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Biomedical subjects

R B Schuessler

Publications and source records attributed to R B Schuessler.

At least 19 recordsLinked to original sources
PubMed1992

Cholinergically mediated tachyarrhythmias induced by a single extrastimulus in the isolated canine right atrium.

Cholinergic agonists and vagal stimulation potentiate the inducibility of atrial fibrillation. To describe the activation patterns and determine the mechanisms that sustain cholinergic fibrillation, tachyarrhythmias were induced with a single extrastimulus in the isolated Krebs-Henseleit-perfused canine right atrium (n = 11) at increasing concentrations of acetylcholine (from 10(-7.5) to 10(-4.5) M). Bipolar electrograms were recorded from 250 epicardial sites simultaneously during control conditions and during extrastimulation (S1S1, 300 msec; S1S2, effective refractory period+5 msec) with and without acetylcholine. Activation sequence maps were constructed from each recording. Without acetylcholine, no tachyarrhythmias were induced. With increasing concentrations of acetylcholine, the refractory period decreased, and nonsustained (< 2 seconds) rapid repetitive responses were induced. At higher concentrations, a sustained (> 2-minute) fibrillation was induced. Activation sequence maps revealed that the rapid repetitive responses were characterized by multiple reentrant circuits. The number of circuits and wavelets increased in a dose-dependent fashion. However, unexpectedly, this trend did not continue when the tachyarrhythmia became sustained. Instead, the reentry tended to stabilize to a small, single, relatively stable reentrant circuit. In conclusion, the data suggest that, in this model, below a critical level of refractory period (< 95 msec) atrial reentrant circuits, unassociated with anatomic obstacles, can become stable and dominate activation.

Acetylcholine↗
PubMed1992

The effect of augmented atrial hypothermia on atrial refractory period, conduction, and atrial flutter/fibrillation in the canine heart.

The purpose of this study was to test the assumption that the cause for postoperative atrial flutter/fibrillation after cardiopulmonary bypass is inadequate atrial myocardial protection. Dogs were subjected to cardioplegic arrest for 60 minutes without augmented atrial hypothermia (seven dogs, control group) or augmented atrial hypothermia with topical atrial cooling (seven dogs, study group). Twenty-five electrodes (15 on the right atrium and 10 on the left atrium) were fixed on the atria to measure effective refractory period and conduction time. Data were taken before bypass, immediately after bypass, and 2 hours after bypass. During cardioplegic arrest the mean temperatures measured in the atria were significantly lower (p less than 0.001) in the study group (13.5 degrees +/- 7.0 degrees C) than in the control group (23.7 degrees +/- 3.2 degrees C). There was no significant change in the mean effective refractory period after bypass in the control or study groups or in the prevalence of inducibility of atrial flutter/fibrillation by extrastimulation (3/7 dogs in the control group and 2/7 in the study group). During right atrial pacing, total conduction times were significantly longer (p less than 0.025 at cycle lengths of 300 and 350 msec) in the control group (74 +/- 5 msec and 75 +/- 7 msec, respectively) than in the study group (65 +/- 9 msec and 64 +/- 8 msec, respectively) immediately after bypass. Two hours after bypass, however, there were no significant differences under the same conditions between the two groups. There were no significant differences in conduction during left atrial pacing after bypass. Comparing those atria that were inducible with those not inducible demonstrated a significantly increased dispersion of effective refractory period (90 +/- 23 msec versus 74 +/- 18 msec, p less than 0.05) and increased conduction time in the inducible group. We concluded that augmented atrial hypothermia during cardioplegic arrest had no effect on the inducibility of fibrillation, had no effect on repolarization, and had only a small effect on conduction, which resolved within 2 hours after bypass. However, the study demonstrates that when the atria are inducible the substrates are an increased dispersion of refractoriness and a prolongation of conduction time.

Animals↗
PubMed1991

Successful surgical treatment of atrial fibrillation. Review and clinical update.

