Biomedical subjects

G Ndrepepa

Publications and source records attributed to G Ndrepepa.

33 records · Page 2Linked to original sources

PubMed2000

The recording of monophasic action potentials with fractal-coated iridium electrodes in humans.

The present study was designed to evaluate the feasibility of the recording of monophasic action potentials (MAP) with fractal-coated iridium electrodes in a clinical setting. In 18 patients who underwent an electrophysiological study for various arrhythmias, we performed MAP recordings with both 1.3-mm2 and 6-mm2 tip surface area fractal-coated iridium and standard silver--silver chloride (Ag/AgCl) electrodes in the high right atrium and two ventricular positions. Amplitude and MAP duration at 90%, 50%, and 25% of repolarization were calculated during steady-state pacing at 600, 500, and 400 ms cycle lengths with extrastimuli application. Morphology comparisons of MAP signals recorded with both types of electrodes were performed by regression analysis using 5% of the repolarization segments of the MAP trajectory. Differences between MAP duration at 90%, 50%, and 25% of repolarization recorded with fractal-coated and Ag/AgCl electrodes were statistically insignificant. Amplitude values recorded with 6-mm2 tip electrodes were significantly smaller than those recorded with Ag/AgCl electrodes for all comparisons. During steady-state pacing, the correlation coefficients between Ag/AgCl and fractal-coated 1.3-mm2 and 6-mm2 tip electrodes were within the range of 0.93-0.999 and 0.87-0.999, respectively. The correlation of MAP amplitude and duration at 90%, 50%, and 25% of repolarization following the extrastimulus S2, recorded with both types of electrodes, was significantly weaker for right atrial recordings (r value range 0.78-0.92) as compared to ventricular recordings (r value range 0.92-0.99). The MAP sensing features of fractal-coated iridium and Ag/AgCl electrodes are comparable. The best results for recording of MAPs with fractal-coated electrodes can be achieved with small surface area tip electrodes.

Action Potentials↗

PubMed2000

Block of the lower interatrial connections: insight into the sources of electrocardiographic diversities in common type atrial flutter.

Whether the conduction disturbances of the interatrial connections play a role in the genesis of ECG variants of atrial flutter is almost completely unknown. We present a patient with typical counterclockwise atrial flutter in whom the ablation of the coronary sinus (CS) area during ongoing atrial flutter produced significant ECG changes without alterations in the activation sequence within the right atrium (RA). This case highlights the possible role of alterations of the interatrial connections in the genesis of atypical ECG manifestations of common type atrial flutter.

Aged↗

PubMed2000

Basket catheter-guided three-dimensional activation patterns construction and ablation of common type atrial flutter.

Construction of three-dimensional activation maps and evaluation of ablation-created bidirectional block in the tricuspid valve-inferior vena caval (TV-IVC) isthmus in patients with atrial flutter (AF) are difficult with conventional mapping technique. In 36 patients with type I AF (25 men, 11 women; mean age 62 +/- 10.5 years) a multielectrode basket catheter (BC) was deployed in the right atrium (RA). Out of 64 BC electrodes, 56 bipolar electrograms were derived. Three-dimensional activation patterns were constructed with a software program. Stable electrograms of satisfactory quality were obtained in 49 +/- 2 electrode pairs. Capture was possible in 36 +/- 3 of bipoles. In counterclockwise AF (CCW-AF) and clockwise AF (CW-AF) episodes, cycle lengths and TV-IVC isthmus conduction times were 248 +/- 26 ms and 251 +/- 23 ms, (P = 0.74) and 105 +/- 28 ms and 106 +/- 33 ms (P = 0.92), respectively. Conduction velocity in the TV-IVC isthmus was lower than in the anterior or septal limbs of the circuit, in counterclockwise or clockwise episodes. Double potentials were recorded in 94% of patients. Three-dimensional activation patterns were delineated and displayed as isochronal maps. The reentry circuit involved the TV-IVC isthmus, septal, and anterior walls and a part of the RA roof anterior to superior vena cava. Postablation isthmus conduction was evaluated through the sequence criteria, local electrogram-based criteria, and the analysis of three-dimensional activation patterns of the paced rhythms. The complete isthmus block was associated with a significant increase of the low anterior low septal conduction interval (152 +/- 29 vs 104 +/- 32 ms, P = 0.001) and the low septal-low anterior conduction interval (150 +/- 31 vs 107 +/- 33 ms, P = 0.001). Radiofrequency ablation was successful in 32 (90%) of 36 patients. In conclusion, the current mapping system enables construction of three-dimensional activation patterns and facilitates evaluation of the postablation TV-IVC isthmus block in patients with AF.

