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Biomedical subjects

R W Henthorn

Publications and source records attributed to R W Henthorn.

At least 37 records · Page 2Linked to original sources
PubMed1990

A perspective on ventricular arrhythmias: patient assessment for therapy and outcome.

Clinical management of patients with ventricular arrhythmias continues to evolve. It is generally accepted that patients with sustained ventricular tachyarrhythmias (ventricular tachycardia [VT] or fibrillation) require treatment. It is also generally accepted that patients with frequent or complex ventricular ectopy or nonsustained VT, in the absence of underlying heart disease, do not require treatment unless relief of symptoms is warranted. Whether patients with frequent or complex ventricular ectopy or nonsustained VT require treatment in the presence of underlying organic heart disease remains uncertain. The concern is that these ventricular arrhythmias may be a precursor for sustained, potentially life-threatening ventricular tachyarrhythmias. Available data suggest that patients with underlying heart disease, particularly coronary artery disease and a previous myocardial infarction, who manifest frequent or complex ventricular ectopy or nonsustained VT are at increased risk for sudden cardiac death. However, no studies have shown that treatment of these arrhythmias will affect outcome. Data are accumulating to suggest that use of the principles of risk stratification permits identification of patients at very high risk for developing sustained ventricular tachyarrhythmias. Carefully designed clinical trials are required before one can provide firm guidelines for the management of these patients. Nevertheless, when several risk factors for sudden cardiac death (e.g., abnormal ejection fraction, a late potential on a signal-averaged electrocardiogram, and frequent or complex ventricular ectopy or nonsustained VT) are present in a patient, especially after a recent myocardial infarction, invasive electrophysiologic testing may help identify those who need treatment (sustained VT is inducible) and those who do not (no sustained VT is inducible).

Arrhythmias, Cardiac↗
PubMed1990

Evolving patterns in the surgical treatment of malignant ventricular tachyarrhythmias.

The advent of the automatic implantable cardioverter defibrillator (AICD), generally viewed as a safe and effective intervention, has in some measure discouraged the use of electrophysiologically directed endocardial resection for intractable ventricular arrhythmias. We reviewed the records of 127 patients undergoing either AICD procedures or resection over a 6-year period. Thirty-day mortality was 5.6% (5/89 patients) for all AICD procedures, 10.7% (3/28) for AICD placement plus coronary artery bypass grafting, and 11.8% (4/34) for resection. These mortality figures are not significantly different. Patients undergoing resection were less likely to require antiarrhythmic agents than patients given an AICD (33% versus 61%). Survival at 2 years was 78% in the resection group and 72% in the AICD group. Survival at 4 years was still 78% in the resection group. Only 1 late sudden death occurred in the AICD group and none in the resection group. We conclude that resection continues to be a valuable alternative, offering a greater overall benefit at only slightly increased risk.

Adolescent↗
PubMed1989

Use of transient entrainment during ventricular tachycardia to localize a critical area in the reentry circuit for ablation.

We have previously shown that demonstration of any of the criteria for transient entrainment is possible only when pacing is performed orthodromically proximal to the area of slow conduction in a reentrant circuit with an excitable gap. Pacing orthodromically distal to the area of slow conduction will not permit demonstration of the transient entrainment criteria (concealed entrainment). Additionally, the demonstration of one form of concealed entrainment, namely pacing during a ventricular tachycardia from a site which increases the tachycardia to the pacing rate but does not change the morphology of the QRS complexes, we suggest also identifies the area of slow conduction is a keystone for maintenance of the reentrant circuit, ablation of this area should be expected to provide effective therapy of the tachycardia. Thus, we propose that using the principles of transient entrainment, one should be able to localize a critical area of slow conduction in the reentrant circuit of a ventricular tachycardia, ablate it effectively, and thereby successfully treat the ventricular tachycardia.

Atrial Flutter↗
PubMed1989

Prevention of symptomatic recurrences of paroxysmal atrial fibrillation in patients initially tolerating antiarrhythmic therapy. A multicenter, double-blind, crossover study of flecainide and placebo with transtelephonic monitoring. Flecainide Supraventricular Tachycardia Study Group.

