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Biomedical subjects

J M Wharton

Publications and source records attributed to J M Wharton.

At least 19 recordsLinked to original sources
PubMed1999

Desmoplastic malignant melanoma: diagnosis of early clinical lesions.

Desmoplastic malignant melanoma (DMM) is an uncommon but potentially devastating malignancy that can be cured with early recognition and surgery. DMM has clinical as well as histological features that may be subtle and overlooked, or misdiagnosed as other benign or malignant lesions that would require less aggressive therapy for cure. We have reviewed the preliminary clinical diagnoses and histological features of 18 cases of desmoplastic malignant melanoma, defined as either an inapparent lesion clinically, or a papule or small nodule less than 0.7 cm, which proved histologically to be DMM. Nine of 18 cases (50%) were clinically pigmented. Histologically, early lesions were characterized by superficial tumor fascicles, and random diffuse hypercellularity in the upper dermis identified as elongated hyperchromatic pleomorphic spindle cells with stromal myxoid change. Neuroidal melanocytic structures, invasion of adventitial dermis, islands of inflammation, and epidermal lentiginous melanocytic hyperplasia were often present. The most reliable and characteristic features of an early lesion of DMM are aggregates of lymphocytes, tumor cell cytological atypia, stromal myxoid change, and poor circumscription of the dermal infiltrate. DMM is a disease best treated by complete excision at the time of initial surgery, but is also a lesion easily missed or misdiagnosed in the early stages. Features of early DMM are identified and illustrated to enable early diagnosis and cure of these lesions.

Adult↗
PubMed1999

Effect of increased parasympathetic and sympathetic tone on internal atrial defibrillation thresholds in humans.

UNLABELLED: Although changes in autonomic tone affect ventricular defibrillation, little is known about the effect of increased parasympathetic or sympathetic tone on the atrial defbrillation threshold. METHODS: To evaluate the effect of reflexly increased parasympathetic and increase alpha- and beta-adrenergic tone on the atrial defibrillation threshold (ADFT), atrial fibrillation was induced in 14 patients. ADFTs, right atrial refractory period (RARP), and monophasic action potential duration (MAPD) were determined before and after autonomic intervention. ADFTs were determined with a step-up protocol using 3/3-ms biphasic shocks delivered through decapolar catheters in the right atrial appendage and coronary sinus. Two groups were studied. Group I (N = 8) had ADFTs determined at baseline, after receiving phenylephrine (PE), and with PE plus atropine (A). Group 2 (N = 6) had ADFTs determined at baseline and after receiving isoproterenol (ISO). RESULTS: Group I: PE significantly increased sinus cycle length (SR-CL) compared to baseline (742 +/- 123 to 922 +/- 233 ms) without significantly changing RARP, MAPD, or ADFT (2.3 +/- 1.3 J vs 2.3 +/- 0.8 J). With PE + A, SR-CL significantly decreased (529 +/- 100 ms vs 742 +/- 123 ms) and MAPD shortened (231 +/- 41 ms vs 279 +/- 49 ms) without altering RARP or ADFT (1.94 +/- 0.9 J vs 2.25 +/- 1.25 J). Group 2: ISO decreased SR-CL (486 +/- 77 ms vs 755 +/- 184 ms) and MAPD (169 +/- 37 ms vs 226 + 58 ms) but not RARP or ADFT (2.25 +/- 1.21 J vs 2.33 +/- 1.75 J). CONCLUSIONS: Increasing parasympathetic, alpha-, or beta-adrenergic tone does not affect the ADFT despite causing significant electrophysiological changes in the atria.

Adolescent↗
PubMed1998

Radiofrequency catheter ablation of multiple haemodynamically unstable ventricular tachycardias in a patient with surgically repaired tetralogy of Fallot.

A patient with repaired tetralogy of Fallot presented with recurrent syncope and had multiple haemodynamically unstable ventricular tachycardias unresponsive to antiarrhythmic medications. Ventricular tachycardias became haemodynamically tolerated with amiodarone, procainamide and dopamine, permitting activation and entrainment mapping. Radiofrequency ablation of three tachycardia circuits was performed. Ventricular tachycardia could not be induced 1 week, and 3 and 9 months later. Radiofrequency ablation is feasible for multiple, haemodynamically unstable ventricular tachycardias in repaired tetralogy of Fallot.

