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Biomedical subjects

L A Saxon

Publications and source records attributed to L A Saxon.

At least 19 recordsLinked to original sources
PubMed2000

Rate smoothing with cardiac pacing for preventing torsade de pointes.

Cardiac pacing remains one of the most effective means for preventing torsade de pointes in patients with long QT syndrome (LQTS). However, fatal arrhythmias may occur despite combined therapy with beta blockers and pacing, and it is possible that failure of cardiac pacing for preventing arrhythmias in the long run is related (at least in part) to suboptimal pacemaker programming. Preventing sudden pauses may be especially important for preventing arrhythmias in the LQTS because such pauses are highly proarrhythmic in this patient population. Unfortunately, properly functioning pacemakers cannot be expected to prevent postextrasystolic pauses. The use of a pause-prevention pacing algorithm-rate smoothing-for preventing pause-dependent torsade de pointes is described in 12 patients with cardiac arrest or syncope due to congenital LQTS who were followed for 21 +/- 11 months.

Algorithms↗
PubMed2000

Body surface mapping of counterclockwise and clockwise typical atrial flutter: a comparative analysis with endocardial activation sequence mapping.

OBJECTIVES: This study was directed at developing spatial 62-lead electrocardiogram (ECG) criteria for classification of counterclockwise (CCW) and clockwise (CW) typical atrial flutter (Fl) in patients with and without structural heart disease. BACKGROUND: Electrocardiographic classification of CCW and CW typical atrial Fl is frequently hampered by inaccurate and inconclusive scalar waveform analysis of the 12-lead ECG. METHODS: Electrocardiogram signals from 62 torso sites and multisite endocardial recordings were obtained during CCW typical atrial Fl (12 patients), CW typical Fl (3 patients), both forms of typical Fl (4 patients) and CCW typical and atypical atrial Fl (1 patient). All the Fl wave episodes were divided into two or three successive time periods showing stable potential distributions from which integral maps were computed. RESULTS: The initial, intermediate and terminal CCW Fl wave map patterns coincided with: 1) caudocranial activation of the right atrial septum and proximal-to-distal coronary sinus activation, 2) craniocaudal activation of the right atrial free wall, and 3) activation of the lateral part of the subeustachian isthmus, respectively. The initial, intermediate and terminal CW Fl wave map patterns corresponded with : 1) craniocaudal right atrial septal activation, 2) activation of the subeustachian isthmus and proximal-to-distal coronary sinus activation, and 3) caudocranial right atrial free wall activation, respectively. A reference set of typical CCW and CW mean integral maps of the three successive Fl wave periods was computed after establishing a high degree of quantitative interpatient integral map pattern correspondence irrespective of the presence or absence of organic heart disease. CONCLUSIONS: The 62-lead ECG of CCW and CW typical atrial Fl in man is characterized by a stereotypical spatial voltage distribution that can be directly related to the underlying activation sequence and is highly specific to the direction of Fl wave rotation. The mean CCW and CW Fl wave integral maps present a unique reference set for improved clinical detection and classification of typical atrial Fl.

Aged↗
PubMed2000

Ventricular contraction abnormalities in dilated cardiomyopathy: effect of biventricular pacing to correct interventricular dyssynchrony.

OBJECTIVE: To measure ventricular contractile synchrony in patients with dilated cardiomyopathy (DCM) and to evaluate the effects of biventricular pacing on contractile synchrony and ejection fraction. BACKGROUND: Dilated cardiomyopathy is characterized by abnormal ventricular activation and contraction. Biventricular pacing may promote a more coordinated ventricular contraction pattern in these patients. We hypothesized that biventricular pacing would improve synchrony of right ventricular and left ventricular (RV/LV) contraction, resulting in improved ventricular ejection fraction. METHODS: Thirteen patients with DCM and intraventricular conduction delay underwent multiple gated equilibrium blood pool scintigraphy. Phase image analysis was applied to the scintigraphic data and mean phase angles computed for the RV and LV. Phase measures of interventricular (RV/LV) synchrony were computed in sinus rhythm and during atrial sensed biventricular pacing (BiV). RESULTS: The degree of interventricular dyssynchrony present in normal sinus rhythm correlated with LV ejection fraction (r = -0.69, p < 0.01). During BiV, interventricular contractile synchrony improved overall from 27.5 +/- 23.1 degrees to 14.1 +/- 13 degrees (p = 0.01). The degree of interventricular dyssynchrony present in sinus rhythm correlated with the magnitude of improvement in synchrony during BiV (r = 0.83, p < 0.001). Left ventricular ejection fraction increased in all thirteen patients during BiV, from 17.2 +/- 7.9% to 22.5 +/- 8.3% (p < 0.0001) and correlated significantly with improvement in RV/LV synchrony during BiV (r = 0.86, p < 0.001). CONCLUSIONS: Dilated cardiomyopathy with intraventricular conduction delay is associated with significant interventricular dyssynchrony. Improvements in interventricular synchrony during biventricular pacing correlate with acute improvements in LV ejection fraction.

