Paulo Roberto Benchimol-Barbosa

Efeitos da idade e da aptidão aeróbica na recuperação da frequência cardíaca em homens adultos

BACKGROUND Physiological aging leads to cardiac autonomic dysfunction, which is associated with the onset and worsening of cardiovascular disease and an increased risk of death. Currently, physical exercise is considered a cardioprotective strategy and more research is needed on its benefit on cardiac autonomic function. OBJECTIVE To evaluate the autonomic control of heart rate in healthy young and middle-aged volunteers with different levels of aerobic fitness. METHODS The study included 68 volunteers, stratified for age and level of aerobic fitness. Based on aerobic fitness assessed by the submaximal exercise test, subjects were separated into two groups, good fitness and poor fitness. Assessment of cardiac autonomic control was performed based on measurements of heart rate variability at rest and heart rate recovery post-exercise. Analysis of variance with two factors was used to compare the variables investigated. RESULTS The heart rate variability is significantly lower in middle-aged volunteers than in young individuals, regardless of the aerobic fitness level (p <0.01). Higher levels of aerobic fitness in middle-aged volunteers are associated with earlier post-effort vagal reentry - rate of HR decline after 1min30s: 39.6% good aerobic fitness vs. poor 28.4% (p < 0.01). CONCLUSION Better levels of aerobic fitness act beneficially on the autonomic control of post-exercise heart rate, preserving the vagal reentry velocity in healthy middle-aged volunteers. However, it does not attenuate the decrease in heart rate variability due to the natural aging process.

Assessing autonomic function in hypertrophic cardiomyopathy

OBJECTIVE Assess the autonomic function in hypertrophic cardiomyopathy (HCM) through heart rate variability (HRV) and to correlate it to echocardiographic data. METHODS Two groups were studied, and compared for gender, age and HR: A) Ten (10) patients reporting septal HCM (70% non-obstructive); B) Ten (10) healthy volunteers. HRV was analyzed along four successive stages: at rest, under controlled breathing, while bending, and controlled breathing associated to bending. Variables means were compared between groups and intra-groups in the different stages; in Group A, variables means were correlated to echocardiographic measurements (interventricular septum and left atrial diameter). RESULTS No HRV difference was reported among groups in the first 3 stages. In the fourth stage vagal activity was shown to be higher in Group A [quadratic mean log between RR intervals (RMSSD) - 1.35+/-0.14 vs 1.17+/-0.16; p=0.019; high frequency component logarithm (LogHF)- 4.89+/-0.22 vs 4.62+/-0.26; p=0.032]. Along the stages, vagal measurements [rate of pairs of consecutive RR intervals whose difference is > or =50 ms (pNN50) and LogHF] also showed lower reduction in the third stage in Group A, while LogHF showed some increase in last stage (p=0.027), thus indicating marked parasympathetic activity in that group. Group A HRV analysis showed no difference among patients reporting larger hypertrophy or atrial diameter. CONCLUSION 1) Parasympathetic prevalence was shown during autonomic stimulation in HCM patients; 2) No correlation was found between HRV and echocardiographic measurements under analysis.

O eletrocardiograma de alta resoluçäo no domínio da frequencia. Utilizaçäo de técnicas estatísticas de correlaçäo espectral para identificaçäo de pacientes com taquicardia ventricular monomórfica sustentada