Adult↗

PubMed2000

Left atrial fibrillation with regular right atrial activation and a single left-to-right electrical interatrial connection: multisite mapping of dissimilar atrial rhythms.

We report two patients who had isolated atrial fibrillation in the left atrium and regular activation of the entire right atrium. Mapping of the arrhythmia was performed using a 64-electrode basket catheter that was inserted intravenously and deployed in the right and left atria. Both patients manifested a single, stable interatrial electrical connection conducting in a left-to-right direction, consistent with Bachmann's bundle location. The right and left sides of the interatrial septum were activated discordantly, each reflecting activation characteristics of the respective atria. A filtering effect at the level of interatrial septum was demonstrated by calculating the fibrillation intervals on both sides of the operative interatrial connection. It was concluded that differences in activation of the left and right surfaces of the interatrial septum and preferential use and the filtering effect of the interatrial connections play a significant role in explaining the differences in activation patterns of the left and right atria in patients with atrial fibrillation.

Atrial Fibrillation↗

PubMed2000

Noncontact mapping-guided catheter ablation of atrial fibrillation associated with left atrial ectopy.

We report the use of a novel noncontact mapping system used to perform left atrial mapping and to guide radiofrequency ablation in two patients, each with atrial fibrillation (AF) triggered by left atrial ectopy. A noncontact multielectrode probe and ablation catheter were advanced into the left atrium through a transseptal puncture or a patent foramen ovale. Isopotential mapping delineated the focal origin at the ostium of the right lower pulmonary vein in one patient and close to the ostium of the left upper pulmonary vein in the other patient. The ablation catheter was guided to the target sites using a locator signal. The foci were ablated successfully in both patients. No recurrences of AF were observed during follow-up at 4 and 6 months, respectively.

Atrial Fibrillation↗

PubMed2000

ECG changes in a 25-year-old woman with hypocalcemia due to hypoparathyroidism. Hypocalcemia mimicking acute myocardial infarction.

The case of a 25-year-old woman presenting with chest pain, ECG changes, and laboratory findings suggestive of myocardial infarction is reported. Cardiac catheterization showed impaired left ventricular performance but otherwise normal coronary arteries. Laboratory analyses revealed primary hypoparathyroidism, and supplementation with calcium and vitamin D(3) was initiated. There was subsequent improvement in laboratory findings as well as echocardiographically determined left ventricular performance. Thereafter, the patient remained asymptomatic. Apart from some persisting ECG repolarization disturbances, there was complete normalization of the initial changes. This case demonstrates a combination of clinical, blood biochemical, and ECG findings mimicking acute myocardial infarction.

Adult↗

PubMed1999

Clinical experience with a novel multielectrode basket catheter in right atrial tachycardias.

