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Biomedical subjects

G Hindricks

Publications and source records attributed to G Hindricks.

At least 91 records · Page 5Linked to original sources
PubMed1992

Characteristics of local electrogram predicting successful transcatheter radiofrequency ablation of left-sided accessory pathways.

OBJECTIVES: The purpose of this study was to analyze and compare the local electrograms recorded at successful and unsuccessful sites of ablation to identify the criteria that may predict successful sites and minimize unnecessary radiofrequency delivery. BACKGROUND: Transcatheter ablation of accessory pathways using radiofrequency energy requires extremely precise localization of an accessory pathway. METHODS: Local electrograms from 50 consecutive patients with left-sided accessory pathways who underwent transcatheter radiofrequency ablation were analyzed. During catheter ablation, localization of accessory pathways was performed in 39 pathways during pre-excited sinus rhythm and in 14 pathways during orthodromic tachycardia. A total of 429 local electrograms at target sites obtained before delivery of radiofrequency current was analyzed. A prospective study was performed in another 20 patients using the criteria derived from the retrospective study. RESULTS: Accessory pathway conduction block was achieved in 36 (92%) of 39 pathways in which mapping was performed during pre-excited sinus rhythm and in 9 (64%) of 14 pathways in which mapping was performed during orthodromic tachycardia (p less than 0.05). When mapping was performed during pre-excited sinus rhythm, a combination of four variables (that is, an accessory pathway potential, stability of local electrograms, atrial activation greater than 1 mV and ventricular activation preceding the onset of the delta wave) showed a 62% probability of success. In contrast, excluding these variables resulted in a 95% probability of failure (noneffective or transiently effective). The prospective study shows that the use of these criteria can significantly reduce the number of current applications. When mapping was performed during orthodromic tachycardia, recording the earliest atrial activation was the most powerful predictor of success. A stable local electrogram with a small notch on the ventricular potential, presumed to be an accessory pathway potential, may add predictive value. CONCLUSIONS: Transcatheter radiofrequency ablation is highly effective in the treatment of patients with left-sided accessory pathways. Specific characteristics of local electrograms can be important predictors of success or failure. Mapping during pre-excited rhythm renders ablation more effective than does mapping during orthodromic tachycardia.

Adolescent↗
PubMed1992

Echinococcal cyst of the interventricular septum: a rare cause of myocardial ischemia.

A 30-year-old woman developed ischemia-like chest pain due to myocardial compression by an intracardiac cyst. The cyst was located in the interventricular septum. Its etiology could not be ascertained despite several diagnostic measures but exstirpation was indicated by the clinical symptoms. Intraoperatively the diagnosis of echinococcosis was established. The cyst was extirpated in toto without perforation of the thinned interventricular septum. Postoperatively the patient was symptomfree.

Adult↗
PubMed1992

Nd:YAG laser-photocoagulation: acute electrophysiological, hemodynamic, and morphological effects in large irradiated areas.

Laser-photocoagulation (LPC) of arrhythmogenic myocardium has been reported to successfully ablate ventricular tachycardia. The purpose of this study was to investigate the acute hemodynamic and electrophysiological effect of continuous laser energy (Nd:YAG, 1060 nm) applied via a 0.4-mm quartz fiberoptic on the epicardial surface of the heart in nine dogs. A total of 51 +/- 2.3 pulses was delivered in each animal to induce homogeneous tissue necrosis. Applied energy was 12.3 +/- 2.7 J/mm2, irradiated surface measured 12.6 +/- 3.0 cm2, lesion depth was 6.3 +/- 1.2 mm (range: 5.0-8.1 mm), lesion volume was 8.1 +/- 2.8 cm3 (6.8% of left ventricular [LV] mass). After LPC, epicardial stimulation threshold significantly rose from 1.0 +/- 0.3 to 10.2 +/- 4.9 mA in the border zone to nontreated tissue and from 0.9 +/- 0.4 to 32 +/- 15.7 mA in the center of the lesions. Loss of epicardial activation in the irradiated areas could be demonstrated by epicardial mapping. Ventricular extrasystoles during LPC were seen in all dogs, ventricular tachycardia in seven, and ventricular fibrillation in two dogs. After LPC, cardiac output and LV dP/dtmax significantly decreased by 14.2% and 11.2%. LPC induced predictable homogeneous tissue edema, eosinophilic staining, contraction band necrosis, and sharp demarcated hemorrhagic border zones with a sharp electrical border zone to nontreated tissue and loss of epicardial activation. During LPC, various arrhythmogenic effects could be observed. However, no persistent arrhythmic activity developed after LPC. The results confirm the feasibility of epicardial LPC of the myocardium. Although not rested in this study, LPC of arrhythmogenic tissue may also be feasible as a treatment modality of ventricular tachycardia.

