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Biomedical subjects

D Katritsis

Publications and source records attributed to D Katritsis.

At least 37 records · Page 2Linked to original sources
PubMed1994

Antiarrhythmic drug classifications and the clinician: a gambit in the land of chaos.

Several classifications of antiarrhythmic drugs have appeared and all suffer considerable limitations. Recently a Task Force of the Working Group on Arrhythmias of the European Society of Cardiology proposed a novel classification of antiarrhythmic drugs (the so-called Sicilian Gambit) based on their action on the most vulnerable parameter of an arrhythmogenic mechanism. The present article attempts a critical reappraisal of the antiarrhythmic drug actions and the relationship of vulnerable parameters with cellular mechanisms such as ion channels. The clinical applicability of these concepts, the implications of the new classification in the pharmacologic therapy of arrhythmias, and its potential limitations are discussed.

Anti-Arrhythmia Agents↗
PubMed1994

Is there an abnormal QT interval in sudden cardiac death survivors with a "normal" QTc?

Correcting the QT interval for heart rate may mask ventricular repolarization abnormalities and may lead to a misinterpretation of the physiologic and pathophysiologic findings. In this study the QT/R-R relationship was studied in eight sudden cardiac death (SCD) survivors without overt structural heart disease and compared with eight age- and sex-matched normal subjects. All patients were in a drug-free state. The QT intervals and their preceding R-R intervals were measured on electrocardiogram (ECG) strips from 24-hour Holter recordings at hourly intervals. The differences in mean heart rate, mean QT intervals, and QTc values between SCD survivors and normal subjects were not statistically significant. There was a significant correlation between the QT and R-R intervals in normal subjects (tau = 0.71 +/- 0.13, p < 0.05) and in SCD survivors (tau = 0.79 +/- 0.07, p < 0.05). However, the regression line of the QT interval against the R-R interval was significantly (p < 0.01) altered in SCD survivors compared with normal subjects. These observations suggest that there is abnormal ventricular repolarization (QT interval) despite an apparently normal QTc using Bazett's formula in these patients. Evaluation of the QT/R-R relationship by means of 24-hour ambulatory Holter ECG monitoring may provide a useful clinical tool for the assessment of ventricular repolarization abnormalities.

Adult↗
PubMed1994

Radiofrequency ablation of accessory pathways: implications of accumulated experience and time dedicated to procedures.

Previous reports on radiofrequency ablation of accessory pathways have shown that the experience of the operator is of crucial importance in reducing fluoroscopy time and achieving higher success rates. However, a detailed analysis of this important issue has not been previously attempted. We analysed 71 consecutive ablation procedures undertaken at St George's Hospital by the same electrophysiology group and always with the same first operator. Of all procedures, 66 (91.6%) were successful, as judged by abolition of accessory pathway conduction without recurrence within the next 24 h. Failures included two out of 38 left-sided pathway procedures (5.3%), one out of 11 intermediate septal (9.1%) and four out of 22 right-sided pathway procedures (18.2%). These differences were not statistically significant. Average procedure and screening times for all procedures were 162.9 +/- 86.0 min and 56.8 +/- 48.2 min respectively, whereas the median of the number of discharges was 12, ranging from one to 51. There was no significant difference between pathway groups or between concealed and non-concealed pathways in respect to procedure and screening time or number of discharges. There was a significant tendency towards decreased procedure and screening times with accumulating experience and this was similar for all pathway groups. There was also a tendency towards improved cumulative success rates with time dedicated to procedures. We conclude that a certain amount of ablation experience is required, even by experienced electrophysiologists, before a relatively high success rate without long radiation exposure can be achieved, regardless of the location or the mode of conduction of the pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Alteration of the QT/RR relationship in patients with idiopathic ventricular tachycardia.

It has been shown that alterations in QT/RR relationship may be associated arrhythmogenesis in several clinical settings. In the present study the QT/RR relationship was studied in 20 patients with idiopathic ventricular tachycardia (12 men and 8 women, aged 41 +/- 14 years) compared to 20 normal subjects (9 men and 11 women, aged 39 +/- 13 years). All the patients were off any antiarrhythmic drugs and had no evidence of intraventricular conduction defects. The QT intervals and their preceding RR intervals were measured on electrocardiogram strips from 24-hour Holter tapes at hourly intervals. The differences in the maximum, minimum, and mean of either the QT interval or its corrected values between patients with idiopathic ventricular tachycardia and normal subjects were not statistically significant. There was a significant correlation between the QT and RR intervals in normal subjects (gamma = 0.73 +/- 0.12, P < 0.05) and in patients with idiopathic ventricular tachycardia (gamma = 0.80 +/- 0.10, P < 0.05). However, the linear regression line of the QT interval against the RR interval were significantly (P < 0.001) altered in patients with idiopathic ventricular tachycardia (QT = 0.24 +/- 0.18 RR) compared to normal subjects (QT = 0.27 +/- 0.12 RR). We conclude that although there is no significant change in the QT interval and its corrected values, the QT/RR relationship is significantly altered in patients with idiopathic ventricular tachycardia as compared to normal subjects. This may be of importance in the pathogenesis of idiopathic ventricular tachycardia in these patients.

