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Biomedical subjects

E Rowland

Publications and source records attributed to E Rowland.

At least 55 records · Page 3Linked to original sources
PubMed1994

Effects of intravenous adenosine on verapamil-sensitive "idiopathic" ventricular tachycardia.

The mechanism of ventricular tachycardia (VT) that occurs in the absence of structural heart disease ("idiopathic" VT) is unknown, but may involve triggered activity or reentry through calcium channel-mediated conduction pathways. It has been suggested that termination of VT by adenosine is specific to ventricular arrhythmias caused by cyclic adenosine monophosphate-mediated triggered activity. The effects of vagotonic maneuvers, and intravenous adenosine (up to 0.25 mg/kg in incremental doses) and verapamil (0.145 mg/kg) administered to 9 patients with "idiopathic" VT were studied during electrophysiologic study. Seven patients had inducible fascicular VT and 2 had incessant right ventricular outflow tract tachycardia. Vagal maneuvers did not have any effect on any VT. Adenosine interrupted both right ventricular outflow tract tachycardias for a period (2 to 15 seconds) that was dependent on the dose of adenosine, but had no effect on VT in any patient with fascicular VT. Verapamil produced stuttering termination of right ventricular outflow tract tachycardia with no preceding change in RR interval in patients with this arrhythmia. Administration of verapamil to patients with fascicular VT was followed by gradual slowing of the arrhythmia (cycle length increased from 397 +/- 45 to 506 +/- 86 ms; p < 0.01) in all 7 patients and by termination of VT in 6. In conclusion, the differential response of fascicular and right ventricular outflow tract tachycardias to both adenosine and verapamil suggests that: (1) These 2 forms of idiopathic VT have different mechanisms. (2) Fascicular VT is unlikely to be due to cyclic adenosine monophosphate-mediated triggered activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1994

Clinical anatomy of the atrioventricular junctions.

OBJECTIVES: This study reevaluated the anatomy of the areas anterior and posterior to the atrioventricular (AV) septal structures, previously said to represent anterior and posterior septal areas. BACKGROUND: In descriptions of the locations of accessory AV pathways within the AV junctions, four regions have been recognized: the left and right free walls and the anterior and posterior septums. On the basis of known facts concerning cardiac structure, it is questionable whether these so-called septums are truly septal. METHODS: Ten human hearts were dissected to elucidate the clinical anatomy of these purportedly septal regions, together with the overall arrangement of the AV junctions. RESULTS: The true septal components of the AV junctions are the muscular and membranous AV septal areas. These separate the cavity of the right atrium from that of the left ventricle. The region previously designated as the anterior septum is part of the right parietal junction. It is contiguous with the membranous part of the septum but extends anteriorly and laterally from the septum as part of the supraventricular crest of the right ventricle ("crista supraventricularis"). In the region posterior to and beneath the mouth of the coronary sinus, only the most anterior extent, in continuity with the central fibrous body, is part of the muscular AV septum. The posterior extent of this area roofs over the diverging right and left ventricular walls and is filled in with fibroareolar tissue of the AV groove. CONCLUSIONS: The larger part of the regions anterior and posterior to the true AV septal areas are not septal but are parts of the parietal AV junctions. An understanding of these anatomic relations is essential for those wishing to modify conduction across the AV junctions.

Atrioventricular Node↗
PubMed1994

The Wolff-Parkinson-White syndrome: the cellular substrate for conduction in the accessory atrioventricular pathway.

The longstanding quest for the anatomical basis of the Wolff-Parkinson-White syndrome has left many unanswered questions. The ultrastructural morphology of the myocytes comprising accessory atrioventricular pathways, which are capable of rapid and variable conduction, is central to understanding the development and behaviour of this congenital anomaly, but remains unknown. Examination of three surgically resected pathways was performed to determine their underlying cellular morphology and the pattern of intercellular coupling, by correlative light microscopy, electron microscopy and confocal scanning laser microscopy combined with immunohistochemical localization of the cardiac gap-junctional protein, connexin43. Two left-sided pathways were composed of myocardium of 'normal working ventricular' type. The right-sided pathway was composed almost entirely of highly abnormal myocytes characterized by aberrant myofibril organisation, with a lack of A-band material and abnormal mitochondria, but normal intact intercalated disks no different from those seen in left-sided pathways. The gap junctions of all pathways were composed of connexin43 distributed as in ventricular myocardium, and not as found in atrial or atrioventricular nodal tissues. While myocytes of abnormal structure were present in one of the accessory atrioventricular pathways examined, all pathways had morphologically normal gap junctions, the structures responsible for efficient intercellular coupling, with a pattern of distribution suggestive of working ventricular myocardium.