Adult↗
PubMed2000

Heart failure management using implantable devices for ventricular resynchronization: Comparison of Medical Therapy, Pacing, and Defibrillation in Chronic Heart Failure (COMPANION) trial. COMPANION Steering Committee and COMPANION Clinical Investigators.

BACKGROUND: Although pharmacological therapy has ameliorated symptoms and improved the survival of patients with chronic heart failure (CHF), this chronic syndrome remains a progressive disease causing incremental morbidity and early mortality. A new therapy for the treatment of CHF should ideally decrease mortality, alleviate symptoms, and improve functional capacity. A growing body of evidence suggests that the use of implantable devices to resynchronize ventricular contraction may be a beneficial adjunct in the treatment of CHF. METHODS: The Comparison of Medical Therapy, Pacing, and Defibrillation in Chronic Heart Failure (COMPANION) trial is a randomized, open-label, 3-arm study of patients in New York Heart Association class III or IV with an ejection fraction of 35% or less and a QRS duration of 120 milliseconds or less. The COMPANION study objectives are to determine whether optimal pharmacological therapy used with (1) ventricular resynchronization therapy alone or (2) ventricular resynchronization therapy combined with cardioverter-defibrillator capability is superior to optimal pharmacological therapy alone in reducing combined all-cause mortality and hospitalizations; reducing cardiac morbidity; improving functional capacity, cardiac performance, and quality of life; and increasing total survival.

Cardiovascular Agents↗
PubMed1999

Use of electroanatomic mapping to delineate transseptal atrial conduction in humans.

BACKGROUND: Interaction between wave fronts in the right and left atrium may be important for maintenance of atrial fibrillation, but little is known about electrophysiological properties and preferential routes of transseptal conduction. METHODS AND RESULTS: Eighteen patients (age 44+/-12 years) without structural heart disease underwent right atrial electroanatomic mapping during pacing from the distal coronary sinus (CS) or the posterior left atrium. During distal CS pacing, 9 patients demonstrated a single transseptal breakthrough near the CS os, 1 patient in the high right atrium near the presumed insertion of Bachmann's bundle and 1 patient near the fossa ovalis. The mean activation time from stimulus to CS os was 48+/-15 ms compared with 86+/-15 ms to Bachmann's bundle insertion (P<0.01) and 59+/-23 ms to the fossa ovalis (P=NS and P<0.01, respectively). During left atrial pacing, the earliest right atrial activation was near Bachmann's bundle in 5 and near the fossa ovalis in 4 patients. The activation time from stimulus to CS os was 70+/-15 ms compared with 47+/-16 ms to Bachmann's bundle (P<0.01) and 59+/-25 ms to the fossa ovalis (P=NS). Whereas the total septal activation time was not significantly different during CS pacing compared with left atrial pacing (41+/-16 versus 33+/-17 ms), the total right atrial activation time was longer during CS pacing (117+/-49 versus 79+/-15 ms; P<0.05). CONCLUSIONS: Three distinct sites of early right atrial activation may be demonstrated during left atrial pacing. These sites are in accord with anatomic muscle bundles and may have relevance for maintenance of atrial flutter or fibrillation.

Adult↗
PubMed1999

Biventricular pacing in patients with congestive heart failure: two prospective randomized trials. The VIGOR CHF and VENTAK CHF Investigators.

