Mark D. Rodefeld

Relationship Between Local Atrial Fibrillation Interval and Refractory Period in the Isolated Canine Atrium

BACKGROUNDnAtrial refractory periods and their spatial distribution are important determinants of atrial reentrant arrhythmias. The objective of this study was to demonstrate a correlation between the local atrial fibrillation interval (AFI) and local effective refractory period (ERP).nnnMETHODS AND RESULTSnTo measure the local ERP and local AFI under stable conditions without hemodynamic, autonomic, or reflex influences, isolated perfused canine whole atria were used (n = 8). The isolated atria were mounted on two endocardial electrodes. Bipolar electrograms were simultaneously recorded from 253 endocardial sites, and 16 to 20 randomly distributed electrodes were used to measure the local ERP by the extrastimulus technique. In all studies, several episodes of AF were induced by a single extrastimulus. The ERP and minimum AFI converged with increasing duration of AF. The convergence was more rapid if the total duration of AF analyzed came from multiple episodes of AF. The correlation coefficient between the local ERP and minimum local AFI was .92 (n = 119, P < .001). The minimum AFI was used to construct AFI distribution maps at all 253 sites. Activation block during premature stimulation correlated with regions of long AFI.nnnCONCLUSIONSnThe minimum local AFI measured from at least 10 seconds of AF approximates the local ERP. Construction of a minimum local AFI map during AF can be used to predict the distribution of refractoriness and can be used to predict sites of functional block. Contrary to studies done in intact animals and patients, the AFI were longer than the ERPs, suggesting that reflex changes may shorten ERP in the intact heart.

Atrial flutter after lateral tunnel construction in the modified Fontan operation: A canine model

Intraatrial reentrant tachycardia, or atrial flutter, is a common postoperative problem after Fontan repair, which involves an atriopulmonary connection. A modification of Fontan repair, total cavopulmonary connection, minimizes the portion of the right atrium exposed to stretch and hypertension; however, atrial flutter continues to occur after this procedure. We postulated that the intraatrial lateral tunnel suture line of total cavopulmonary connection, in the absence of physiologic alterations such as atrial hypertension or stretch, provides the necessary electrophysiologic substrate for atrial flutter. The purpose of this study was to produce a canine model of total cavopulmonary connection (1) to establish that the intraatrial suture line alone is sufficient to permit sustained atrial flutter and (2) to characterize the pathways of resulting reentrant arrhythmias. After induction of general anesthesia, 25 to 30 kg dogs (n = 17) underwent median sternotomy, cradling of the pericardium, and placement of a pacing electrode on the right atrial appendage. Normothermic cardiopulmonary bypass was initiated. The total cavopulmonary connection suture line was placed through a standard right atriotomy,simulating construcion of the lateral tunnel. After closure of the atriotomy, 253 point unipolar atrial endocardial form-fitting electrodes were placed through bilateral ventriculotomies. By means of atrial burst pacing and programmed extrastimulation, induction of atrial flutter was attempted. If atrial flutter could not be induced, isoproterenol was infused and the stimulation protocol was repeated. After induction of atrial flutter, mapping of the activation sequence was performed. Before suture line placement, no dog had inducible atrial flutter. After placement of the suture line, sustained atrial flutter was reproducibly induced in every dog, although isoproterenol was required for this in three (17.6%). The mean flutter cycle length was 177 +/- 30 msec. In each case, the atrial flutter circuit was limited to the right atrium, with the left atrium being passively activated. The atrial flutter circuit was dependent on a corridor of myocardium that resulted from conduction block on the free wall, created by the lateral margin of the total cavopulmonary connection. In no case was the atriotomy integral to the atrial flutter circuit. This study establishes that the total cavopulmonary connection baffle suture line alone, without alteration in circulatory physiology, creates a sufficient anatomic substrate for atrial flutter in a short-term canine model. Delineation of the anatomic boundaries of the reentrant circuit raises the possibility of targeting areas within the circuit that could be modified, potentially reducing the incidence of postoperative atrial flutter after total cavopulmonary connection.

