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Biomedical subjects

T A Simmers

Publications and source records attributed to T A Simmers.

17 recordsLinked to original sources
PubMed2000

Ventricular tachycardia as a complication of atrial flutter ablation.

A 61-year-old woman with dilated cardiomyopathy, who previously underwent successful radiofrequency catheter ablation for atrial flutter, developed monomorphic ventricular tachycardia (VT). The site of VT origin was the inferobasal right ventricle adjacent to the previous atrial isthmus ablation area. The most likely mechanism for the VT was scar-related reentry, the scar being the result of previous radiofrequency lesions in the atrial isthmus. The VT was successfully ablated.

Atrial Flutter↗
PubMed1999

[The use of an implantable ECG recorder in the diagnosis of puzzling sporadic syncopes].

A 70-year-old man had passed out three times in six years, and was suspected of having a rhythm or conduction disturbance. Repeated hospitalization with telemetric monitoring had not revealed any disease. An implantable ECG recorder finally revealed the occurrence of symptomatic sinus arrest (Adams-Stokes attack), a month after discharge from the hospital. The patient was treated with a pacemaker. The cause of recurrent syncope can be difficult to diagnose. There is always a danger of overdiagnosis or under-treatment. Prospective study and cost effectiveness analysis are needed to determine the proper place of the implantable ECG recorder in the diagnosis of this disease.

Adams-Stokes Syndrome↗
PubMed1999

Minimally invasive treatment of thoracic empyema.

BACKGROUND: The present study was undertaken to assess the efficacy of serial thoracocentesis and saline irrigation for the treatment of pleural empyema, for post-pneumonia versus other causes. METHODS: Included were 42 consecutive patients with complicated pleural effusion (n=14) or frank pus (n=28) at diagnostic thoracocentesis, of mean age 57.5 +/- 23.7 years. Pneumonia was the probable cause in 29 patients, other causes (principally thoracic surgery) in 13. In addition to antibiotics in all patients, ultrasonography-guided serial suction thoracocentesis with saline irrigation was used as therapy of first choice in most patients: 28/29 post-pneumonia and 9/13 non-pneumonic empyema. Exceptions were mainly on the grounds of preceding thoracic surgery. RESULTS: Success rate was 86% in the post-pneumonia group, with no crossovers to more invasive therapy. Mortality was 14%, none empyema-related. Treatment was less successful in the non-pneumonia group at 69%, with a 56% crossover rate from thoracocentesis due to therapy failure. Mortality was 23 %. CONCLUSIONS: Results indicate that timely, minimally invasive therapy is a feasible modality for the management of post-pneumonia thoracic empyema. Serial thoracocentesis was less suitable for the treatment of non-pneumonic empyema, however, particularly if it was a surgical complication. More invasive strategies seem preferable in such cases.

Adolescent↗
PubMed1998

Effects of intracavitary blood flow and electrode-target distance on radiofrequency power required for transient conduction block in a Langendorff-perfused canine model.

OBJECTIVES: We sought to quantify the effects of electrode-target distance and intracavitary blood flow on radiofrequency (RF) power required to induce transient conduction block, using a Langendorff-perfused canine ablation model. BACKGROUND: Given the thermally mediated nature of RF catheter ablation, cooling effects of intracavitary blood flow and electrode-target distance will influence lesion extension and geometry and electrophysiologic effects. METHODS: In eight Langendorff-perfused canine hearts, the right ventricular free wall was opened, and the right bundle branch (RBB) carefully localized by multielectrode activation mapping. The right atrium was paced at cycle length of 500 ms. Proximal and distal electrodes were attached at the endocardial aspect of the RBB, and the perfused heart was submerged in heparinized blood at 37 degrees C. A standard 4-mm tip ablation electrode was positioned at a constant contact pressure of 5 g between the two electrodes at the site of maximal RBB potential (0 mm) and 2 and 4 mm distant from this site along a line perpendicular to the RBB. RF pulses (500 kHz) were delivered for 30 s at 0.5-W increments until transient bundle branch block. In four hearts, intracavitary flow was simulated by directing a 30-cm/s jet of blood parallel to the septum at the ablation site, and the protocol was repeated to assess the effects on power required for block. In one heart, the effect of variable flow was assessed (0, 15 and 30 cm/s). RESULTS: An exponential distance-related increase was seen in power required for block, from 1.8 +/- 0.9 W (mean +/- SD) at 0 mm to 5.4 +/- 1.1 W at 4 mm. In the presence of 30-cm/s flow, an increase to 3.9 +/- 0.8 W at 0 mm and 13.1 +/- 2.4 W at 2 mm was seen. At 4 mm, coagulum formation invariably occurred before block could be induced. For 15-cm/s flow, less power was required: 3 and 7 W at 0 and 2 mm, respectively. CONCLUSIONS: Increasing the ablation electrode-target distance causes an exponential increase in power required for conduction block; this relation is profoundly influenced by intracavitary flow. Given the geometry of endomyocardial RF lesions, these findings are particularly relevant for directly subendocardial ablation targets.

