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Biomedical subjects

M Block

Publications and source records attributed to M Block.

At least 91 records · Page 5Linked to original sources
PubMed1993

Radiofrequency catheter ablation of ventricular tachycardia following implantation of an automatic cardioverter defibrillator.

OBJECTIVES: The present study reports on the complementary role of two nonpharmacological options of antiarrhythmic therapy. BACKGROUND: Catheter ablation, antitachycardia surgery, and the implantable cardioverter defibrillator (ICD) have become important tools in the management of ventricular tachyarrhythmias. However, the emergence of ventricular tachyarrhythmias after implantation of an ICD is possible because the arrhythmogenic substrate is not affected. PATIENTS AND METHODS: Six of 180 patients developed frequent episodes of monomorphic ventricular tachycardia (n = 2) or incessant ventricular tachycardia (n = 4) following implantation of an ICD and underwent radiofrequency (RF) catheter ablation. Catheter ablation was performed using a RF generator HAT 200. Energy was delivered between a 4-mm tip electrode of the ablation catheter and a patch electrode. RESULTS: Catheter ablation was done 6.8 +/- 5 months following ICD implantation; 6 +/- 2.2 RF impulses were delivered at the site of origin of ventricular tachycardia characterized by early endocardial activation during ventricular tachycardia, identical pace mapping and long latency between stimulus, and QRS-complex in five patients. New bundle branch reentry was the underlying mechanism of ventricular tachycardia in one patient. RF catheter ablation resulted in termination of incessant ventricular tachycardia. Immediately postablation, the documented ventricular tachycardia was rendered noninducible in all patients. No ICD malfunctions have been observed. One patient died due to heart failure 24 hours after successful ablation of the incessant ventricular tachycardia. During a follow-up of 5-19 months, episodes of ventricular tachycardia recurred in four patients. All episodes could be controlled by the ICD without frequent cardioversions. CONCLUSION: RF catheter ablation is a complementary therapeutic option in case of frequent or incessant ventricular tachycardia after ICD implantation.

Adult↗
PubMed1993

[Therapy of ventricular tachyarrhythmia with implantable cardioverters/defibrillators--mortality and complications using epicardial electrodes].

Technical improvements of third generation implantable cardioverter defibrillators (ICD) like antitachycardia pacing modalities lead to an extended use of ICDs, not only in patients with aborted sudden cardiac death, but also in patients with hemodynamically tolerable ventricular tachycardia. In addition, anticipated results of current prospective studies might indicate the prophylactic use of ICDs in patients with high risk for sudden cardiac death, but without documented ventricular tachyarrhythmias. This report reviews mortality and complications associated with the ICDs with epicardial defibrillation leads. Mortality is separated in cardiac death, sudden cardiac, arrhythmogenic "not so sudden" cardiac death, and overall mortality. Pulmonary complications and infections are related to the underlying disease and the surgical procedure. Device- and lead-related complications, high defibrillation thresholds, pacemaker interactions, inappropriate shocks, arrhythmic effects, syncope, and psychosocial problems are reported, respectively.

Adolescent↗
PubMed1993

[Diagnostic and therapeutic problems in idiopathic prolonged QT syndrome. A case report].

The case of a 36-year-old woman with suspected idiopathic long QT syndrome is reported. Diagnosis was made late after syncopal attacks and several episodes of resuscitation had occurred. Although therapy with a beta-blocking agent was initiated and a cardioverter/defibrillator was implanted, the patient died, due to a hydrocephalus internus resulting in cerebral damage. Diagnostic and therapeutic problems in idiopathic long QT syndrome are discussed.

Adult↗
PubMed1992

Doppler echocardiographic assessment of the pressure gradient during bicycle ergometry in hypertrophic cardiomyopathy.

To assess the behavior of the subvalvular pressure gradient under physical exercise, 13 patients with obstructive hypertrophic cardiomyopathy were examined during upright bicycle ergometry by means of Doppler echocardiography. Additionally, right-sided cardiac catheterization was performed within 7 days. In 10 patients adequate Doppler tracings could be obtained during exercise. The Doppler-derived systolic pressure gradient increased from 75 +/- 24 to 140 +/- 42 mm Hg (p less than 0.0005). This was associated with an increase in the duration of the systolic mitral-septal contact from 59 +/- 21 to 136 +/- 28 ms (p less than 0.0005). Correlation between the pressure gradient and the duration of mitral-septal contact at rest and during exercise was good (r = 0.86), whereas correlation between the resting and exercise pressure gradient (r = 0.34) did not reach statistical significance. The increase in stroke volume during exercise, from 90 +/- 18 to 95 +/- 24 ml, was significant (p less than 0.05) but minimal. Therefore, only a moderate increase in systolic flow, from 205 +/- 54 to 268 +/- 78 ml/s (p less than 0.0005), was observed. Outflow tract resistance, defined as the ratio of the pressure gradient to systolic flow, increased from 0.38 +/- 0.11 to 0.57 +/- 0.24 mm Hg.s/ml (p less than 0.01). Thus, in a selected group of patients with hypertrophic cardiomyopathy a substantial increase in the maximal pressure gradient during upright bicycle ergometry was demonstrated in most patients. Exercise Doppler echocardiography may be valuable to assess the hemodynamic significance of obstruction in individual patients in a physiologic setting and has a potential to monitor the effect of therapeutic interventions.