Lateral tunnel suture line variation reduces atrial flutter after the modified Fontan operation

BACKGROUNDnAtrial flutter (AFL) is a common postoperative sequela of the modified Fontan operation, or total cavopulmonary connection. We hypothesized that injury to the crista terminalis (CT) by the lateral tunnel suture line contributes to the development of AFL in this setting. This study was designed to determine the effects of alteration of the lateral tunnel suture line, relative to the CT, on the inducibility of AFL in an acute canine model of the modified Fontan operation.nnnMETHODSnAdult mongrel dogs (n = 25) underwent a median sternotomy and normothermic cardiopulmonary bypass. In groups 1, 2, and 3, through a right atriotomy, a suture line was placed to simulate the lateral tunnel of the modified Fontan operation (n = 20). The lateral aspect of the suture line ran along the CT in group (n = 10), 5 mm medial to the CT in group 2 (n = 5), and 10 mm anterior to the CT, incorporated into the atriotomy closure, in group 3 (n = 5). In group 4 (n = 5), only the lateral portion of the suture line, along the CT, was placed. Form-fitting 253-point unipolar endocardial mapping electrodes were inserted in the left and right atria via bilateral ventriculotomies. Induction of AFL was then attempted using atrial burst pacing. If sustained AFL could not be induced, isoproterenol was administered and the pacing protocol repeated. Endocardial activation sequence maps of spontaneous rhythm and AFT were constructed.nnnRESULTSnUnder baseline conditions, after placement of the suture line, sustained AFL could reproducibly be induced in 8/10 dogs in group 1, 0/5 dogs in group 2, 0/5 dogs in group 3, and 5/5 dogs in group 4 (p < 0.001). After isoproterenol administration, sustained AFL was reproducibly inducible in the remaining 2 dogs in group 1, 4/5 dogs in group 2, and 0/5 dogs in group 3 (p = 0.01). The mean cycle length of AFL was 189 +/- 25 ms in group 1, 136 +/- 8 ms in group 2, and 182 +/- 20 ms in group 4 (p < 0.001). Atrial activation sequence maps, during sinus rhythm, demonstrated a line of conduction block along the lateral portion of the suture line in all cases in groups 1 and 4 and in only those cases in group 2 in which sustained AFL was inducible. During AFL this block facilitated unidirectional conduction, permitting propagation of the reentrant wavefront. Mean conduction velocity along the CT during sinus rhythm was 0.63 +/- 0.10 m/s in group 1, 1.04 +/- 0.17 m/s in group 2, 1.01 +/- 0.12 m/s in group 3, and 0.44 +/- 0.13 m/s in group 4 (p < 0.01).nnnCONCLUSIONSnIn an acute canine model of the modified Fontan operation, conduction block imposed by the lateral tunnel suture line is an essential component of the AFL circuit. The inducibility of AFL is increased by suture line placement along the CT. Slow conduction, resulting from injury to the CT, promotes this increased inducibility. Avoidance of the CT may reduce the incidence of AFL in children undergoing the modified Fontan operation.

New Mechanistic and Therapeutic Targets for Pediatric Heart Failure Report From a National Heart, Lung, and Blood Institute Working Group

