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Biomedical subjects

F Ammirati

Publications and source records attributed to F Ammirati.

30 records · Page 2Linked to original sources
PubMed1997

Local capture by atrial pacing in spontaneous chronic atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is considered to be maintained by multiple reentrant circuits without or with a very short excitable gap. However, the possibility of local atrial capture has been shown recently in experimental AF or induced AF in humans. METHODS AND RESULTS: This study was undertaken to evaluate the feasibility of atrial capture-suggestive of an excitable gap-in spontaneous chronic AF. Decremental pacing was performed in 47 right atrial sites in 14 patients with chronic AF, not taking antiarrhythmic drugs. A Franz catheter (for pacing and monophasic action potential recording) and a recording quadripolar catheter positioned about 10 mm apart were used. Local capture was achieved in 41 (87.2%) sites for a total of 100 captures. In 71 episodes the capture was lost within 15 seconds, while in the remaining 29, pacing was stopped after 15 seconds of stable capture. AF types immediately before capture were type 1 in 83 and type 2 in 17 episodes. Type 3 AF was never captured. Pacing cycle at capture was 175.7 +/- 20.9 ms. The baseline atrial interval (FF) was 185.4 +/- 24.5, significantly longer than the FF recorded during pacing immediately before capture (176.0 +/- 19.8 ms) (P < .02). CONCLUSIONS: During spontaneous chronic AF in humans, (1) local capture by atrial pacing is possible up to at least 15 mm from the pacing site, (2) regional entrainment is possible during type 1 and type 2 AF but not type 3 AF, and (3) pacing before capture accelerates AF, probably by transient or local capture. These findings suggest that an excitable gap is present in chronic AF, therefore supporting the hypothesis that leading circle reentry is not the unique electrophysiological mechanism maintaining the arrhythmia.

Aged↗
PubMed1997

Influence of digital and analogue cellular telephones on implanted pacemakers.

UNLABELLED: The aim of this study was to find out whether digital and analogue cellular 'phones affect patients with pacemakers. The study comprised continuous ECG monitoring of 200 pacemaker patients. During the monitoring certain conditions caused by interference created by the telephone were looked for: temporary or prolonged pacemaker inhibition; a shift to asynchronous mode caused by electromagnetic interference; an increase in ventricular pacing in dual chamber pacemakers, up to the programmed upper rate. The Global System for Mobile Communications system interfered with pacing 97 times in 43 patients (21.5%). During tests on Total Access of Communication System telephones, there were 60 cases of pacing interference in 35 patients (17.5%). There were 131 interference episodes during ringing vs 26 during the on/off phase; (P < 0.0001); 106 at maximum sensitivity level vs 51 at the 'base' value; P < 0.0001). Prolonged pacing inhibition (> 4 s) was seen at the pacemaker 'base' sensing value in six patients using the Global system but in only one patient using Total Access. CONCLUSION: Cellular 'phones may be dangerous for pacemaker patients. However, they can be used safely if patients do not carry the 'phone close to the pacemaker, which is the only place where high risk interference has been observed.

Adult↗
PubMed1996

Ventricular arrhythmias and athlete's heart. Role of signal-averaged electrocardiography.

The aim of this study was to assess the prevalence and the prognostic value of ventricular late potentials in apparently healthy top-level athletes with ventricular arrhythmias, and the effect of physiological myocardial hypertrophy (athlete's heart) on the electrogenesis of the signal-averaged electrocardiogram (ECG). Two groups of asymptomatic athletes without underlying heart disease were studied: group A consisted of 35 athletes without arrhythmias and group B of 25 athletes with frequent and complex ventricular arrhythmias (ventricular ectopic beats > 5000.24 h-1 and ventricular couplets > 15.24 h-1). Late potentials were present if athletes had significantly prolonged filtered QRS and low amplitude signal duration and low root mean square voltages at both 25-250 Hz and 40-250 Hz filters. While late potentials were absent in all normal athletes of group A, they were present in seven of 25 (28%) athletes with arrhythmias of group B (P < 0.003). Ten of 25 athletes (five with and five without late potentials) of group B underwent programmed ventricular stimulation using a protocol comprising up to three extrastimuli. No episode of sustained ventricular tachycardia was induced. In four of five athletes with late potentials and in one of five without them, unsustained ventricular responses were induced. Echocardiographically determined left ventricular mass found in both groups of athletes did not influence the pathological result of the signal-averaged ECG parameters. This study shows the applicability of the signal-averaged ECG in identifying ventricular late potentials in a selected population of top-level athletes with frequent and complex ventricular arrhythmias and without overt heart disease; it also shows that the presence of late potentials is not influenced by left ventricular mass, even if extreme ( > 350 g), and it is correlated to a non-sustained ventricular response during an electrophysiological study.

Action Potentials↗
PubMed1995

Transthoracic DC shock may represent a serious hazard in pacemaker dependent patients.

