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Biomedical subjects

F M Leonelli

Publications and source records attributed to F M Leonelli.

17 recordsLinked to original sources
PubMed2000

False positive head-up tilt: hemodynamic and neurohumoral profile.

OBJECTIVES: This study examined differences in mechanisms of head-up tilt (HUT)-induced syncope between normal controls and patients with neurocardiogenic syncope. BACKGROUND: A variable proportion of normal individuals experience syncope during HUT. Differences in the mechanisms of HUT-mediated syncope between this group and patients with neurocardiogenic syncope have not been elucidated. METHODS: A 30-min 80 degrees HUT was performed in eight HUT-negative volunteers (Group I), eight HUT-positive volunteers (Group II) and 15 patients with neurocardiogenic syncope. Heart rate and blood pressure (BP) were monitored continuously. Epinephrine and norepinephrine plasma levels, as well as left ventricular dimensions and contractility determined by echocardiography, were measured at baseline and at regular intervals during the test. RESULTS: The main findings of this study were the following: 1) All parameters were similar at baseline in the three groups; and 2) During tilt: a) the time to syncope was shorter in Group III than in group II (9.5 +/- 3 vs. 17 +/- 3 min p < 0.05); b) there was an immediate, persisting drop in mean BP in Group III; c) the decrease rate of left ventricular end-diastolic dimensions was greater in Group III than in Group II or Group I (-1.76 +/- 0.42 vs. -0.87 +/- 0.35 and -0.67 +/- 0.29 mm/min, respectively, p < 0.05); d) the leftventricular shortening fraction was greater in Group III than in the other two groups (39 +/- 1 vs. 34 +/- 1 and 32 +/- 1%, respectively, p < 0.05); and e) although the norepinephrine level remained comparable among the groups, there was a significantly higher peak epinephrine level in Group III than in Group II and Group I (112.3 +/- 34 vs. 77.6 +/- 10 and 65 +/- 12 pg/ml, p < 0.05). CONCLUSIONS: Mechanisms of syncope during HUT appeared to be different in normal volunteers and patients with neurocardiogenic syncope. In the latter, there was evidence of an impaired vascular resistance response from the beginning of the orthostatic challenge. Furthermore, in the patients there was more rapid peripheral blood pooling, as indicated by the echocardiographic measurements of left ventricular end-diastolic changes, leading to more precocious symptoms. In syncopal patients, the higher level of plasma epinephrine probably mediated the increased cardiac contractility and possibly contributed to the impaired vasoconstrictive response.

Adult↗
PubMed2000

Time-frequency representation of epicardial electrograms during ventricular fibrillation.

In the present study we quantified changes in dominant frequency, which is reciprocal of activation interval or cycle period, during ventricular fibrillation (VF). We used a Smoothed Pseudo Wigner Distribution (SPWD) to estimate time-frequency representations of epicardial electrograms recorded in swines. We used a sock with 64 electrodes spaced equally to record electrograms during 30 seconds of electrically induced VF. Results from 29 trials in three animals showed a mean dominant frequency of 6.64 Hz. We observed considerable variation in dominant frequencies during VF. Temporally, the frequencies varied by as much as +/- 1.24 Hz (2 standard deviations). Spatial variation in frequencies was +/- 1.20 Hz. Cycle periods were computed as the reciprocal of dominant frequencies obtained from the SPWD. These cycle periods were verified to be numerically similar to the cycle periods estimated using activation times detected from differentiated electrograms. Results of recent studies by others have shown that cycle periods during VF are correlated with refractory periods. Our results show that a non-stationary analysis technique such as the SPWD can be used to track spatio-temporal variation in cycle periods. These changes can be used to investigate spatio-temporal variation in cellular properties such as the effective refractory periods during VF. The substantial temporal variation in dominant frequencies that we observed suggest the possibility that the excitable gap at any epicardial location also varies considerably from one instance to another during a VF episode.

Animals↗
PubMed2000

Time averaged spatial distribution of epicardial dominant frequencies during ventricular fibrillation.