BACKGROUND: The complexity of atrial tachycardias (ATs) makes the electroanatomic characterization of the arrhythmogenic substrate difficult with conventional mapping techniques. The aim of our study was to evaluate possible advantages of a novel multielectrode basket catheter (MBC) in patients with AT. METHODS AND RESULTS: In 31 patients with AT, an MBC composed of 64 electrodes was deployed in the right atrium (RA). The possibility of deployment, spatial relations between MBC and RA, MBC recording and pacing capabilities, mapping performance, and MBC-guided ablation were assessed. MBC deployment was possible in all 31 patients. The MBC was left in the RA for 175+/-44 minutes. Stable bipolar electrograms were recorded in 88+/-4% of electrodes. Pacing from bipoles was possible in 64+/-5% of electrode pairs. The earliest activity intervals, in relation to P-wave onset, measured from the MBC and standard roving catheters were 41+/-9 and 46+/-6 ms, respectively (P=0.21). Radiofrequency ablation was successful in 15 (94%) of 16 patients in whom it was attempted, including 2 patients with polymorphic right atrial tachycardia (RAT), 2 with RAT-atrial flutter combination, 1 with macroreentrant AT, and 1 with focal origin of atrial fibrillation. CONCLUSIONS: These data demonstrate that MBC can be used safely in patients with right atrial arrhythmias. The simultaneous multielectrode mapping aids in the rapid identification of sites of origin of the AT and facilitates radiofrequency ablation procedures. The technique is especially effective for complex atrial arrhythmias.

Adult↗

PubMed1999

Recent advances in cardiac mapping techniques.

Recently several new mapping modalities have been introduced into clinical electrophysiologic laboratories, including basket catheter mapping, electromagnetic mapping, and noncontact mapping. In addition, intracardiac echocardiography is being used increasingly to visualize important intracardiac structures for catheter ablation. Basket catheter mapping and noncontact mapping are simultaneous mapping devices, whereas electromagnetic mapping is a sequential mapping tool. The new basket-shaped catheters provide up to 64 electrodes mounted on a variable number of splines that encircle the cardiac contour. Animation programs help in identifying the earliest activation and analyzing the activation sequence. Electromagnetic mapping uses low density magnetic fields to navigate the catheter position and to allow nonfluoroscopic mapping and ablation. Sequential recording of intracardiac potentials produces a real-time, color-coded, three-dimensional activation map. Noncontact mapping does not require direct contact with the endocardium and permits the reconstruction of more than 3000 simultaneous computed electrograms via mathematical algorithms. Three-dimensional isopotential maps are generated to visualize the impulse propagation and guide catheter ablation.

Algorithms↗

PubMed1999

Computer-assisted animation of atrial tachyarrhythmias recorded with a 64-electrode basket catheter.

OBJECTIVES: The aim of this study was to assess the value of a new mapping technique based on computer-assisted animation of multielectrode basket catheter (BC) recordings in patients with atrial arrhythmias. BACKGROUND: The three-dimensional activation patterns of cardiac arrhythmias are not completely understood owing to limitations of conventional mapping techniques. METHODS: The study included 32 patients with atrial tachycardia (AT) and 38 patients with atrial flutter (AFL). A software program was developed to analyze the activation patterns based on 56 bipolar electrograms recorded with a 64-electrode BC deployed in the right atrium (RA). RESULTS: The total time needed for the animation of activation patterns of atrial arrhythmias was 5 +/- 0.8 min. In 22 patients with right AT, the animated maps revealed that arrhythmia was unifocal in 15 patients, multifocal in 2 patients, polymorphic in 4 patients and reentrant in 1 patient. In 10 patients with left AT, breakthroughs on the right side of the septum (2 in 8 patients and 1 in 2 patients) and a left-to-right activation of the RA were demonstrated. In patients with typical AF, the reentrant excitation was a broad activation front with preferential propagation around the tricuspid annulus. In patients with atypical AFL, the reentry circuit involved one of the venae cavae and a line of block located in the posterior wall. CONCLUSIONS: The computer-assisted animation of multiple electrograms recorded with a BC is a valuable mapping tool that delineates the three-dimensional activation patterns of various atrial arrhythmias. The technique is appropriate for complex, short-lived or unstable arrhythmias.

Adult↗

PubMed1998

The influence of pacing rate and autonomic blockade on human primary and secondary atrial pacemakers.