Adult↗
PubMed1992

Prediction of the site and severity of obstruction in hypertrophic cardiomyopathy by color flow mapping and continuous wave Doppler echocardiography.

OBJECTIVE: We investigated whether the site and severity of an obstruction in hypertrophic cardiomyopathy can be accurately predicted by the combined use of color-coded and continuous wave Doppler echocardiography. BACKGROUND: Predicting the site of obstruction by end-systolic cavity shape is not reliable. Therefore, hemodynamic localization of the obstruction is required before surgery is performed. Such localization should be possible with color flow imaging, which provides two-dimensional velocity mapping reflecting the distribution of pressures within the left ventricle. Discrepancies in assessment of the pressure gradient by Doppler echocardiography and cardiac catheterization (which are usually not performed simultaneously) may be due to spontaneous variation of the dynamic obstruction in addition to technical factors related to both methods. METHODS: Twenty consecutive patients with hypertrophic cardiomyopathy were examined 1 day before transseptal left heart catheterization. The obstruction site was defined by color flow mapping. The pressure gradient was determined by continuous wave Doppler echocardiography. Measurements were also performed simultaneously in 10 patients during cardiac catheterization. RESULTS: Midventricular obstruction was correctly identified in 4 patients and subvalvular obstruction in 15 patients. One patient had no obstruction at rest. Invasively and noninvasively determined pressure gradients correlated well (r = 0.89, SEE = 16.3 mm Hg). Multiple single-beat analysis in 10 patients, also simultaneously examined with Doppler echocardiography and catheterization, yielded an excellent correlation (r = 0.97, SEE = 13.1 mm Hg). Comparing the simultaneous (r = 0.96, SEE = 12.5 mm Hg) and nonsimultaneous (r = 0.81, SEE = 23.8 mm Hg) recordings in these patients, we found that the spontaneous variation of the dynamic obstruction mainly accounted for discrepancies (p less than 0.05). CONCLUSION: The combined use of color-coded and continuous wave Doppler echocardiography provides the relevant hemodynamic information required for decision-making in patients with hypertrophic cardiomyopathy who are considered for transaortic myectomy.

Adult↗
PubMed1992

Implantation of a cardioverter/defibrillator in the subpectoral region combined with a nonthoracotomy lead system.

An implantable cardioverter defibrillator was placed into a subpectoral pocket via the incision for cephalic venotomy during implantation of a nonthoracotomy lead system. The approach obviated another incision and subcutaneous tunneling of the leads. There were no perioperative complications and after 6 months of follow-up, the patient continues to tolerate the device satisfactorily.

Electric Countershock↗
PubMed1992

Role of ventricular tachycardia surgery and catheter ablation as complements or alternatives to the implantable cardioverter defibrillator in the 1990s.

Although the implantable cardioverter defibrillator is used increasingly, other nonpharmacological approaches have their indications and merits. Furthermore, as the natural history of ventricular tachyarrhythmias or their underlying structural cardiac abnormality, i.e., coronary artery disease, dilated cardiomyopathy, arrhythmogenic right ventricular disease, etc. change, the mode of therapy may be modified accordingly. Because of the disappointing results of the CAST study in previously asymptomatic patients after myocardial infarction and the evidence that failure of one or two antiarrhythmic drugs tested by programmed ventricular stimulation in patients with documented sustained ventricular tachycardia or fibrillation predicts further drug failure, there will be a significant increase in the use of implantable cardioverters defibrillators in the 1990s. However, care should be taken to avoid inappropriate use of these devices.

Adult↗
PubMed1992

Efficacy of automatic multimodal device therapy for ventricular tachyarrhythmias as delivered by a new implantable pacing cardioverter-defibrillator. Results of a European multicenter study of 102 implants.