Activities of Daily Living↗
PubMed1994

Decreased heart rate variability in survivors of sudden cardiac death not associated with coronary artery disease.

BACKGROUND: Although heart rate variability has already been studied in survivors of sudden cardiac death secondary to coronary artery disease, an assessment of heart rate variability in survivors of sudden cardiac death not associated with coronary artery disease has not been made. METHODS: 10 patients with aborted sudden cardiac death not associated with coronary artery disease (seven patients with primary ventricular fibrillation and three with unclassified mild cardiomyopathy) underwent two channel 24 hour Holter monitoring in a drug free state. All subjects were in sinus rhythm and had normal atrioventricular conduction and normal cardiac function. Spectral heart rate variability was analysed on a Holter analysis system and was expressed as total (0.01-1.00 Hz), low (0.04-0.15 Hz) and high (0.15-0.40 Hz) frequency components for each hour. Heart rate variability index was calculated for the 24 hour periods. 10 age and sex matched healthy subjects were taken as a control group. RESULTS: The spectral heart rate variability over 24 hours was significantly lower in survivors of sudden cardiac death than in controls (total 38(15) v 48(14) ms; low, 25(11) v 32(13) ms; and high, 13(8) v 18(8) ms; p < 0.05 for all comparisons). The differences in the ratio of low/high (2.19(0.76) v 1.98(0.50), p = 0.132), mean heart rate (77(12) v 69(12) beats/min, p = 0.070), and heart rate variability index (38(12) v 44(16), p = 0.287) over 24 hours between survivors of sudden cardiac death and controls did not reach significance. Comparisons of the hourly heart rate variability over the 24 hour period between the two groups showed that the differences in all components of heart rate variability, low/high ratio and mean heart rate were highly significant. Furthermore, there was no significant difference in the maximum hourly heart rate variability over the 24 hour period. The minimum hourly heart rate variability was, however, significantly lower in survivors of sudden cardiac death than in controls (total, 20(8) v 28(4) ms; low, 12(6) v 17(3) ms; high, 6(2) v 8(2) ms; p < 0.05 for all comparisons). CONCLUSIONS: These findings suggest that there is abnormal autonomic influence on the heart in patients without coronary artery disease at risk of sudden cardiac death. Hourly analysis of heart rate variability throughout the 24 hour period may provide additional information important in the identification of high risk patients.

Adolescent↗
PubMed1994

Differences in autonomic nerve function in patients with silent and symptomatic myocardial ischaemia.

BACKGROUND: Autonomic neuropathy provides a mechanism for the absence of symptoms in silent myocardial ischaemia, but characterisation of the type of neuropathy is lacking. AIM: To characterise and compare autonomic nerve function in patients with silent and symptomatic myocardial ischaemia. METHODS AND RESULTS: The Valsalva manoeuvre, heart rate variation (HRV) in response to deep breathing and standing, lower body negative pressure, isometric handgrip, and the cold pressor test were performed by patients with silent (n = 25) and symptomatic (n = 25) ambulatory ischaemia and by controls (n = 21). No difference in parasympathetic efferent function between patients with silent and symptomatic ischaemia was recorded, but both had significantly less HRV in response to standing than the controls (p < 0.005 for silent and p < 0.01 for symptomatic). Patients with silent ischaemia showed an increased propensity for peripheral vasodilatation compared with symptomatic patients (p < 0.02) and controls (p < 0.04). Impaired sympathetic function was found in patients with pure silent ischaemia (n = 4) compared with the remaining patients with silent ischaemia whose pain pathways were presumed to be intact. CONCLUSIONS: Patients with silent ischaemia and pain pathways presumed to be intact have an enhanced peripheral vasodilator response, and if this applied to the coronary vasculature it could provide a mechanism for limiting ischaemia to below the pain threshold. Patients with pure silent ischaemia have evidence of sympathetic autonomic dysfunction.