External defibrillation is widely used for the termination of various atrial and ventricular tachyarrhythmias, including pacemaker patients. Our study was intended to evaluate the effects of DC shocks in 36 patients with unipolar pacemakers implanted in the right pectoral region (25 DDD, 10 VVI, 3 AAI). The shocks were delivered with paddles on the anterior surface of the thorax, as far as possible away from the pacemaker. The pacing output was programmed at 0.5 msec and 5 V (25 patients), 4 V (1 patient), and 2.5 V (10 patients). Transient loss of capture occurred in 18 patients (50%). These patients, compared with those without capture failure, received higher peak and cumulative shock energies, respectively, 216 +/- 99 versus 123 +/- 50 joules (P < 0.002) and 352 +/- 62 versus 147 +/- 98 joules (P < 0.004) and had a lower pacemaker pulse amplitude (4.0 +/- 1.2 vs 4.6 +/- 1.0 V, P = 0.11). Failure to capture lasted from 5 seconds to 30 minutes (mean 157 sec). In 15 patients the ventricular stimulation threshold was measured before and serially after cardioversion. A six-fold threshold increase was observed 3 minutes after the shock (P < 0.004) with gradual recovery to nearly baseline values at 24 hours. Transient sensing failure occurred in 7 of the 17 patients in whom it could be evaluated (41%). Furthermore, three cases of shock induced pacemaker malfunctions were observed requiring replacement of the stimulator in two patients. In conclusion, the incidence of loss of capture in pacemaker patients subjected to electrical cardioversion/defibrillation is high.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Do European GSM mobile cellular phones pose a potential risk to pacemaker patients?

A series of in vivo trials were carried out in order to verify whether the electromagnetic field radiated by GSM (Groupe Systemes Mobiles) mobile cellular phones might affect implanted pacemakers. Two European GSM phones of 2-watt power were tested and trials conducted on 101 pacemaker implanted outpatients attending day hospital for routine check-up, who volunteered for trials. Forty-three pacemaker models from 11 manufacturers were tested in all. When the sensing threshold of the pacemakers was set at a minimum and the antenna of the phone was in direct contact with the patient's chest, interference was detected for 26 implanted pacemakers. Specifically, pulse inhibition in 10 of 101 cases, ventricular triggering in 9 of 46 DDD-VDD pacemakers, and asynchronous pacing in 4 of 52 devices. Pulse inhibition was also observed combined with asynchronous pacing in 1 of 52 cases and with ventricular triggering in 2 of 46 cases. Minimum effect duration was ca. 3 seconds but in 6 cases effects continued as long as the interfering GSM signal was on. No permanent malfunctioning or changes in the programmed parameters were detected. Whenever interference was detected, trials were repeated to determine the maximum sensing threshold at which interference persisted (with the antenna in contact with the skin over the pacemaker). Then maximum distance between antenna and pacemaker at which interference occurred was determined at pacemaker maximum and minimum sensing threshold. Under our experimental conditions electromagnetic interference effects were detected at a maximum distance of 10 cm with the pacemaker programmed at its minimum sensing threshold.(ABSTRACT TRUNCATED AT 250 WORDS)

Electricity↗
PubMed1993

Usefulness of transesophageal pacing during exercise for evaluating palpitations in top-level athletes.

The aim of this study was to verify the use of transesophageal atrial pacing in reproducing tachyarrhythmias in 22 top-level athletes symptomatic for palpitations, with no evidence of arrhythmias or cardiac anomalies by the standard noninvasive diagnostic techniques. The transesophageal stimulation protocol was divided in 2 sections: at rest and during exercise on the bicycle ergometer in the upright position. Although transesophageal pacing at rest did not induce any arrhythmias in 18 of 22 athletes, during exercise it induced tachyarrhythmias. This occurred in all 16 athletes who had palpitations during physical activity. Electrophysiologic characteristics of induced atrial tachyarrhythmia suggested reentry within the atrioventricular node in 9 of 18 athletes: atrial fibrillation in 5, atrial flutter in 2, orthodromic reciprocating tachycardia due to concealed anomalous pathway in 1, and automatic atrial tachycardia in 1. This study stresses the clinical importance of palpitations during physical exercise and shows that transesophageal pacing performed during exercise is an important diagnostic tool in reproducing the previously described symptoms and in detecting the underlying tachyarrhythmias.

Adolescent↗
PubMedDate not supplied

Electrophysiological characteristics of the human atria after cardioversion of persistent atrial fibrillation.

BACKGROUND: In animal models, induced atrial fibrillation shortens the atrial effective refractory period (ERP) and reverses its physiological adaptation to rate. It is not clear whether this process, known as "electrical remodeling," occurs in humans. METHODS AND RESULTS: We determined the ERPs, at 5 pacing cycle lengths (300 to 700 ms) and in 5 right atrial sites, after internal cardioversion of chronic atrial fibrillation in 25 patients (14 in pharmacological washout and 11 on amiodarone). The ERPs were 195.5+/-18.8 ms in the washout and 206.3+/-17.9 ms in the amiodarone patients (P<0.0001). ERPs were closely correlated with the stimulation rates (r=0.95 in the washout and r=0.94 in the amiodarone group), and slope values indicating a normal (>/=0.07) or nearly normal (0.05 to 0.06) adaptation of ERP to rate were found in 77% of the 84 paced sites. The mean ERP was shorter in the lateral wall (198.1+/-17.9 ms) than in the atrial roof (203.3+/-21.5 ms) and in the septum (210.5+/-20.0 ms) (P<0.03). After 4 weeks of sinus rhythm, the mean ERP, determined again in 8 patients (4 in wash-out and 4 on amiodarone), was significantly increased compared with the basal study (221. 4+/-21.4 versus 197.8+/-18.3 ms, P<0.0001). CONCLUSIONS: After cardioversion of chronic atrial fibrillation, (1) atrial ERP adaptation to rate was normal or nearly normal in the majority of the cases, (2) a significant dispersion of refractoriness between different right atrial sites was present, and (3) ERPs were significantly increased after 4 weeks of sinus rhythm in both washout and amiodarone patients.

Adaptation, Physiological↗