BACKGROUND: Third-generation implantable cardioverter-defibrillators are devices designed to treat ventricular tachycardia (VT) and ventricular fibrillation (VF) by means of overdrive pacing, cardioversion, or defibrillation. So far, the efficacy of tiered therapy has been documented only in small series. Therefore, a European multicenter clinical evaluation study of a new tachyarrhythmia control device, the Medtronic PCD pacer-cardioverter-defibrillator with epicardial patch-lead configuration, was undertaken. METHODS AND RESULTS: We report on 102 patients (mean age, 55 +/- 13 years) from 11 European centers. PCD devices implanted between May 1989 and February 1991 were included. The patients suffered from hemodynamically significant ventricular tachyarrhythmias not suppressed by antiarrhythmic drug therapy and unrelated to acute myocardial infarction; one patient had nonsustained VT and severely depressed left ventricular function. Seventy patients had coronary artery disease with old myocardial infarctions, 23 had cardiomyopathies of various etiologies, and nine patients had no detectable heart disease. Mean ejection fraction was 36 +/- 14% (range, 10-76%). Mean intraoperative defibrillation threshold (51 patients) was 10.6 +/- 5.1 J (range, 2-18 J). The documented follow-up ranged from 1 to 21 months (mean, 9.4 +/- 5.8 months), or 79.9 cumulative patient-years. Perioperative mortality was 3.9%. The actuarial survival rate at 12 months was 91%. One sudden arrhythmic death occurred. Sixty patients (58%) received device therapy. Seventeen patients had therapies only for "VF" episodes, 16 patients only for VT, and 28 patients for VT and "VF" episodes. Based on device memory data, 1,235 spontaneous VT episodes were detected and treated in 43 patients. Twelve hundred four of these VT episodes received painless initial antitachycardia pacing therapy, restoring sinus rhythm in 91%. The 108 ongoing episodes received 209 multiple therapeutic attempts. Eighty-five additional overdrive pacing therapies restored sinus rhythm in 30%. Initial ineffective antitachycardia pacing therapies received 51 cardioversion pulses. The success rate was 61%. Seventy-three additional cardioversion pulses were delivered to backup ineffective pacing therapy as well as ineffective secondary cardioversion pulses. Their success rate was only 40%. Two hundred eighty-six spontaneous episodes were detected in 44 patients as "VF." Overall defibrillation efficacy was 97.6%. CONCLUSIONS: The implanted device nearly eliminates sudden arrhythmic death in patients with documented, potentially fatal ventricular tachyarrhythmias. Automatic tiered therapy is highly effective to restore sinus rhythm, provided that an integrated two-zone tachycardia detection algorithm is used, assigning lower tachycardia rates to overdrive pacing and/or cardioversion and higher tachycardia rates to defibrillation. In general, spontaneous VTs can be terminated by automatic overdrive pacing, and painful or disturbing countershock therapies are not required to terminate the majority of spontaneous VT episodes.

Death, Sudden, Cardiac↗
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↗
PubMed1991

Ultrastructural abnormalities of mitochondria and deficiency of myocardial cytochrome c oxidase in a patient with ventricular tachycardia.

A 30-year-old woman presented with life-threatening ventricular tachycardia without overt heart disease. Ultrastructural investigation of endomyocardial biopsy disclosed abnormally structured and often enlarged mitochondria. Morphometry revealed the ratio of volume density of mitochondria to myofibrils to be markedly increased to 0.667 as compared with five controls (mean: 0.46; range: 0.445-0.479). Investigation of mitochondrial respiratory chain enzymes revealed a 90% reduction in activity of cytochrome c oxidase. Our data suggest that mitochondrial cardiomyopathy may induce malignant ventricular arrhythmias.

Adult↗
PubMed1991

Decreased norepinephrine and epinephrine contents in chromaffin tissue of rainbow trout (Oncorhynchus mykiss) exposed to diethyldithiocarbamate and amylxanthate.

1. Rainbow trout (Oncorhynchus mykiss) were exposed to 0.5 or 5.0 microM of diethyldithiocarbamate (DDC) or amylxanthate (AX) for 24 hr. 2. Both DDC (0.5-5.0 microM) and AX (5.0 microM) significantly decreased norepinephrine and epinephrine levels in the head kidney as well as the quotients epinephrine/dopamine and/or norepinephrine/dopamine. 3. The results probably reflect an inhibition of dopamine-beta-hydroxylase, the enzyme responsible for the synthesis of norepinephrine and epinephrine from dopamine. 4. It is concluded that an exposure of fish to these complexing agents could disturb physiological processes controlled by catecholamines. 5. Diethyldithiocarbamate may prove to be a valuable pharmacological tool for the study of catecholamine function in fish.

Animals↗
PubMed1991

Implantable cardioverter/defibrillators (ICD): a new lead-system using transvenous-subcutaneous approach in patients with prior cardiac surgery.