Recent evidence suggests that the dominant frequencies during ventricular fibrillation (VF) may be used as indicators of dispersion in repolarization and in activation patterns. In the present study, we quantified dominant frequencies from multiple epicardial electrodes to investigate if there are differences in the averaged frequencies within the electrograms recorded from the left and the right ventricles. Further, we quantified whether the difference in average frequency between the two ventricles changed during 30 seconds of VF. Results from eighteen trials in two pigs showed that during the entire duration of VF the average dominant frequencies of all electrodes over the left ventricle were higher than those over the right ventricle (p < 0.005). The dominant frequencies are reciprocal of cycle periods or activation intervals during VF. Our results show that on average, activations in the left ventricle occurred at a faster rate than those in the right ventricle. Activation intervals at any site are determined by the refractory period at that site and the arrival time of next activation. Although differences in cellular properties may have contributed to the observed differences in activation intervals between the ventricles, it is possible that activation arrival times may be different as well. It is possible that the increased tissue mass of the left ventricle may increase the probability that any site will get excited at a faster rate after it is recovered from previous activation.

Animals↗
PubMed1999

Energy steering of biphasic waveforms using a transvenous three electrode system.

The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two pathway configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV-->C) or a three (RV-->SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV-->C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV-->SVC + C). Configuration 3 (W3): The RV-->C was used for the first 25% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 4 (W4): The RV-->C was used for the first 50% of f+ and RV-->SVC + C for the remainder of the discharge including f 2 Configuration 5 (W5): The RV-->C was used for the first 75% of f+ and RV-->SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV-->C was used for f+ and RV-->SVC + C for f 2. As an increasing fraction of the waveform was discharged using the RV-->SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV-->SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV-->SVC + C required the lowest stored energy to defibrillate. This method of energy steering could be used to optimize current delivery in a three electrodes system.

Animals↗
PubMed1999

Epicardial mapping and radiofrequency catheter ablation of ischemic ventricular tachycardia using a three-dimensional nonfluoroscopic mapping system.

Endocardial radiofrequency catheter ablation of ischemic left ventricular tachycardia has been of variable success due to multiple factors. Two such factors include the location of the reentrant circuit in the deep myocardium or on the epicardial surface and the inherent limitations of fluoroscopy as a guide for target localization. We report a patient in whom successful epicardial mapping and radiofrequency catheter ablation of an ischemic left ventricular tachycardia was performed using pericardial access and the CARTO electroanatomic mapping system.

Aged↗
PubMed1999

Human histopathologic findings following radiofrequency ablation of the tricuspid-inferior vena cava isthmus.

Radiofrequency (RF) ablation of the tricuspid valve-inferior vena cava isthmus is now the first line of treatment in the management of typical atrial flutter. Successful ablation is associated with conduction block in this region, although the histopathologic changes following this procedure have never been reported. We describe the pathologic changes following RF ablation of this region in an explanted heart of a patient undergoing heart transplantation 4 months after successful atrial flutter ablation. The findings confirm the ability of RF ablation to create in the isthmus a chronic full thickness fibrosis, which represents the histopathologic counterpart of the conduction block demonstrated at the end of procedure.

Atrial Flutter↗
PubMed1998

Selective interference with pacemaker activity by electrical dental devices.

OBJECTIVE: We sought to determine whether electromagnetic interference with cardiac pacemakers occurs during the operation of contemporary electrical dental equipment. STUDY DESIGN: Fourteen electrical dental devices were tested in vitro for their ability to interfere with the function of two Medtronics cardiac pacemakers (one a dual-chamber, bipolar Thera 7942 pacemaker, the other a single-chamber, unipolar Minix 8340 pacemaker). Atrial and ventricular pacemaker output and electrocardiographic activity were monitored by means of telemetry with the use of a Medtronics 9760/90 programmer. RESULTS: Atrial and ventricular pacing were inhibited by electromagnetic interference produced by the electrosurgical unit up to a distance of 10 cm, by the ultrasonic bath cleaner up to 30 cm, and by the magnetorestrictive ultrasonic scalers up to 37.5 cm. In contrast, operation of the amalgamator, electric pulp tester, composite curing light, dental handpieces, electric toothbrush, microwave oven, dental chair and light, ENAC ultrasonic instrument, radiography unit, and sonic scaler did not alter pacing rate or rhythm. CONCLUSIONS: These results suggest that certain electrosurgical and ultrasonic instruments may produce deleterious effects in medically fragile patients with cardiac pacemakers.

Arrhythmias, Cardiac↗
PubMed1998

The effects of endocardial defibrillation on left ventricular function: a transoesophageal echocardiographic study.