Epidemiologic studies suggest that 20-30% of patients diagnosed with symptomatic congestive heart failure (CHF) have intraventricular conduction disorders characterized by a discoordinate contraction pattern and wide QRS. Biventricular pacing is an emerging therapy allowing simultaneous electrical stimulation of the right and left ventricles with the use of an implantable pacing system. The aim of this article is to describe 2 prospective randomized multicenter trials examining the effects of biventricular pacing on functional capacity, quality of life, and hemodynamic status in patients with dilated cardiomyopathy and intraventricular delay. The VIGOR CHF Trial is designed to assess functional and symptomatic improvement in heart failure patients with biventricular pacing and without a concomitant indication for conventional bradycardia pacemaker therapy. To assess for potential placebo effects, patients are randomized to receive either biventricular pacemaker therapy or no pacing therapy for the first 6 weeks, after which both groups receive pacing therapy. The VENTAK CHF trial uses an implantable cardioverter defibrillator system (ICD) designed to provide chronic biventricular pacing therapy in addition to treating ventricular tachyarrhythmias. All patients receive conventional ICD and CHF therapy throughout the study and are randomized in a 2-period crossover design to receive either no pacing or biventricular pacing for 3-month intervals. Patient enrollment in both studies is ongoing, with a closed analysis. The unique designs of these trials provide the opportunity to study this therapy in high-risk patients who have been optimally treated for heart failure.

Adult↗
PubMed1999

Electrophysiologic effects of adenosine in patients with supraventricular tachycardia.

BACKGROUND: We correlated the electrophysiologic (EP) effects of adenosine with tachycardia mechanisms in patients with supraventricular tachycardias (SVT). METHODS AND RESULTS: Adenosine was administered to 229 patients with SVTs during EP study: atrioventricular (AV) reentry (AVRT; n=59), typical atrioventricular node reentry (AVNRT; n=82), atypical AVNRT (n=13), permanent junctional reciprocating tachycardia (PJRT; n=12), atrial tachycardia (AT; n=53), and inappropriate sinus tachycardia (IST; n=10). There was no difference in incidence of tachycardia termination at the AV node in AVRT (85%) versus AVNRT (86%) after adenosine, but patients with AVRT showed increases in the ventriculoatrial (VA) intervals (13%) compared with typical AVNRT (0%), P<0.005. Changes in atrial, AV, or VA intervals after adenosine did not predict the mode of termination of long R-P tachycardias. For patients with AT, there was no correlation with location of the atrial focus and adenosine response. AV block after adenosine was only observed in AT patients (27%) or IST (30%). Patients with IST showed atrial cycle length increases after adenosine (P<0.05) with little change in activation sequence. The incidence of atrial fibrillation after adenosine was higher for those with AVRT (15%) compared with typical AVNRT (0%) P<0.001, or atypical AVNRT (0%) but similar to those with AT (11%) and PJRT (17%). CONCLUSIONS: The EP response to adenosine proved of limited value to identify the location of AT or SVT mechanisms. Features favoring AT were the presence of AV block or marked shortening of atrial cycle length before tachycardia suppression. Atrial fibrillation was more common after adenosine in patients with AVRT, PJRT, or AT. Patients with IST showed increases in cycle length with little change in atrial activation sequence after adenosine.

Adenosine↗
PubMed1998

Radiofrequency catheter ablation of ventricular tachycardia after myocardial infarction.

BACKGROUND: Patients with ventricular tachycardia (VT) after myocardial infarction often have multiple morphologies of inducible VT, which complicates mapping and is viewed by some as a relative contraindication to ablation. Attempting to identify and target a single "clinical" VT is often limited by inability to obtain 12-lead ECGs of VTs that are terminated emergently or by defibrillators. This study assesses the feasibility of ablation in patients selected without regard to the presence of multiple VTs by targeting all VTs that allow mapping. METHODS AND RESULTS: Radiofrequency catheter ablation targeting all inducible monomorphic VTs that allowed mapping was performed in 52 patients with prior myocardial infarction. Antiarrhythmic drug therapy had failed in 41 (79%) patients including amiodarone in 36 (69%) patients. An average of 3.6+/-2 morphologies of VT were induced per patient. More than 1 ablation session was required in 16 (31%) patients. Complications occurred in 5 (10%) patients, including 1 (2%) death caused by acute myocardial infarction. During follow-up 59% of patients continued to receive amiodarone; 23 (45%) had implantable defibrillators. During a mean follow-up of 18+/-15 months (range 0 to 51 months) 1 patient died suddenly, 2 died from uncontrollable VT, and 5 died from heart failure. Three-year survival rate was 70+/-10%, and rate for risk of VT recurrence was 33+/-7%. CONCLUSIONS: Radiofrequency catheter ablation controls VT that is sufficiently stable to allow mapping in 67% of patients despite failure of antiarrhythmic drug therapy and multiple inducible VTs. However, ablation was largely adjunctive to amiodarone and defibrillators in this referral population.

