Mikhail Matveev

Transthoracic impedance study with large self-adhesive electrodes in two conventional positions for defibrillation

External defibrillation requires the application of high voltage electrical impulses via large external electrodes, placed on selected locations on the thorax surface. The position of the electrodes is one of the major determinants of the transthoracic impedance (TTI) which influences the intracardiac current flow during electric shock and defibrillation success. The variety of factors which influence TTI measurements raised our interest to investigate the range of TTI values and the temporal TTI variance during long-term application of defibrillation self-adhesive electrodes in two conventional positions on the patients chest--position 1 (sub-clavicular/sub-axillar position) and position 2 (antero-posterior position). The prospective study included 86 randomly selected volunteers (39 male and 49 female, 67 patients with normal skin, 13 patients with dry skin and 6 patients with greasy skin, 16 patients with chest pilosity and 70 patients without chest pilosity). The TTI was measured according to the interelectrode voltage drop obtained by passage of a low-amplitude high-frequency current (32 kHz) between the two self-adhesive electrodes (active area about 92 cm2). For each patient, the TTI values were measured within 10 s, 1 min and 5 min after sticking the electrodes to the skin surface, independently for the two tested electrode positions. We found that the expected TTI range is between 58 Omega and 152 Omega for position 1 and between 55 Omega and 149 Omega for position 2. Although the two TTI ranges are comparable, we measured significantly higher TTI mean of about (107.2 +/- 22.3) Omega for position 1 compared to (96.6 +/- 19.2) Omega for position 2 (p = 0.001). This fact suggested that the antero-posterior position of the electrodes is favourable for defibrillation. Within the investigated time interval of 5 min, we observed a significant TTI reduction with about 6.9% (7.4 Omega/107.2 Omega) for position 1 and about 5.3% (5.1 Omega/96.6 Omega) for position 2. We suppose that the long-term application of self-adhesive electrodes would lead to improvement of the physical conditions for conduction of the defibrillation current and to diminution of energy loss in the electrode-skin contact impedance. We found that gender is important when position 1 is used because women have significantly higher TTI (111 +/- 20.3) Omega compared to the TTI of men (102.6 +/- 24) Omega (p = 0.0442). Although we found some specifics of the electrode-skin contact layer, we can conclude that because of the insignificant differences in TTI, the operator of the defibrillator paddles does not need to take into consideration the skin type and pilosity of the patients. Analysis of the correlations between TTI and the individual patient characteristics (chest size, weight, height, age) showed that these patient characteristics are unreliable factors for prediction of the TTI values and optimal defibrillation pulse parameters and energy.

Evaluation of the Schiller Br-102 plus noninvasive ambulatory blood pressure monitor according to the International Protocol introduced by the Working Group on Blood Pressure Monitoring of the European Society of Hypertension

ObjectiveTo evaluate the SCHILLER BR-102 plus (Schiller AG, Baar, Switzerland) noninvasive ambulatory blood pressure recorder according to the International Protocol for validation of blood pressure measuring devices in adults introduced by the Working Group on Blood Pressure Monitoring of the European Society of Hypertension. MethodOne SCHILLER BR-102 plus blood pressure recorder was tested by a validation team, consisting of three persons: two observers (nurses) and a doctor, acting as supervisor and ‘expert’. The European Society of Hypertension International Protocol comprises two phases. Fifteen participants were recruited for the first phase and, following a successful test, a further 18 persons (giving a total of 33) were recruited additionally. For phase 1, five of the 15 participants had systolic blood pressure and diastolic blood pressure in each of the ranges: low, medium and high. For phase 2, 11 of the 33 participants (including the first 15 participants) had systolic blood pressure and diastolic blood pressure in each of the ranges. The mercury standard for validation was preferred over the optional Sphygmocorder. Because the SCHILLER BR-102 plus has the oscillometric method as backup to the basic auscultatory measurement, both systems of measurement were subjected to individual validations. ResultsResults obtained show that the SCHILLER BR-102 plus noninvasive ambulatory blood pressure recorder meets all the requirements specified in the International Protocol for both oscillometric and auscultatory methods. ConclusionOn the basis of these results, the SCHILLER BR-102 plus can be recommended for ambulatory blood pressure measurement in clinical practice using both auscultatory and oscillometric modes.