Atrial fibrillation is the most common of all sustained cardiac arrhythmias, yet it has no effective medical or surgical therapy. During the past decade, multipoint computerized electrophysiological mapping systems were used to map both experimental and human atrial fibrillation. On the basis of these studies, a new surgical procedure was developed for atrial fibrillation. Between September 25, 1987, and July 1, 1991, this procedure was applied in 22 patients with paroxysmal atrial flutter (n = 2), paroxysmal atrial fibrillation (n = 11), or chronic atrial fibrillation (n = 9) of 2 to 21 years' duration. All patients were refractory to all antiarrhythmic medications, and each patient failed to receive the desired therapeutic benefits of an average of five drugs administered preoperatively. There were no operative deaths and all perioperative morbidity resolved. All 22 patients have been successfully treated for atrial fibrillation with surgery alone. Three patients developed one late isolated episode of atrial flutter at 5, 6, and 15 months postoperatively, and each of these patient's symptoms is now controlled by a single antiarrhythmic drug. Preservation of atrial transport function has been documented in all patients postoperatively, and all have experienced marked clinical improvement.

Adult↗
PubMed1991

Operations for atrial fibrillation.

Atrial fibrillation is the most common of all sustained cardiac arrhythmias, yet it has no effective medical or surgical therapy. During the past decade, multipoint computerized electrophysiological mapping systems were used to map both experimental and human atrial fibrillation. On the basis of these studies, a new surgical procedure was developed for atrial fibrillation. Between September 25, 1987, and May 1, 1991, this procedure was applied in 22 patients with either paroxysmal atrial flutter (n = 2), paroxysmal atrial fibrillation (n = 11), or chronic atrial fibrillation (n = 9) of 2 to 21 years' duration. All patients were refractory to all antiarrhythmic medications and each patient failed an average of 5.2 drugs preoperatively. There were no operative deaths and all perioperative morbidity resolved. All 22 patients have been cured of atrial fibrillation with surgery alone. One late isolated episode of atrial flutter occurred in a patient who is now receiving encainide. Preservation of atrial transport function has been documented in all of the patients postoperatively and all have experienced marked clinical improvement.

Adult↗
PubMed1991

Spontaneous tachyarrhythmias after cholinergic suppression in the isolated perfused canine right atrium.

Atrial fibrillation occurs spontaneously after bradycardia induced by acetylcholine infusion or vagal stimulation. To determine the mechanism of initiation of this tachyarrhythmia, we infused acetylcholine (5 ml, 10(-3.5) M) into Krebs-Henseleit-perfused isolated canine right atria (n = 10). Unipolar electrograms were recorded from 250 sites simultaneously during control rhythms, pacing (cycle length = 300 msec) with and without acetylcholine, and recovery of spontaneous activity. Activation sequence maps were constructed from each recording. Stable spontaneous rhythm was present in all preparations during control conditions. Activation sequence maps, recorded during continuous pacing with and without acetylcholine, demonstrated no dromotropic changes due to the acetylcholine. Focal asynchronous recovery of spontaneous activity was initiated from different sites, resulting in bigeminal or trigeminal premature depolarizations in 41 of 73 cases after infusion of acetylcholine. A reentrant tachyarrhythmia was initiated in 24 of 41 cases by the closely coupled recovery beats (A1A2 = 100 +/- 37 msec; A2A3 = 97 +/- 27 msec). The reentry was initiated by interaction of the premature impulse with regions of functional block that were a result of the cholinergically induced dispersion of refractoriness. All the tachyarrhythmias terminated spontaneously, and stable spontaneous control rhythms returned. In conclusion, the data suggest that the premature depolarizations that initiate the reentrant tachyarrhythmia are caused by the asynchronous recovery of multiple right atrial pacemakers accompanied by variable entrance block at the later depolarizing sites.

Acetylcholine↗
PubMed1991

The surgical treatment of atrial fibrillation. I. Summary of the current concepts of the mechanisms of atrial flutter and atrial fibrillation.