Animals↗
PubMed1997

Thymic tuberculosis: a case report.

Tuberculosis of the thymus is an extremely rare diagnosis, only three cases having been reported in the literature to date. Clinical, roentgenographic and histopathological findings are presented in a 29-year-old woman. The patient underwent sternotomy for a mediastinal mass suspected to be a thymoma, which was histopathologically diagnosed as thymic tuberculosis.

Adult↗
PubMed1997

Endobronchial lipoma posing as carcinoma.

Endobronchial lipoma is an extremely rare tumour. Although it is benign, recurrent obstructive pneumonia may cause significant morbidity and induce cytological findings suggestive of carcinoma. A case is presented demonstrating clinical, diagnostic and histopathological findings in this disease.

Aged↗
PubMed1997

Internal jugular vein thrombosis after cervical traction.

A clinically and roentgenographically typical case of internal jugular vein thrombosis is presented in a patient having undergone repeated sessions of Glisson traction for neck and backache. In this mode of therapy, axial traction is applied to the neck by attaching a weight, via a pulley, to a construction of straps encompassing the head. This particular trauma to the neck has not previously been described to be associated with spontaneous internal jugular vein thrombosis.

Female↗
PubMed1997

Salmonellosis: an unusual complication of hepatocellular carcinoma.

Salmonella abscess of a tumor is extremely rare, only three occurrences having been described to date. An unusual case is presented in which Salmonella infantis septicemia was the presenting symptom of multicentric hepatocellular carcinoma in a previously healthy 67-year-old man.

Aged↗
PubMed1996

Tropical pyomyositis in a temperate climate: a case report.

Pyomyositis is an abscess-forming infection of large skeletal muscles, usually with Staphylococcus aureus. Although it is common in the tropics and relatively rare in temperate climates, imported cases due to growing global mobility may be expected to increase its incidence outside tropical regions. Early diagnosis and correct management are imperative in this potentially fatal disorder, and require a high degree of clinical suspicion. A case report is presented demonstrating typical aspects of diagnosis and treatment.

Abscess↗
PubMed1996

Effects of heating with radiofrequency power on myocardial impulse conduction: is radiofrequency ablation exclusively thermally mediated?

INTRODUCTION: Although it is generally accepted that radiofrequency (RF) ablation causes exclusively thermally mediated effects, it has never been proved. METHODS AND RESULTS: In a previous report, temperatures required to induce conduction block in superfused canine epicardial ventricular myocardium were identified by exposure to heated superfusate: 50.3 degrees +/- 1.1 degrees C and 53.6 degrees +/- 0.6 degree C for transient and permanent block, respectively. In the present study, heating was performed using RF power in an otherwise identical model. Nine preparations from four dogs were used. A 1-cm diameter electrode was placed beneath the center of each preparation for RF delivery. Incisions were made to create a conductive isthmus over the ablation electrode. Preparations were paced to one side of the isthmus and electrograms recorded from the center of the isthmus and to either side. Temperature was measured using a miniature thermocouple located just below the epicardial surface, adjacent to the recording electrode in the heated zone. RF was delivered for 30 seconds at 5-minute intervals with increments in power per episode causing increments in temperature of approximately 2 degrees C. Temperature during pulses at which transient block occurred was 50.7 degrees +/- 3.0 degrees C; temperature at 30 seconds of heating in pulses leading to permanent block was 58.0 degrees +/- 3.4 degrees C. CONCLUSION: These findings provide evidence suggesting that the electrophysiologic effects of RF ablation are exclusively thermally mediated and are otherwise unrelated to the dissipation of high-frequency current.

Animals↗
PubMed1995

Effects of heating on impulse propagation in superfused canine myocardium.

