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Biomedical subjects

M D Lesh

Publications and source records attributed to M D Lesh.

At least 55 records · Page 3Linked to original sources
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

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

Slow AV nodal pathway ablation utilizing a unique temperature controlled radiofrequency energy system.

Thirty-nine consecutive patients with symptomatic AV nodal reentrant tachycardia (AVNRT) underwent temperature guided slow AV nodal pathway ablation (group 1). Forty-three consecutive patients undergoing nontemperature guided slow AV nodal pathway ablation late in our experience compose the control population (group 2). Slow pathway ablation was achieved in all patients of both groups. The mean fluoroscopy and ablation times for group 1 were significantly shorter than for group 2 (26.1 +/- 14.9 vs 33.9 +/- 18.9 min, P < 0.05; 19.9 +/- 12.1 vs 30.9 +/- 23.3 min, P < or = 0.02). There were no episodes of coagulum formation in group 1, while there were 15 episodes (7.1% of energy applications) in group 2 (P = 0.0006) despite a significantly higher applied power in group 1 (53.4 +/- 25.1 vs 35.6 +/- 9.5W, P = 0.0001). Successful energy applications were associated with significantly higher temperatures than unsuccessful applications in group 1 (55.6 degrees +/- 5.8 degrees C vs. 52.9 degrees +/- 6.8 degrees C, P < or = 0.03). The minimum temperature required for successful ablation was 48 degrees C for two patients (5%) and was > or = 50 degrees C for the remainder of patients (37/39 [95%]). The catheter ablation system used in this study was safe, effective, and prevented coagulum formation while delivering relatively high power. In addition, shorter ablation times and radiation exposure were seen with this system. Although successful energy applications and the production of junctional rhythm were associated with higher achieved temperatures, temperature alone did not predict either endpoint. Future prospective, randomized trials are needed to confirm these findings and further evaluate the value of temperature monitoring.

Atrioventricular Node↗
PubMed1997

Use of intracardiac echocardiography in interventional electrophysiology.

Intracardiac echocardiography is emerging as a potentially useful tool during RF ablation procedures. There are a number of potential benefits of direct endocardial visualization during RF ablation including: (1) precise anatomical localization of the ablation catheter tip in relation to important endocardial structures, which cannot be visualized with fluoroscopy; (2) reduction in fluoroscopy time; (3) evaluation of catheter tip tissue contact; (4) confirmation of lesion formation and identification of lesion size and continuity; (5) immediate identification of complications; and (6) as a research tool to help in understanding the critical role played by specific endocardial structures in arrhythmogenesis. This article will review existing data and speculate as to possible future roles for intracardiac echocardiography in interventional electrophysiology.

Animals↗
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↗
PubMed1997

Mode of onset of malignant ventricular arrhythmias in idiopathic ventricular fibrillation.

INTRODUCTION: The mode of onset of malignant ventricular arrhythmias (ventricular tachycardia [VT] or ventricular fibrillation [VF]) has been well described in patients with organic heart disease and in patients with the long QT syndromes. Less is known about the mode of onset of VF in patients with out-of-hospital VF who have no evidence of organic heart disease or identifiable etiology. METHODS AND RESULTS: We reviewed the ECGs of all our patients with idiopathic VF. Documentation of the onset of spontaneous arrhythmias was available for 22 VF episodes in 9 patients (6 men and 3 women; age 41 +/- 16 years). In all instances, spontaneous VF followed a rapid polymorphic VT, which was initiated by premature ventricular complexes (PVCs) with very short coupling intervals. The PVC initiating VF had a coupling interval of 302 +/- 52 msec and a prematurity index of 0.4 +/- 0.07. These PVCs occurred within 40 msec of the peak of the preceding T wave. Pause-dependent arrhythmias were never observed. CONCLUSION: Cardiac arrest among patients with idiopathic VF has a very distinctive mode of onset. Documentation of a polymorphic VT that is not pause dependent is of diagnostic value.

Adult↗
PubMed1997

Potential role of 'hybrid therapy' for atrial fibrillation.