Pediatric heart failure (HF) is the inability of the heart of an infant, child, or adolescent to meet the body’s metabolic demands. It involves circulatory, neurohumoral, and molecular abnormalities that manifest as edema, respiratory distress, growth failure, and exercise intolerance. The myriad causes include inherited and acquired myocardial anomalies (cardiomyopathy [CM]), volume overload (intracardiac shunts, valvular regurgitation), and the unique hemodynamics predicated by a functional single ventricle (palliated complex congenital heart disease [CHD]).nnAlthough the societal and financial costs of adult HF are well known, the burden of pediatric HF is less familiar, but no less onerous. New-onset HF requiring hospital admission occurs in 0.87 per 100 000 children,1 yet that does not include the growing population with CHD-related HF. In 2006, there were nearly 14 000 pediatric hospitalizations for HF from all causes in the United States.2 The rate of HF-related admissions was nearly 18 per 100 000 children,2 which is comparable to severe sepsis.3nnThe mortality for pediatric HF hospitalizations is significant. The 7% overall hospital mortality rate exceeds the 4% mortality of adult HF admissions4 and represents a 20-fold increase over children without HF.2 With comorbidities like renal failure, sepsis, or stroke, hospital mortality in pediatric HF can exceed 20%,2 yet the risk does not end with discharge. After an initial HF hospitalization, only 21% of children in 1 study avoided readmission, death, or transplantation.5nnPediatric HF treatment is resource intensive. Although the total healthcare costs for pediatric HF are lower than for adults, per-patient costs are higher. The estimated hospital charge per pediatric HF admission in 2006 was >

ANATOMICALLY BASED ABLATION OF ATRIAL FLUTTER IN AN ACUTE CANINE MODEL OF THE MODIFIED FONTAN OPERATION

135 000, with aggregate charges exceeding

Spontaneous Atrial Flutter in a Chronic Canine Model of the Modified Fontan Operation

1.8 billion.6 Certain subpopulations of pediatric HF incurred disproportionally higher costs. For example, single-ventricle CHD averaged >

A canine model of atrial flutter following the intra-atrial lateral tunnel fontan operation

200 000 per hospitalization,7 whereas adult …

Parahiatal hernia with volvulus and incarceration: laparoscopic repair of a rare defect

BACKGROUNDnLateral tunnel total cavopulmonary connection, also called the modified Fontan operation, uses a baffle through the right atrium. We established, in an acute canine model, that atrial flutter after total cavopulmonary connection revolves around a line of conduction block imposed by the free wall lateral tunnel suture line. We hypothesized that a line of conduction block between the free wall total cavopulmonary connection suture line and the tricuspid anulus would interrupt atrial flutter in this model.nnnOBJECTIVEnOur objective was to determine whether a cryolesion placed between the free wall total cavopulmonary connection suture line and the tricuspid anulus would terminate atrial flutter in an acute canine model.nnnMETHODSnSeven adult dogs underwent median sternotomy and institution of cardiopulmonary bypass. A suture line was placed through a right atriotomy to simulate total cavopulmonary connection lateral tunnel construction. Form-fitting 253-point biatrial endocardial mapping electrodes were placed via bilateral ventriculotomies. Atrial flutter was induced by atrial burst pacing. A cryothermal lesion was then placed between the free wall total cavopulmonary connection suture line and the tricuspid anulus in the low lateral right atrium (i.e., CRYO 1 procedure), and reinduction of atrial flutter was attempted. If atrial flutter was reinduced, the cryolesion was modified superiorly to include the caudal portion of the atriotomy (i.e., CRYO 2 procedure). Activation sequence maps were generated for sinus rhythms before and after the cryolesions were placed and for induced arrhythmias.nnnRESULTSnIn all seven cases, atrial flutter was inducible after suture line placement, before placement of a cryolesion. The reentrant circuit incorporated both caval orifices in five of seven cases and was successfully ablated by the CRYO 1 approach in each case. Atrial flutter was not inducible after placement of the CRYO 2 lesion in the remaining two cases, in which breakthrough of the wave front occurred across the lateral tunnel suture line in the intercaval region. Activation sequence maps of sinus rhythm after placement of the cryolesions demonstrated a conduction block at the site of the lesion.nnnCONCLUSIONSnA linear cryothermal lesion placed between the free wall aspect of the total cavopulmonary connection suture line and the tricuspid anulus created a line of conduction block that successfully ablates atrial flutter in the canine model.