Time-related heart autonomic balance characteristics in healthy subjects

Changes of the heart autonomic balance between morning (8-9 h) and afternoon (14-15 h) measurements were studied in 22 healthy subjects. The selection of these two daytime periods was substantiated by the established higher risk of cardiovascular incidents in the morning and the relative balance of the vegetative nervous system in the afternoon hours. The changes were analysed by RR-variability indices from ECG recordings in the resting state and with vegetative nervous system stimulation by the handgrip test and Valsalva manoeuvre. It was shown that there were no significant differences between the morning and afternoon values of the respective indices, between morning and afternoon handgrip tests and between morning and afternoon Valsalva manoeuvres. However, there were significant differences in comparison of the index values between resting state and handgrip test and resting state and Valsalva manoeuvre, both from morning and afternoon measurements. Moreover, the significantly differing indices were clustered in different groupings, when comparing resting state recordings with morning and afternoon stimulation tests. For this reason, the authors introduced an indicator for time-related autonomic balance changes. The indicator evaluates the power of each RR-variability index to respond to changes in the autonomic control, in comparisons between resting state and stimulation data in the morning and afternoon measurements. These evaluations showed low power of the frequency-domain indices to respond to time-related autonomic balance changes in stimulation, with respect to the resting state. The time-domain indices have considerably higher power to react to relative morning and afternoon changes in the two vegetative nervous system components. Based on the estimations of the RR-variability indices obtained by the introduced indicator, a profile was constructed to represent time-related heart autonomic balance changes in healthy subjects. It was established that in spite of the relative stability of the vegetative nervous system in healthy subjects, hypersympatheticotonia and relatively lower parasympathetic tone were present in the risky morning hours.

Prognostic value of the Time Related Autonomic Balance Indicator for risk evaluation of cardiovascular events in patients with ischemic heart disease

The study comprised patients with unstable angina (UA), morning (MMI) and non-morning myocardial infarction (NMMI). The heart autonomic balance (HAB) circadian changes were assessed by time related autonomic balance indicator - a non-parametric criterion for estimating the balance by HRV indices from ECG recordings in rest and by parasympathetic or sympathetic stimulation. The results indicated that: i) in patients with UA the sympathetic part in HAB is more time-dependent than in healthy subjects; the vagal circadian characteristic is normal and thus secures a favorable long-term prognosis; ii) in patients with MMI circadian characteristics of HAB consist of sympathetic hyper-activity and normal parasympathetic tone. The sympathetic dysfunction is the reason for the morning peak of CVE; iii) in patients with NMMI the circadian nature of the sympathetic activity is preserved, but the parasympathetic activity are almost absent.

Time-related heart vegetative balance characteristics in healthy subjects

Changes of the heart autonomic balance between morning (8 to 9 h) and afternoon (14 - 15 h) measurements were studied in 22 healthy subjects. The selection of these two daytime periods was substantiated by the established higher risk of cardiovascular incidents in the morning and the relative balance of the vegetative nervous system in the afternoon hours. The changes were analyzed by RR-variability indices from ECG recordings in resting state and with vegetative nervous system stimulation by handgrip test and Valsalva maneuver. The authors introduced an indicator for time-related autonomic balance changes. The indicator evaluates the power of each RR-variability index to respond to changes in the autonomic control, in comparisons between resting state and stimulation data in the morning and afternoon measurements.

Assessment of the potential of morphological ECG features for person identification

This study investigates the potential of ECG morphological feature set for person identification. The measurements are done over 145 pairs of ECG recordings from healthy subjects, acquired 5 years apart. Time, amplitude, area and slope descriptors of the QRS-T pattern are analyzed in 4 ECG leads, forming quasi-orthogonal lead system (II&III, V1, V5). The inter-subject variation, the difference of means in 1st vs. 2nd recording measurements, as well as the cross-correlation between features are estimated. Thus, 2 area and 4 amplitude descriptors of the QRS complex are highlighted. The population heterogeneity in the space of the selected features is verified via Factor analysis by Principal components extraction method. It confirms the orthogonality of the 6 features (each of them has significant factor loading for a particular factor). The analysis shows that the first 3 factors have eigenvalues higher than 1, both for the measurements in the 1st and the 2nd ECG recording and they accumulate respectively 68% and 64 % of the total data variation, which is a sign for their person identification potential.