Atrial fibrillation is the most common sustained arrhythmia in clinical practice. Several new non-pharmacological technologies are emerging which may offer hope for effective therapy and quality of life improvement of patients with atrial fibrillation. While both catheter-based atrial segmentation and implanted atrial defibrillators have the potential to revolutionize the treatment of patients with atrial fibrillation, both are also associated with the potential for significant limitations. Catheter ablation with the goal of curing atrial fibrillation may be a lengthy procedure and if left atrial lesions are required there is the potential for complications. As regards implanted atrial defibrillators an important question is whether many patients will tolerate the discomfort associated with energy levels required to restore sinus rhythm. The concept of 'hybrid therapy' is that in a given patient a combination of modalities might be used so as to achieve a synergistic effect, with each technology improving the efficacy of the other. For example, the presence of a more 'organized' pattern of fibrillation implies a lower defibrillation threshold. Data in a canine model of atrial fibrillation suggests that linear lesions in the right atrium alone may organize the atrial fibrillation in both atria and in so doing lower the atrial defibrillation threshold. Hybrid therapy may also employ drugs and pacing in combination with ablative lesions and an implanted atrial defibrillator.

Animals↗
PubMed1996

Deconvolution: a novel signal processing approach for determining activation time from fractionated electrograms and detecting infarcted tissue.

BACKGROUND: Two important signal processing applications in electrophysiology are activation mapping and characterization of the tissue substrate from which electrograms are recorded. We hypothesize that a novel signal-processing method that uses deconvolution is more accurate than amplitude, derivative, and manual activation time estimates. We further hypothesize that deconvolution quantifies changes in morphology that detect electrograms recorded from regions of myocardial infarction. METHODS AND RESULTS: To determine the accuracy of activation time estimation, 600 unipolar electrograms were calculated with a detailed computer model using various degrees of coupling heterogeneity to model infarction. Local activation time was defined as the time of peak inward sodium current in the modeled myocyte closest to the electrode. Deconvolution, minimum derivative, and maximum amplitude were calculated. Two experienced electrophysiologists blinded to the computer-determined activation times marked their estimates of activation time. F tests compared the variance of activation time estimation for each method. To evaluate the performance of deconvolution to detect infarction, 380 unipolar electrograms were recorded from 10 dogs with infarcts resulting from ligation of the left anterior descending coronary artery. The amplitude, duration, number of inflections, peak frequency, bandwidth, minimum derivative, and deconvolution were calculated. Metrics were compared by Mann-Whitney rank-sum tests, and receiver operating curves were plotted. CONCLUSIONS: Deconvolution estimated local activation time more accurately than the other metrics (P < .0001). Furthermore, the algorithm quantified changes in morphology (P < .0001) with superior performance, detecting electrograms recorded from regions of myocardial infarction. Thus, deconvolution, which incorporates a priori knowledge of electrogram morphology, shows promise to improve present clinical metrics.

Algorithms↗
PubMed1996

Mode of onset of torsade de pointes in congenital long QT syndrome.

OBJECTIVES: We sought to describe the mode of onset of spontaneous torsade de pointes in the congenital long QT syndrome. BACKGROUND: Contemporary classifications of the long QT syndrome (LQTS) refer to the congenital LQTS as "adrenergic dependent" and to the acquired LQTS as "pause dependent." Overlap between these two categories has been recognized, and a subgroup of patients with "idiopathic pause-dependent torsade" has been described. However, it is not known how commonly torsade is preceded by pauses in the congenital LQTS. METHODS: We reviewed the electrocardiograms (ECGs) of all our patients with congenital LQTS evaluated for syncope or sudden death (30 patients). Documentation of the onset of torsade de pointes was available for 15 patients. All these patients had "definitive LQTS" by accepted clinical and ECG criteria. RESULTS: Pause-dependent torsade de pointes was clearly documented in 14 of the 15 patients (95% confidence interval 68% to 100%). The cycle length of the pause leading to torsade was 1.3 +/- 0.2 times longer than the basic cycle length, and most pauses leading to torsade were unequivocally longer than the preceding basic cycle length (80% of pauses were > 80 ms longer than the preceding cycle length). CONCLUSIONS: The "long-short" sequence, which has been recognized as a hallmark of torsade de pointes in the acquired LQTS, plays a major role in the genesis of torsade in the congenital LQTS as well. Our findings have important therapeutic implications regarding the use of pacemakers for prevention of torsade in the congenital LQTS.

Adult↗
PubMed1996

Modeling triggered cardiac activity: an analysis of the interactions between potassium blockade, rhythm pauses, and cellular coupling.

