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Biomedical subjects

A Michelucci

Publications and source records attributed to A Michelucci.

At least 19 recordsLinked to original sources
PubMed1995

Wavelength index at three atrial sites in patients with paroxysmal atrial fibrillation.

The purpose of this study was to evaluate the wavelength index (WLI) at three atrial sites in a group of 23 patients with recurrent episodes of lone paroxysmal atrial fibrillation (LPAF) and a control group (n = 20). All patients underwent programmed atrial stimulation (paced cycle length = 600 ms) at high, medium, and low lateral right atrial wall. P wave duration, sinus cycle length, and corrected sinus node recovery time were not significantly different between the two study groups. WLI was calculated according to the following formulas: atrial effective refractory period (AERP)/duration of atrial extrastimulus electrogram (A2) or AERP/A2 + atrial latency; and atrial functional refractory period (AFRP)/A2. WLI was significantly shorter in LPAF than in the control group at each of the paced atrial sites independently of the formula used. Duration of premature atrial electrogram appeared to play the major role in determining the difference in WLI between patients with paroxysmal atrial fibrillation and the control group.

Atrial Fibrillation↗
PubMed1994

Plasma levels of natriuretic peptides during ventricular pacing in patients with a dual chamber pacemaker.

The mechanism(s) responsible for the release of brain natriuretic peptide (BNP), a cardiac hormone of ventricular origin, are still not completely understood. We measured plasma atrial natriuretic peptide (ANP) and BNP in 15 subjects (10 men, mean age 67 +/- 3 years) with a dual chamber pacemaker and unimpaired heart function during ventricular pacing, which is known to induce an increase in atrial pressure and plasma ANP concentration. Under ECG monitoring, all subjects received sequential atrioventricular pacing for 30 minutes and ventricular pacing for 30 minutes, at the same rate of 80 beats/min. Arterial pressure and plasma BNP and ANP levels were measured every 10 minutes throughout the study. Ventricular pacing led to atrioventricular dissociation in eight subjects and to retrograde ventriculo-atrial conduction in seven. Arterial pressure remained unchanged in all subjects. In the group with atrioventricular dissociation, plasma ANP increased from 10.14 +/- 0.58 to 16.72 +/- 0.92 fmol/mL at the 60th minute (P < 0.0001), whereas plasma BNP did not change at all (from 1.26 +/- 0.07 to 1.16 +/- 0.09 fmol/mL). In the group with retrograde conduction, plasma ANP concentration doubled (from 10.95 +/- 1.66 to 21.40 +/- 1.51 fmol/mL, P < 0.0001), BNP increased 1.5-fold (from 1.16 +/- 0.06 to 1.64 +/- 0.14 fmol/mL, P < 0.001), and the ANP:BNP ratio augmented from 10:1 to 13.4:1. These results indicate that the release of ANP and BNP is regulated by different mechanisms, supporting the view that there is a dual natriuretic peptide system, comprising ANP from the atria and BNP from the ventricles.

Aged↗
PubMed1992

[Arrhythmogenicity in left ventricular hypertrophy in mild to moderate arterial hypertension].