Animals↗
PubMed1992

Radiofrequency ablation of accessory pathways: characteristics of transiently and permanently effective pulses.

The purpose of this study was to characterize and compare the radiofrequency current applications that produced permanent or transient accessory pathway conduction block. One hundred fifty-two radiofrequency energy applications that induced permanent (permanently effective pulses, n = 48) or transient (transiently effective pulses, n = 104) accessory pathway block in 57 patients with 60 accessory pathways were analyzed. The time from the onset of current application to disappearance of preexcitation or termination of supraventricular tachycardia by permanently effective pulses was 1-15 seconds (mean 3.6 +/- 3.8 sec) compared to 2-29 seconds (mean 11.5 +/- 7.5 sec) by transiently effective pulses (P less than 0.01). After transiently effective pulses that induced block in accessory pathway, conduction resumed within 5 minutes while induced block by permanently effective pulses persisted in 44 of 48 patients (92%) during follow-up of 11 +/- 12 months. The accessory pathway conduction returned in the remaining four patients after ablation 2 weeks to 7 months. After transiently effective pulses, 41 impulses were delivered to the same site using a higher power output (n = 32) and/or longer energy delivery duration (n = 20) without new mapping of accessory pathway location. Thirty-six of these impulses again resulted in transient accessory pathway block, four had no effect, only one impulse induced a permanent block in the accessory pathway. Pulses with higher power outputs tended to induce transient effects more frequently than pulses with lower energy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

How to evaluate class III antiarrhythmic drug efficacy clinically: the benefits and shortcomings of the invasive approach.

Ventricular tachycardia and ventricular fibrillation are frequent complications of organic heart disease. There is sufficient evidence that serial electrophysiologic testing is able to predict long-term efficacy of antiarrhythmic agents in patients with malignant ventricular tachyarrhythmias. This approach has not only been useful for the evaluation of class I drugs, but recent studies have shown that this invasive method may also be useful for the management of patients undergoing treatment with class III antiarrhythmic agents such as amiodarone and sotalol. The results of several studies suggest that class III agents are more effective than class I drugs in patients presenting with ventricular tachycardia or ventricular fibrillation. Proarrhythmic complications in patients treated with class III antiarrhythmic drugs are mainly characterized by torsades de pointes. Their incidence does not exceed 5%. Further studies are necessary to elucidate the mechanisms underlying this type of proarrhythmia. By the use of currently available stimulation techniques, patients who might develop torsades de pointes while on therapy with a class III agent cannot be identified.

Amiodarone↗
PubMed1992

[Initial presentation of ventricular pre-excitation after catheter ablation of concealed retrograde conducting accessory atrioventricular pathways].

Catheter ablation using radiofrequency or direct current energy was performed in 19 consecutive patients with concealed accessory pathways. Four patients developed manifest preexcitation for the first time following ablation. The concealed accessory pathways of these four patients were localized at right lateral, left posteroseptal, left posterolateral, and left lateral sites, respectively. In two patients, manifest preexcitation developed immediately after attempted ablation. In the other two patients, preexcitation occurred after 4 and 14 days. Electrophysiologic testing revealed in all four patients that the origin of manifest preexcitation corresponded to the site of the concealed pathway. Successful catheter ablation using radiofrequency current was performed in three patients. One patient preferred surgical interruption of the accessory pathway. The reason for this sudden emergence of preexcitation of these patients with only retrograde conducting pathways remains to be investigated. The anterograde conduction capacity might have been modified by damaging the site of the accessory pathway insertion.

Adult↗
PubMed1992

[Percutaneous high frequency current catheter ablation in permanent ventricular tachycardia of the "bundle-branch reentry" type after implantation of an automatic cardioverter-defibrillator].