Adult↗
PubMed1998

Ventricular tachycardia and fibrillation in normal hearts.

Although ventricular tachyarrhythmias usually occur in the setting of definable heart disease, up to 15% of ventricular tachycardias and 10% of ventricular fibrillation occur in patients without heart disease. Of the various clinical entities comprising these idiopathic ventricular tachyarrhythmias, a few well-defined clinical syndromes have been described, such as idiopathic right ventricular outflow tract tachycardia, idiopathic left posterior fascicular ventricular tachycardia, and the right bundle branch block and ST segment elevation syndrome of idiopathic ventricular fibrillation. Many advances have been made in the past few years in our understanding and treatment of idiopathic ventricular tachyarrhythmias, and these advances are the subject of this review.

Catheter Ablation↗
PubMed1998

Concealed mechanical bradycardia: an indication for permanent pacemaker implantation.

We report a 51-year-old man with severe ischemic cardiomyopathy and heart failure in whom incessant bigeminal ventricular ectopy failed to generate a detectable arterial pressure. This created a mechanical bradycardia despite an adequate electrical heart rate. Dual chamber pacing increased the effective heart rate and allowed discontinuation of an intraaortic balloon pump from which the patient could not otherwise be weaned.

Arrhythmia, Sinus↗
PubMed1997

Internal atrial defibrillation in humans. Improved efficacy of biphasic waveforms and the importance of phase duration.

BACKGROUND: The optimal waveform for internal atrial defibrillation (IAD) in humans is unknown. This study tested the effect of waveform duration and phase duration on the efficacy of biphasic waveforms for IAD. METHODS AND RESULTS: Electrodes were positioned in the right atrial appendage and coronary sinus in 13 patients. In part 1, the atrial defibrillation thresholds (ADFTs) for 5 monophasic waveforms (2, 4, 6, 10, and 20 ms) and 5 symmetrical biphasic waveforms (1/1, 2/2, 3/3, 5/5, and 10/10 ms) were compared in 6 patients. In part 2, the ADFTs for two asymmetrical biphasic waveforms (7.5/2.5 and 2.5/7.5 ms) were compared with those for a symmetrical biphasic waveform (5/5 ms) and a monophasic waveform (10 ms) in 7 patients. In part 1, biphasics with total durations of 4 to 20 ms had significantly lower ADFTs than monophasic waveforms of the same total duration. For a total duration of 2 ms, there was no significant difference in ADFTs between the biphasic and the monophasic waveforms. There was no difference between symmetrical biphasic waveforms of 4 to 20 ms. In part 2, the 7.5/2.5 ms asymmetrical biphasic had significantly lower ADFTs than the three other waveforms tested. Both the 7.5/2.5 ms asymmetrical and the 5/5 ms symmetrical biphasic waveform had significantly lower ADFTs than the 2.5/7.5 ms asymmetrical biphasic and the 10 ms monophasic waveforms. CONCLUSIONS: For IAD in humans, biphasic waveforms were more efficacious than monophasic waveforms. This improved efficacy is related to the total duration of the biphasic waveform and each individual phase duration of the biphasic waveform.

Adult↗
PubMed1997

Safety of slow pathway ablation in patients with long PR interval: further evidence of fast and slow pathway interaction.

Whether the presence of abnormal PR before selective slow pathway ablation for AV node reentrant tachycardia increased the risk of complete heart block remains controversial. We report our experience in seven patients with prolonged PR intervals undergoing catheter ablation for AV reentry tachycardia. Their mean age was 66 +/- 12 years; four patients were female and three were male. RF ablation was performed using an anatomically guided stepwise approach. In six patients, common type AV node reentry was induced and uncommon type was observed in the remaining patient. In all seven patients, successful selective slow pathway ablation was associated with no occurrence of complete heart block and was followed by shortening of the AH interval in five patients. In all seven patients, successful ablation was achieved at anterior sites (M1 in two patients and M2 in five patients). Despite AH shortening after ablation, the 1:1 AV conduction was prolonged after elimination of the slow pathway, excluding either sympathetic tone activation or parasympathetic denervation. In conclusion, selective slow pathway ablation can be performed safely in the majority of patients with prolonged PR interval before the procedure. Because successful ablation is achieved at anterior sites in most patients, careful selection and monitoring of catheter position is required.