This study evaluates the immediate effects of the endocardial electrical shocks delivered by a transvenous defibrillation system on left ventricular (LV) function in a pig model. A triple-lead system consisting of two endocardial electrodes, in the right ventricular apex and the junction of superior cava-right atrium, and a custom-made defibrillation can implanted subcutaneously in the thorax was set up in 10 close-chest pigs. Transesophageal echocardiography with two dimensional image, m-Mode, and pulse Doppler was performed at baseline and after several episodes of fibrillation/defibrillation (F/DF). Each animal underwent an average of 8 (range 6 to 11) episodes of ventricle F/DF for a total of 210 (range 165 to 290) joules of biphasic-waveform defibrillation shocks. Heart rate, blood pressure, LV end-systolic area, end-diastolic area and fractional area contraction, isovolumic relaxation time, and both ratios of velocities and time-velocity integrals in transmitral Doppler flow E and A waves were unchanged after the shocks. This animal study suggests that multiple countershocks up to 210 joules delivered by a transvenous defibrillation system do not cause LV global systolic and/or diastolic dysfunction.

Animals↗
PubMed1997

Systolic and diastolic effects of variable atrioventricular delay in patients with complete heart block and normal ventricular function.

This study was designed to demonstrate the effects of varying the atrioventricular delay (AVD) on ventricular diastolic filling dynamics and the resultant stroke volume in patients with complete heart block and normal cardiac function. We studied 7 patients with normal cardiac function in whom a dual chamber pacemaker had been implanted because of complete heart block. Doppler and M-mode echocardiography was performed at 70, 100, 140, 180, and 220 ms, AVD with the device in DDD mode at a rate of 80 beats/min. The effects of these variable intervals on the contribution of the E and A waveform to the diastolic filling, on the stroke volume, and on the systolic intervals were evaluated. Optimization of this interval, with a 19% increase in stroke volume was achieved in the group of patients at an AVD of 140 ms. When considered individually, the AVD associated with the largest stroke volume, was 100 ms in 2 patients and 140 ms in the remaining 5. At this individual optimal AVD the ventricular septal contraction occurred 31 +/- 14 ms, before the end of the transmitral flow. The optimal AVD is, therefore, the one which synchronizes the ventricular and atrial systole so that the first ventricular septal contraction occurs after the peak of the A wave, just before the end of the transmitral flow. Because of the different functional cardiovascular status of the single patient, this parameter should be individualized; this can be clinically important as it may lead, in this patient population, to an improvement of the stroke volume up to 42%.

Adult↗
PubMed1997

The vanishing defibrillator syndrome: incidence, mechanism, and clinical relevance.

Intraperitoneal migration of an abdominally implanted cardioverter defibrillator is a complication not yet fully described. In a consecutive series of 195 patients, migration occurred between 1 and 20 months in 5 (8%) of the 63 patients in whom a subrectus abdomini placement of the generator was chosen. It was unrelated to the patients' clinical characteristics or the defibrillator model. Dysuria and inability to interrogate the device were present in every subject, and the diagnosis was confirmed by the characteristic abdominal x-ray appearance and the findings at the time of surgery. Adhesions involving the omentum, and in one case, the small bowels, were present in three patients and seem to be related to the length of intraabdominal permanence of the generator. Because this complication may be due to specific anatomical characteristics of the aponeurosis of the abdominal muscles, it is likely that its incidence will be unchanged by the use of smaller devices. A close follow-up of the generators implanted deep to the rectus fascia is therefore advisable.

Abdomen↗
PubMed1996

Natural history, determinants, and clinical relevance of conduction abnormalities following orthotopic heart transplantation.