OBJECTIVES: The goal of the study was to quantify the response of myocardial impulse propagation to hyperthermia and identify the temperatures required for transient and permanent block in conduction. BACKGROUND: Although it is generally accepted that the effects of radiofrequency ablation are thermally mediated, the precise response of myocardial impulse conduction to heating remains to be quantified. METHODS: Twenty-three preparations of ventricular myocardium from 10 beagle dogs were superfused at 36.5 to 37.5 degrees C and paced at a cycle length of 600 ms. Heating was performed for 30 s at 5-min intervals by an independent flow of heated superfusate. A 16-electrode grid was used to record extracellular electrograms directly before each heating episode (control value) and at 10, 20 and 30 s. RESULTS: Between 38.5 and 45.4 degrees C, conduction velocity was higher than that at the directly preceding control value (p < 0.05), reaching a maximum of 114% between 41.5 and 42.5 degrees C. Above 45.4 degrees C, a gradual decrease occurred, with transient block (absence of impulse conduction for < or = 5 min) after heating to 49.5 to 51.5 degrees C. This was followed by tachycardia in 69% of all cases immediately after cessation of heating. Permanent block occurred after a significantly higher temperature of 51.7 to 54.4 degrees C had been reached. Pacing at sites allowing preferential conduction either parallel or perpendicular to fiber orientation caused no difference in reaction to heating. Repeated heating of some preparations to 47.0 to 50.5 degrees C revealed no cumulative effects on conduction velocity. CONCLUSIONS: Transient and permanent block in impulse conduction occurred at 49.5 to 51.5 degrees C and 51.7 to 54.4 degrees C, respectively, in superfused canine myocardium, the former frequently being followed directly by tachycardia. Reaction of conduction velocity to hyperthermia was independent of myocardial fiber orientation and number of preceding heating episodes. Results may contribute to a better understanding of electrophysiologic phenomena observed during radiofrequency ablation procedures.

Animals↗
PubMed1995

Myocardial temperature response during radiofrequency catheter ablation.

During radiofrequency catheter ablation, steady-state electrode-tissue interface temperatures are reached within 5 seconds. Within the myocardium, however, a much slower temperature rise has been observed in vitro with stabilization after approximately 2 minutes. The discrepancy suggests that tissue temperature rise time depends on distance from the ablation electrode and, thus, that temperature rise measured at the electrode-tissue interface does not correspond with temperature rise within the myocardium. In five beagles, closed-chest radiofrequency catheter ablation was performed in the vicinity of intramural thermocouples. Sequences of 60 seconds, 10- and 25-watt pulses were delivered in the unipolar mode via the 4-mm distal electrode of a 7 French steerable catheter. At all distances > 3 mm from the ablation electrode, the rate of myocardial temperature rise was low: relative rise after 5, 10, 20, and 30 seconds was 22%, 32%, 48%, and 63% of that achieved at 60 seconds, and even then steady-state temperatures had not yet been reached. Temperature rise was faster at sites closer to the ablation electrode. There was no difference in rate of rise between first and second pulses at the same site. A 6% higher myocardial temperature was reached with a second identical pulse at the same site. Tissue temperatures achieved with 25 watts were 2.4 times higher than with a preceding 10-watt pulse at the same ablation site.

Animals↗
PubMed1995

Change in delay of atrioventricular conduction after radiofrequency catheter ablation for atrioventricular nodal re-entry tachycardia.

OBJECTIVE: To monitor atrioventricular conduction after radiofrequency ablation for atrioventricular nodal re-entry tachycardia. DESIGN: Measurement of PR interval from 12 lead surface electrocardiograms before; at 0, 24, 48, 72, and 96 hours; and at 1 and 6 months after radiofrequency ablation. PATIENTS: 40 consecutive patients with atrioventricular nodal re-entry tachycardia. The anterior approach was used in 23 patients, the posterior approach in 17. RESULTS: With the anterior approach the PR interval increased significantly and progressively until 48 hours after ablation (maximum 282 (SD 62.2) ms, before ablation 142 (29.5) ms; P < 0.0001). Up to 96 hours no further change was observed, but one month after ablation the PR interval had decreased to a value not significantly different from that 24 hours after the procedure (231 (51.2) ms). In one patient total atrioventricular block developed 24 hours after an uncomplicated procedure and a permanent pacemaker was implanted. With the posterior approach the PR interval increased slightly in the first 24 hours (156 (22.7) ms, before ablation 144 (21.2) ms P = 0.004), but it had returned to preablation values at 1 month. One patient developed second degree atrioventricular block during the first 24 hours after ablation, despite delivery of all radiofrequency pulses posterior to Koch's triangle at sites without His bundle deflection. PR intervals at 6 months did not differ significantly from the values at 1 month. CONCLUSION: After the anterior approach the progressive delay in atrioventricular conduction up to 48 hours after radiofrequency ablation for atrioventricular nodal re-entry tachycardia warrants continuous in hospital monitoring of patients for at least two days after the procedure.

Atrioventricular Node↗
PubMed1994

Unipolar electrogram models for prediction of outcome in radiofrequency ablation of accessory pathways.