BACKGROUND: Several studies have evidenced that hypertensive patients (pts) with left ventricular hypertrophy (LVH) have an increased incidence of malignant ventricular arrhythmias and sudden death. The purpose of our study was to investigate the prevalence of risky ventricular arrhythmias in uncomplicated hypertensive pts (untreated during last 10 days) in comparison with normotensive ones. In this context, not only the value of left ventricular mass index (LVMI) was taken into account, but also the type of LVH and the related functional behaviour. PATIENTS AND METHODS: 59 untreated mild to moderate essential hypertensives (EH), without symptoms or signs of coronary artery disease, were classified in 3 groups: normal (i.e. without hypertrophy) EH (NEH: 12 pts, 6 M and 6 F, mean age +/- SD 52 +/- 10 yrs), concentric hypertrophic EH (CEH: 30 pts, 15 M and 15 F, mean age +/- SD 59 +/- 10 yrs), and eccentric hypertrophic EH (EEH: 17 pts, 7 M and 10F, mean age +/- SD 60 +/- 10 yrs), according to echocardiographic measurements. Values and duration of arterial hypertension were comparable among the groups. A normotensive, age-matched group was studied as control (C: 21 pts, 11 M and 10 F, mean age +/- SD, 57 +/- 10 yrs). 24-hour Holter electrocardiographic monitoring (ECG-H) and Signal-Averaged electrocardiography (SAECG) were performed seeking to identify the arrhythmogenic risk. Echocardiographic analysis was accomplished by means of a computerized system: LVMI, ratio of LV wall thickness to LV internal radius (relative wall thickness = RWTh), systolic velocity of circumferential fractioning (VCFs), peak of LV relaxation rate (pLVRr) and peak-systolic stress (pSS) were evaluated. RESULTS: Normal LV systolic function was generally found, but both NEH and EEH groups showed a significant reduction in pLVRr in comparison with C and CEH groups (mean values +/- SD: 3.52 +/- 1,3 and 3.40 +/- 0.9 vs 4.92 +/- 0.4 and 4.27 +/- 1.4 sec-1, respectively, p < .05 for both). pSS was significantly higher in EEH and NEH than in CEH and C (mean values +/- SD: 149 +/- 42 and 157 +/- 66 vs 116 +/- 28 and 122 +/- 15 10(3) dynes/cm2, respectively; p < .05 for both). At ECG-H, EEH had a prevalence of potentially malignant ventricular arrhythmias (PMVA: ventricular extrasystoles > or = 30/h; ventricular couplets, > or = 2 episodes/24h, or triplets, > or = 1 episode/24h; R on T), significantly larger than in C (35.3% vs 4.8%, p < .05) and almost significantly larger than in NEH and CEH (8.3% and 10%, respectively). No differences in LVMI were found between EEH with or without PMVA. In respect of functional LV behaviour, the former group showed lower values of VCFs (2.33 +/- 0.6 vs 3.71 +/- 1.32 sec-1, (p < .005) than the latter group. At SAECG, the EEH exhibited again a greater prevalence of abnormal findings than C (35.3% vs 0%, p < 0.5). No correlations were found between ECG-H and SAECG abnormalities, nor between the latter group and LVMI or LV functional indexes. Among pts showing a more pronounced impairment of diastolic function (pLVRr < 4 sec-1), EEH exhibited the highest prevalence of both PMVA (50%) and late potentials (41%). CONCLUSIONS: Our data suggest that uncomplicated mild to moderate essential hypertension may be associated with higher risk of ventricular arrhythmias, particularly when cardiac involvement is characterized by eccentric LVH. On the contrary, in this stage of hypertensive disease, LVMI as well as LV function do not seem to influence the ventricular arrhythmogenesis. The clinical importance of these findings is uncertain, and further studies are needed.

Adult↗
PubMed1991

Effect of right atrial stimulation on both atrial pressure and atrial natriuretic peptide release in essential hypertension.

UNLABELLED: Several reports indicated a direct relationship between atrial pacing and atrial natriuretic peptide (ANP) blood levels, but few controlled hemodynamic studies have been reported. In particular, the relationship between increase in heart rate, release of ANP and increase in right atrial pressure (RAP) are still uncertain. Moreover, the effect of accelerated heart rate on ANP secretion in patients with essential hypertension has not yet been fully elucidated. For this, we studied 12 untreated essential hypertensive (EH; WHO stage I-II) and 10 age-matched normotensive subjects (NO) as control by right atrial stimulation (parasinusal site) in consecutive steps of 110, 130 and 150 b.p.m., each step lasting for 5 min. Both before and during stimulation at each pacing rate (after 5 min) RAP and systolic blood pressure (SBP) were measured and blood was drawn from the right atrium for ANP measurements (radioimmunoassay method). During stimulation we observed significant differences in the ANP release in comparison to the initial values: at 130 (p less than 0.05) and at 150 b.p.m. (p less than 0.01) in EH; at 150 b.p.m. (p less than 0.005) in NO. RAP and SBP did not differ significantly at each pacing rate from initial values both in EH and NO. No significant differences in ANP and RAP were found between EH and NO. IN CONCLUSION: (a) ANP release increases in both EH and NO, even if beginning at 130 in EH and at 150 b.p.m. in NO; (b) in both EH and NO, there is no relationship between RAP or SBP values and ANP secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Natriuretic Factor↗
PubMed1990

Effects of training on the electrophysiologic properties of atrium and accessory pathway in athletes with Wolff-Parkinson-White syndrome.

