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Biomedical subjects

R N Hauer

Publications and source records attributed to R N Hauer.

67 records · Page 4Linked to original sources
PubMed1989

Electrode catheter ablation for ventricular tachycardia: efficacy of a single cathodal shock.

Electrode catheter ablation was used to treat 11 distinct types of sustained ventricular tachycardias in eight patients. Rigid electrophysiological criteria were used to identify five left and five right ventricular arrhythmogenic sites; one of them gave rise to tachycardia with two distinct configurations. A single R-wave-synchronised 250 or 150 J cathodal shock was delivered at each site. One patient had mildly symptomatic episodes of sustained ventricular tachycardia during the first four days after the shock--there were no other complications. At discharge none of the patients was taking antiarrhythmic drugs. They were followed for 8-20 months (mean 14). Ablation abolished five of the 11 ventricular tachycardias. There was no recurrence in three of the eight patients. In two patients identical ventricular tachycardias recurred because the identification of the arrhythmogenic site was incorrect.

Adult↗
PubMed1989

Control of radiofrequency lesion size by power regulation.

The influence of power and exposure duration on lesion size in radiofrequency catheter ablation was investigated in 15 closed-chest dogs. Radiofrequency energy was delivered to the right ventricular endocardium between the tip of a standard 6F electrode catheter and a large W and durations of 5, 10, 20, 30, and 60 seconds. At necropsy 1 week later, well-demarcated homogeneous lesions were found when power had exceeded a threshold level that decreased from 1.8 W at 5 seconds to 0.7 W at 60 seconds. Lesion size ranged from 0 to 7.5 mm in depth and 0 to 9 mm in diameter. For the 5, 10, and 20 second ablations, lesion size was determined by exposure duration and power level. However, after a 20 second exposure, lesion size had reached maturity and was related to delivered power only. Therefore, a gradual, controlled growth of the lesion can be obtained by a stepwise increase of the radiofrequency power level with ample exposure duration at each level to allow for stabilization. At levels exceeding 7 W, the formation of a thin insulating layer of blood coagulum on the electrode surface caused an abrupt increase of impedance within approximately 30 seconds. Therefore, lesion size is limited to 8.5 mm in radiofrequency ablation with a standard 6F endocardial electrode catheter.

Animals↗
PubMed1988

Reentry as a cause of ventricular tachycardia in patients with chronic ischemic heart disease: electrophysiologic and anatomic correlation.

In this report we describe electrophysiologic and histologic findings in hearts and endocardially resected preparations from patients with sustained ventricular tachycardias in the chronic phase of myocardial infarction. We recorded simultaneously from 64 endocardial sites during tachycardia in 72 patients that were operated on for medically intractable ventricular tachycardias. Two other patients underwent heart transplantation, and mapping was performed on the explanted isolated heart connected to a Langendorff perfusion set-up. During operation 139 tachycardias with different morphologies could be induced. Although the majority of evidence supports the concept of a reentrant mechanism for these tachycardias, we found that 105 tachycardias appeared to arise at a focal area of less than 1.4 cm2. In only three cases macroreentry around the infarction scar could be detected. Of 21 tachycardias in which the "origin" appeared to be focal, earliest subendocardial activation was preceded by discrete electrograms of low amplitude (presystolic activity). In three tachycardias presystolic activity was detected at several sites, permitting reconstruction of its route. Histology of the endocardial resected preparation in one of these cases revealed separate zones of viable myocardial fibers in areas in which presystolic activity was recorded. These zones were located intramurally and subendocardially, supporting the concept that reentry occurred via isolated bundles of surviving myocytes at the border of the infarct and the larger subendocardial muscle mass. Conduction velocity through the isolated tracts was on the order of 25 cm/sec. Similar reentrant pathways were found in the two isolated hearts. Extracellular and intracellular recordings were made from 20 endocardial preparations that were excised from areas in which tachycardia originated. Preparations were superfused in a tissue bath. These experiments showed that action potentials were usually close to normal, but occasionally action potentials with reduced amplitude and slow upstrokes were found. In addition, there were cells that exhibited both fast and slow upstrokes, depending on the direction of the wavefront. Histology of seven resected preparations and the isolated hearts showed subendocardially as well as intramurally located zones of viable myocardium. Fractionation of extracellular electrograms and slow conduction were found in areas where surviving muscle fibers and strands of fibrous tissue were interwoven, and in zones where muscle fibers were oriented in parallel but isolated by strands of connective tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Proarrhythmic effects of ventricular electrical catheter ablation in dogs.