Paroxysmal atrial fibrillation (PAF) is a problematic clinical arrhythmia that is usually symptomatic. Unfortunately, few adequate trials and trial methods are available for assessment of the value of therapy, and traditional treatment has often been ineffective or associated with unacceptable side effects. Transtelephonic monitoring is a new method that allows evaluation of paroxysmal arrhythmias and arrhythmia-related symptoms in outpatients. We used a patient-initiated transtelephonic monitor system to evaluate the potential of flecainide, a class 1C antiarrhythmic, in prevention of symptomatic recurrences of PAF. Sixty-four patients qualified for the study (two or more PAF attacks documented within a 4-week baseline period) and entered a dose-finding phase to determine drug tolerance. Dose was incremented at weekly intervals from 200-300 and finally to 400 mg/day. The largest dose that was well tolerated was selected for the 4-month, double-blind, randomized, crossover comparison with placebo. Fifty-five patients entered and 53 received both treatments in the double-blind phase; 48 of these patients without protocol violations were evaluable for efficacy comparisons. Evaluable patients had undergone an average of 3.8 previous drug trials (range, 1-8); 30 were men, 18 had hypertension, and 14 had ischemic heart disease. The study demonstrated a highly significant correlation (p less than 0.0001) between perceived symptoms and documented PAF by transtelephonic monitoring. The rate of symptoms and PAF attacks was also significantly reduced by therapy (median dose, 300 mg/day). The first PAF attack occurred after a median of 3 days on placebo versus 14.5 days on flecainide (p less than 0.001) therapy. Similarly, the time interval between attacks was lengthened, from a median of 6.2 days on placebo to 27.0 days on flecainide (p less than 0.001) therapy. PAF was prevented in 15 patients (31%) during flecainide and four (9%) during placebo therapy (p = 0.013). However, during the study, 13 patients dropped out, seven because of adverse effects (five cardiac), five for other reasons, and one because of cardiac arrest/death. Adverse cardiac events occurred in a total of seven patients (11%) during flecainide therapy. Thus, transtelephonic monitoring is a useful method for documentation of the occurrence of paroxysmal arrhythmias such as PAF and its related symptoms during daily living and for assessment of new therapies in an outpatient setting.

Atrial Fibrillation↗
PubMed1988

Use of procainamide with rapid atrial pacing for successful conversion of atrial flutter to sinus rhythm.

Rapid atrial pacing is a useful technique and often the therapy of choice to terminate atrial flutter in patients. However, interruption of atrial flutter by rapid atrial pacing may not always produce sinus rhythm, but rather may result in atrial fibrillation. Twelve patients with spontaneous atrial flutter that had been present for greater than 24 h were studied to assess the efficacy of atrial pacing, alone and in combination with procainamide, to convert atrial flutter to normal sinus rhythm. Rapid atrial pacing for greater than or equal to 15 s from selected atrial sites at selected pacing rates were performed during atrial flutter. The initial pacing rate was always at a cycle length 10 ms shorter than the atrial flutter cycle length. If atrial flutter persisted after cessation of pacing, it was repeated at progressively shorter cycle lengths until either a rate of 400 beats/min was achieved or atrial fibrillation was induced. In two patients, atrial flutter was converted to sinus rhythm with pacing alone. Three patients developed sustained atrial fibrillation as a result of the rapid atrial pacing, this rhythm ultimately reverting back to atrial flutter in two. Ten patients received procainamide and 9 of the 10 had lengthening of the atrial flutter cycle length by a mean of 68 ms (1 patient continued to have atrial fibrillation). Then, using the same atrial pacing protocol, high right atrial pacing alone at a mean cycle length of 227 ms interrupted atrial flutter in all these patients, returning their rhythm to sinus rhythm. It is concluded that intravenous procainamide effectively augments the efficacy of rapid atrial pacing to convert atrial flutter to sinus rhythm.

Adolescent↗
PubMed1988

A fourth criterion for transient entrainment: the electrogram equivalent of progressive fusion.