Adult↗
PubMed1998

Anatomic and electrophysiologic relation between the coronary sinus and mitral annulus: implications for ablation of left-sided accessory pathways.

To determine whether precise left-sided accessory pathway localization is possible from the coronary sinus, electrocardiogram (ECG) characteristics from the coronary sinus pair demonstrating earliest activation via the accessory pathway were compared to simultaneous mitral annular ablation catheter ECGs at successful ablation sites in 48 patients. To define the coronary sinus-mitral annular relation, the coronary sinus to mitral annulus distance (D) was measured at sequential distances from the coronary sinus os in 10 cadaver hearts. Mitral annular ECGs demonstrated earliest activation via the accessory pathway more frequently than the earliest coronary sinus pair (p < 0.001), more frequent continuous electrical activity (p < 0.001), and more frequent accessory pathway potentials (p < 0.01). D was >10 mm at 20, 40, and 60 mm, respectively, from the coronary sinus os. Coronary sinus ECGs do not precisely localize left-sided accessory pathways, which may be due in part to an average anatomic separation of more than 10 mm between the coronary sinus and accessory pathways bridging the mitral annulus.

Adult↗
PubMed1998

Narrow complex tachycardia with VA block: diagnostic and therapeutic implications.

To review our experience with cases of narrow complex tachycardia with VA block, highlighting the difficulties in the differential diagnosis, and the therapeutic implications. Prior reports of patients with narrow complex tachycardia with VA block consist of isolated case reports. The differential diagnosis of this disorder includes: automatic junctional tachycardia, AV nodal reentry with final upper common pathway block, concealed nodofascicular (ventricular) pathway, and intra-Hissian reentry. Between June 1994 and January 1996, six patients with narrow complex tachycardia with episodes of ventriculoatrial block were referred for evaluation. All six patients underwent attempted radiofrequency ablation of the putative arrhythmic site. Three of six patients had evidence suggestive of a nodofascicular tract. Intermittent antegrade conduction over a left-sided nodofascicular tract was present in two patients and the diagnosis of a concealed nodofascicular was made in the third patient after ruling out other tachycardia mechanisms. Two patients had automatic junctional tachycardia, and one patient had atrioventricular nodal reentry with proximal common pathway block. Attempted ablation in the posterior and mid-septum was unsuccessful in patients with nodofascicular tachycardia. In contrast, those with atrioventricular nodal reentry and automatic junctional tachycardia readily responded to ablation. The presence of a nodofascicular tachycardia should be suspected if: (1) intermittent antegrade preexcitation is recorded, (2) the tachycardia can be initiated with a single atrial premature producing two ventricular complexes, and (3) a single ventricular extrastimulus initiates SVT without a retrograde His deflection. The presence of a nodofascicular pathway is common in patients with narrow complex tachycardia and VA block. Unlike AV nodal reentry and automatic junctional tachycardia, the response to ablation is poor.

Adolescent↗
PubMed1998

Acute effects of intraoperative multisite ventricular pacing on left ventricular function and activation/contraction sequence in patients with depressed ventricular function.