Autonomic Nervous System↗
PubMed1993

New and combined sensors for adaptive-rate pacing.

A new potential indication for cardiac pacing is chronotropic incompetence, that is, an inadequate cardiac rate response to exercise and other metabolic demands. Many patients who have been paced for indications such as complete heart block or sick sinus syndrome also have chronotropic incompetence. Such patients are not adequately treated when fitted with a constant rate pacemaker. Adaptive-rate pacemakers increase the pacing rate in proportion to signals derived from a biosensor which is sensitive to exertion and possibly to other metabolic requirements. These pacemakers have proven valuable for patients with overt chronotropic incompetence. However, no single sensor/algorithm is ideal and improvement has been sought by introducing new sensors, adjusting the algorithms by which biosensor signals are converted to the most appropriate pacing rate, or by combining sensors in such a way that a composite biosensor signal is derived which bears a close linear relationship with the appropriate heart rate. An example of a new sensor is the accelerometer, which is sensitive to a fuller range of movements than the piezo crystal. A successful new algorithm is the rate augmentation algorithm for use with minute ventilation, which provides a better initial pacing rate response. A combination of minute ventilation sensed by impedance changes and movement sensed with piezo crystals maintains the rapid response from the piezo crystal and overcomes its lack of proportionality. Another successful new combination of sensors is QT sensing from the evoked ventricular potential and motion sensing with a piezo crystal. As yet, these innovations have not been exhaustively tested and shown to confer clinical benefit but the improvements are such that an advantage can be expected.

Body Temperature↗
PubMed1993

AAI pacing mode: when is it indicated and how should it be achieved?

AAI pacing offers better hemodynamic characteristics than dual-chamber pacing and is the optimal mode for patients with sick sinus syndrome without AV conduction disorders. AAI pacing may be achieved by single-chamber atrial pacing, by programming a dual-chamber pacemaker to the AAI mode, or by programming a dual-chamber pacemaker to DDD mode with a long AV delay. The annual incidence of AV block development in patients with sick sinus syndrome is low, probably 1-5%, but there is no method of detecting patients immune or prone to future development of AV block. Chronotropic incompetence is often present in patients with sick sinus syndrome but the value of additional rate response is not yet firmly established. Our recommendations for the choice of the optimal method of pacing are discussed.

Atrioventricular Node↗
PubMed1993

Atrioventricular junctional reentrant tachycardia utilizing multiple retrograde fibers during ablation of the slow pathway.

This report deals with a patient with atrioventricular (AV) reentrant junctional tachycardia who, during radiofrequency ablation of her slow pathway, developed both anterior and posterior type of slow-fast atrioventricular nodal reentry; in both tachycardias different fibers were alternately utilized for retrograde conduction, thus resulting in alternating tachycardia cycle lengths. This observation provides further evidence in favor of the multifiber structure of the AV node in patients with AV reentrant junctional tachycardia.

Adult↗
PubMed1993

Regional sympathetic innervation of the heart by means of metaiodobenzylguanidine imaging in silent ischemia.

Metaiodobenzylguanidine was used to determine regional cardiac sympathetic innervation and whether it is reduced in silent ischemia. Patients with silent ischemia (group 1, n = 6) and angina (group 2, n = 5) and normal subjects (n = 6) underwent single-photon emission tomography at 4 hours. From base to midventricle, uptake increased in group 1 (p < 0.006), group 2 (p < 0.01), and the normal subjects (p < 0.004). In group 1 anterior ventricular uptake was greater than inferior uptake at the midventricle (p < 0.03) and apex (p < 0.05). In group 2 the same relationship was demonstrated at midventricle (p < 0.01) and apex (p < 0.05). Group 2 uptake was only significantly greater than group 1 at midventricle (p < 0.05). Innervation is greatest in midventricle and the apex of the left ventricle and greater in the anterior wall compared with the inferior wall. There is no evidence of reduced innervation in silent ischemia.

3-Iodobenzylguanidine↗
PubMed1993

Radiofrequency current delivery by way of a bipolar tricuspid annulus-mitral annulus electrode configuration for ablation of posteroseptal accessory pathways.