Atrial fibrillation is a common arrhythmia that is frequently resistant to medical therapy and has no satisfactory surgical therapy. The development of an effective surgical procedure to treat atrial fibrillation has been hampered by the paucity of clinically relevant information on the basic mechanisms responsible for the arrhythmia. This paper summarizes the current concepts of the electrophysiologic abnormalities in atrial flutter and fibrillation.

Animals↗
PubMed1991

The surgical treatment of atrial fibrillation. II. Intraoperative electrophysiologic mapping and description of the electrophysiologic basis of atrial flutter and atrial fibrillation.

Computerized mapping of atrial fibrillation was performed in animals and man. To study atrial fibrillation in a systematic manner, we developed a clinically relevant experimental model of atrial fibrillation. Chronic mitral regurgitation was created surgically in 25 dogs without opening the pericardium. After several months of chronic mitral regurgitation, the atria became enlarged and sustained atrial fibrillation could be induced by standard programmed electrical stimulation techniques. Computerized isochronous activation maps of the atria were recorded during atrial fibrillation from 208 bipolar electrodes simultaneously. In a parallel study, human atrial fibrillation was mapped with a separate 160-channel intraoperative mapping system in patients with paroxysmal atrial fibrillation who were undergoing surgical correction of the Wolff-Parkinson-White syndrome. The canine activation sequence maps demonstrated a spectrum of rhythm abnormalities ranging from simple atrial flutter to complex atrial fibrillation. They also showed that macroreentrant circuits within the atrial myocardium were responsible for the entire spectrum of arrhythmias. Atrial reentry was also documented during human atrial fibrillation. All patients had nonuniform conduction around regions of bidirectional block in both atria resulting in multiple discrete wave fronts. In addition, six patients had a single reentrant circuit in the right atrium in which bidirectional block of the activation wave front occurred along the sulcus terminals between the venae cavae. The left atrium in all patients demonstrated multiple wave fronts and conduction block, but left atrial reentry could not be detected. Both the experimental study and the clinical study demonstrated that multiple wave fronts, nonuniform conduction, bidirectional block, and large (macroreentrant) reentrant circuits occur during atrial fibrillation. The presence of macroreentrant circuits and the absence of either microreentrant circuits or evidence of atrial automaticity suggests that atrial fibrillation should be amenable to surgical ablation.

Adult↗
PubMed1991

The surgical treatment of atrial fibrillation. III. Development of a definitive surgical procedure.

On the basis of the known electrophysiologic mechanisms of atrial fibrillation, multiple surgical procedures were designed and tested in dogs to determine the feasibility of developing a surgical cure for human atrial fibrillation. These experimental studies culminated in a surgical approach that effectively creates an electrical maze in the atrium. The atrial incisions prevent atrial reentry and allow sinus impulses to activate the entire atrial myocardium, thereby preserving atrial transport function postoperatively. Since September 1987, this surgical procedure has been applied in seven patients, five with paroxysmal atrial fibrillation of 2 to 9 years' duration and two with chronic atrial fibrillation of 3 and 10 years' duration. All seven patients have been cured of atrial fibrillation and none is receiving any postoperative antiarrhythmic medications.

Adult↗
PubMed1991

Feasibility of closed heart discrete cryomodification of atrioventricular conduction. Electrophysiologic effects in the canine heart.

Discrete cryosurgical modification of atrioventricular conduction abolishes refractory atrioventricular node reentry tachycardia with preservation of antegrade atrioventricular nodal conduction. This procedure presently requires cardiopulmonary bypass. To modify atrioventricular conduction without cardiac surgery, we evaluated the electrophysiologic effects of cryolesions applied to the peri-nodal area in the closed heart in 16 dogs before operation, during cryothermic exposure, and at 1 hour and 3 hours after operation. The electrophysiologic effects were evaluated in 10 of the 16 dogs at 2 weeks postoperatively. The dogs were given general anesthetics, and a cryoprobe was introduced into the right atrial cavity through the right atrial appendage. Cryolesions (-60 degrees C) were placed at nine to eleven preselected points around the perinodal area guided by electrodes on the tip of the cryoprobe. Postoperatively, there were significant prolongations of the atrio-His interval, Wenckebach's point, effective refractory period, and functional refractory period of the atrioventricular node. Atrial echo beats were eliminated or decreased in frequency. There was also a significant increase in retrograde ventriculoatrial conduction time. In the long-term observation period the atrio-His intervals remained significantly prolonged in comparison with the preoperative values, the atrial echoes progressively decreased, and ventriculoatrial conduction was absent in five of seven animals. A serendipitous atrioventricular node reentry tachycardia that was inducible in one animal with dual atrioventricular node conduction pathways was successfully eliminated and was not inducible at 2 weeks postoperatively. Complete atrioventricular block occurred during attempts to produce greater atrio-His prolongation in three of the 16 animals and persisted in two for the 2-week period of observation. Closed heart intracardiac cryomodification of atrioventricular conduction is feasible, with the cryoprobe in normothermic blood, producing changes in atrioventricular conduction similar to the open cardiac procedure.