INTRODUCTION: We hypothesized that simultaneous right and left ventricular apical pacing would result in improvement in left ventricular function due to improved coordination of segmental ventricular contraction. Structural changes in ventricular muscle present in dilated cardiomyopathy compromise ventricular excitation and mechanical contraction. METHODS AND RESULTS: Eleven patients with depressed left ventricular function having cardiac surgery underwent epicardial multisite pacing with continuous transesophageal echocardiographic imaging. Quantitative measurement of percent fractional area change was performed, and segmental changes in contraction sequence resulting from simultaneous right and left ventricular pacing were assessed by application of phase analysis to recorded transesophageal images. There was no statistically significant difference between the paced QRS duration achieved with simultaneous right and left ventricular apical pacing and the native QRS duration (139+/-39 msec vs 106+/-18 msec, P = NS), but all other paced modes resulted in longer QRS durations. Percent fractional area change improved with simultaneous right and left ventricular apical pacing but not with other paced modes (41.5+/-11.9 vs 34.3+/-9.7, P < 0.01). Phase analysis demonstrated a resequencing of segmental left ventricular activation/contraction when compared to baseline ventricular activation. CONCLUSION: Simultaneous right and left ventricular apical pacing results in acute improvements in global ventricular performance in patients with depressed ventricular function. Improvements may result from pacing-induced global coordination through recruitment of left and right ventricular apical and septal segments critical to effective ventricular contraction.

Cardiac Pacing, Artificial↗
PubMed1997

Risk of thromboembolism in chronic atrial flutter.

Anticoagulant therapy is not conventionally used in the treatment of patients with atrial flutter. This recommendation has been based on sparse clinical experience, and recent preliminary reports suggest a significant risk of thromboembolism for these patients. A retrospective study was undertaken to assess the frequency of thromboembolic events as well as potential risk factors for these events in a cohort of patients with atrial flutter referred for radiofrequency ablation treatment. Eighty-six consecutive patients with a primary diagnosis of atrial flutter were evaluated. A history of embolic events was noted in 12 of 86 patients (14%) with atrial flutter, with an annual risk of approximately 3%. There were no differences in the prevalence of coronary artery disease, cardiomyopathy, valvular disease, or atrial fibrillation between the 2 groups of patients having an embolic event and those of patients without embolic events. Left ventricular function and left atrial size were also similar between the 2 groups. The only significant risk factor was hypertension (p < 0.05). However, in a regression model with other clinical variables (i.e., age, gender, left atrial size, presence or absence of any cardiac disease, length of time in flutter, left ventricular function, type of flutter, flutter cycle length, type of secondary arrhythmias) no significant predictors were found. Patients with transient ischemic attacks or pulmonary emboli were then excluded from the analysis in order to compare the thromboembolic risk in the present study to that reported in major atrial fibrillation trials. The overall risk becomes 7% (6 of 86), which over a mean follow-up period of 4.5 years yields an annual risk of approximately 1.6%. Although this risk is only 1/3 of that for patients with atrial fibrillation, this risk is higher than previously recognized for patients with chronic atrial flutter. Anticoagulant therapy should be seriously considered for these patients.

Adult↗
PubMed1997

Mechanism of initiation of atrial flutter in humans: site of unidirectional block and direction of rotation.

OBJECTIVES: Using a standardized induction protocol, we investigated the mechanism of initiation of atrial flutter, before ablation, to determine the site of initiating unidirectional block and to test the hypothesis that the direction of rotation of atrial flutter depends on the pacing site from which it initiates. BACKGROUND: The high recurrence rate of atrial flutter after presumed successful ablation may be due to difficulty in reinduction after termination. In addition, induction of clockwise flutter is currently of unknown clinical importance. METHODS: Ten patients with documented typical flutter were studied before ablation. A standard protocol consisting of single and double extrastimuli followed by burst pacing was performed from four sites in the right atrium (high and low trabeculated and smooth right atrium) to assess efficacy at inducing atrial flutter. A 20-pole halo catheter placed around the tricuspid annulus and a decapole catheter placed in the coronary sinus were used for mapping during initiation to determine type of flutter induced and the site of unidirectional block during initiation. RESULTS: Atrial flutter was induced in 52 (6.2%) of 838 attempted inductions. Of these, 33 were counterclockwise and 20 were clockwise. Of the 20 inductions resulting in clockwise flutter, 18 were from the trabeculated right atrium, whereas all the counterclockwise inductions were from the smooth right atrium. In all but the two inductions, the site of unidirectional block was identified between the os of the coronary sinus and the low lateral right atrium for both counterclockwise and clockwise flutter, in the same isthmus at which ablation is targeted. CONCLUSIONS: Even in patients with clinical counterclockwise flutter, clockwise flutter is frequently induced before ablation and is dependent on the site of induction: Pacing from the smooth right atrium induces counterclockwise flutter, whereas pacing from the trabeculated right atrium induces clockwise flutter. The site of the unidirectional block during the initiation of either form of flutter is in the low right atrium isthmus.