A 65-year-old female patient with a history of recurrent sustained ventricular tachycardia presented with an incessant ventricular tachycardia (cycle length 360-400 ms) following implantation of a cardioverter-defibrillator (ICD). The tachycardia could not be terminated by antiarrhythmic drug treatment, antitachycardia pacing or internal defibrillation via the ICD. An invasive electrophysiologic study revealed that the mechanism of this newly occurring tachycardia was bundle branch reentry. The patient underwent emergency catheter ablation using radiofrequency (RF) current. Endocardial mapping of the right bundle branch and of the distal His bundle was performed and a bundle branch reentry tachycardia was diagnosed. After delivery of the fifth RF-impulse, the tachycardia terminated and complete AV block was induced. No malfunction of the ICD was observed following RF-ablation. The patient was hemodynamically stable with a junctional escape rhythm and antibradycardia pacing back-up of the ICD (VVI-mode). This case report demonstrates the feasibility of RF catheter ablation in the treatment of incessant bundle branch reentry tachycardia as a complementary option after implantation of an ICD.

Aged↗
PubMed1992

[High frequency current catheter coagulation using pulsed energy delivery. Results with isolated myocardial tissue].

The feasibility and efficacy of pulsed radiofrequency (RF) current delivery was assessed and compared to results obtained by continuous energy delivery. Energy was delivered to ventricular preparations of isolated porcine hearts (HAT 100, 500 kHz, Osypka, FRG). In the pulsed mode, impulse duration and pause duration were varied between 50 and 500 ms. Total duration of coagulation was 30 s in all cases. The depth of induced lesions was significantly enhanced by a short impulse- and pause duration (50-70 ms) compared to continuous RF energy delivery. At long pause durations (200-500 ms) and short impulse duration, depth and diameter of lesions significantly decreased. The incidence of sudden increases in impedance was markedly attenuated when energy was delivered discontinuously. Thus, pulsed RF energy delivery can be used to enhance the depth of RF lesions. The decreased incidence of sudden rises in impedance during pulsed energy delivery further enhances the feasibility of RF coagulation. An improvement in heat transfer to deeper tissue layers can be considered as the mechanism responsible for these effects.

Animals↗
PubMed1992

[Biophysical aspects of high frequency catheter ablation. Studies of the significance of sudden changes in impedance].

UNLABELLED: To determine the effects and the underlying mechanisms of sudden rise of impedance during radiofrequency (RF) catheter ablation, 60 RF applications were delivered to isolated preparations of ventricular myocardium at three different power levels (mean: 3.7, 11.3, 19.3 watts). Pulse duration was 30 s, current voltage and catheter tip temperature were continuously monitored. Impedance rise occurred during 34 of 60 applications; the incidence of impedance rise increased at higher power levels. Impedance rise was significantly more often observed when the preparations were superfused with heparinized blood compared to saline solution (p less than 0.05). Catheter-tip temperature during radiofrequency application without impedance rise was significantly lower compared to applications with impedance rise (mean = 108 degrees C vs. 121 degrees C, p less than 0.01). The increase of catheter-tip temperature and maximal-tip temperature following impedance rise was significantly higher in blood when compared to saline solution (mean = +48 degrees C vs. +13 degrees C (p less than 0.001), Tmax: 121 degrees C vs. 245 degrees C). Following impedance rise, insulation defects of the electrode catheter and vaporized crater formation of the myocardium was often observed. CONCLUSIONS: During radiofrequency catheter ablation impedance rise occurs following overheating of the catheter electrode (greater than 110 degrees C). After impedance rise, catheter-tip temperature markedly increases. Insulation defects of the catheter and vaporized craters in the myocardium frequently occur after impedance rise. The results have important implications for the clinical use of RF-currents for catheter ablation; energy application should be immediately stopped after the occurrence of impedance rise.

Animals↗
PubMed1992

[Catheter ablation of ventricular tachycardia].