Twenty-two subjects with Wolff-Parkinson-White (WPW) electrocardiographic pattern performing agonistic physical activity were referred to our laboratory to assess arrhythmogenic risk (group 1). This allowed us to evaluate a less known aspect, namely that of effects of training on the electrophysiologic properties of the atrium and accessory pathway. This was done utilizing a control group of 10 WPW patients who did not perform agonistic physical activity (group 2). All subjects were symptom free, and without signs of associated cardiopathy if we exclude 1 patient of group 1, who presented moderate mitral valve prolapse. Group 1 patients showed significantly higher mean values for basic cycle length (p less than 0.001), atrial effective (p less than 0.04) and functional (p less than 0.02) refractory period, and anterograde effective refractory period of the accessory pathway (p less than 0.02). The different behavior observed in group 1 patients could be explained considering the known influence of training on the equilibrium of the autonomic nervous system. Moreover, it is noteworthy that the two groups did not differ for inducibility of atrial fibrillation (AF). This should be taken into account considering the importance of AF in WPW. In conclusion, our study does not demonstrate any negative electrophysiologic effects of training in patients with WPW.

Adolescent↗
PubMed1989

Relationship between age and anterograde refractoriness of the accessory pathway in Wolff-Parkinson-White patients.

In 22 patients (age range 13-40 years) with Wolff-Parkinson-White ECG pattern without evidence of associated cardiomyopathy we measured the anterograde effective refractory period of the accessory pathway (ERP-AP) by extrastimulus method (at twice diastolic threshold) during atrial pacing (100/min). The ERP-AP range was 220-480 ms. There was a significant direct correlation between age and ERP-AP (r = 0.50, p less than 0.01). An ERP-AP less than or equal to 250 ms was found in 4 patients (age less than or equal to 23 years). This is noteworthy in the light of reports that, over the years: (1) typical Wolff-Parkinson-White ECG signs can disappear and (2) the frequency of tachycardic episodes decreases. Our data suggest a lower risk of high ventricular rates during atrial fibrillation with increasing age.

Adolescent↗
PubMed1989

[Atrial electrophysiologic properties in paroxysmal atrial fibrillation. Study conducted with the stimulation of 5 atrial sites].

Programmed atrial stimulation at five atrial sites was performed to evaluate electrophysiologic atrial properties in 17 control patients (14 M, 3F, mean age 61 +/- 9 years) (Group A) and in 18 patients with paroxysmal atrial fibrillation (13 M, 5 F, mean age 61 +/- 5 years) (Group B) with normal sinus node function. The mean value of the P wave duration was similar in both groups. Programmed atrial stimulation was performed at five atrial sites: high, medium and low lateral wall, and high and low medial wall. We evaluated the following parameters: A) local conduction delay measured at the functional refractory period as the difference between A1-A2 and S1-S2 intervals; B) widening of local electrogram measured at the functional refractory period as the difference between A1-A2 interval measured at the end of each local electrogram and A1-A2 interval measured at the beginning of each local electrogram. We evaluated the mean and the maximum value of the two above-mentioned parameters; C) dispersion of effective refractory period and functional refractory period, determined as the longest minus the shortest refractory period from the range of refractory periods measured in each patient; D) the mean of effective refractory periods and functional refractory periods observed at five atrial sites. Mean and maximum local conduction delay, mean effective and functional refractory periods did not present significant differences in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Atrial electrophysiologic properties of patients with asymptomatic Wolff-Parkinson-White syndrome.

To evaluate the existence of a peculiar atrial electrophysiologic substrate, we studied 18 patients with asymptomatic Wolff-Parkinson-White (WPW) syndrome. These patients were compared with 10 age-matched normal subjects (N). Effective and functional refractory periods were determined at two right atrial sites (high and low in the lateral wall), during atrial pacing (100 min-1) and at twice diastolic threshold. Disperson (D) of effective (ERP) and functional (FRP) refractoriness was evaluated as the difference between refractory periods at the two atrial sites. WPW patients showed significantly lower mean values of effective and functional refractoriness at both atrial sites and significantly higher mean values of D-ERP and D-FRP. Moreover, in calculating the highest normal values of D-ERP and D-FRP (as mean values of N plus 2SD) it was observed that WPW with abnormal values of D showed a statistically (chi 2 test) higher incidence (100%) of induced atrial fibrillation (AF). These findings indicate the existence of both an abnormal atrial electrophysiologic substrate and of a higher vulnerability in WPW. Finally, AF was induced generally at the site with the lower refractoriness (i.e. low lateral site). This should be taken into account when considering how atrial fibrillation can be induced more easily.