Aged↗
PubMed1997

Exploring postinfarction reentrant ventricular tachycardia with entrainment mapping.

Ventricular tachycardia late after myocardial infarction is usually due to reentry in the infarct region. These reentry circuits can be large, complex and difficult to define, impeding study in the electrophysiology laboratory and making catheter ablation difficult. Pacing through the electrodes of the mapping catheter provides a new approach to mapping. When pacing stimuli capture the effects on the tachycardia depend on the location of the pacing site relative to the reentry circuit. The effects observed allow identification of various portions of the reentry circuit, without the need for locating the entire circuit. Isthmuses where relatively small lesions produced by radiofrequency catheter ablation can interrupt reentry can often be identified. A classification that divides reentry circuits into one or more functional components helps to conceptualize the reentry circuit and predicts the likelihood that heating with radiofrequency current will terminate tachycardia. These methods are helping to define human reentry circuits.

Cardiac Pacing, Artificial↗
PubMed1997

Electrophysiology of "incisional" reentrant atrial tachycardia complicating surgery for congenital heart disease.

Intraatrial reentrant tachycardia, which occurs frequently in patients who have undergone corrective surgery for congenital heart disease, presents a challenge to successful management. Because the surgical repair sites are invariably critical to the development and maintenance of reentrant atrial tachycardia, we use the term "incisional reentry" to describe these arrhythmias. An understanding of the electrophysiology of such "incisional reentry," and techniques to identify a critical isthmus, are essential for successful ablation of these circuits. A critical isthmus may be identified by the presence of entrainment with concealed fusion. Confirmation that the site is critical to the tachycardia circuit is obtained by an analysis of the relationship between the postpacing interval and the tachycardia cycle length. Advances in mapping from multiple simultaneous sites, along with the ability to create larger, deeper lesions will be needed in order to cure a larger number of these patients. Ultimately, in some cases one must consider each procedure palliative rather than curative, as the disease progresses and substrate evolves and more tachycardia circuits become active.

Atrioventricular Node↗
PubMed1997

Electrocardiographic and electrophysiologic characterization of atypical atrial flutter in man: use of activation and entrainment mapping and implications for catheter ablation.

INTRODUCTION: Although the circuit in typical counterclockwise atrial flutter has been clearly delineated, the mechanisms of "atypical atrial flutters" have been less well characterized. The purpose of this study was to investigate the ECG and electrophysiologic (EP) characteristics of atypical atrial flutter. METHODS AND RESULTS: Thirty-three patients with at least one form of atypical atrial flutter underwent EP evaluation with multipolar atrial activation and entrainment mapping. Nineteen patients with clockwise flutter had: (1) stereotypic ECG morphology; (2) same cycle length as counterclockwise flutter; (3) clockwise activation around the tricuspid annulus; (4) recording of discrete split potentials along the length of the crista terminalis, suggesting the presence of conduction block; (5) concealed entrainment from the low right atrial isthmus; (6) successful ablation in this isthmus. Twenty patients with atypical flutter not consistent with a clockwise mechanism ("true atypical flutter") showed: (1) heterogeneous ECG morphology; (2) cycle length shorter than that of clockwise flutter; (3) frequent transitions from and to atrial fibrillation; (4) could be entrained in only six patients and, when accomplished, demonstrated surface fusion when entraining from the low right atrial isthmus. CONCLUSIONS: Atypical flutter falls into two broad categories. Clockwise flutter uses the same circuit with the same endocardial barriers as its counterclockwise counterpart and is best considered a form of typical flutter. True atypical flutter induced in the EP laboratory is a heterogeneous group of arrhythmias that are transitional to atrial fibrillation. Although it may superficially resemble clockwise or counterclockwise flutter based on the 12-lead ECG alone, the distinction can be readily made from a combined evaluation including activation and entrainment mapping.

Adult↗