To study the long-term evolution, determinants, and clinical relevance of the conduction abnormalities after orthotopic heart transplantation, 87 patients, followed for a mean of 105 +/- 72 weeks, were divided into 3 groups according to the characteristics of their electrocardiograms compared with their initial electrocardiogram recorded at study entry. The first group consisted of 24 patients whose initial electrocardiogram was normal, and subsequent electrocardiograms remained normal throughout the study. The second group included 27 patients who developed electrocardiographic evidence of progressive conduction system damage. The third group comprised 36 patients whose initial electrocardiogram was abnormal and subsequent electrocardiograms remained unchanged during follow-up. Although the hemodynamic and echocardiographic evaluation of right and left ventricular function were initially similar among the 3 groups, groups 2 and 3 demonstrated a significant deterioration of left ventricular ejection fraction (62 +/- 12% to 55 +/- 16% and 62 +/- 8% to 57 +/- 14%, respectively; p < 0.05) and cardiac index (2.7 +/- 0.6 to 2.3 +/- 0.5 and 3.0 +/- 0.9 to 2.5 +/- 0.9 L/min/m2, respectively; p < 0.05) while patients in group 1 maintained their normal baseline indices. Incidence and progression of coronary artery disease, as well as frequency of rejection episodes, were comparable among the groups. Mortality was higher in the 2 groups with evidence of conduction defects. Sudden death associated with complete heart block (2 patients) or ventricular arrhythmias (3 patients) was exclusively confined to patients with evidence of progressive electrocardiogram abnormalities. We conclude that, following orthotopic heart transplantation, stable or progressive conduction system damage on the electrocardiogram is associated with left ventricular dysfunction and increased mortality. Sudden death is not uncommon among patients demonstrating worsening cardiac conduction and, in some cases, is related to the development of potentially preventable complete heart block.

Adult↗
PubMed1995

A long thin electrode is equivalent to a short thick electrode for defibrillation in the right ventricle.

We hypothesized that a long thin right ventricular (RV) electrode would have equivalent defibrillation threshold (DFT) performance to a short thick electrode with approximately the same surface area. This could lead to thinner transvenous lead systems, which would be easier to implant. A thin (5.1 French) lead was compared to a standard control (10.7 French). The thin lead had an 8-cm RV electrode length with a surface area of 4.26 cm2. The standard lead had a RV electrode length of 3.7 cm and a surface area of 4.12 cm2. A 140-mu French capacitor 65%/65% tilt biphasic defibrillation shock was delivered between the RV electrode and a 14-cm2 subcutaneous patch. DFTs were determined following 10 seconds of fibrillation in 11 dogs by a triple determination averaging technique. The thin lead had a lower resistance (77.1 +/- 27.4 omega vs 88.9 +/- 30.3 omega, P < 0.001) than did the thick lead. There was no significant difference in stored energy DFTs (9.9 +/- 2.5 vs 10.3 +/- 2.7, P = 0.098 2-sided, P = 0.049 1- sided). This was in spite of the fact that the long thin lead had a portion of its RV coil extending above the tricuspid valve and, thus, not contributing efficiently to the ventricular gradients in the small dog heart. We conclude that a long thin right ventricular electrode and a standard short thick electrode had equivalent defibrillation performance. This preliminary result should be confirmed in clinical studies as it could lead to significantly thinner transvenous lead systems.

Animals↗
PubMed1995

Woven wire patches are superior to solid disks for subcutaneous electrodes: implications for active can defibrillation.

The housing of the implantable cardioverter defibrillator (ICD) is being considered for a remote electrode to replace the conventional subcutaneous woven wire patch. It is not clear that the solid smooth and rigid metal surface of the ICD housing will provide the same performance as does the woven wire patch. We compared a solid titanium disk to a titanium woven wire patch for defibrillation performance in a canine model. The patch had a smaller outline area, a slightly smaller conductive perimeter, and slightly less of a small feature surface area than did the disk. The remote electrode (disk or patch) was inserted at the point of maximal apical cardiac impulse. A commercially available endocardial electrode was placed in the right ventricle (RV). Conventional biphasic shocks (140-microFrench capacitor and 65% tilt) were delivered between the RV and subcutaneous electrode. The patch had significantly lower resistances than did the disk (81.6 +/- 8.0 omega vs 90.0 +/- 11.6 omega P < 0.006). The patch also had significantly lower stored energy defibrillation thresholds than did the disk (8.0 +/- 2.6 J vs 9.3 +/- 3.3 J, P < 0.007). In spite of smaller values for every geometrical dimension, the woven wire patch out performed the solid disk for defibrillation with conventional biphasic waveforms. Since the ICD housing is typically smooth titanium, the use of waveforms better suited for the active can configuration may deserve a systematic evaluation.

Animals↗
PubMed1995

Defibrillation thresholds are lower with smaller storage capacitors.