Changes in the electrocardiogram induced by coronary artery bypass grafting

ECG recordings of coronary artery bypass grafting (CABG) surgery patients have been collected: number of patients 20 (men 95%, age 64.4±8.4), records duration 10-15 minutes. The number of bypasses for each individual is from 1 to 4 (40% of the patients are with 4). ECG recordings are pre- and post-surgery, from 2 to 10 days after intervention. All parameters were measured on an average P-QRS-T interval in order to avoid accidental events or noise. QRS amplitude, T-wave amplitude and ST elevation did not change, comparing pre- vs. post-stages. T-wave alternans (TWA) showed a clear upward trend (p=0.080) in the post-stage, and QRS-T angle in the frontal plane showed a clear downward trend (p=0.070) in the poststage, although both have no statistical significance. Significant increase (p=0.0010) in the post-stage was obtained for the heart rate (HR). Four patients had negative T-waves in lead V2 in both pre- and post-stages, highly correlated with the number of TWA episodes: 5 + 2.4 episodes per person with negative T-waves, vs. 2.9 + 3.2 episodes in those with positive T-waves. The observed increase in TWA and HR during the early postoperative period suggests that this period could be a more vulnerable one regarding cardiac complications.

DYNAMIC CHANGES OF VISUAL EVOKED POTENTIALS AND BRAINSTEM AUDITORY EVOKED POTENTIALS IN PATIENTS WITH MULTIPLE SCLEROSIS

Evoked potentials are widely used in diagnosis of multiple sclerosis (MS), but not sufficient data are available for their prospective role in the course of disease. The presentation is a longitudinal study in the Clinic of Neurology at MHAT – NHH – Sofia from Aug 2009 to Mar 2012. It includes 52 patients with clinically definite multiple sclerosis according to revised MacDonald criteria (2005/2010). Paternal visual evoked potentials (PVEP) and brainstem auditory evoked potentials (BAEP) were examined consecutively during the study and these results were compared with the grade of disability according to Expanded Disability Statement Scale (EDSS). The follow-up was done at registered relapses and also at patients without new complaints – one or two years since the initial examination. For quantitative assessment of pathological EP changes, a total evoked potential (EP) score was formulated. This score is a sum of the individual PVEP and BAEP scores. The time interval to the first change of total EP score and the time interval to the first change in EDSS were assessed. The results were compared to Kaplan–Meier survival curves. We found more prominent sensitivity of the total EP score compared to EDSS in the course of disease. Our study concludes that the neurophysiologic method is more sensitive test than EDSS for earlier detection of deterioration and disease progression.

Risk Evaluation of Perioperative Acute Coronary Syndromes and Other Cardiovascular Complications During Emergency High Risky Noncardiac Surgery

The cardiac risk (CR) in noncardiac surgery represents the probability of acute cardiovascular conditions appearance, assessed as perioperative complications. The most frequent perioperative complications are the acute manifestations of coronary or noncoronary ischemia; acute or exacerbated chronic heart failure (CHF); acute rhythm and conductive disorders; acute cardiac inflammatory processes; increased arterial blood pressure or hypertensive crisis; cardiogenic shock and sudden cardiac death. These conditions are either early signs, or represent a manifestation of progress or decompensation of present cardiac diseases. Specific indication may be found in their origin, if it is explicitly or implicitly associated with the present surgical disease or with a completed surgical intervention, giving weight to the special features of the perioperative period [1]. The major surgical interventions, e.g. in the thoracic cavity and the upper abdominal cavity, as well as the neurosurgical and the major orthopedic operations, are related to increased CR. Previous myocardial infarction, unstable stenocardia and decompressed chronic cardiac insufficiency are powerful predictors for the emergence of acute perioperative cardiovascular complications (CVC) and mortality. The patients with such specified pathologies need additional evaluation before major surgical intervention. The cardiac postoperative morbidity and mortality are closely related to the basic surgical disease and the corresponding intervention. Many scientific publications report on the high number of complications, accompanying the major surgical abdominal and intrathoracic interventions, emergency surgical interventions, surgery of malignant neoplasm, major peripheral vascular manipulations [1, 2, 3]. The CR evaluation will not change the course and the result of the intervention in emergency conditions, e.g. rupture of abdominal aortic aneurism, heavy trauma, perforations etc., but may have influence upon the care during the early postoperative period. In emergency but noncritical states (e.g. biliary obstruction), the evaluation may contribute to risk reduction without influence upon the decision about the necessity of the intervention. In some cases, the CR evaluation may influence the surgical intervention planning and the choice of less invasive

High‐Frequency Electrocardiography: Optimizing the Diagnosis of the Acute Myocardial Infarct with ST‐Elevation

The analysis of the received digital signal by computer microprocessor in high‐frequency electrocardiography, used in our research, makes possible synthesis of vectorcardiographic images and loops, allowing improved qualitative and quantitative diagnosing of the myocardial injury.