OBJECTIVES: This report describes a novel technique for ablation of "difficult" posteroseptal pathways. BACKGROUND: Although radiofrequency ablation of accessory atrioventricular (AV) pathways is successful in > or = 90% of cases, particular difficulty may be encountered with some bypass tracts in the posteroseptal region. METHODS: In eight patients with posteroseptal accessory pathways (two concealed), radiofrequency catheter ablation using conventional unipolar current applications from favorable sites along the tricuspid or mitral annulus, or both, was unsuccessful. Subsequently, a bipolar technique was adopted, with current application between the distal electrodes of two catheters positioned against the septal region at sites of early activation along both mitral and tricuspid annuli. RESULTS: The bipolar configuration proved effective in all cases. The number of bipolar lesions required for success was one (five patients), five (two patients) and nine (one patient). In five patients, bipolar current application abolished pathway conduction using positions at which delivery of unipolar lesions had been ineffective or caused transient block. The AV or ventriculoatrial interval at successful sites varied from 20 to 65 ms, and the time from delta wave onset to local ventricular activation was zero or negative. There were no complications attributable to the bipolar technique. During follow-up of 8 to 36 weeks, pathway conduction has not recurred in any patient. CONCLUSIONS: Bipolar radiofrequency current delivery across the septal region using a tricuspid annulus-mitral annulus electrode configuration may abolish accessory pathway conduction when conventional unipolar applications have proved ineffective. The technique may reduce procedure duration, radiation exposure and overall failure rate in these problematic cases.

Adolescent↗
PubMed1993

New class III antiarrhythmic drugs.

Several new antiarrhythmic compounds with pure class III activity are currently under development and seem to possess considerable antiarrhythmic potential. The primary electrophysiological action of class III agents is selective prolongation of repolarization without conduction slowing. This effect is usually mediated by block of one or more potassium currents which results in prolongation of the action-potential duration and refractoriness in both atrial and ventricular myocardium. The magnitude of increases in effective refractory period decreases as the heart rate is increased, i.e. these drugs display 'reverse use-dependence'. Initial animal and clinical studies have shown that class III agents are effective against re-entrant supraventricular and ventricular arrhythmias without having any important negative inotropic effect in the compromised ventricle. Animal studies have also suggested that these drugs may be useful in suppressing postinfarction arrhythmias and preventing arrhythmic sudden death. However, concerns have been raised by reports of substantial proarrhythmic tendency associated with these drugs, mainly in the form of torsade de pointes. Careful clinical evaluation is required to establish the clinical benefits of these potentially promising new compounds.

Action Potentials↗
PubMed1993

Low-energy DC catheter ablation of left atrial ectopic tachycardia that had resulted in reversible cardiomyopathy.

Catheter ablation of automatic atrial tachycardia has been previously reported in a small number of adult cases in which the ectopic focus was predominantly located in the right atrium. We report on a patient with atrial automatic tachycardia originating in the left atrium, in whom successful low-energy DC catheter ablation was performed via a transseptal puncture. The patient presented with severe congestive cardiac failure that resolved following the procedure. Catheter ablation in such cases is feasible, it can reverse tachycardia induced ventricular function impairment, and should be attempted before resorting to open heart surgical ablation.

Adult↗
PubMed1993

Atrial adaptive rate pacing in sick sinus syndrome: effects on exercise capacity and arrhythmias.

OBJECTIVE: To test the hypotheses that adaptive rate atrial (AAIR) pacing: significantly increases maximal exercise capacity, and results in significant suppression of supraventricular and ventricular arrhythmia compared with fixed rate atrial (AAI) pacing. DESIGN: Prospective, randomised, single blind, crossover study with maximal treadmill exercise testing and 24 hour ambulatory electrocardiographic monitoring in AAIR and AAI modes. SETTING: Regional pacing centre. PATIENTS: 30 consecutive patients (mean SD age 65 (12) years) with sick sinus syndrome who required permanent pacing, without evidence of conduction disturbance on 12 lead electrocardiograms or 24 hour ambulatory electrocardiographic monitoring and without other cardiovascular or systemic disease. INTERVENTIONS: Activity sensing or minute ventilation driven systems (AAI/AAIR) were implanted alternately. RESULTS: The mean (SD) peak heart rate in AAI mode was 122(28)v 130(22) in AAIR mode (p < 0.02) for the whole group and 104(17) v 120(5) (p < 0.003) for the patients with chronotropic incompetence. Exercise time was 12.3 (4.1) minutes in AAI and 12.3 (3.8) minutes in AAIR mode (NS) in the chronotropically incompetent patients. There were no significant differences in the Borg scores at peak exercise in AAI v AAIR mode in either group. The frequency per hour of atrial and ventricular arrhythmias showed no significant differences between the two modes in either the group as a whole or in the subgroups with chronotropic incompetence. CONCLUSION: AAIR pacing confers little benefit in sick sinus syndrome compared with AAI pacing.