Aged↗
PubMed1997

Interactions between transvenous nonthoracotomy cardioverter defibrillator systems and permanent transvenous endocardial pacemakers.

Limited information is available regarding potential adverse interactions between transvenous nonthoracotomy cardioverter defibrillators and pacemakers. We describe our experience with 37 patients who have undergone successful implantation of both a transvenous defibrillator and pacemaker. The patients' mean age was 64 +/- 12.9 years. Thirty-three were male and four were female. The mean LVEF was 30.8% +/- 11.8%. The indications for pacemaker implantation included sick sinus syndrome in 13 patients, complete heart block in 15 patients, sinus bradycardia secondary to medications in 8 patients, and neurocardiogenic syncope in 1 patient. The indications for insertion of a defibrillator included medically refractory VT in 27 patients and sudden cardiac death in 10 patients. Twenty-three patients received an Endotak lead and 14 patients received a Transvene lead. Eighteen patients had a pacemaker prior to an ICD, 14 patients had an ICD prior to a pacemaker, and 4 patients had both devices placed simultaneously. Interaction was evaluated at implant of the second device and 1-3 days after both devices were placed. Detection of VF/VT was analyzed during asynchronous pacing (DOO/VOO) with maximum pacing output. In addition, in six patients, DFT was determined before and after pacemaker implantation. In 14 patients (38%), device interactions that could not always be optimally corrected were observed. In five patients, the pacemaker was reset to the "noise reversion" mode after high energy ICD discharge. Oversensing of atrial pacemaker stimuli resulted in inappropriate ICD firings in four patients. This was observed only with a specific device and could not be prevented by atrial lead repositioning in two of them, but required reprogramming of the pacemaker to the VVI mode. An increase in DFT was observed in five patients who had a pacemaker implanted after an ICD. Compared with previously published studies, a greater frequency of transvenous ICD and pacemaker interactions were observed. Considering that almost 50% of the patients already have a pacemaker at the time of ICD implant, the availability of defibrillators with dual chamber pacing capability will not eliminate the potential for this problem.

Aged↗
PubMed1997

Transient data stream dissociation in computerized data acquisition system masquerading as a sensing abnormality.

During testing of a CPI model 1715 ICD, an apparent sensing abnormality was noted following shock delivery for VF. Close inspection of the recording prior to the defibrillation attempt revealed that the surface leads spontaneously lost 848 ms of data while the event marker was unaffected. Computer simulations revealed that an inadequate buffer size for the amplified (surface ECG) data was the likely source of data loss. It is important to recognize that a discordance between surface leads and event marker may represent an abnormality in the data acquisition system and simulate an ICD or lead malfunction.

Aged↗
PubMed1997

Ventricular fibrillation resulting from synchronized internal atrial defibrillation in a patient with ventricular preexcitation.

This case describes ventricular proarrhythmia as a result of a synchronized internal atrial defibrillation shock in a 29-year-old man with Ebstein's anomaly referred for radiofrequency ablation of a right posterior accessory pathway. During the electrophysiologic study, atrial fibrillation was induced and 3/3 msec shocks of various strengths were delivered between two decapolar defibrillation catheters in the coronary sinus and right atrial appendage. A 2.0-J biphasic shock synchronized to an R wave after a short-long-short ventricular cycle length pattern with a preshock coupling interval of 245 msec induced ventricular fibrillation, which was externally defibrillated with 200 J. This observation has implications for the development of implantable atrial defibrillators.

Adult↗
PubMed1996

Effect of continuous vagal enhancement on concealed conduction and refractoriness within the atrioventricular node.