Prior data pertaining to transient entrainment and associated phenomena have been best explained by pacing capture of a reentrant circuit. On this basis, we hypothesized that rapid pacing from a single site of two different constant pacing rates could constantly capture an appropriately selected bipolar electrogram recording site from one direction with a constant stimulus-to-electrogram interval during pacing at one rate, yet be constantly captured from another direction with a different constant stimulus-to-electrogram interval when pacing at a different constant pacing rate. To test this hypothesis, we studied a group of patients, each with a representative tachycardia (ventricular tachycardia, circus-movement tachycardia involving an atrioventricular bypass pathway, atrial tachycardia, and atrial flutter). For each tachycardia, pacing was performed from a single site for at least two different constant rates faster than the spontaneous rate of the tachycardia. We observed in these patients that a local bipolar recording site was constantly captured from different directions at two different pacing rates without interrupting the tachycardia at pacing termination. The evidence that the same site was captured from a different direction at two different pacing rates was supported by demonstrating a change in conduction time to that site associated with a change in the bipolar electrogram morphology at that site when comparing pacing at each rate. The mean conduction time (stimulus-to-recording site electrogram interval) was 319 +/- 69 msec while pacing at a mean cycle length of 265 +/- 50 msec, yet only 81 +/- 38 msec while pacing at a second mean cycle length of 233 +/- 51 msec, a mean change in conduction time of 238 +/- 56 msec. Remarkably, the faster pacing rate resulted in a shorter conduction time. The fact that the same electrode recording site was activated from different directions without interruption of the spontaneous tachycardia at pacing termination is difficult to explain on any mechanistic basis other than reentry. Also, these changes in conduction time and electrogram morphology occurred in parallel with the demonstration of progressive fusion beats on the electrocardiogram, the latter being an established criterion for transient entrainment.(ABSTRACT TRUNCATED AT 400 WORDS)

Atrial Flutter↗
PubMed1987

Phenytoin in the treatment of inducible ventricular tachycardia: results of electrophysiologic testing and long-term follow-up.

Phenytoin treatment of inducible ventricular tachyarrhythmias was assessed by serial electrophysiologic studies (EPS) in 64 patients with spontaneous ventricular tachycardia, cardiac arrest, or symptoms compatible with a ventricular tachyarrhythmia. Coronary artery disease was the primary cardiac disease in 75% of the patients. All subjects had either inducible ventricular tachycardia (greater than or equal to 10 repetitive beats) or ventricular fibrillation at electrophysiologic study. Phenytoin was administered intravenously in 38 studies and orally in 31 studies. The mean serum phenytoin level was 19.5 +/- 4.7 mcg/ml. Only seven patients (11%) had a negative electrophysiologic study (less than or equal to 10 repetitive beats) after the administration of phenytoin and were classified as phenytoin responders (group I). The remaining 54 patients (89%) were classified as nonresponders (group II). For the nonresponders, phenytoin increased the cycle length of identical monomorphic ventricular tachycardias from a mean of 31 ms to a mean of 327 ms (p less than 0.001). For the four patients tested receiving both intravenous and oral phenytoin, the intravenous response always predicted the oral response. For the seven patients in whom electrophysiologic study indicated phenytoin efficacy, two are alive and arrhythmia-event free, two had sudden death when the regimen was changed (one case, quinidine added; one case, subtherapeutic serum level), and three died from nonarrhythmic causes. For the 10 patients treated empirically with phenytoin, either alone (seven patients) or in combination with another antiarrhythmic agent (three patients), four died secondary to an arrhythmic event.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Demonstration of the presence of slow conduction during sustained ventricular tachycardia in man: use of transient entrainment of the tachycardia.