The morphology of the first spontaneous post-pacing P wave was assessed in 106 patients who underwent electrophysiological study for various arrhythmias. An overall number of 589 atrial pacing sessions, from 60-200 b/min, were analyzed (mean 5.55 +/- 1.3 session per patient). After cessation of 138 (23.42%) of them, spontaneous post-pacing P wave arose from extrasinus foci. Nonsinus spontaneous post-pacing P waves were recorded after 1 or more pacing rates (from 1 to 7) in 58 patients (54.7%, Group 1). In the remaining 48 patients the spontaneous post-pacing P waves were sinus after all pacing sessions (45.3%, Group 2). Sinus node disease (SND) was present in 32.7% of Group 1 patients and in 2% of Group 2 (p = 0.002). Spontaneous post-pacing P wave of extrasinus origin was recorded in 19/20 of SND patients (95%) compared to 39/86 of patients with normal sinus function (45.34%, p < 0.001). SND patients had a greater number of pacing sessions resulting in nonsinus spontaneous post-pacing P waves. Pacing rate associated with nonsinus spontaneous post-pacing P waves was lower in SND patients compared to patients with normal sinus node function. In the SND group, nonsinus spontaneous post-pacing P waves were recorded beyond the first spontaneous one in 9 patients compared to only 1 in patients with normal sinus node function (p < 0.005). Extrasinusal first spontaneous post-pacing P waves at a pacing rate of 140 b/min had the highest sensitivity (75%). Increasing of pacing rate from 60 to 140 b/min was associated with progressive arousal of secondary foci with highest value of 36.8% in pacing rate of 140 b/min. Further increase of pacing rate resulted in a slight reduction of spontaneous post-pacing firing from secondary foci. Atropine was administered in 12 Group 1 patients and abolished all measurable morphological changes of spontaneous post-pacing P waves compared to pre-pacing. Autonomic blockade was performed in 14 Group 1 patients and 16 Group 2 patients. In 35.7% of Group 1 patients autonomic blockade abolished the appearance of nonsinus spontaneous post-pacing P waves, while in the remaining patients increased the lowest pacing rate resulting in nonsinus spontaneous post-pacing P waves. In 12.5% Group 2 patients autonomic blockade resulted in nonsinus spontaneous post-pacing P waves after cessation of atrial pacing. In conclusion, the extrasinus spontaneous rise of atrial impulse is a very frequent phenomenon after atrial pacing especially in patients with SND. Pacing rate has different quantitative effects on sinus and secondary atrial pacemakers. Secondary pacemakers are less under autonomic control compared to sinus node.

Adult↗

PubMed1997

Actions of lidocaine on reentrant ventricular rhythms in the subacute myocardial infarction period in dogs.

The actions of lidocaine were studied in 18 dogs, 4 days after ligation of the left anterior descending artery, by computerized mapping. Lidocaine only occasionally suppressed the induction of reentry. At fast heart rates, lidocaine actually facilitated the induction of reentry. The effects on conduction and refractoriness of normal and ischemic myocardium were measured using high-resolution techniques. Lidocaine promoted reentry by a rate-dependent increase in refractory gradient, resulting in additional block, and a selective decrease in conduction velocity in ischemic tissue, resulting in additional conduction delay. Lidocaine could prevent reentry through a rate-independent differential increase in refractory period gradient at the entrance to the common pathway of the circuit, causing block of the reentrant impulse. We conclude that the proarrhythmic effect of lidocaine is due to increased conduction delay and block while the antiarrhythmic effect is due to block of the reentrant impulse by prolonged refractoriness in the common pathway.

Animals↗

PubMed1995

Reentrant arrhythmias in the subacute infarction period. The proarrhythmic effect of flecainide acetate on functional reentrant circuits.