It is known that under certain conditions, a combination of potassium channel blockade, sympathetic nervous activity, and pauses in sinus rhythm can increase the occurrence of cardiac arrhythmias. Although the arrhythmogenic interactions of these three factors are not completely understood, it is believed that the associated arrhythmias may be initiated by afterpotentials via a process that we refer to as propagated triggered activity. Using a two-cell computational model of ventricular action potential kinetics, we simulate nonuniform potassium blockade, sympathetic nervous activity, and pauses in sinus rhythm under conditions of hypokalemia. Under these conditions, the two-cell model suggests that (1) the arrhythmogenic interactions of potassium blockade and sympathetic nervous activity are highly dependent on heart rate; (2) triggered activity induced by potassium blockade would most likely occur during a pause in sinus rhythm; (3) during a sufficiently large pause in sinus rhythm, potassium blockade can induce triggered activity at normal levels of sympathetic activity; and (4) potassium blockade can increase the probability of triggered activity only if heart rate falls within a critical range. We also show that during pauses in sinus rhythm, two-cell triggering interactions between potassium blockade and sympathetic activity closely parallel the parametric displacement of the dynamic instability underlying the afterpotentials. Our results indicate that the behavior of the triggering mechanism studied here is consistent with that of pause-induced arrhythmias.

Action Potentials↗
PubMed1996

Percutaneous multielectrode endocardial mapping during ventricular tachycardia in the swine model.

BACKGROUND: Identification of critical areas within the ventricular tachycardia circuit is a prerequisite for catheter ablation. Currently, mapping during ventricular tachycardia, usually performed with standard catheters, is difficult and time-consuming and can be used only in patients with hemodynamically stable tachycardia. METHODS AND RESULTS: A total of 43 pigs underwent closed-chest induction of myocardial infarction. A basket-shaped catheter carrying 64 electrodes was deployed in the left ventricle during normal sinus rhythm. Unipolar pacing at 3 mA was successful in 78% of the basket catheter electrodes, demonstrating good electrode-tissue contact. Hemodynamic and echocardiographic measurements did not reveal any significant interference with myocardial or valvular function during or after catheter deployment. One hundred eighteen episodes of monomorphic ventricular tachycardia were induced in 28 pigs through right ventricular stimulation, 81 of which were mapped and analyzed. Ventricular tachycardia mapping was rapid, requiring only several beats and < 10 seconds to complete. Presystolic potentials, a possible target for ablation, were identified in 58% of the tachycardia episodes mapped. Pathological examination revealed only minor valvular and endocardial catheter-induced lesions immediately after mapping and none a month later. CONCLUSIONS: The multielectrode catheter enables rapid and safe percutaneous endocardial mapping of ventricular tachycardia in the swine model. Exploration of the clinical potential of the multielectrode catheter seems warranted.

Animals↗
PubMed1996

Activation and entrainment mapping defines the tricuspid annulus as the anterior barrier in typical atrial flutter.

BACKGROUND: The importance of anatomic barriers in the atrial flutter reentry circuit has been well demonstrated in canine models. It has been shown previously that the crista terminalis and its continuation as the eustachian ridge form a posterior barrier. In this study we tested the hypothesis that the tricuspid annulus forms the continuous anterior barrier to the flutter circuit. METHODS AND RESULTS: Thirteen patients with typical atrial flutter were studied. A 20-pole halo catheter was situated around the tricuspid annulus. A mapping catheter was used for activation and entrainment mapping from seven sequential sites around the tricuspid annulus and from three additional sites including the tip of the right atrial appendage, at the fossa ovalis, and in the distal coronary sinus. Sites were considered to be within the circuit when the postpacing interval minus the flutter cycle length and the stimulus time minus the activation time were < or = 10 ms; sites were considered to be outside the circuit when these intervals were > 10 ms. All seven annular sites were within the circuit; activation occurred sequentially around the annulus and accounted for 100% of the flutter cycle length. The fossa ovalis, the distal coronary sinus, and the right atrial appendage were outside the circuit. CONCLUSIONS: Closely spaced sites around the tricuspid annulus are activated sequentially, and are all within the flutter circuit according to entrainment criteria. This demonstrates that the tricuspid annulus constitutes a continuous anterior barrier constraining the reentrant wave front of human counterclockwise atrial flutter.

Aged↗
PubMed1996

Mapping and radiofrequency ablation of intraatrial reentrant tachycardia after the Senning or Mustard procedure for transposition ofthe great arteries.