Catheter ablation of ventricular tachycardias was performed in a total of 80 patients whose tachycardias were considered as drug refractory and who were not considered to be candidates for antitachycardic surgery or implantation of an automatic cardioverter defibrillator. After careful endocardial catheter mapping including pacing interventions, either direct-current (DC) (n = 61) or radiofrequency current (RF) (n = 13) or both (n = 6) were applied of the "site of origin" of ventricular tachycardia or the "zone of slow conduction". 42 of 51 patients with coronary heart disease were discharged; ventricular tachycardia recurred in 8 cases, and 2 patients died suddenly. In the remaining 32 patients, there were no recurrences of ventricular tachycardia during a mean follow-up period of 12 month. Three patients died perioperatively. In 21 of 29 patients without coronary artery disease, no recurrences of ventricular tachycardia were observed (mean duration of follow-up 17 months) whereas 8 cases had a recurrence of ventricular tachycardia.

Cardiac Catheterization↗
PubMed1992

Catheter ablation of ventricular tachycardia using radiofrequency current.

Catheter ablation techniques have evolved as an alternative to map-guided surgery and proven effective in a variety of supraventricular tachyarrhythmias. Direct current catheter ablation has been shown to be effective in about 50 to 70% of cases. Approximately, 60% of patients with structural heart disease and monomorphic ventricular tachycardia were successfully treated using direct current ablation techniques. This overall success rate and possible risks associated with the use of direct current have stimulated the search for other energy sources appropriate for catheter ablation. Presently, only a few preliminary reports on the clinical efficacy of radiofrequency energy for the treatment of ventricular tachyarrhythmias in man exist. 23 patients with identifiable heart disease at a mean age of 52 +/- 17 years underwent radiofrequency catheter ablation. 16 patients had coronary artery disease, one patient dilative cardiomyopathy and six patients had arrhythmogenic right ventricular disease. All patients presented with chronic current sustained ventricular tachycardia. After detailed endocardial catheter mapping radiofrequency energy was applied at the site of earliest ventricular activation during ventricular tachycardia which could be entrained during fixed rate ventricular pacing at the site of origin of ventricular tachycardia. At all ablation sites a long latency between the stimulus and QRS complex was noted. Of 23 patients 18 were treated with radiofrequency alone whereas in five patients a second ablation procedure using direct current was performed. Following the ablation procedures, 14 patients (61%) remained free of ventricular tachycardia. One patient died due to congestive heart failure 21 months following ablation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Catheterization↗
PubMed1991

Cardiopulmonary effects of constant-flow ventilation in experimental myocardial ischaemia.

The cardiopulmonary effects of constant-flow ventilation were investigated in dogs with normal heart function (control-phase, n = 14) and after development of acute myocardial ischaemia (ischaemia phase, n = 14). Heated, humidified and oxygen-enriched air was continuously delivered with an inspiratory flow rate of 1.21.kg-1.min-1 via two catheters positioned within each mainstem bronchus. Continuous positive pressure ventilation with a positive end-expiratory pressure of 0.5 kPa (5 cmH2O) was used as a reference. During control, neither continuous positive pressure ventilation nor constant-flow ventilation showed impairment of cardiopulmonary performance. Oxygenation and CO2 removal were more efficiently achieved by continuous positive pressure ventilation (P less than or equal to 0.05). Acute myocardial ischaemia was induced by occlusion of the left anterior descending (LAD) coronary artery; measurements during the ischaemia phase were performed 60 min following LAD occlusion. Myocardial ischaemia resulted in moderate changes of cardiac output, left ventricular end-diastolic pressure and dP/dtmax. Both modes of ventilation were well tolerated in the ischaemia phase, and cardiovascular performance revealed no significant differences between continuous positive pressure ventilation and constant-flow ventilation. Haemodynamic parameters could be more precisely assessed during constant-flow ventilation. Oxygenation deteriorated, but hypoxaemia did not occur in any animal and CO2 elimination remained unchanged. It is concluded that 'non-conventional' ventilation by continuous intrabronchial gas flow maintains adequate gas exchange with no adverse effects on haemodynamics in dogs with acute myocardial ischaemia. Constant-flow ventilation may be advantageous in the experimental setting to study cardiac function without cyclic heart-lung interaction due to airway pressure alterations.

Animals↗
PubMed1991

Sodium channel blockers in the treatment of ventricular arrhythmias: different effects in the normal, ischaemic or failing heart?

