[The spectral analysis of heart rate variability. The methodological aspects]. / Análisis espectral de la variabilidad de la frecuencia cardíaca. Aspectos metodológicos.

OBJECTIVES: A study is made of the influence of methodology on the analysis of cardiac cycle variability in terms of frequency and time domains. METHODS: Twenty-five individuals were divided into three groups: 1) non-smokers (n = 10); 2) smokers (n = 8); and 3) non-smokers without guided respiratory frequency (n = 7). An analysis was made of RR variability during 5 min intervals in time domain (standard deviation, variation coefficient, and difference between maximum and minimum RR), and frequency domain (spectral analysis, Fast Fourier Transform algorithm using 5 types of data windows). RESULTS: On comparing the results obtained in the 25 individuals with the 5 data windows, significant differences were observed (ANOVA; p < 0.001) in maximum and total amplitudes of the spectrum (in absolute terms) in the low frequency band (0.04-0.15 Hz). No significant differences were found between the normalized values or between the low/high (0.15-0.40 Hz) frequency ratio: W1 = 1.63 +/- 0.30; W2 = 1.62 +/- 0.29; W3 = 1.65 +/- 0.31; W4 = 1.52 +/- 0.26, and W5 = 1.55 +/- 0.27 (X +/- SE). On averaging the RR intervals each 5 cycles, significant differences were encountered for great part of the parameters studied. No significant differences were encountered for great part of the parameters studied. No significant differences were noted between the non-smokers as regards the use or non-use of a metronome (low/high frequency ratio in group 1 = 1.85 +/- 0.39 vs group 3 = 1.78 +/- 0.43; NS). The linear regressions between the variability parameters in terms of time and frequency domains (absolute values), and age (group 1) were significant, with greater regression coefficients on using the linear transformation of an exponential model. On comparing groups 1 and 2, a non statistically significant trend towards smaller maximum and total amplitudes (absolute values) was noted in group 2 for both frequency bands. CONCLUSIONS: 1) The type of data window (Fourier analysis) introduces significant modifications of some parameters expressed in absolute values, but not between normalized values; 2) signal averaging greatly modifies the information obtained; 3) the decrease in variability parameters observed with age fits better to an exponential model; 4) no differences were detected on guiding or not respiratory frequency, and 5) smoking appears to induce a tendency towards reducing cardiac cycle variability.

P and R wave detection in complete congenital atrioventricular block.

Complete atrioventricular block (type III AVB) is characterized by an absence of P wave transmission to ventricles. This implies that QRS complexes are generated in an autonomous way and are not coordinated with P waves. This work introduces a new algorithm for the detection of P waves for this type of pathology using noninvasive electrocardiographic surface leads. The proposed algorithm is divided into three stages. In the first stage, the R waves located by a QRS detector are used to generate the RR series and time references for the other stages of the algorithm. In the second stage, the ventricular activity (QT segment) is removed by using an adaptive filter that obtains an averaged pattern of the QT segment. In the third stage, a new P wave detector is applied to the residual signal obtained after QT cancellation in order to detect P wave locations and get the PP time series. Eight Holter records from patients with congenital type III AVB were used to verify the proposed algorithm. Although further improvements should be made to improve the algorithm's performance, the results obtained show high average values of sensitivity (90.52%) and positive prediction (90.98%).

Thoracic epidural analgesia in coronary artery bypass graft surgery: seven years' experience.

OBJECTIVE: To evaluate the risk of neurologic complications caused by an epidural hematoma in a series of patients who had coronary artery bypass graft surgery with cardiopulmonary bypass under combined general and thoracic epidural anesthesia (TEA). DESIGN: Prospective observational study. SETTING: General hospital associated with a university. PARTICIPANTS: Seven hundred fourteen patients who had coronary artery bypass grafting surgery over a 7-year period. INTERVENTIONS: An epidural catheter was inserted at T(1)-T(3) as soon as the patient was in the operating room and local anesthetic was administered as a bolus and then as a continuous infusion throughout the operation and postoperatively. A set of safety guidelines was routinely followed. A protocol for postoperative neurologic evaluation was used to rule out any signs of spinal compression. MEASUREMENTS AND MAIN RESULTS: Preoperatively, a battery of coagulation tests was systematically performed including APTT, platelet count, and prothrombin time. Antiplatelet drugs (aspirin) were stopped at least 7 days before surgery. No patient required parenteral opiates postoperatively. Seventy-five percent of the patients were extubated in the operating room. No clinical epidural hematomas were detected. CONCLUSION: In this study, some of the benefits previously reported during cardiac surgery under TEA, such as excellent analgesia and early extubation, were confirmed. In addition, the series adds further evidence that adherence to a set of standard safety measures, in this setting, averts the occurrence of symptomatic epidural hematomas.

Bilateral paravertebral blockade for conventional cardiac surgery.

This prospective observational study aimed to assess the feasibility and efficacy of bilateral continuous paravertebral blockade combined with general anaesthesia in "on-pump" cardiac surgery. One hundred and eleven elective patients had two paravertebral catheters inserted: one either side of the midline within 2.5 cm of the spinous process of the third or fourth thoracic vertebrae, through which a mixture of ropivacaine and fentanyl was infused during and after surgery. In the first 47 patients, haemodynamic and analgesia data were recorded. In all patients, time to tracheal extubation, length of stay in the intensive care unit and the hospital, morbidity and mortality, and any complication attributable to the regional blockade were recorded. The technique was associated with good haemodynamic stability, good postoperative analgesia and short times to tracheal extubation, with few significant complications.

Modifications in the evolution of the dominant frequency in ventricular fibrillation induced by amiodarone, diltiazem, and flecainide. An experimental study.

In 22 anesthetized mongrel dogs, spectral methods were used to analyze the surface electrocardiogram (ECG) for the time course of the dominant frequency in ventricular fibrillation and its modifications under the influence of amiodarone, diltiazem, and flecainide. The ECG was recorded over 5 minutes after triggering ventricular fibrillation. Following A/D conversion and by applying the Fourier fast transform, the frequency spectrum of the signals was obtained. In group 1 (5 dogs), the ECGs were obtained without prior drug administration; group 2 (5 dogs) first received amiodarone, 5 mg/kg; group 3 (7 dogs) received diltiazem, 0.2 mg/kg; and group 4 (5 dogs) received flecainide, 2 mg/kg. All drugs were administered intravenously. An initial increase in the dominant frequency of ventricular fibrillation was found in the control group and also in the groups that received amiodarone, diltiazem, or flecainide. Diltiazem significantly increased the dominant frequency and diminished the arrhythmia-slowing process. Amiodarone and flecainide tended to diminish the dominant frequency.