The Senning and Mustard procedures are often associated with the development of atrial tachyarrhythmias, which may be a cause of sudden death. We hypothesized that atrial surgery creates barriers to impulse propagation, establishing potential routes for atrial reentry, and that mapping combined with knowledge of the surgical anatomy could identify zones that are critical to the tachycardia to be targeted for radiofrequency catheter ablation. Patients underwent mapping to identify early sites of atrial activation that were related to anatomic or surgically created obstacles, with confirmation by pacing to demonstrate concealed entrainment. Radiofrequency lesions were placed to connect these obstacles, while observing for tachycardia termination. Thirteen tachycardias were attempted in 10 patients, 10 successfully. Three patients had 2 distinct tachycardias. Successful sites were in right atrial tissue, although in many, a retrograde approach to the pulmonary venous atrium was necessary. Ablation of the clinically documented tachycardia was successful in 9 of 10 patients. The most common successful site was the region of the coronary sinus mouth, approached antegrade or retrograde. Ablation of intraatrial reentrant tachycardias after the Senning or Mustard procedure is feasible using concealed entrainment mapping techniques, but requires a detailed knowledge of the individual surgical anatomy and the ability to approach the pulmonary venous atrium. Radiofrequency ablation offers significant advantages over other management modalities in this patient group.

Adolescent↗
PubMed1996

Results of radiofrequency catheter ablation for atrial flutter.

RF catheter ablation for symptomatic typical atrial flutter is associated with a high procedural success rate, but a second RF procedure may be required in up to one third of subjects, particularly those with right atrial enlargement. In those subjects with both established AF and flutter, RF ablation for atrial flutter may decrease the recurrence rate of AF. However, patients remain at risk for the development of newly documented AF, most likely secondary to the high incidence of underlying structural heart disease.

Aged↗
PubMed1996

Ablation of 'incisional' reentrant atrial tachycardia complicating surgery for congenital heart disease. Use of entrainment to define a critical isthmus of conduction.

BACKGROUND: Intra-atrial reentrant tachycardia occurs frequently after surgery for congenital heart disease and is difficult to treat. We tested the hypotheses that intra-atrial reentrant tachycardia in patients who had undergone prior reparative surgery for congenital heart disease could be successfully ablated by targeting a protected isthmus of conduction bounded by natural and surgically created barriers and that entrainment techniques could be used to identify these zones. METHODS AND RESULTS: Eighteen consecutive patients with 26 intra-atrial reentrant tachycardias complicating surgery for congenital heart disease (9 atrial septal defect repair, 4 Fontan, 2 Mustard, 2 Senning, and 1 Rastelli procedure) underwent electrophysiological study and ablation attempts. Mapping of activation was facilitated by the deployment of catheters with multiple electrodes. Sites for ablation were sought that demonstrated entrainment with concealed fusion and at which the postpacing interval minus the tachycardia cycle length and the stimulus to P wave minus the activation time were < 30 ms. These sites were considered to be within a narrow isthmus critical to the tachycardia mechanism. Anatomic barriers bordering the critical isthmus of conduction were identified on anatomic grounds, by the presence of areas of electrical silence or by the demonstration of split potentials signifying a line of block. Success was achieved in 15 patients with 21 arrhythmias. The median number of radiofrequency applications was 5. There was a wide range of activation times at successful sites (-30 to -250 ms). At a mean duration of follow-up of 17 +/- 8 months, 11 patients were asymptomatic and 9 did not require antiarrhythmia therapy. CONCLUSIONS: Successful ablation of intra-atrial reentrant tachycardia complicating surgery for congenital heart disease may be achieved by creation of an ablative lesion in a critical isthmus of conduction bounded by anatomic barriers. This isthmus may be identified by the presence of entrainment with concealed fusion and an analysis of the relationship between the postpacing interval and the tachycardia cycle length and between the activation time and the stimulus time. Because this isthmus is invariably confined on at least one aspect by a surgical repair site that is of central importance to the tachycardia mechanism, we suggest that this type of arrhythmia be given the descriptive designation of "incisional reentry."

Adolescent↗
PubMed1996

Autonomic nervous system and sudden cardiac death.

In the United States, sudden cardiac death is a major public health problem, accounting for approximately 300,000 deaths annually. Accurate identification of those patients at highest risk for this event has been problematic. The use of signal-averaged electrocardiography, Holter monitoring and assessment of left ventricular function have been shown to be predictive of future arrhythmic events in patients after a myocardial infarction. However, the clinical utility of these tests has been limited by their low sensitivity and positive predictive value. It has become increasingly clear that the autonomic nervous system is extremely important in the pathogenesis of ventricular arrhythmias and sudden cardiac death. The two most important techniques used to study the autonomic nervous system--heart rate variability and baroreflex sensitivity--are reviewed, and the clinical and experimental data suggesting that these techniques are powerful predictors of future arrhythmic events are discussed in depth.

Animals↗