Electrical catheter ablation of arrhythmogenic sites is a new therapy for ventricular tachycardia that is still being investigated. Recent studies have shown, however, that the procedure itself can provoke serious ventricular arrhythmias. The incidence, course and mechanism of these arrhythmias were studied in 10 beagles treated with a single R wave-synchronized cathodal shock delivered to the endocardial ventricular wall (5 dogs left ventricular, 5 dogs right ventricular). Shocks were delivered at 30 (four dogs), 80 (two dogs) or 250 J (four dogs). Each dog underwent programmed electrical stimulation at or near the ablation site before, within 1 hour after and 1 week after the shock. Holter electrocardiographic monitoring (24 hours) was performed during day 1 and 7 after the shock in all the dogs, and extended Holter monitoring was done during the first 5 days in four dogs. All dogs survived for 1 week. Within 10 minutes after the shock, a sustained ventricular tachycardia was recorded in nine dogs; deterioration into ventricular fibrillation occurred in two dogs. In nine dogs, 60 to 169 monomorphic ventricular tachycardia episodes (mean 101) occurred on day 1 and 0 to 11 (mean 3) occurred on day 7; Holter monitoring failed for technical reasons in one dog. Extended Holter monitoring showed a marked decline in the incidence of tachycardia during the first 3 days. Early activation during ventricular tachycardia was always derived at or near the ablation site, and the QRS configuration during pre- and postablation pacing at this site was identical to the tachycardia configuration. Ventricular tachycardia was never inducible with programmed stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Electrical catheter ablation in the left and right ventricular wall in dogs: relation between delivered energy and histopathologic changes.

Electrical catheter ablation of arrhythmogenic sites is now being used for the treatment of ventricular tachycardias. However, the extent and type of the ablation lesion in relation to energy level are controversial and not well known. In 10 beagles, single cathodal shocks of 30 (4 dogs), 80 (2 dogs) or 250 J (4 dogs) were delivered to the endocardial ventricular wall (5 dogs left ventricular, 5 dogs right ventricular). One week after ablation the dogs were killed for histopathologic examination. In the left ventricular wall, ablation lesion volumes calculated from measured extensions in three perpendicular directions were 0.4 and 0.9 cc at 30 J, 1.9 cc at 80 J and 2.8 and 3.4 cc at 250 J; in the right ventricular wall they were 0.4 and 0.5 cc at 30 J, 1.3 cc at 80 J and 2.5 and 4.2 cc at 250 J. In the right ventricular wall all 30 to 250 J lesions were transmural, whereas in the left ventricular wall only 250 J lesions were transmural. All lesions showed a necrotic area surrounded by granulation tissue with degenerated myofibrils. Thus, the size of the ablation lesion depends on delivered energy, whereas the pattern of histopathologic change is identical in the 30 to 250 J energy range. These results suggest that with accurate localization of the arrhythmogenic site one low energy shock may be successful with less myocardial damage.

Animals↗
PubMed1986

Endocardial catheter mapping: validation of a cineradiographic method for accurate localization of left ventricular sites.