To test the hypothesis that an area of slow conduction is present during reentrant ventricular tachycardia in man, and that the earliest activation site during ventricular tachycardia is within or orthodromically just distal to the area of slow conduction in the reentry loop, we studied 12 episodes of ventricular tachycardia (mean rate 185 +/- 32 beats/min) that were induced in nine patients with ischemic heart disease. Rapid ventricular pacing was performed at selected sites during ventricular tachycardia while recording electrograms from an early activation site relative to the onset of the QRS complex (site A) and from a site close to the pacing site (site B). Rapid pacing from the right ventricular apex during ventricular tachycardia with a right bundle branch block pattern and from selected left ventricular sites during ventricular tachycardia with a left bundle branch block pattern (mean pacing rate 202 +/- 38 beats/min) resulted in constant ventricular fusion beats on the electrocardiogram except for the last captured beat (i.e., the ventricular tachycardia was entrained) in 11 of 12 episodes. During entrainment: sites A and B were activated at the pacing rate, conduction time from the last pacing impulse to the last captured ventricular electrogram at site A (St-A interval) was 359 +/- 69 msec and spanned the diastolic interval, while that at site B (St-B interval) was only 28 +/- 13 msec, site A had the same ventricular electrogram morphology as that during ventricular tachycardia, while site B had a different electrogram morphology, indicating that site A was activated in the same direction during entrainment as during ventricular tachycardia. Eight episodes of ventricular tachycardia were entrained at two or more different pacing rates. The St-A interval increased during pacing at the faster rate(s) in four of eight episodes, while the St-B interval remained unchanged. Rapid ventricular pacing performed from the same site during sinus rhythm (mean pacing rate 201 +/- 37 beats/min) resulted in an St-A interval of 103 +/- 37 msec (p less than .001 vs the value during entrainment) and an St-B interval of 31 +/- 15 msec (p = NS vs the value during entrainment). It is concluded that an area of slow conduction not demonstrable during sinus rhythm exists during ventricular tachycardia, and that the earliest activation site during ventricular tachycardia is at or orthodromically distal to this area of slow conduction.

Aged↗
PubMed1986

"Incessant" atrioventricular (AV) reciprocating tachycardia utilizing left lateral AV bypass pathway with a long retrograde conduction time.

Two patients with incessant or nearly incessant episodes of atrioventricular (AV) reciprocating tachycardia were studied and were found to be unique because of the location of a slowly conducting retrograde AV bypass pathway in the left lateral position. During the tachycardia in both patients, negative P waves were present not only in ECG leads II, III, and aVF, but also in leads I and aVL. The R-P'/P'-R ratios were 1.3 and 1.9, respectively. Cardiac electrophysiologic study revealed that in both tachycardias, retrograde ventriculoatrial conduction occurred utilizing a concealed left lateral AV bypass pathway with a long conduction time. Verapamil prolonged conduction over the AV bypass pathway in both patients. One patient was successfully treated with oral verapamil. The other patient underwent successful surgical interruption of the AV bypass pathway.

Adult↗
PubMed1985

Further observations on transient entrainment: importance of pacing site and properties of the components of the reentry circuit.

Transient entrainment of circus-movement tachycardia utilizing an atrioventricular (AV) bypass pathway was studied in 13 patients (nine with the orthodromic form, two with the antidromic form, and two with both the orthodromic and antidromic forms). All patients had a left-sided AV bypass pathway. Pacing at selected rates faster than the spontaneous rate was performed during the tachycardia at a site proximal or distal to the AV node, an area of slow conduction within the reentry loop. Rapid pacing from a site proximal to the AV node (from the right atrium during the orthodromic form of the arrhythmia or the right ventricle during the antidromic form of the arrhythmia) always demonstrated at least one of the three entrainment criteria: constant fusion beats except for the last captured beat, which was entrained but not fused (first criterion); progressive fusion (second criterion); localized conduction block to a site(s) for 1 paced beat associated with interruption of the tachycardia followed by activation of that site(s) by the next paced beat from a different direction and with a shorter conduction time (third criterion). In contrast, rapid pacing from a site distal to the AV node (from the right ventricle during the orthodromic form of the arrhythmia, or the right atrium during the antidromic form of the arrhythmia) transiently entrained the tachycardia, but never demonstrated any entrainment criteria because the antidromic wave front from the pacing impulse always blocked in the AV node (concealed entrainment). We conclude that the location of the pacing site relative to the components of a reentry loop is critical to the demonstration of the criteria of transient entrainment; i.e., if it is proximal to an area of slow conduction and/or unidirectional block within a reentry loop, transient entrainment should be demonstrable, but if it is distal, it will not be demonstrable.