Present implantable cardioverter defibrillators use a wide range of capacitance values for the storage capacitor. However, the optimal capacitance value is unknown. We hypothesized that a smaller capacitor, by delivering its charge in a time closer to the heart chronaxie, should lower the defibrillation threshold (DFT). We compared the energy required to defibrillate 10 open-chest dogs, after 15 seconds of ventricular fibrillation, with a monophasic, time-truncated waveform delivered from either a 85-microF or a 140-microF capacitor. Shocks were delivered through a pair of 14-cm2 epicardial patch electrodes: The two capacitors were randomly tested twice with each dog using a modified 3-reversal method for each DFT determination. The average stored and delivered DFT energies for the 85-microF capacitor were 6.0 +/- 1.7 joules and 5.2 +/- 1.5 joules, respectively, compared to 6.7 +/- 1.7 joules and 6.0 +/- 1.5 joules for the 140-microF capacitor (P = 0.01 and P = 0.004, respectively). The mean leading edge voltages were higher, the pulse duration shorter, and the mean impedance lower for the 85-microF capacitor. The impedance was inversely related to the pulse duration and the voltage decay suggesting that, at least in part, the mechanism of improved defibrillation could be accounted for by the waveform electrical characteristics. There was an equal number of episodes of postshock bradyarrhythmias and tachyarrhythmias following discharges from each capacitor. Moreover, there was no relationship between the likelihood of these arrhythmias and either the initial voltage or the delivered current nor there was a higher number of episodes of postshock hypotension following the smaller capacitor discharges.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Frequency and significance of conduction defects early after orthotopic heart transplantation.

To define the clinical significance of conduction defects after orthotopic heart transplantation sequential electrocardiograms (ECG) of 124 patients were analyzed during their postoperative hospital stay. The first ECG was abnormal in 90 patients (73%), with a predominance of right bundle branch block, and normal in 34 (27%). Sex, age, mean donor ischemic time, duration of aortic cross clamping and use of previous antiarrhythmic therapy were not significantly different in the 2 groups. During hospital follow-up, patients were grouped according to evolution of the initial electrocardiographic abnormalities. In group 1, 25 patients continued to have an initially normal ECG. In groups 2 and 3, 30 and 48 patients, respectively, had evidence of transient and permanent conduction defects. The 21 patients in group 4 showed progressive deterioration of conduction with either a new (9 patients) or worsening preexisting conduction defect (12 patients). The evolution of the initial ECG was strongly dependent on the duration of the donor heart ischemic time and the severity of the in-hospital cardiac rejection. Patients with persistent conduction abnormalities had a statistically longer ischemic time than either patients with normal or transient conduction defects (182 +/- 84 vs 144 +/- 68 and 130 +/- 66 minutes, p = 0.04). Although the overall percentage of patients with histologic evidence of moderate to severe rejection was similar across the groups, 66.6 and 46.1% of patients in groups 3 and 4, respectively, had multiple episodes of rejection compared with 16.6 and 0% in the remaining 2 groups (p = 0.044).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Plasma levels of the lyso-derivative of platelet-activating factor in acute severe systemic illness.

1. Evidence suggests that activation of phospholipase A2 and production of eicosanoids and platelet-activating factor (PAF) are involved in various responses associated with severe tissue damage and shock. It was postulated that the plasma level of the precursor and degradation product of PAF, lyso-platelet-activating factor (lyso-PAF), might be increased in acute severe illness. 2. After plasma extraction, lyso-PAF was acetylated in vitro to PAF, which was measured by bioassay using 5-[14C]hydroxytryptamine-labelled rabbit platelets. Measurements were made in 18 severely ill patients (five with cardiogenic shock; five with severe infection, five after repair of abdominal aortic aneurysm, two with acute pancreatitis; 13 males, five females). Plasma lyso-PAF in these patients was 33 +/- 15 (SD)ng/ml (range 5-111 ng/ml), whereas values in normal males (40-65 years) ranged from 102 to 253 ng/ml (n = 15) and in females from 74 to 174 ng/ml (n = 10). Depression of plasma lyso-PAF did not relate closely to the patient group nor to specific therapy, but repeated measurements in each of 10 patients showed an increase in plasma lyso-PAF (P less than 0.002), associated with clinical improvement. 3. Evidence was obtained indicating that neither the presence of an inhibitor in the assay system nor reconversion of PAF to lyso-PAF in vitro produced the unexpected depression of plasma lyso-PAF. 4. The mechanisms responsible, which may have therapeutic implications, remain to be elucidated.

Acute Disease↗