Animals↗
PubMed1990

Computerized activation sequence mapping of the human atrial septum.

To delineate the propagation of electrical activation in the atrial septum, atrial epicardial and atrial septal maps were recorded intraoperatively using a 156-channel computerized mapping system in 12 patients during sinus rhythm (n = 10), supraventricular tachycardia associated with septal pathways in Wolff-Parkinson-White syndrome (n = 3), atrioventricular (AV) node reentrant tachycardia (n = 4), and atrial flutter (n = 5). The epicardial and septal data were recorded simultaneously from 156 atrial electrodes, digitized, analyzed, and displayed as isochronous maps on a two-dimensional diagram of the atria. During sinus rhythm, the activation wave fronts propagated most rapidly along the large muscle bundles of the atrial septum. During supraventricular tachycardia associated with Wolff-Parkinson-White syndrome, the earliest site of retrograde atrial activation usually corresponded to the position of atrial insertion of the septal pathways. However, the earliest site of activation during orthodromic supraventricular tachycardia was different from that during ventricular pacing in 1 patient with a posterior septal accessory pathway localized by the epicardial mapping study. The data document the rationale for dividing the ventricular end of the accessory pathways (ie, the endocardial technique) rather than the atrial end (ie, the epicardial technique) in patients with Wolff-Parkinson-White syndrome. During AV node reentrant tachycardia, atrial activation data suggested that atrial tissue lying outside the confines of the anatomical AV node is a necessary link in this common arrhythmia. Thus, these atrial septal maps explain why surgical dissection, or properly positioned small cryolesions placed in the region of the AV node, can ablate AV node reentrant tachycardia without altering normal AV node function. The maps recorded during atrial flutter suggest the importance of the atrial septum as one limb of a macroreentrant circuit responsible for the arrhythmia, and imply that atrial flutter is amenable to control by surgical techniques. These studies demonstrate the details of normal atrial septal activation, the importance of the atrial septum in a variety of different atrial arrhythmias, and the basis of and potential for surgical ablation of the most common types of supraventricular arrhythmias.

Adolescent↗
PubMed1990

Computerized potential distribution mapping: a new intraoperative mapping technique for ventricular tachycardia surgery.

This study evaluated potential distribution mapping as a method for localizing the site of origin of ventricular tachycardia (VT). In contrast to conventional activation time maps, potential distribution maps require less editing and thus can be more automated and rapidly processed for interpretation of multiple beats of VT. As a series of potential distribution maps during VT is required for detailed analysis, an on-line computerized system was designed to display potential distribution maps sequentially at 1-ms intervals as a color movie. Potential distribution maps and activation time maps were constructed from 182 epicardial and endocardial unipolar electrodes during 12 episodes of reproducible monomorphic VT in 9 dogs four to six days after experimental myocardial infarction (mean cycle length, 162 +/- 21 ms). At the onset of each depolarization during VT, a potential minimum abruptly developed on the surviving epicardium and another on the surviving endocardium of the left ventricle, both immediately adjacent to the subendocardial infarct. These two minima on the initial potential distribution maps corresponded to the sites of earliest epicardial and endocardial activation breakthrough recorded on the activation time maps. These two minima subsequently expanded or moved into the adjacent area and coincided with the spread of activation fronts on the epicardial and endocardial surfaces. Thus, the rapid display of sequential, computerized potential distribution maps of multiple beats of VT provides a dynamic means of identifying the site of origin of VT, and therefore should facilitate intraoperative mapping.