Adolescent↗
PubMed1994

Maze 3 for atrial fibrillation: two cuts too few?

The Maze procedure has been developed as a surgical approach to the management of patients with atrial fibrillation refractory to medical treatment. The recent modification of the technique (Maze 3) achieves good rate control with coordinated AV contractions. However, the procedure involves cuts that completely isolate a block of left atrial (LA) wall, including the four ostia of the pulmonary veins. The electrical and mechanical activity of this isolated LA block are dissociated from the rest of the atrium, and the area may, in fact, continue to fibrillate. This may provide a nidus for the development of mural thrombus. The weight and endocardial surface area of the LA block and of the entire LA were estimated in ten formalin fixed hearts from trauma victims with no evidence of cardiac disease. In these samples, the LA block represented 35% of the endocardial surface area of the entire LA and 29% of the weight. The LA block is of sufficient size to allow macroreentrant circuits to form and has the potential to fibrillate if isolated from the rest of the atrium. We modified the Maze 3 procedure to recruit the otherwise isolated LA block by using two additional cuts around each pair of pulmonary veins as they enter the LA. The first patient who underwent the modified procedure demonstrated sinus rhythm on Holter monitoring postoperatively and remained in sinus rhythm following burst atrial pacing at 300 and 420 beats/min each for 30 seconds. In addition, atrial contractions were found to contribute 19% of the cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Fibrillation↗
PubMed1994

Arrhythmias.

Explore the source record for details and available documents.

Arrhythmia, Sinus↗
PubMed1993

Atrioventricular junctional reentrant tachycardia utilizing multiple retrograde fibers during ablation of the slow pathway.

This report deals with a patient with atrioventricular (AV) reentrant junctional tachycardia who, during radiofrequency ablation of her slow pathway, developed both anterior and posterior type of slow-fast atrioventricular nodal reentry; in both tachycardias different fibers were alternately utilized for retrograde conduction, thus resulting in alternating tachycardia cycle lengths. This observation provides further evidence in favor of the multifiber structure of the AV node in patients with AV reentrant junctional tachycardia.

Adult↗
PubMed1993

Low-energy DC catheter ablation of left atrial ectopic tachycardia that had resulted in reversible cardiomyopathy.

Catheter ablation of automatic atrial tachycardia has been previously reported in a small number of adult cases in which the ectopic focus was predominantly located in the right atrium. We report on a patient with atrial automatic tachycardia originating in the left atrium, in whom successful low-energy DC catheter ablation was performed via a transseptal puncture. The patient presented with severe congestive cardiac failure that resolved following the procedure. Catheter ablation in such cases is feasible, it can reverse tachycardia induced ventricular function impairment, and should be attempted before resorting to open heart surgical ablation.

Adult↗
PubMed1993

Long-term follow up of patients treated with a software based antitachycardia pacemaker.