BACKGROUND: The Cardiac Arrhythmia Suppression Trial has shown that flecainide was associated with an increased incidence of sudden cardiac death in postinfarction patients. The exact mechanism(s) of the proarrhythmic effects of flecainide remain unclear. We performed a detailed analysis of the electrophysiological and proarrhythmic effects of flecainide in a well-characterized model of reentrant arrhythmias in the subacute phase of myocardial infarction. METHODS AND RESULTS: Sixteen dogs were studied 4 days after ligation of the left anterior descending coronary artery. Isochronal mapping of ventricular activation showed that flecainide facilitated both the induction and sustenance of ventricular tachycardia, especially at shorter basic cycle lengths. Flecainide had negligible effect on the length of the arc of functional conduction block but markedly depressed conduction of the common reentrant wave front that was usually oriented parallel to fiber axis. Whole heart mapping was analyzed in combination with basic measurements of the effects of flecainide on conduction and refractory properties of both normal and ischemic myocardia using a high-resolution cross electrode consisting of four orthogonal arms, each comprised of 16 poles with an interelectrode spacing of 500 microns. The electrode was especially designed to study the effects of the drug on anisotropic conduction as determined by a linear regression of activation time and distance in each direction. Flecainide resulted preferentially in more marked rate-dependent depression of conduction in ischemic compared with normal myocardium. On the other hand, the effect of flecainide on refractoriness in both normal and ischemic myocardia was negligible. CONCLUSIONS: Because flecainide caused no significant change in refractoriness in both normal and ischemic myocardia, there was no difference in the dimension of the potential reentrant pathway, that is, the continuous line of functional conduction block, around which the reentrant wave fronts circulate. Yet, flecainide resulted in significant rate-dependent slowing of conduction preferentially in ischemic myocardium. The additional slowing of conduction of the common reentrant wave front coupled with minimal changes in the length of the reentrant pathway allowed additional time for the wave front to reexcite normal myocardium on the proximal side of the arc of block. After flecainide, reentry could be induced in hearts in which reentry could not be induced during control. The same proarrhythmic mechanism explains the propensity of nonsustained figure-8 reentrant tachycardias to become sustained after flecainide.

Animals↗

PubMed1995

Activation time determination by high-resolution unipolar and bipolar extracellular electrograms in the canine heart.

INTRODUCTION: To identify the optimal criteria for activation time (AT) determination of bipolar electrograms from normal hearts, a high-resolution cross electrode array comprising 128 unipolar electrodes of 500-microns spacing was used to record extracellular potentials from the left ventricular epicardium of 12 dog hearts. METHODS AND RESULTS: Recordings were made during broad wavefront propagation (B wave) and local elliptical wavefront propagation (E wave). Characteristics of 863 bipolar electrograms (1-mm spacing) were constructed from unipolar data standardized for differences in polarity, then classified morphologically. Features for bipolar AT determination were compared to the time of the negative peak of the first temporal derivative of a unipolar electrogram situated mid-way between the bipoles. During B wave, three distinct morphologies were observed: uniphasic (61%), biphasic (23%), and triphasic (16%). Peak voltage of uniphasic and triphasic signals was the best predictor of AT (error: 0.6 +/- 0.6 msec and 0.6 +/- 0.8 msec, respectively). During E wave, parallel orientation of the bipoles with respect to the direction of impulse propagation wavefront resulted in uniphasic signals (> 99%), while for perpendicular orientation of the bipoles, electrogram morphology was variable. For parallel orientation of the bipoles, peak negative voltage was the best predictor of AT for both longitudinal and transverse propagation, while for perpendicular bipole orientation, peak negative voltage was a less reliable predictor for propagation along both fiber axes. Increasing interpolar distance resulted in a degradation in AT accuracy for B wave (from 0.6 +/- 0.6 msec at 1 mm to 1.1 +/- 1.2 msec at 7 mm) and for E wave (from 0.4 +/- 0.3 msec at 1 mm to 3.1 +/- 2.9 msec at 7 mm). CONCLUSIONS: (1) The accuracy of bipolar electrograms is sensitive to wavefront direction, bipole orientation, and interpolar distance; (2) peak negative voltage of uniphasic and triphasic signals is a reliable predictor of AT, but only for B wave; (3) a maximum interpolar distance of 2 mm and bipole orientation parallel to the direction of the impulse wavefront are minimally required for accurate determination of AT during impulse propagation initiated near the recording electrodes; and (4) for impulses initiated near the recording site in normal tissue, a biphasic or triphasic morphology almost certainly indicates that the bipolar electrode is oriented perpendicular to the wavefront direction, irrespective of fiber orientation.