This study examined the complex interaction between vagal enhancement and how a concealed atrial impulse alters atrioventricular (AV) nodal function. In theory, vagal augmentation could increase or decrease the effect that a premature atrial beat has on the subsequent beat. In 10 patients we established the AV nodal effective refractory period (ERP) without and with a conditioning atrial stimulus (Sc); the stimulation protocol was then repeated after enhancing reflex vagal tone with a continuous phenylephrine infusion. During phenylephrine infusion, the sinus cycle length prolonged from 827 +/- 99 to 1,029 +/- 223 ms (p < 0.001) and AV nodal ERP increased from 331 +/- 51 to 425 +/- 64 ms (p < 0.005). At control, AV nodal ERP in the presence of Sc prolonged to 536 +/- 69 ms (p < 0.001), and during phenylephrine infusion increased to 579 +/- 57 ms (p < 0.01), a change significantly less than during control (58 +/- 14% vs 31 +/- 14%, respectively, p < 0.01). Further experiments suggest that the effect of Sc was reduced because it occurred earlier relative to the vagally prolonged AV nodal ERP. In conclusion, this study demonstrates a complex relation between the timing of a premature atrial beat causing concealed conduction and the degree of vagal tone. The concealed beat, as related to the AV node ERP, has a substantial effect on subsequent AV nodal conduction. These data give insights into clinical AV nodal function.

Adrenergic beta-Agonists↗
PubMed1996

Impact of defibrillator-can size on defibrillation success with a single-lead unipolar system.

In a study of 11 dogs, we assessed whether the defibrillation energy requirements of a single transvenous right ventricular electrode/defibrillator can system depended on the can size. We compared the defibrillation threshold obtained with 65% fixed-tilt biphasic shocks with 20, 40, and 80 ml surface area defibrillator cans. The energy was delivered between a right ventricular coil inserted through the jugular vein and the can placed in the subcutaneous tissue of the left superior chest wall. The testing order of each can size was randomly determined. Triplicate defibrillation thresholds were obtained with each can. Despite a higher impedance (20 ml 85 +/- 22 ohms vs 80 ml 71 +/- 16 ohms, p < 0.01), the 20 ml can resulted in a similar defibrillation threshold compared with the 80 ml (20 ml 7.6 +/- 2.8 J vs 80 ml 7.5 +/- 3.4 J) and the 40 ml cans (20 ml 7.6 +/- 2.8 J vs 7.5 +/- 3.4 J). In conclusion, with the unipolar lead system the can size does not appear to be a factor limiting defibrillation success. Even a can the size of a pacemaker does not appear to significantly affect the defibrillation efficacy of this lead system.

Animals↗
PubMed1996

Radiofrequency ablation of atrial flutter and atrial tachycardias in patients with permanent indwelling catheters.

UNLABELLED: The presence of chronic indwelling leads in the area targeted for RF ablation may pose a technical challenge and reduce the chance of success of the ablation. In addition, application of lesions in close proximity to pacemaker leads or other permanent catheters could affect their function. Fourteen patients referred for RF ablation of atrial flutter/fibrillation and atrial tachycardia, who had a permanent dual chamber pacemaker (10 patients), ICD (1 patient), or both (3 patients) were studied to assess the safety, efficacy, and effects of the ablative procedure on device function. Lead impedance, R and P wave amplitude, and pacing threshold of the defibrillator and pacemaker were measured before and after ablation. The procedure was successful in all patients. In one patient who underwent both atrial flutter and atrial fibrillation ablation, the atrial pacing threshold increased from 1.0 preablation to 2.0 V postablation. No P wave was detectable after ablation. In another patient, the P wave amplitude went from 4.0 to 2.0 mV postablation. In both patients the device converted to the power reset mode. No changes were observed in the remaining patients. Postablation defibrillator testing showed no malfunction. Follow-up reinterrogation of the devices revealed no alterations. IN CONCLUSION: (1) RF ablation of atrial flutter and/or tachycardia is feasible even in patients with multiple chronic atrial and ventricular indwelling catheters; and (2) RF applications in close proximity of defibrillator and pacing catheters does not appear to alter their function unless lesions are produced in the area surrounding the distal pacing electrode.