Adolescent↗
PubMed1985

Significance of transient entrainment in pacing treatment of tachyarrythmias.

Rapid pacing techniques can be used to interrupt reentrant tachyarrhythmias whose reentry circuit includes an excitable gap. These rhythms include classic atrial flutter (Type I), ectopic atrial tachycardia, AV nodal reentrant tachycardia, AV junctional reentrant tachycardia involving an AV bypass pathway, ventricular tachycardia, and probably sinus node reentrant tachycardia. When utilizing rapid pacing techniques to interrupt any of these arrhythmias, it is necessary to pace at a critically rapid rate, and then for a critical duration of time at that rapid rate in order to interrupt the tachycardia. Pacing at rates short of the critically rapid rate, or short of the critical duration, will simply transiently entrain the tachycardia to the pacing rate without interrupting it. Therefore, when such pacing is terminated, the tachycardia will resume promptly at its previous spontaneous rate. Furthermore, for some arrhythmias, pacing may be achieved at an appropriately rapid rate to interrupt the tachycardia and the pacing may be maintained for an appropriate period of time. However, in the latter instances, the phenomenon of termination and reinitiation of the arrhythmia sometimes may occur, in which case cessation of pacing is not associated with interruption of the arrhythmia. Knowledge of this phenomenon is important when using either permanent or temporary pacing techniques to interrupt reentrant arrhythmias.

Atrial Flutter↗
PubMed1984

Temporary epicardial wire electrodes in the diagnosis and treatment of arrhythmias after open heart surgery.

The demonstrated safety, efficacy, and ease of utilization of the temporarily placed epicardial wire electrodes strongly support their routine use. By having temporary stainless steel wire electrodes available in the postoperative period, the diagnosis of arrhythmias after open heart surgery is greatly facilitated. Furthermore, because of the clinical advantages of cardiac pacing, it has become the treatment of choice for many, if not most, arrhythmias in the postoperative period.

Arrhythmias, Cardiac↗
PubMed1984

Diagnosis and treatment of arrhythmias during and following open heart surgery.

The ability to record electrograms directly from the atria and to pace the atria and/or ventricles provides an effective, rapid, easy, and remarkably safe way to treat most disorders of rhythm and conduction in patients during and following open heart surgery. This article reviews various applications of those techniques.

Arrhythmias, Cardiac↗
PubMed1984

Demonstration of the mechanism of transient entrainment and interruption of ventricular tachycardia with rapid atrial pacing.

An unusual case is presented in which ventricular tachycardia at a rate of 141 beats/min was transiently entrained by rapid atrial pacing at rates of 150, 155 and 160 beats/min, and was interrupted by rapid atrial pacing at a rate of 165 beats/min. During each period of transient entrainment, constant ventricular fusion beats were present except for the last entrained beat, and progressive ventricular fusion (different fusion QRS complexes) was demonstrated when comparing QRS complex configurations during transient entrainment at each pacing rate. Interruption of the ventricular tachycardia was associated with localized conduction block to the right ventricular recording site, followed by activation of that site from a different direction and with a shorter conduction time by the subsequent pacing impulse. These data clearly distinguish transient entrainment of a tachycardia from overdrive suppression of a tachycardia, and strongly suggest that reentry was the underlying mechanism of the ventricular tachycardia.

Adult↗
PubMed1984

Relevance of electrograms and transient entrainment for antitachycardia devices.

Clearly, understanding what occurs during rapid pacing of tachyarrhythmias due to reentry with an excitable gap does not provide the panacea to the rapid pacing treatment of these arrhythmias. However, it does advance the field considerably, and provides insights which should be useful for the development of improved antitachycardia pacing techniques.

Atrial Fibrillation↗