Adolescent↗
PubMed1988

Effects of propafenone on directly measured sinoatrial conduction time.

Electrophysiologic investigation of the effects of antiarrhythmic drugs on sinoatrial conduction time (SACT) is conditioned by the inadequacies of indirect methods employing premature or asynchronous atrial stimulation. Direct recording of sinus node electrogram (SNE) is unaffected by the limitations of the indirect methods and is particularly useful when the effect of a drug on SACT is to be studied. In the present study the effect of propafenone on SACT directly (D) measured from SNE in 12 patients (7 male and 5 female subjects, 61 +/- 10 years) with normal sinus node function (NSNF) was investigated. DSACT, sinus node cycle length (SCL) and corrected sinus node recovery time (CSNRT) were evaluated before and 20 min after i.v. administration of 1 mg/kg propafenone. The following results (mean +/- SD) were obtained: in control condition SCL was 854 +/- 143 ms; CSNRT 316 +/- 82 ms; DSACT 88 +/- 20 ms. After propafenone SCL was 849 +/- 119 ms; CSNRT 340 +/- 93 ms; DSACT 97 +/- 15 ms (p less than 0.05). DSACT ranged from 60 to 105 ms and from 60 to 120 ms, respectively, before and after propafenone. In conclusion, in patients with NSNF propafenone 1. does not affect sinus node automatism and 2. prolongs significantly DSACT, which, however, remains within the upper normal limit.

Adult↗
PubMed1986

Influence of current strength on excitability and conduction of human atrium and atrioventricular node.

The influence of current strength on excitability and conduction of atrium and atrioventricular node was assessed in 25 patients using different current strengths (2, 3, 4, 5, 7, 10, 15 mA) and introducing extrastimuli (parasinusal zone) after the eighth paced complex of a basic drive (100 beats X min-1). Bipolar stimulation with the distal pole as cathode was performed so that effective and functional refractoriness of atrium and atrioventricular node, and the maximum value of atrial latency (interval between the extrastimulus and the beginning of atrial activity), intra-atrial conduction time, and AH interval could be determined at each current strength. In some patients atrioventricular nodal effective refractoriness could or could not be determined at each current strength, whereas in others the determination was possible only at the highest or the lowest current strengths. Moreover, the increase in current strength induced a progressive parallel reduction in both atrial effective and functional refractoriness; induced a progressive lengthening of intra-atrial conduction time (this was seen only in patients with a history of atrial arrhythmias); allowed the maximum possible lengthening of AH interval; and did not visibly influence atrioventricular nodal refractoriness and atrial latency. By altering atrial refractoriness and intra-atrial conduction time current strength affects the prematurity of the atrial impulse and the time at which it reaches the atrioventricular node. These findings should be taken into account when diagnostic and therapeutic electrophysiological procedures are performed.

Electric Stimulation↗
PubMed1985

Anterograde sinuatrial conduction evaluated by sinus node electrogram in atropine blocked retrograde atrial conduction.

Two cases are described where atropine induced the disappearance of reset zone as response to premature atrial stimulation for blocked retrograde atrial conduction. Because of this, sinuatrial conduction time could not be estimated. The sinus node electrogram allowed the direct measurement of sinuatrial conduction and showed a facilitated anterograde conduction through the perinodal fibers after administration of the drug.

Atropine↗
PubMed1985

Effects of pharmacologic autonomic blockade on atrial electrophysiologic properties in normal subjects and in patients with sinus node disease.

In order to elucidate the influence of autonomic nervous system on atrial electrophysiologic properties, we studied 10 patients with sinus node dysfunction and 10 age-matched normal subjects. In each of them effective and functional refractory periods of the right atrium (near its junction with the superior caval vein) were measured, during atrial pacing (100/min) and using variable current strengths (2, 3, 4, 5, 7, 10, and 15 mA), before and after pharmacologic autonomic blockade (using intravenous propranolol 0.2 mg/kg and atropine 0.04 mg/kg). Mean values of effective and functional refractory periods at each current strength were significantly higher in patients with sinus node disease than in normal subjects both before and after autonomic blockade. Blockade did not significantly modify mean values of effective and functional refractory periods at any current strength, either in patients with sinus node disease or in normal subjects. Furthermore, autonomic blockade did not change the effects of the increase of current strength on atrial refractoriness in either group. We conclude that our data indicate a prolonged refractoriness to be present in patients with sinus node disease even in the absence of influences from the autonomic nervous system. Thus, we can suggest a "primary" involvement of atrial fibers in this pathophysiological condition. Propranolol together with atropine did not induce changes of atrial refractoriness. Indeed, they probably exerted an opposite effect. The effects of the increase of current strength on atrial excitability do not seem to be mediated by autonomic humoral agents.