Aged↗
PubMed1993

Abnormal autonomic modulation of QT interval in patients with idiopathic ventricular tachycardia associated with clinically normal hearts.

BACKGROUND: Idiopathic ventricular tachycardia (VT) occurs in a small but important subset of patients without clinically overt heart disease. The mechanism of the arrhythmogenesis remains unclear in these patients. This study examines modulation of the QT interval by the autonomic nervous system in a group of patients with idiopathic ventricular tachycardia. METHODS: Cardiac autonomic activity and ventricular repolarisation were studied in 27 patients with VT associated with a clinically normal heart (NHVT) and in 20 normal subjects. All the patients were in sinus rhythm, had normal atrioventricular conduction, and were in a drug free state. Cardiac efferent autonomic activity was measured by spectral analysis of heart rate variability from 24 hour ambulatory electrocardiograms on a Holter analysis system (Marquette). Ventricular repolarisation was evaluated by measuring the QT intervals from the same 24 hour Holter tapes at one hour intervals. RESULTS: There was no difference in any of the QT interval variables including the maximum, minimum, and mean of both the QT interval and its corrected value (Bazett's formula) between patients with NHVT and normal subjects. The high frequency component (0.04-0.15 Hz) of heart rate variability was significantly decreased in patients with NHVT compared with normal subjects (16 (8) v 21 (12) ms, p < 0.05). There was a significant correlation between the spectral variables of heart rate variability and the mean, maximal, and minimal QT intervals in normal subjects, whereas the relation was lost in patients with NHVT. No difference was found in mean heart rate between normal subjects and patients with NHVT (70 (9) v 72 (13) beats/min, NS). CONCLUSIONS: The high frequency component of heart rate variability is significantly decreased and the relation of QT interval to heart rate variability is significantly altered in patients with NHVT as compared with normal subjects. These findings suggest that abnormal modulation of the QT interval by the autonomic nervous system may play an important part in the arrhythmogenesis of NHVT. This might result from impaired vagal efferent cardiac activity in these patients.

Adolescent↗
PubMed1993

Radiofrequency ablation of accessory atrioventricular pathways: predictive value of local electrogram characteristics for the identification of successful target sites.

BACKGROUND: Radiofrequency catheter ablation of accessory arterioventricular pathways has been shown to be a highly effective treatment in patients with paroxysmal superventricular tachycardia. There is, however, considerable variability in the number of attempted ablation sites, contributing to lengthy operations in some cases. The purpose of this study was to investigate the predictive value of local electrogram characteristics for the identification of successful target sites. METHODS AND RESULTS: Local bipolar electrograms from 60 patients recorded at 568 sites of attempted ablation were analysed. There were 511 sites at which ablation was guided by antegrade mapping, with 49 successful sites and 462 failed sites including 61 at which accessory pathway conduction was blocked temporarily. In multivariate analysis, the time of local ventricular activation relative to onset of the QRS complex (QRS-V interval) (p < 0.001) and the presence of a possible accessory pathway potential (p < 0.05) were found to be independent predictors of successful outcome, whereas the atrioventricular interval, atrioventricular amplitude ratio, stability of local electrogram, and presence of continuous electrical activity were not. A QRS-V interval of < or = +10 ms identified successful sites with a sensitivity of 98%, but the positive predictive accuracy was only 11%. Even a QRS-V interval of < or = 20 ms resulted in only a 24% probability of success with a sensitivity of just 18%. Combining the QRS-V interval with the presence of a possible accessory pathway potential greatly reduced the sensitivity at all cut off values, but failed to increase positive predictive accuracy above 25%. There were no significant differences in electrogram characteristics between the successful sites and the sites at which conduction of the accessory pathway was interrupted transiently. There were 57 sites (nine successful, 48 failed) at which ablation was guided by retrograde mapping, but none of the local electrogram characteristics analysed emerged as independent predictors of successful pathway ablation. CONCLUSION: Local electrogram characteristics used to guide radiofrequency catheter ablation are all associated with a low positive predictive accuracy, which significantly contributes to duration of the operation. It is unlikely that this problem will be resolved solely by modification of the mapping techniques. It could require advances in catheter technology and power sources to enable larger tissue lesions to be delivered more reliably than is possible with the equipment in current use.

Adolescent↗