In past decades, numerous experimental and clinical studies have improved our knowledge of the electrophysiological effects of sodium channel blockers, as well as of the mechanisms of arrhythmogenesis. However, the mechanisms of antiarrhythmic as well as potentially proarrhythmic drug action have been less well clarified. Sodium channel blocker agents have different effects on the normal, ischaemic, and failing heart since their antiarrhythmic actions depend on the substrate and the mechanisms of arrhythmogenesis, as well as other mostly interrelated cardiac and non-cardiac factors. Strict criteria of efficacy and safety have to be applied when sodium channel blockers are used for the treatment of ventricular arrhythmias.

Anti-Arrhythmia Agents↗
PubMed1991

[Non-pharmacological treatment of arrhythmia using the method of trans-catheter ablation].

Trans-catheteral ablation is an important therapeutic method for nonpharmacological management of various types of cardiac arrhythmias. Since its introduction into clinical practice in 1982, it has proved its efficacy in disturbance or change of the type of atrioventricular conduction and conduction along accessory abnormal atrioventricular conduction pathways. Positive results have also been attained in the treatment of some patients with ventricular tachycardia. The energy sources used for ablation include direct current pulses possessing large energy, high-frequency currents, and laser energy. Ablation with direct current and high-frequency current is already used successfully in patients, while the use of laser energy for ablation of myocardial arrhythmogenic tissue is limited mainly to operations on the open heart. The use of alternating high-frequency current has attracted particular attention in the last years. Trans-coronary chemical ablation is another recently introduced method which is not connected with the use of electric current. Only experimental and a small clinical experience with this new method has been gained to date. This survey systemasizes the current knowledge of the biophysical bases of the various method of ablation from the standpoint of the mechanisms of treatment, the methodology and the main types of tissue response. Clinical experience with trans-catheteral treatment of cardiac arrhythmias is analysed.

Arrhythmias, Cardiac↗
PubMed1991

[Percutaneous endocardial Nd-YAG laser energy: experimental studies of ablation of the ventricular myocardium].

The in vitro and in vivo effects of endocardial laser ablation were assessed. Energy was supplied by a Nd-YAG laser (wavelength approximately 1064 nm) and transmitted via a quartz core fiber (phi: 0.4 mm) housed within a specially designed 7 F catheter. In vitro, the effects of increasing output power (5, 10, 20, 40 watt) and impulse duration (1, 2, 4, 8 s) on lesion size were assessed in myocardial preparations of canine hearts. Preparations were superfused with saline or blood, respectively; the distance of the optical fiber to the endocardium was 5 mm. Lesion size increased in diameter (range: 0-4.0 mm) and depth (range: 0-5.2 mm) in a power- and time-dependent manner. Superfusion with blood significantly enhanced the diameter of the lesions, whereas depth of the lesions significantly decreased. In 16 anesthetized mongrel dogs, a total of 52 laser impulses (output power: 10, 20, 40 w; impulse duration: 1, 2, 4 s; energy: 10-160 J) were delivered to apical and apico-inferior sites of the left ventricle. Postmortem, 40 lesions with a diameter of 2.6-19.4 mm and a depth of 3.7-16.2 mm were found. 19 lesions revealed central vaporized craters with a depth up to 11.2 mm. Perforation of the left ventricle occurred in two cases following 80 and 160 J, respectively. In vitro and in the intact animal (in apical and apico-inferior sites of the left ventricle) endocardial laser ablation is feasible to induce distinct myocardial lesions in a power- and time-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Catheter ablation using radiofrequency energy.

Recently, transvenous catheter ablation using radiofrequency impulses has been applied in experimental animals as well as in humans. This review describes the biophysics, mechanisms, and tissue effects of radiofrequency alternating current. Ablation of the AV-junction has been performed in experimental studies as well as in a growing number of patients. Complete AV-block or modification of the AV conduction by RF-current application can be achieved in about 45-65% of patients. Presently about 50% of patients with rightsided accessory pathways can be successfully managed using radiofrequency impulses. Certain limitations exist using a biopolar "epi-endocardial" electrode configuration for leftsided accessory pathways. Only few studies are available concerning the use of RF ablation of ventricular tachycardia foci. As most experimental investigations were carried out in structurally nondiseased myocardium, the use of this new technique in fibrotic or scarred tissue warrants further studies. Radiofrequency catheter ablation seems to be feasible and relatively safe for the treatment of otherwise drug-refractory supraventricular arrhythmias; further studies are needed to assess the safety and efficacy in patients with drug-refractory ventricular tachyarrhythmias.

Animals↗