INTRODUCTION: Over the past decade, several advances have been made in the management of tachycardias by pacing techniques, but limited data are available on the long-term outcome of patients treated with antitachycardia pacemakers. PATIENTS AND METHODS: An antitachycardia pacemaker, the Intermedics Intertach, was implanted in 22 (17 female) patients with supraventricular tachycardia over a five year period. All were selected after detailed evaluation and testing of a temporary antitachycardia pacemaker system showed that their arrhythmia could be stopped promptly, reliably, and under different physiological conditions. RESULTS: The 22 patients have been followed up for a mean period of 57.3 (range 19-76) months. All except one of the patients has had frequent episodes of tachycardia reliably ended by the pacemaker. Complications have occurred in seven patients, necessitating removal of the pacing system in four. Of the 18 patients who continue to have pacemakers, seven are being treated with beta blockers or verapamil; no other antiarrhythmic drugs are being taken. CONCLUSIONS: Antitachycardia pacing is an acceptable long-term option for carefully selected patients with supraventricular tachycardia, but even after extensive testing a substantial number of the patients may continue to require drug treatment. Furthermore, the widespread use of curative techniques for supraventricular arrhythmias (catheter ablation and surgery) has decreased the need for this palliative treatment.

Adolescent↗
PubMed1992

Dispersion of monophasic action potential duration: demonstrable in humans after premature ventricular extrastimulation but not in steady state.

Abnormal dispersion of repolarization may contribute to the arrhythmogenic physiologic substrate of ventricular arrhythmia. Geographic dispersion of monophasic action potential duration was determined in steady state (drive cycle lengths 600 and 430 ms) between widely spaced right ventricular endocardial sites (geographic dispersion) in 10 control patients with right ventricular disease and complicating ventricular tachycardia (n = 9), 6 patients with right and left ventricular disease and complicating ventricular tachycardia and 7 patients with ischemic heart disease and complicating ventricular tachycardia. No significant difference in geographic dispersion could be demonstrated among the groups. Difference of monophasic action potential duration at adjacent right ventricular endocardial sites (adjacent dispersion) was determined after ventricular extrastimulation during construction of simultaneous electrical restitution curves in the same patient groups. Maximal adjacent dispersion over the electrical restitution curve was compared between disease and control groups. There was a significant difference in observations of maximal adjacent dispersion in patients with right ventricular disease and complicating ventricular tachycardia (range 5 to 85 ms, median 22.5; 14 pairs of sites; p less than 0.05) and patients with right and left ventricular disease and complicating ventricular tachycardia (range 5 to 50 ms, median 17.5; 14 pairs of sites; p less than 0.05) compared with control patients (range 5 to 20 ms, median 10; 15 pairs of sites). This difference was not evident when patients with ischemic heart disease and complicating ventricular tachycardia (range 5 to 25 ms, median 12.5; 12 pairs of sites) were compared with control patients. Maximal percent monophasic action potential shortening from steady state was significantly greater (p less than 0.001) in both groups with greater adjacent dispersions, and prolongation of activation time at monophasic action potential recording sites after premature extrastimulation tended to be greater in patients with right or right and left ventricular disease and complicating ventricular tachycardia. It is concluded that in disease, exaggeration of monophasic action potential shortening after premature ventricular extrastimulation may contribute to the electrophysiologic arrhythmogenic substrate.

Action Potentials↗
PubMed1992

Histopathological findings in three children with His bundle tachycardia occurring subsequent to cardiac surgery.

This report concerns three children with His bundle tachycardia who died following cardiac surgery. At autopsy the conduction system was examined in detail. In all three, the sinus node was intact and supplied by a well-formed artery. Haemorrhagic tracks were identified invading the penetrating atrioventricular bundle. The tracks originated from stitches placed close to the conduction tissue. The hypothesis that disruption of the conduction tissue results in an arrhythmogenic focus is discussed.

Bundle of His↗
PubMed1992

Electrical restitution in the endocardium of the intact human right ventricle.

OBJECTIVE: To characterise electrical restitution in the intact human heart. PATIENTS AND METHODS: A series of monophasic action potential electrical restitution curves were constructed from a single right ventricular endocardial site in eight patients (three men) without structural heart disease aged 52-68 (mean 55 years). A combination pacing/monophasic action potential electrode was used to pace and record monophasic action potentials at drive cycle lengths of from 350 ms to 1500 ms. Ventricular extrastimuli were delivered at 20 cycle intervals and decreased from the longest coupling interval attainable without escape beats. RESULTS: Restitution curves shifted downward and towards the left; steady state action potential duration shifted from the restitution plateau and descended the curve, the amount of shift being linearly related to drive cycle length in two patients in whom the relation could be assessed; the amount of monophasic action potential shortening was a function of the degree of prematurity and that relation was unaffected by drive rate; the magnitude of restitution and the time constant of the restitution curve were not changed significantly by altered drive cycle length. CONCLUSION: In the intact heart in vivo, electrical restitution (of the monophasic action potential) has similar characteristics to those (of the transmembrane action potential) in cellular preparations in vitro. Thus the alteration of action potential plateau currents by instantaneous rate change or drug effects, which can be directly observed by techniques available to the cellular electrophysiologist, may be indirectly assessed in vivo by characterisation of the effect of these on electrical restitution.