Action Potentials↗
PubMed1990

Effect of neurotransmitters on the activation sequence of the isolated atrium.

Unipolar electrograms were recorded from 360 sites in 20 isolated, perfused canine right atria. In 52% of the preparations, spontaneous activation started in the sinus node region. In 32% of the preparations, spontaneous activation was initiated at the junction of the intercaval band and the crista terminalis. Simultaneous multicentric initiation occurred from both sites in 16% of the preparations. With infusion of incrementally increasing doses of norepinephrine, the superior sinus node site consistently assumed dominance. Infusion of incrementally increasing doses of acetylcholine produced no consistent pattern of pacemaker dominance. Propagation velocity during pacing was unaffected by either neurotransmitter. The results demonstrate the presence of two different pacemaker sites in the posterior right atrium that function spontaneously, devoid of any active or significant autonomic input. Exchange of dominance between the two sites occurs in the presence of norepinephrine and acetylcholine. The two sites appear to have a differential sensitivity to norepinephrine but are not differentially sensitive to acetylcholine. Changes in the pattern of activation seen with either neurotransmitters are mediated exclusively by the site of initiation and not by changes in conduction.

Acetylcholine↗
PubMed1990

Biatrial isolation--a new surgical treatment for supraventricular tachycardia.

Nine adult mongrel dogs were subjected to cardiopulmonary bypass and both right and left atria were surgically isolated, exclusive of the sinoatrial (SA) node, crista terminalis, and interatrial septum. Thus, the SA node remained in continuity with the ventricles despite biatrial isolation. Moreover, of the right and left SA node arteries, the predominant one (right in 7 dogs, left in 2 dogs) was spared. Postoperatively, normal SA node function was preserved in 8 out of 9 dogs, with no difference in sinus rhythm cycle length (preop: 446 +/- 25, postop: 434 +/- 22 sec, p = NS) or sinus node recovery time (preop: 488 +/- 28, postop: 487 +/- 32 msec, p = NS). Simulated supraventricular tachycardia was confined in the isolated right or left atria did not affect sinus rhythm in the remainder of the heart. One out of 9 dogs developed junctional rhythm postoperatively, indicating exclusion of the SA node or a fast atrial pacemaker. In the 8 dogs with postoperative sinus rhythm, the spared SA node artery was occluded at the end of each study. All dogs developed rhythm deterioration including sinus rhythm slowing with prolonged sinus node recovery time (4 dogs), sinus bradyarrhythmia (2 dogs) and atrioventricular nodal rhythm (2 dogs). Thus, biatrial isolation is feasible for the treatment of supraventricular tachycardia, but it is essential to preserve SA node blood supply in order to maintain normal sinus rhythm in the remainder of the heart.

Animals↗
PubMed1989

Pericardiocentesis guided by a pulse generator.

This study was performed to compare pericardiocentesis guided by a pacing current applied through the pericardiocentesis needle with the traditional method of monitoring ST segment elevation from the needle tip electrogram. ST segment elevation was measured at 3 mm from the epicardium, after epicardial contact, after epicardial penetration and again at 3 mm from the epicardium after epicardial penetration. Two millivolts of ST segment elevation gave the highest combined positive (86%) and negative (79%) predictive value for epicardial contact by the pericardiocentesis needle between the two groups with the largest difference: 3 mm from the epicardium before contact and after epicardial penetration. Therefore, ST segment monitoring cannot reliably determine the point of epicardial contact. To determine the optimal stimulus strength for pulse generator-guided pericardiocentesis, pacing studies were performed using 2, 4, 6, 8 and 10 mA unipolar stimulus strengths. The pacing studies were performed both with and without a hemodynamically significant pericardial effusion to determine if increased pericardial pressure altered the pacing threshold. A 4 mA unipolar cathodal stimulus was chosen because it captured the ventricle only with direct contact of the epicardium. Ten dogs were instrumented and cardiac tamponade produced so that a subxiphoid approach to the epicardium with the pacing needle electrode could be attempted. During pericardiocentesis, needle tip electrograms were recorded, alternating with pacing attempts using a 4 mA unipolar stimulus. In all 10 dogs, the effusion was entered and epicardium was contacted as indicated by capture. No myocardial perforation or coronary artery or venous injuries were produced. These findings support the use of a pulse generator to guide pericardiocentesis.

