximum spatial P-wave vector] were calculated in all study participants.

RESULTS

P-wave descriptor values were: mean P-wave duration 84.9 + or - 9.5 ms, maximum P-wave duration 99.0 + or - 9.8 ms, P dispersion 32.2 + or - 12.5 ms, spatial P amplitude 182.7 + or - 69.0 microV. P-wave morphology distribution in the orthogonal leads were: Type I 478 (72.0%), Type II 178 (26.8%), Type III 1 (0.2%), indeterminate 7 (1%). Maximum P-wave duration was positively correlated to age (P < 0.001) and did not differ between sexes (P = 0.339). Using the 90-ms value as cutoff for P-wave duration, 502 (75.6%) children would be classified as having maximum P-wave duration above reference range. The 95th and the 99th percentiles were in the overall population 117 ms and 125 ms, respectively. P-wave morphology type was not in any way correlated to P-wave duration (P = 0.715).

CONCLUSIONS

Abnormal P-wave morphology signifying the presence of interatrial block is very rare in a healthy pediatric population, while widened P waves are quite common, although currently classified as abnormal.

Altered interatrial conduction detected in MADIT II patients bound to develop atrial fibrillation

BACKGROUND

Changes in P-wave morphology have recently been shown to be associated with interatrial conduction route used, without noticeable changes of P-wave duration. This study aimed at exploring the association between P-wave morphology and future atrial fibrillation (AF) development in the Multicenter Automatic Defibrillator Trial II (MADIT II) population.

METHODS

Patients included in MADIT-II without a history of AF with sinus rhythm at baseline who developed AF during the study ("Pre-AF") were compared to matched controls without AF development ("No-AF"). Patients were followed for a mean of 20 months. A 10-minute high-resolution bipolar ECG recording was obtained at baseline. Signal-averaged P waves were analyzed to determine orthogonal P-wave morphology, P-wave duration, and RMS20. The P-wave morphology was subsequently classified into one of three predefined types using an automated algorithm.

RESULTS

Thirty patients (age 68 +/- 7 years) who developed AF during MADIT-II were compared with 60 patients (age 68 +/- 8 years) who did not. P-wave duration and RMS20 in the Pre-AF group was not significantly different from the No-AF group (143 +/- 21 vs 139 +/- 30 ms, P=0.26, and 2.0 +/- 1.3 vs 2.1 +/- 1.0 muV, P=0.90). The distribution of P-wave morphologies was shifted away from Type 1 in the Pre-AF group when compared to the No-AF group (Type 1/2/3/atypical; 25/60/0/15% vs 10/63/10/17%, P=0.04).

CONCLUSIONS

This study is the first to describe changes in P-wave morphology in patients prior to AF development. The results indicate that abnormal interatrial conduction may play a role in AF development in patients with prior myocardial infarction and congestive heart failure.

Noninvasive evidence of shortened atrial refractoriness during sinus rhythm in patients with paroxysmal atrial fibrillation

BACKGROUND

Shortening of the atrial refractory period is the key feature of atrial electrical remodeling during atrial fibrillation (AF). During sinus rhythm (SR), assessment of the atrial refractoriness is hampered by the fact that the atrial repolarization wave (Ta wave) is largely obscured by the following QRST complex. The purpose of this study was to study the Ta wave in subjects with paroxysmal AF during SR with third-degree atrioventricular (AV) block, and in matched controls.

METHODS

Fifteen patients (mean age 70 +/- 10 years, five males) with paroxysmal AF undergoing AV-nodal ablation were studied. Fifteen age- and gender-matched subjects (mean age 71 +/- 9 years, five males) with third-degree AV block, without a history of heart disease, were used as controls. Standard 12-lead electrocardiograms (ECGs) were recorded and transformed to orthogonal leads and studied using P-wave signal averaging technique.

RESULTS

The P to Ta interval was shorter (408 +/- 47 ms vs 451 +/- 53 ms, P = 0.017) and in Lead Y the Ta peak location was earlier (156 +/- 31 ms vs 187 +/- 34 ms, P = 0.002) in subjects with paroxysmal AF than in the controls. The P-wave duration (126 +/- 15 ms vs 129 +/- 17 ms, P = 0.59) and morphology was similar in AF patients and controls.

CONCLUSIONS

In this study, the ECG signs of shorter atrial refractoriness associated with a history of AF are visualized for the first time during SR. The finding of the earlier location of the PTa peak in AF subjects implies that a possible indicator of increased arrhythmia susceptibility may be visible already in the unprocessed ECG.

Detailed ECG analysis of atrial repolarization in humans

INTRODUCTION

Data on human atrial repolarization are scarce since the QRS complex normally obscures its ECG trace. In the present study, consecutive patients with third-degree AV block were studied to better describe the human Ta wave.