Action Potentials↗

PubMed1994

[Complete vagal block in the clinical evaluation of sinus bradycardia].

The authors determined the discriminant threshold of sinus rate (SR) and the degree of its increase after complete vagal block (0.04 mg/kg of atropine sulfate IV) in 34 patients with symptomatic sinus bradycardia, the day after electrophysiological evaluation (performed before and after autonomic block with propranolol 0.2 mg/kg and atropine sulfate 0.04 mg/kg IV). Patients were divided into two groups. Group I included 19 patients (age 43.3 +/- 8) with normal intrinsic sinus automatism with normal intrinsic heart rate (IHRo) and normal intrinsic corrected sinus recovery time (intrinsic CSRT) (< 425 ms). Group II consisted of 15 patients (age 51.8 +/- 12) with abnormal intrinsic sinus automatism with abnormal IHRo and/or intrinsic CSRT (> 425 ms). Following the atropine test, SR in the individuals of Group I increased from 58.1 +/- 11.7 bpm to 103 +/- 16 bpm (delta% = 80 +/- 37), while in Group II it increased from 52.8 +/- 12 bpm to 82.15 bpm (delta% = 55.4 +/- 21). The discriminant threshold of SR and of its percentage increase (delta%) were 91 bpm and 68% respectively, with a sensitivity of 71 and 81% and a specificity of 73 and 63%. The predictive value of a positive test of SR (< 91 bpm) and of its delta% (< 68%) were 71 and 64% respectively. That of a negative test of SR (> 91 bpm) and of its delta% (< 68%) were 73 and 80% respectively. The total predictive accuracy of SR and of its percentage increase was the same: 72%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

The diagnostic significance of real sinus node automaticity depression in symptomatic sinus bradycardia.

Atrial overdrive pacing was performed, before and after autonomic blockade, in 42 consecutive patients (32 males and 10 females, mean age 46 +/- 11 years) with symptomatic sinus bradycardia. Patients were divided into two groups: Group I, 23 patients (mean age 43 +/- 8 years) with normal intrinsic heart rate (IHR) and normal intrinsic corrected sinus node recovery time (intrinsic CSNRT < 425 ms) and Group II, 19 patients (mean age 49 +/- 13 years) with abnormal intrinsic sinus node automaticity identified after autonomic blockade by abnormal IHR and/or by abnormal intrinsic CSNRT (> 425 ms). In addition to sinus cycle length, IHR, maximal CSNRT and sinoatrial conduction time (SACT) the real sinus node automaticity depression (SAD) was also evaluated, calculated after autonomic blockade (intrinsic CSNRT-SACT). Not all patients with an abnormal IHR showed abnormally prolonged CSNRT and not all patients with normal IHR had normal CSNRT. Among Group I (normal IHR) in 19 patients the real SAD was < 300 ms, while among Group II in 8 of 11 patients showing abnormal IHR the real SAD was > 300 ms. The abnormal value of SAD (> 300 ms) observed not only in patients with abnormal IHR and/or abnormally prolonged intrinsic CSNRT but also in several patients with normal IHR, increases the sensitivity of testing and may allow to detect even latent organic sinus node dysfunction. In conclusion, a synopsis of IHR, intrinsic CSNRT and intrinsic SACT with real SAD may be useful to estimate more accurately the degree of the impairment of intrinsic sinus node automaticity helping to differentiate the organic sinus node dysfunction from the autonomic one.

Adult↗