Action Potentials↗
PubMed1992

Impact of catheter and surgical ablation on arrhythmia treatment in a tertiary referral centre.

Invasive cardiac electrophysiology studies began as diagnostic studies. The past decade has seen the introduction of several new treatments which have broadened the scope of invasive electrophysiology studies. In particular, the development of catheter ablation techniques increasingly allows curative treatment to be delivered in the catheter laboratory. The workload of electrophysiological procedures has steadily increased in our tertiary referral centre. Over 1000 patients have been treated in the past 20 years and it is projected that 219 new patients will be treated in 1991 and 342 procedures will be carried out. Over 25% of patients now receive either catheter or surgical ablation and almost 80% of these are cured permanently without the need for further drug treatment. The development of safer techniques for catheter ablation has led to its increased use and a decline in surgical ablations. Because catheter ablation is a much simpler and less traumatic procedure than surgical ablation there are great advantages both for the patient and in terms of cost-effectiveness. Antitachycardia pacing, relatively common in 1985, has now largely been supplanted by ablation and implantation of defibrillators. As the tendency to non-pharmacological treatment increases and evidence mounts that cost-effectiveness is greater for electrophysiological treatments, the implications for the funding of electrophysiology services grow. The initially high cost of curative treatment needs to be balanced against the longer term and potentially higher costs of palliative drug treatment. The potential to cure patients with catheter procedures may lead to a greater demand for this expertise and a need for an increase in training and facilities.

Arrhythmias, Cardiac↗
PubMed1992

Nonpharmacological treatment of supraventricular tachycardia.

Although pharmacological treatment is often effective in preventing or controlling attacks of tachycardia it is palliative rather than a cure. Some Arrhythmias are refractory to drug therapy and long-term antiarrhythmic agents are associated with side-effects, life-threatening toxicity, poor patient compliance and considerable cost. On the other hand, enhanced knowledge of electrophysiological mechanisms and advanced technology have resulted in the more and more widespread use of several nonpharmacological methods of treating arrhythmias. It is the purpose of this review to discuss the present status of nonpharmacological therapy of supraventricular tachycardia and comment upon its current role in the management of patients presenting with these arrhythmias.

Atrioventricular Node↗
PubMed1991

Sudden cardiac death while taking amiodarone therapy: the role of abnormal repolarization.

Torsade de pointes may occur as a complication of amiodarone therapy. We report a patient receiving amiodarone who was resuscitated from cardiovascular collapse and documented ventricular fibrillation. At subsequent electrophysiology study, while the patient was taking amiodarone therapy, monophasic action potentials with early after depolarisations were recorded which were not present when the patient was restudied 6 weeks after discontinuation of amiodarone. Early after-depolarisations may be important in the genesis of polymorphic ventricular tachycardia complicating amiodarone therapy.

Adult↗
PubMed1991

Low energy catheter ablation of a posteroseptal accessory pathway associated with a diverticulum of the coronary sinus.

A 23-year-old man was resuscitated from ventricular fibrillation and subsequently shown to have the Wolff-Parkinson-White syndrome. Electrophysiological study demonstrated a posteroseptal accessory pathway, and coronary sinus angiography demonstrated that this was associated with a diverticulum of the coronary sinus. Catheter ablation was performed using a new low energy system. Five shocks were delivered within the coronary sinus diverticulum, with a cumulative energy of 39 joules (J). Accessory pathway conduction was blocked successfully, and there were no complications.

Adult↗