Aged↗
PubMed1996

Internal cardioversion in two patients with atrial fibrillation refractory to external cardioversion.

A 26-year-old man underwent an electrophysiological study for evaluation of a history of congenital heart disease, presyncope, and wide complex tachycardia. During the study the patient developed sustained atrial fibrillation with a rapid ventricular response. A 17-year-old man with a history of sick sinus syndrome developed sustained atrial fibrillation. Both patients failed four attempts at external cardioversion with a maximum delivered energy of 360 J. Low energy cardioversion was successful in both patients using biphasic waveforms and internal transvenous defibrillation electrodes. Internal cardioversion using a transvenous electrode system can be successful in patients with atrial fibrillation refractory to external cardioversion.

Adolescent↗
PubMed1996

Ventricular fibrillation induction using nonsynchronized low energy external shock during rapid ventricular pacing: method of induction when fibrillation mode of ICD fails.

Third-generation implantable cardioverter defibrillators (ICD) are frequently implanted with nonthoracotomy systems and provide noninvasive methods for electrical stimulation and ventricular fibrillation induction. These modalities facilitate postoperative testing of the ICD. Rapid right ventricular burst pacing via the defibrillator is commonly used for initiation of ventricular tachyarrhythmias. However, with the available third-generation devices, ventricular fibrillation (VF) induction may be impossible in up to 19% of the patients. In these cases, transvenous placement of a right ventricular catheter has been required to generate VF and appropriately evaluate the device. We report a new technique of noninvasive induction of VF using a low energy external nonsynchronized shock delivered during ICD fibrillation induction pacing. In three patients, after all efforts to induce VF by the Ventritex Cadence V-100 had failed, a 20 J nonsynchronized shock was delivered during rapid RV pacing. This resulted in VF on the first attempt in all patients. This noninvasive technique of VF initiation may provide a useful clinical approach to ICD testing that eliminates the costs and risks of an invasive procedure.

Adult↗
PubMed1996

Bundle branch reentry tachycardia and possible sustained interfascicular reentry tachycardia with a shared unusual induction pattern.

A case of bundle branch reentry tachycardia with an unusual induction pattern is presented. Unlike typical cases of this arrhythmia in which tachycardia is usually inducible with routine programmed ventricular stimulation and/or short-long sequences, tachycardia in this case was inducible only with atrial stimulation. It also arose spontaneously during atrial flutter and during isoproterenol administration. After ablation of the right bundle, possible interfascicular reentry tachycardia with a similar induction pattern was observed. This tachycardia was successfully ablated in the region of the posterior fascicle of the left bundle branch.

Aged↗
PubMed1995

Ventricular tachycardias with left bundle branch block morphology.

The differential diagnosis of VTs with LBBB morphology includes several well-defined syndromes. Although the majority of cases are attributable to acquired structural heart disease, including ischemia, prior infarction, or dilated cardiomyopathy, consideration of specific right ventricular processes is essential to proper evaluation and treatment. The approach to older patients or those with evidence for heart disease should begin with an evaluation for coronary artery disease and an assessment of biventricular function. Careful evaluation for bundle branch reentry should be performed during electrophysiological study, especially when there is underlying conduction system disease. Younger patients, those without overt heart disease, or those with isolated right ventricular disease, should receive a complete noninvasive evaluation of right and left ventricular size and function. An abnormal SAECG or identification of intracardiac late potentials suggest right ventricular dysplasia or cardiomyopathy, whereas responsiveness to adenosine and absence of detectable heart disease support the diagnosis of idiopathic right VT. Newer techniques, including MRI, show promise in identifying subtle right ventricular disease not otherwise detectable even in the setting of presumed idiopathic right VT. Following surgical repair of selected congenital heart defects, particularly tetralogy of Fallot, symptoms of recurrent palpitations, near syncope, syncope, or aborted sudden death may be attributable to recurrent VT, and diagnostic electrophysiological study should be considered for these patients. Finally, SVTs with LBBB morphology, particularly cases associated with right-sided or septal accessory pathways, should always be considered in this differential diagnosis.

Bundle of His↗