Aged↗
PubMed1984

Aging and atrial electrophysiologic properties in man.

In order to assess the influence of age on atrial electrophysiologic properties, we studied 17 normal subjects, whose ages were homogeneously distributed between 17 and 78 years, measuring in each of them effective (ERP) and functional (FRP) refractory periods at 3 sites of the right atrium (high, middle and low in the lateral wall) at the same driven frequency (120/min). Twice threshold stimuli of 2 msec duration were applied. Dispersion of atrial refractoriness was measured as the longest minus the shortest refractory period. A significant direct correlation was observed between age and dispersion of atrial refractoriness (of ERP: r = 0.75, P less than 0.001; of FRP: r = 0.82, P less than 0.001). Moreover, age showed a significant direct correlation with refractoriness at high right atrium (ERP: r = 0.66, P less than 0.01; FRP: r = 0.76, P less than 0.001), but did not correlate with that at the other two sites. We suggest that ageing modifies atrial refractoriness in a non-uniform manner inducing a progressive increment of dispersion of atrial refractoriness. The impression is that a slow but continuous process takes place from juvenility to old age.

Adolescent↗
PubMed1984

The effects of atropine on sinoatrial conduction time directly measured from sinus node electrogram. A comparison with results furnished by indirect methods.

The effects of atropine on sinoatrial conduction time (SACT) measured directly (SACTD) from the sinus node electrogram (SNE) were investigated in 15 patients with normal sinus node function. A comparison was undertaken with the results furnished by indirect methods which employ premature (SACTS) and asynchronous atrial stimulation (SACTN) to calculate SACT. In the control state SACTD was 92.5 +/- 16.4 ms, SACTS 78.2 +/- 22 ms, and SACTN 97.9 +/- 32.2 ms. After atropine SACTD was 70.6 +/- 15.6 ms (P less than 0.0005), SACTS 46.7 +/- 14.3 ms (P less than 0.0005) and SACTN 43.1 +/- 12.7 ms (P less than 0.0005). Mean percent decreases of SACTN (51.6 +/- 21) and SACTS (37.4 +/- 18) were statistically greater than that of SACTD (23.5 +/- 13.3) (P less than 0.0005 and P less than 0.01 respectively). While the reduction of SACTS and SACTN was greater than that of sinus cycle length (SCL) (29.2%), SACTD showed a reduction significantly less than that of SCL (P less than 0.005). Thus, SNE recording confirms that atropine induces a shortening of SACT in normal patients, but significantly less than that indicated by indirect methods.

Adult↗
PubMed1984

[Comparison of Narula's technic of direct and estimated sinoatrial conduction at increasing rates in normal subjects].

Twenty eight normal subjects in sinus rhythm underwent direct measurement of sinoatrial conduction time (SACTD) by sinus node potential recordings (SNP) and indirect evaluation by Strauss (SACTS) and Narula's methods (SACTN) using the extrastimulus technique. Stimulation in Narula's method was undertaken at three different rates, 3, 6 and 9 beats per minute faster than the spontaneous rate of the subject (SACTN3, SACTN6, SACTN9). The mean values (+/- SD) were as follows: SACTD 84 +/- 18, SACTN3 85 +/- 29, SACTN6 96 +/- 33, SACTN9 101 +/- 36. The mean value of the SACTD was significantly lower than that of the SACTN9 (p less than 0,01) but there were no significant differences between SACTD and SACTN3 and SACTN6. The three values of the SACTN were closely related to each other but not to the values of the SACTD.

Action Potentials↗
PubMed1984

Clinical electrophysiological effects of chronic administration of verapamil: the phenomenon of overdrive excitation of junctional pacemaker.

The electrophysiological effects of chronic administration of verapamil were studied in 10 patients with normal sinus node function, who received 160 mg of the drug every eight hours for at least two weeks. Uncorrected and corrected sinus node recovery time, sino-atrial conduction time, effective and functional refractory periods were normal in each case. In three patients, at the cessation of atrial pacing, an overdrive excitation of junctional pacemaker with short lasting A-V dissociation was observed.

Electric Stimulation↗