To guide surgical therapy for ventricular tachycardia by preoperative endocardial catheter mapping, accurate anatomic localization of arrhythmogenic sites is mandatory. For this reason we developed a mathematical cineradiographic method to compute left ventricular sites relative to three anatomic reference points: the centers of aortic and mitral valve ostia and the left ventricular apex. To validate the method 14 epicardial left ventricular markers were implanted in four dogs to simulate arrhythmogenic sites. Distances between markers and the anatomic references were calculated and the results were compared with postmortem measurements. The difference between calculated and measured distances was 0.5 +/- 3.1 mm (mean +/- SD), confirming accurate localization of anatomic marker sites. However, in surgery the results have to be displayed in a practically applicable, unambiguous way. Therefore, wire skeletons were constructed to represent calculated endocardial marker sites relative to the anatomic reference points. To validate this approach, 14 markers were implanted in the left ventricular subendocardium in four dogs. Wire skeletons were constructed, one for each marker site, and inserted postmortem into the left ventricular cavity via a 2 cm incision. In all cases the correct indication of a marker site by the corresponding wire skeleton was confirmed by fluoroscopic inspection in multiple projections. This wire skeleton technique may enhance the practical usefulness of preoperative endocardial catheter mapping.

Animals↗
PubMed1986

Endocardial catheter mapping: wire skeleton technique for representation of computed arrhythmogenic sites compared with intraoperative mapping.

Guiding surgical therapy of ventricular tachycardia by preoperative endocardial catheter mapping necessitates improvement of the accuracy of localization of the arrhythmogenic site. We therefore used a new mathematical cineradiographic method during catheter mapping to compute the position of left ventricular arrhythmogenic sites relative to three anatomic reference points: the centers of aortic and mitral valve ostia and the left ventricular apex. To enable the surgeon to identify the position of the computed sites, a wire skeleton (one for each patient) representing a single or multiple arrhythmogenic site(s) relative to the anatomic reference points was constructed. This wire skeleton was inserted into the left ventricular cavity during surgery. Side branches of the device indicated preoperatively localized arrhythmogenic sites. Results in eight consecutive patients were compared with those of intraoperative simultaneous mapping of 64 endocardial sites. Sixteen morphologically distinct monomorphic ventricular tachycardias were mapped by catheter and 15 by intraoperative mapping. In 12 ventricular tachycardias an identical morphology was recorded during both techniques. The distance between arrhythmogenic sites localized with both methods was 1 cm or less in 11 of these 12 ventricular tachycardias and 2 cm in one ventricular tachycardia. These results indicate that endocardial catheter mapping combined with wire skeleton representation of computed positions of arrhythmogenic sites is reliable for guiding surgical therapy of ventricular tachycardia and since some of the ventricular tachycardias were inducible only during either preoperative or intraoperative mapping, both techniques have an additive value. In addition, the wire skeleton proved convenient during surgery by identifying the arrhythmogenic sites.

Cardiac Catheterization↗
PubMed1985

Role of atrial fibrillation and atrioventricular conduction (including Wolff-Parkinson-White syndrome) in sudden death.

A short refractory period of the accessory pathway is considered a major threat for sudden death in patients with Wolff-Parkinson-White syndrome and atrial fibrillation. RR interval and QRS signal analysis together with signal analysis of a bipolar high right atrial electrogram were obtained in six patients with Wolff-Parkinson-White syndrome and either induced or spontaneous atrial fibrillation. A record of a sufficiently long episode of atrioventricular (AV) conduction by way of the bypass tract that could be used for satisfactory RR interval sequence and QRS analysis was obtained from only one patient. The results were compared with those of a representative patient with atrial fibrillation and normal AV nodal-His conduction. In a patient with Wolff-Parkinson-White syndrome, atrial fibrillation and AV conduction by way of the bypass tract may exhibit high ventricular rates (median RR intervals of about 300 ms) and long/short RR interval ratios of just over 1 (RR intervals not exceeding 400 ms). The right atrial electrogram showed a noiselike excitation pattern. This study suggests that rather than a short refractory period of the bypass tract, it is lack of concealed conduction, responsible for the presence of long RR intervals, that allows the ventricles to reach very high ventricular rates and at times to fibrillate. The normal AV nodal-His system seems to protect the heart against high ventricular rates and ventricular fibrillation during atrial fibrillation by its relatively long refractory period and capacity to induce long RR intervals by means of concealed conduction.