Animals↗
PubMed1989

Surgery for atrial fibrillation.

The observations made under controlled experimental conditions provided us with a clearer understanding of the mechanisms involved in the generation and perpetuation of atrial fibrillation. The magnitude and rapidity of change that occurs in the activation patterns during atrial fibrillation were not appreciated, however, until the arrhythmia was studied in similar detail in humans. These studies provided the scientific basis for devising a surgical treatment for atrial fibrillation that has been successful in three patients. By converting the atrial fibrillation to normal sinus rhythm, all three of the detrimental sequelae of atrial fibrillation have been alleviated in each of these patients. Despite the fact that these clinical results are preliminary at this point, our experience documents that atrial fibrillation can be cured by surgical means. In the absence of other effective forms of therapy and in view of the devastating complications of the arrhythmia, surgical intervention should be considered a viable option for the treatment of atrial fibrillation.

Animals↗
PubMed1989

Potential mapping in septal tachycardia. Evaluation of a new intraoperative mapping technique.

A recently developed computer program is capable of rapidly (less than 5 minutes) constructing a series of potential-distribution maps (PDMs) for every msec of a 4-second window of ventricular tachycardia (VT). This study was performed to assess the ability of a series of PDMs to localize the site of earliest activation of VT originating in the interventricular septum. In 12 dogs, 13 morphologies of VT were initiated with programmed electrical stimulation 3-6 days after anterior septal coronary artery infarction. VT was mapped with endocardial and epicardial unipolar electrodes with a multipoint, computer-assisted mapping system. PDMs were compared with activation-time maps, and the former correctly identified the site of earliest activation of all 13 VT morphologies. When PDMs were viewed in sequence on a computer monitor, the site of earliest activation was signaled by abrupt development of a negative potential of less than -3.0 mV. The initial negative point subsequently expanded, and the spread of this negative-potential field correlated with activation sequence. PDMs provide an accurate, unambiguous, rapid means of analyzing large numbers of electrograms acquired with multipoint, computer-assisted mapping systems.

Action Potentials↗
PubMed1988

Computerized global electrophysiological mapping of the atrium in patients with Wolff-Parkinson-White syndrome.

The activation sequence of the human atrium has been inferred previously from a limited number of atrial electrograms recorded sequentially with a single-point mapping system. In 10 patients with Wolff-Parkinson-White (WPW) syndrome, three form-fitted, flexible templates containing a total of 156 bipolar electrodes were fixed to the epicardial surface of both atria. Data were recorded continuously from all 156 electrodes simultaneously during normal sinus rhythm, left atrial pacing, right atrial pacing, and reciprocating tachycardia. In all 10 patients, the site of the accessory pathway correlated with the results of the preoperative electrophysiological study and of the standard intraoperative band electrode mapping. The accessory pathway was located in the left free wall position in 8 patients, the right free wall position in 1 patient, and the posterior septal position in 1 patient. In 4 of the 8 patients with left free wall pathways, activation maps of retrograde atrial activation during reciprocating tachycardia demonstrated a broad base of initial atrial depolarization. This finding suggests that some accessory pathways may have a broad band of insertion on the atrium, and supports our practice of wide dissection of the entire anatomical space associated with each pathway to avoid recurrences of WPW syndrome. Simultaneous global atrial-activation mapping in patients with WPW syndrome provides a clearer understanding of atrial activation during reciprocating tachycardia.

Cardiac Pacing, Artificial↗