Meticulous catheter positioning close to the accessory pathway is essential for successful radiofrequency ablation. The aim of this study was to identify local unipolar electrogram characteristics predictive of radiofrequency ablation outcome, enabling more accurate accessory pathway localization and catheter positioning. So far mainly bipolar electrogram parameters have been evaluated, stressing the importance of the presence of an accessory pathway potential. However, especially in the absence of this parameter, the unipolar recording mode can be expected to hold several advantages. Nine local unipolar electrogram characteristics were analyzed in preexcited sinus rhythm directly preceding radiofrequency pulses in 35 consecutive patients with a manifest accessory atrioventricular pathway. A total of 1,230 unipolar electrogram complexes were analyzed and recorded at 138 ablation sites. Ablation was successful in 30/35 patients (86%). Multivariate analysis provided two unipolar models for prediction of ablation outcome: in Model I, sites with a suspected accessory pathway potential, local AV interval < or = 30 msec and catheter stability had 76% probability of success, but no more than 1% in their absence. In contrast, using the bipolar recording mode, presence of a suspected accessory pathway potential was the only one of these parameters shown to differentiate between successful and unsuccessful sites, with a predicted chance of success of 48%. Model II, not requiring assessment of possible accessory pathway potentials, showed a 63% probability of success for the combination of initial positivity of the local ventricular signal < or = 0.1 mV, AV interval < or = 30 msec, and catheter stability, but no more than 7% in their absence. Moreover, gradual decrease of initial ventricular positivity and AV interval while approaching a subsequently successful site allows the use of these parameters as dynamic mapping tools. Local unipolar electrogram parameters may thus facilitate precise accessory pathway localization and catheter positioning while offering important information supplementary to the bipolar mode, and enable accurate prediction of ablation outcome at a given site also in the absence of accessory pathway potential recording.

Adolescent↗
PubMed1994

In vivo ventricular lesion growth in radiofrequency catheter ablation.

While radiofrequency catheter ablation has proved highly effective in the treatment of various supraventricular tachyarrhythmias, results in the treatment of ventricular tachycardia invite improvement. Knowledge of lesion growth in vivo might improve understanding of this discrepancy. So far only information from in vitro and in vivo studies using a small 2 mm tip electrode is available. Growth of ventricular radiofrequency lesions created with a 4 mm ablation electrode was studied in 11 closed-chest dogs. Endocardial ablations were performed at 31 left and 15 right ventricular sites at a power setting of 25 Watts and 5, 10, 20, 30 or 60 seconds pulse duration. Macroscopic and histopathologic lesion examination were performed after one week survival. Mean lesion volume increased from 52 mm3 after 5 seconds pulse duration to a maximum 388 mm3 and approximately 7 mm depth after 30 seconds. Lesions were prolate spheroid in form, with a sparing of subendocardial myocardium and maximum lesion diameter at some millimeters depth. Results indicate that catheter positioning at no more than 7 mm from the target is required for successful ablation. Due to lesion geometry, subendocardial targets demand even more exact catheter positioning, while subepicardial substrates may not be ammenable to ablation if ventricular wall thickness exceeds 7 mm at the ablation site. Repeated pulses at adjacent sites may be required for ablation of extended arrhythmogenic areas. Volume at 5 seconds was only approximately 15% of mature lesions. Therefore, the use of a short 'test pulse' after careful mapping may be useful to pinpoint the most appropriate site for ablation in discrete pathways.

Animals↗
PubMedDate not supplied

Doppler echocardiographic evaluation of left ventricular diastolic function after surgical correction of atrial septal defect during childhood.

Transmitral flow was studied using Doppler echocardiography with the A/E ratio as a parameter of left ventricular diastolic function in 21 patients (ages 2.5-30.0 years) who had undergone early surgical correction of an isolated secundum type atrial septal defect (ASD) compared to a healthy cohort of 21 subjects. Pre- and postoperative M-mode recordings were compared in 12 of the 21 patients to evaluate the effect of operation on interventricular septal motion (IVS) and left ventricular (LV) and right ventricular (RV) end-diastolic diameter ratio (LVDD/RVDD) as parameters of right ventricular volume overload. No significant difference in A/E ratio was found between the patient and control groups. IVS was shown to normalize in 11 of 12 patients postoperatively and to improve from paradox to flattened in 1 of 12. LVDD/RVDD increased from 1.26 +/- 0.31 to 2.10 +/- 0.51 (p = 0.0008), with no significant difference remaining between the control and patient groups postoperatively. These findings support the conclusion that an intrinsic abnormality of the left ventricle is not responsible for its diastolic dysfunction in patients with ASD who develop left ventricular failure, thereby implicating an acquired abnormality. Mechanical sequelae of right ventricular volume overload were shown to normalize in all patients subsequent to operation in the present study, and therefore cannot be excluded as a cause of left ventricular failure in ASD.

Adolescent↗