The current approach in cardioverter-defibrillator implantation requires placement of epicardial leads which may lead to pericardial and/or pleural effusion and pneumonia during the perioperative period. Although ICD implantation is less invasive than other surgical techniques for the treatment of rhythm disturbances, the perioperative mortality must be considered. Minimizing the operative procedure could lead to a reduction in perioperative mortality. Therefore, we investigated an approach without the need for thoracotomy using a transvenous/subcutaneous lead system. In nine patients with prior cardiac surgery, defibrillator implantation was performed by a transvenous/subcutaneous approach. There was no perioperative mortality. In all patients, a sufficient defibrillation threshold was achieved. The defibrillation pulses were delivered as two sequential pulses between a right ventricular electrode (cathode) and a coronary sinus or superior caval vein electrode (anode 1) and a subcutaneous patch electrode (anode 2). Intubation of the coronary sinus was necessary in 4 patients in order to obtain satisfactory defibrillation thresholds. These data demonstrate that a transvenous/subcutaneous approach is feasible in patients with prior cardiac surgery obviating the need for thoracotomy. Sensing function of the RV-electrode, intubation of the coronary sinus and the intraoperative use of an epicutaneous patch electrode are current problems of this new technique.

Adult↗
PubMed1991

Smoking-cessation treatment combining transdermal nicotine substitution with behavioral therapy.

Effects of smoking-cessation treatment combining transdermal nicotine substitution with behavioral therapy were investigated in two studies. A total of 403 smokers underwent nine weeks of behavioral self-control treatment. For seven weeks, groups with transdermal nicotine substitution were also provided with nicotine patches that continuously release nicotine through the skin into the circulatory system. The effects of treatment were measured by total abstinence. The results showed that the nicotine concentration in the patch, special relapse prevention methods, and the type of dosage (individual versus fixed dose) had no influence on therapeutic success. Nicotine concentration played a decisive role in the compatibility of the patch. Combining transdermal nicotine substitution with behavioral therapy produced 12-month success rates (total abstinence) of about 35%.

Administration, Cutaneous↗
PubMed1991

Cardiopulmonary effects of internal cardioverter/defibrillator implantation.

Cardiopulmonary effects of electrophysiological testing of internal cardioverter/defibrillator (ICD) devices were studied in ten patients undergoing general anaesthesia. In the control-phase, haemodynamic performance and oxygenation were slightly impaired. After completion of the electrophysiological procedures (ICD-phase), cardiopulmonary function had deteriorated significantly. Cardiac index declined by 16%, whereas left ventricular filling pressure and pulmonary vascular resistance increased (P less than or equal to 0.01). Oxygenation, but not CO2-elimination deteriorated (P less than or equal to 0.01) and venous admixture increased by 72% (P less than or equal to 0.01). Alveolo-arterial PO2-difference (PA-aO2) increased by 43% (P less than or equal to 0.01), indicating ventilation-perfusion (VA/Q) mismatching. Repeated inductions of ventricular tachycardia and/or fibrillation subject the myocardium to transient global ischaemia, leading to acute congestive heart failure, and positive inotropic intervention was necessary in 40% of the patients. Partial pulmonary insufficiency resulted possibly from interstitial oedema and VA/Q-inhomogeneities. ICD implantation has detrimental effects on haemodynamics and gas exchange in patients with impaired left ventricular function.

Aged↗
PubMed1991

[Initial clinical experiences with a transvenous-subcutaneous defibrillation system].

In 19 patients with an indication for an implantable defibrillator, it was tried to avoid thoracotomy by using two electrodes positioned via the subclavian vein in the right ventricle (for pacing, sensing, and defibrillation) and the superior vena cava or coronary sinus (for defibrillation), and one electrode positioned subcutaneously near the ventricular apex (for defibrillation). In 17 patients (89%) the transvenous-subcutaneous leads were implanted, whereas in the remaining two patients an epi-/pericardial lead system was subsequently used due to an insufficient defibrillation threshold. Perioperatively, no major complications were observed and patients were rapidly mobilized. Within a follow-up period of 7 +/- 4 months, no malfunction of the lead system became evident. Sixty-eight episodes of spontaneous ventricular tachyarrhythmias occurred, all of which were successfully terminated. In one patient an infection of the lead system developed after 2 months that proved refractory to antibiotics and required surgical removal. Thus, transvenous-subcutaneous placement of leads for implantable defibrillators yielded a sufficient defibrillation threshold in the majority of patients. Long-term efficacy was excellent and no malfunctions were observed. This approach seems to be feasible and advisable in patients with an increased risk for thoracotomy.

Adolescent↗