PURPOSE: To evaluate the diagnostic accuracy of monomorphic ventricular tachycardia (MVT), in patients with structural heart diseases and episodes of sustained MVT, using the signal-averaged ECG (SAECG) in the time (TD) and the frequency domain (FD) with statistical techniques of spectral correlation. METHODS: Twenty seven patients with at least one episode of sustained MVT, 30 patients with structural heart diseases and no evidence of ventricular arrhythmias and 80 subjects with no evidence of heart disease have been studied. SAECG was performed in all patients with the following parameters: duration of the filtered QRS, RMS 40 and LAS40 in TD and the mean and the standard deviation of both signal energy intersegmentar spectral correlation and energy frequency edge track in FD. RESULTS: The sensitivity(S) and positive predict value (PPV) of the SAECG in TD, in FD and combined analysis of both domains were: S = 59.3%, 63.0%, 81.5% and PPV = 80.0%, 81.0%, 84.6%, respectively. CONCLUSION: The combined analysis of SAECG in TD and in FD improves the diagnostic accuracy in patients with S sustained MVT.PURPOSE To evaluate the diagnostic accuracy of monomorphic ventricular tachycardia (MVT), in patients with structural heart diseases and episodes of sustained MVT, using the signal-averaged ECG (SAECG) in the time (TD) and the frequency domain (FD) with statistical techniques of spectral correlation. METHODS Twenty seven patients with at least one episode of sustained MVT, 30 patients with structural heart diseases and no evidence of ventricular arrhythmias and 80 subjects with no evidence of heart disease have been studied. SAECG was performed in all patients with the following parameters: duration of the filtered QRS, RMS 40 and LAS40 in TD and the mean and the standard deviation of both signal energy intersegmentar spectral correlation and energy frequency edge track in FD. RESULTS The sensitivity(S) and positive predict value (PPV) of the SAECG in TD, in FD and combined analysis of both domains were: S = 59.3%, 63.0%, 81.5% and PPV = 80.0%, 81.0%, 84.6%, respectively. CONCLUSION The combined analysis of SAECG in TD and in FD improves the diagnostic accuracy in patients with S sustained MVT.

Refining the deceleration capacity index in phase-rectified signal averaging to assess physical conditioning level.

BACKGROUND Deceleration capacity (DC) of heart rate is a measure of cardiac vagal modulation. This study introduced a DC adaptation (Modified Index) that measured the velocity of change in the phase-rectified signal averaging curve, and assessed its ability to discriminate athletes from controls. MATERIALS AND METHODS The Modified Index was compared to Standard DC approach in a prospective case-control study. Subjects were classified according to maximal metabolic equivalents as the control group (CG) and athlete group (AG). The Modified Index was compared to Standard DC and classical approaches (RMSSD and HF) by the area under receiver operating characteristic curve (AUC) using 10,000 bootstraps. RESULTS In Standard DC and Modified Index bootstrap median values were (ms), respectively, 11.80 and 17.94 (p<0.01) in CG, and 25.98 and 45.62 in AG (p<0.01). AUC (mean±SD) was 0.70±0.12 for Standard DC and 0.96±0.04 for Modified Index (p<0.01). CONCLUSIONS Modified Index appropriately discriminates athletes from healthy sedentary subjects.

The effect of configuration parameters of time-frequency maps in the detection of intra-QRS electrical transients of the signal-averaged electrocardiogram: Impact in clinical diagnostic performance

Time-frequency maps of signal-averaged electrocardiogram based on a short time Fourier transform (STFT) technique analysis was employed to assess the presence of high frequency electrical transients (turbulence) and arrhythmia risk assessment. The optimal configuration set of STFT variables aiming at risk stratification for sustained monomorphic ventricular tachycardia (SMVT) is still undetermined. Different configuration variables, including analyzing time-window widths, starting positions, relative displacements, and zero-padding for STFT time-frequency maps constructions were combined on each analyzing averaged signal from 18 healthy controls and 18 subjects presenting inducible SMVT. Spectral turbulence analysis (STA) was, thus, carried out according to conventional procedures. The optimal configuration set of variables for STA was obtained by assessing the total diagnostic accuracy of all combinations of parameters. The optimal diagnostic performance was found at 86% total diagnostic accuracy as compared to 56% using previous defined normality thresholds (p=0.01). Present configuration set of variables is distinctive from previously defined set of variables and improves risk stratification.

Warfarin resistance and caffeine containing beverages

Warfarin resistance can be defined as the inability to prolong the international normalized ratio (INR) into the therapeutic range when the anticoagulant is given at normally prescribed doses [1]. Warfarin inhibition by abusive green tea intake was ascribed to green tea high vitamin K content [2]. However, when infusions of green tea were analyzed, the concentration of vitamin K was lower than the detection limit [4]. At the Anticoagulation Clinic of Hospital dos Servidores do Estado, Rio de Janeiro, Brazil, three patients could overcomewarfarin resistancewhen caffeine intakewas restricted. It is important to notice that coffee and cola beverages also have low vitamin K content [3]. A 27-year-old female with previous history of four fetal losses and a stroke, had a diagnosis of antiphospholipid syndrome confirmed, and was placed on warfarin. Nonetheless, with 20 mg/day her INR repeatedly remained below 1.3. She was drinking more than 2 l of a Brazilian caffeine-rich soft drink guarana per day, six days a week. After guarana was withhold, her INR reached target range with 7.5 mg/day. She started to drink guarana again and her INR dropped to 1.2 after five days.