METHODS AND RESULTS

Forty patients (mean age 75 years, 17 men) were included. All anti-arrhythmic drugs were discontinued before ECG recording. Standard 12-lead ECGs were recorded, transformed to orthogonal leads and studied using signal-averaged P wave analysis. The average P wave duration was 124 +/- 16 ms. The PTa duration was 449 +/- 55 ms (corrected PTa 512 +/- 60 ms) and the Ta duration (P wave end to Ta wave end) was 323 +/- 56 ms. The polarity of the Ta wave was opposite to that of the P wave in all leads. The Ta peaks were located at 196 +/- 55 ms in Lead Y, 216 +/- 50 ms in Lead X, and 335 +/- 92 in Lead Z. No correlation was found between P wave duration and Ta duration, or between Ta peak amplitude and Ta duration. The morphology of the Ta wave was similar regardless of the interatrial conduction.

CONCLUSIONS

The Ta wave has the opposite polarity, and the duration is generally two to three times that, of the P wave. Although the Ta peak may occasionally be located in the PQ interval during normal AV conduction, it is unlikely that enough information can be obtained from analysis of this segment to differentiate normal from abnormal atrial repolarization. Hence, an algorithm for QRST cancellation during sinus rhythm is needed to further improve analysis.

Signal-averaged P wave analysis for delineation of interatrial conduction - further validation of the method

BACKGROUND

The study was designed to investigate the effect of different measuring methodologies on the estimation of P wave duration. The recording length required to ensure reproducibility in unfiltered, signal-averaged P wave analysis was also investigated. An algorithm for automated classification was designed and its reproducibility of manual P wave morphology classification investigated.

METHODS

Twelve-lead ECG recordings (1 kHz sampling frequency, 0.625 microV resolution) from 131 healthy subjects were used. Orthogonal leads were derived using the inverse Dower transform. Magnification (100 times), baseline filtering (0.5 Hz high-pass and 50 Hz bandstop filters), signal averaging (10 seconds) and bandpass filtering (40-250 Hz) were used to investigate the effect of methodology on the estimated P wave duration. Unfiltered, signal averaged P wave analysis was performed to determine the required recording length (6 minutes to 10 s) and the reproducibility of the P wave morphology classification procedure. Manual classification was carried out by two experts on two separate occasions each. The performance of the automated classification algorithm was evaluated using the joint decision of the two experts (i.e., the consensus of the two experts).

RESULTS

The estimate of the P wave duration increased in each step as a result of magnification, baseline filtering and averaging (100 +/- 18 vs. 131 +/- 12 ms; P < 0.0001). The estimate of the duration of the bandpass-filtered P wave was dependent on the noise cut-off value: 119 +/- 15 ms (0.2 microV), 138 +/- 13 ms (0.1 microV) and 143 +/- 18 ms (0.05 microV). (P = 0.01 for all comparisons). The mean errors associated with the P wave morphology parameters were comparable in all segments analysed regardless of recording length (95% limits of agreement within 0 +/- 20% (mean +/- SD)). The results of the 6-min analyses were comparable to those obtained at the other recording lengths (6 min to 10 s). The intra-rater classification reproducibility was 96%, while the interrater reproducibility was 94%. The automated classification algorithm agreed with the manual classification in 90% of the cases.

CONCLUSION

The methodology used has profound effects on the estimation of P wave duration, and the method used must therefore be validated before any inferences can be made about P wave duration. This has implications in the interpretation of multiple studies where P wave duration is assessed, and conclusions with respect to normal values are drawn.P wave morphology and duration assessed using unfiltered, signal-averaged P wave analysis have high reproducibility, which is unaffected by the length of the recording. In the present study, the performance of the proposed automated classification algorithm, providing total reproducibility, showed excellent agreement with manually defined P wave morphologies.

Age-related changes in P wave morphology in healthy subjects

Background

We have previously documented significant differences in orthogonal P wave morphology between patients with and without paroxysmal atrial fibrillation (PAF). However, there exists little data concerning normal P wave morphology. This study was aimed at exploring orthogonal P wave morphology and its variations in healthy subjects.

Methods

120 healthy volunteers were included, evenly distributed in decades from 20–80 years of age; 60 men (age 50+/-17) and 60 women (50+/-16). Six-minute long 12-lead ECG registrations were acquired and transformed into orthogonal leads. Using a previously described P wave triggered P wave signal averaging method we were able to compare similarities and differences in P wave morphologies.

Results

Orthogonal P wave morphology in healthy individuals was predominately positive in Leads X and Y. In Lead Z, one third had negative morphology and two-thirds a biphasic one with a transition from negative to positive. The latter P wave morphology type was significantly more common after the age of 50 (P < 0.01). P wave duration (PWD) increased with age being slightly longer in subjects older than 50 (121+/-13 ms vs. 128+/-12 ms, P < 0.005). Minimal intraindividual variation of P wave morphology was observed.

Conclusion

Changes of signal averaged orthogonal P wave morphology (biphasic signal in Lead Z), earlier reported in PAF patients, are common in healthy subjects and appear predominantly after the age of 50. Subtle age-related prolongation of PWD is unlikely to be sufficient as a sole explanation of this finding that is thought to represent interatrial conduction disturbances. To serve as future reference, P wave morphology parameters of the healthy subjects are provided.