Atrial Fibrillation↗
PubMed1983

Syncope and ventricular tachycardia in patients with ventricular preexcitation.

Four patients with ventricular preexcitation whose syncope initially was attributed to an arrhythmia utilizing the accessory pathway are presented. At electrophysiologic study, the electrophysiologic characteristics of the accessory pathways were considered unlikely to support a tachycardia of a rate sufficient to result in syncope. Programmed stimulation of the right ventricle, however, reproducibly induced ventricular tachycardia to which the syncope was subsequently attributed in 3 patients. The importance of identifying ventricular tachycardia as the cause of syncope in these patients is emphasized.

Adult↗
PubMed1982

Long-term prognosis in patients with bundle branch block complicating acute anteroseptal infarction.

In a previous study patients with bundle branch block complications acute anteroseptal infarction found to have a high incidence rate of sudden death and late ventricular fibrillation in the first 6 weeks after infarction. Forty-two such consecutive patients were therefore kept within the monitoring area during those 6 weeks. Eighteen (43 percent) of these 42 patients survived and were then followed up for an average of 13 months to assess long-term prognosis and to evaluate whether the in-hospital monitoring period should be extended over 6 weeks. In most of these 18 patients a bifascicular block developed in the acute stage of infarction and in 3 it progressed to transient high degree atrioventricular (A-V) block. Seven of the 18 survivors had potentially lethal complications during the first 6 weeks. Four of these seven underwent aneurysmectomy between 10 and 20 weeks after infarction, and one of them died of a surgical complication. Major cardiac events occurred in 3 of the 17 survivors. None of these patients died during the follow-up period. In one patient complete A-V block developed after aneurysm resection; this was the only patient treated with permanent pacing. Fifteen of the 17 patients were in functional class I or II. These results indicate that (1) patients with bundle branch block complicating acute anteroseptal infarction who survive the first 6 weeks after infarction have a good prognosis during the 1st year, and (2) extension of the in-hospital monitoring period is not necessary. The results further suggest that prophylactic permanent pacing does not affect prognosis in these patients.

Bundle-Branch Block↗
PubMedDate not supplied

Amiodarone and desethylamiodarone concentrations in plasma and tissues of surgically treated patients on long-term oral amiodarone treatment.

The tissue disposition of amiodarone and its metabolite desethylamiodarone was studied in 12 surgical patients with various types of arrhythmias after chronic oral treatment with amiodarone. Amiodarone and desethylamiodarone concentrations in plasma and tissues were determined using a simple and sensitive high performance liquid chromatographic method. The mean plasma level of amiodarone and desethylamiodarone was found to increase from 0.55 microgram/ml to 1.40 microgram/ml and 0.68 microgram/ml to 1.80 microgram/ml for the respective components following the increase of the daily oral dose from 200 mg to 600 mg of amiodarone and indicates a linear relationship between plasma concentrations and dose. The mean levels of both drugs in different parts of the heart varied for amiodarone from 15 to 48 micrograms/g and for desethylamiodarone from 48 to 71 micrograms/g, with the highest values present in the epicardially resected ventricular myocardium. The mean cardiac tissue/plasma ratios ranged for amiodarone from 12 to 35 and for desethylamiodarone from 35 to 61 and show an extensive tissue uptake in the different parts of the heart for both drugs, with the metabolite accumulation 2 to 5 times higher than the parent compound. Relatively low levels, ranging for amiodarone from 2 to 15 micrograms/g and for desethylamiodarone from 5 to 25 micrograms/g, were observed in skeletal muscle, epidermis, skin and femoral artery. By far the largest content of the drugs was found in adipose tissue with mean concentrations of 207 +/- 98 micrograms/g and 82 +/- 43 g/g respectively for the parent compound and its metabolite, which suggests that fat constitutes the main depot of the drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