Effect of aerobic conditioning on ventricular activation

BACKGROUND The athletes heart represents a reversible structural and functional adaptations of myocardial tissue developed through physical conditioning. Surface electrocardiogram (ECG) has the capability to detect myocardial hypertrophy but has limited performance in monitoring physical conditioning-induced myocardial remodeling. The aim of this study was to develop an ECG-derived test for detecting incipient myocardial hypertrophy in well-conditioned athletes based on a principal components (PC) analysis. METHODS Two groups of study composed of 14 sedentary healthy volunteers (CONTROL GROUP) and 14 professional long distance runners (Athlete group) had their maximal metabolic equivalents (MET) estimated (mean ± SD: CONTROL GROUP 9 ± 2 METs vs. Athlete group: 20 ± 1 METs, p<0.05). All participants had their high-resolution ECG (HRECG) recorded, and a 120 ms segment starting at the QRS complex onset and ending in the ST segment was extracted to build a data matrix for PC analysis. The Mahalanobis distance was evaluated by a logistic regression model to determine the optimal separation threshold between groups. HRECG was also analyzed using the classical time domain approach. The comparison of areas under the receiver operating characteristic curve (c-statistic) in 10,000 bootstrap re-samplings measured how well each method detected physical conditioning (α<0.05). RESULTS Average bootstrap c-statistic for PC analysis and time domain approaches were 0.98 and 0.79 (p<0.05), respectively. PC analysis and maximal oxygen consumption exhibited comparable performances to distinguish between groups. DISCUSSION The PC analysis method applied to HRECG signals appropriately discriminates well-conditioned athletes from healthy, sedentary subjects.

Time-frequency analysis of microvolt T-wave alternans in chronic Chagas heart disease

Chagas disease is an endemic infectious disease caused by theprotozoa Trypanosoma cruzi , currently affecting 10–12 million subjectsintheworld [1],primarilyrestrictedtotheAmericancontinent.Infectionis generally acquired early in childhood, with mild nonspecific clinicalpresentation, evolving into a dormant asymptomatic course, defined asindeterminatephase.Inatimecourserangingfrom10to30 years,20to30% of contaminated subjects develop cardiac abnormalities character-izedbyenlargementofcardiacchambersandlifethreateningventriculararrhythmia, the so called Chagas heart disease (ChD). A remarkablecharacteristic of ChD is the occurrence of severe ventricular tachyar-rhythmia(VT)orevensuddencardiacdeath(SCD)asafirstsignofheartdisease. Thus, the development of a diagnostic and risk stratificationmethodtodetectthosesubjectsatahigherriskismandatory,includingthose who may eventually benefit of an implantable cardioverter-defibrillator [2].Microvolt T-wave alternans (MTWA) is a promising noninvasivediagnostic tool, considered capable of detecting subjects with eitherischemicornon-ischemicheartdiseaseatahigherriskforVTandSCD.The method is based on the spectral decomposition of the T-waveamplitude time series of consecutive heartbeats. The occurrence ofalternans is confirmed when the spectral peak the 0.5 cycle-per-beatfrequencyexceedsa predefinedthreshold[3]. Sinceits initialproposaland standardization on early nineties [4,5], several studies hasdemonstrated its clinical utility for risk stratification. However, ithasnotbeentestedinChD.Thepurposeofcurrentstudyistodescribea method and its application for assessing MTWA in ChD.High resolution ECG signals were acquired using orthogonalbipolar XYZ Frank leads during 3 min, in supine position in quietand comfortable environment. Medical instrumentation employed,signal acquisition protocol and pre-processing techniques have beendescribed elsewhere [6]. The routine of ECG signal processingcomprises the following phases: i) Detection of maximum absoluteQRS complex peaks; ii) Identification and delimitation of successiveT-waves; iii) Detection of maximal absolute T-wave peaks, iv)Deployment of a T-wave peaks time series; and v) Time-frequencyanalysis of the generated time series.The QRS complex detection algorithm was based on Pan and Tomp-kins method [7] associated to correlation analysis on a convenienttemplate, which appropriately selected heart beats. A beat editingfacility allowed parameters change for improving detection accuracyand ectopic beats rejection by visual inspection.T-wave detection algorithm considered in short, the followingsteps: i) The onset and the offset of selected T-wave template wasmanually defined; ii) Considering the rate-adaptation processed asdescribed by Bazett formula, the routine further determined theboundaries of the T-wave for each subsequent beat, as oriented byboth the preceding RR interval and the T-wave template interval [8](Fig. 1-a); iii) The maximum absolute value of the analyzing T-waveinterval identified the T-wave peak (Fig. 1-b); iv) A time series ofconsecutiveT-wavepeakswasthusdeployed,whereT-wavealternanswould be eventually assessed (Fig. 1-c). An eventual T-wave peakarising from an ectopic beat in the series was replaced by the averageof accepted beats to avoid spurious oscillation.The spectral analysis was carried out on 3-min T-wave peaktime series segment using a moving short-time Fourier transformalgorithm. To build a time-frequency map, the analyzing time serieswas segmented in 128 beats windows (Fig. 1-d). Each window wasdetrended,multipliedbyaHanningwindowtoavoiddiscontinuities,and then submitted to spectral decomposition via FFT. Each spectralestimate was, then, squared and appropriately transformed tocompose a power spectral density function time–frequency map(Fig. 1-e), in which the following classical indexes were analyzedat each time slice (Fig. 1-f): i) Cumulative voltage alternans (P)(defined as the squared root of the difference between the peakspectral amplitude at 0.5 cycle per beat and the average spectralnoise), where PN1.9 μV was abnormal; and ii) Alternans ration (K)(defined as the difference of the spectral amplitude peak at 0.5 cycleper beat and the average spectral noise, divided by the standarddeviation of spectral noise), where KN3 were abnormal. In thetime frequency map, the Power spectrum is continuously assessedon 128 beats window during the 3-min segment. If at any moment,either indexes overtakes the corresponding normality threshold,alternans is defined.The study protocol was approved by National Institute ofCardiology Ethics Committee (National institute of cardiology proto-col #0190/12.02.2008).A clinically stable subject with ChD, with left ventricular ejectionfraction of 35%, spontaneous episodes of nonsustained ventriculartachycardiaandanimplantedventricularpacemaker-cardioverterwasinvited to participate and provided written informed consent.Ventricular pacemaker was set to an initial ventricular rate of90 bpm, gradually and continuously increased up to 110 bpm andthen decreased back to 100 bpm.The MTWA presence was detected in the ECG signal at aheart rate of 100 bpm. Lead Y provided the best results, and thevoltage alternans (P) and alternans ratio (K) values were, res-pectively,1.2 µV and 3.4 units. Theanalyzed time series of consecutiveT-wave peaks (128 points) where MTWA was detected had noectopic beats.

Repolarização precoce no eletrocardiograma do atleta: bases iônicas e modelo vetorial

O padrao eletrocardiografico do atleta mimetiza variasalteracoes encontradas em diversas cardiopatias, fazendocom que, em um passado recente, tenham sido cometidascondutas equivocadas, como a pressuposicao da presencade cardiopatia e afastamento de esportistas de suas ativida-des. Esta revisao procura rever os mecanismos pelos quais oexercicio modifica a modulacao autonomica sobre o coracao epropoe explicacoes, baseadas em mecanismos eletrofisiolo-gicos e na teoria vetorial da ativacao cardiaca, para o padraoeletrocardiografico conhecido como repolarizacao precoce.

Nonrespiratory Sinus Arrhythmia

We report here 2 cases of sinus arrhythmia considered to be a form of nonrespiratory sinus arrhythmia because they did not have variances in the RR interval sequence within the oscillations modulated by respiration. Because the patients had pulsus alternans similar that observed in bigeminy, and because they did not have signs or symptoms of heart failure, we believe the arrhythmias represent intrinsic alterations of the electric activity of the sinus node