Morphological and membrane characteristics of spider and spindle cells isolated from rabbit sinus node

OBJECTIVESnThis study sought to 1) establish whether the atrial flutter (AFL) inducible acutely occurs spontaneously in a chronic canine model, and 2) characterize any reentrant circuits present chronically.nnnBACKGROUNDnWe previously demonstrated, in an acute canine model of the modified Fontan operation, that the lateral tunnel suture line creates a sufficient electrophysiologic substrate for AFL.nnnMETHODSnUsing cardiopulmonary bypass, a suture line was placed through a right atriotomy in adult dogs (n = 7) to simulate the lateral tunnel of the Fontan operation. Holter recordings were made preoperatively, on the first postoperative day and 2, 4 and 6 weeks postoperatively. At 6 to 8 weeks, through bilateral ventriculotomies, 253-point unipolar atrial electrodes were inserted. AFL was induced using atrial burst pacing, and endocardial activation sequence maps were created.nnnRESULTSnPreoperatively, all dogs were in sinus rhythm. Spontaneous AFL occurred in all dogs postoperatively, with a mean (+/-SD) cycle length of 192 +/- 22 ms. At 6 weeks postoperatively, of six dogs that survived, four had intermittent AFL, and two had incessant AFL. At reoperation, sustained AFL was inducible in six of six dogs, with a mean cycle length of 194 +/- 17 ms. Activation sequence maps demonstrated conduction block at the lateral tunnel suture line, which facilitated unidirectional conduction critical for propagation of the reentrant circuit. The AFL circuit was similar to that observed acutely.nnnCONCLUSIONSnIn a chronic canine model of the modified Fontan operation, the lateral tunnel suture line alone, in the absence of atrial stretch or hypertension, provides an electrophysiologic substrate that promotes spontaneous AFL. This model may be useful for evaluating various forms of treatment and prevention of AFL after the Fontan operation.

The Fontan circulation: Time for a moon shot?

Atrial flutter (AFL) is a common problem in children who have undergone a Fontan operation for single ventricle physiology. Although this has been attributed to the atrial stretch inherent in the earlier forms of this operation, AFL has persisted in spite of a modification that minimizes atrial distension. Therefore, it was hypothesized that AFL following the modified Fontan procedure may result from anatomic barriers related to suture lines rather than from atrial stretch or hypertension. In a series of experiments performed in dogs under general anesthesia, the modified Fontan repair was simulated by placing only the suture line of the intra-atrial repair. No baffle was placed, thus avoiding any hemodynamic alterations. After closure of the atriotomy, 253 point unipolar atrial endocardial form-fitting electrodes were inserted through the mitral and tricuspid valves via bilateral ventriculotomies. Induction of AFL was attempted with atrial burst pacing and programmed extrastimulation, and activation sequence maps of subsequent reentry were generated from the endocardial electrodes. Atrial flutter was induced in all of 17 dogs, with a median cycle length of 177 +/- 31 ms. Activation sequence maps demonstrated conduction block along the crista terminalis corresponding to the free wall portion of the suture line. This created an isthmus between the suture line and tricuspid annulus, which appeared critical for sustaining AFL, although the circuit used both the septal and free wall surfaces of the right atrium. In seven dogs, a cryolesion was placed from the tricuspid annulus to the free wall segment of the suture line, terminating the AFL, in all seven. When the free wall segment of the suture line was moved 5 mm medial to the crista terminalis, AFL was induced in four of five dogs, but only in the presence of isoproterenol and at a shorter cycle length (136 +/- 8 ms, P < .001). Atrial flutter was not inducible, even with the addition of isoproterenol, in any of five dogs in which the suture line was placed 10 mm anterior to the crista terminalis and incorporated into closure of the atriotomy. This acute canine model of the modified Fontan operation demonstrates that conduction block from the free wall portion of the suture line creates an isthmus of tissue between the suture line and the tricuspid annulus. This is a sufficient substrate to produce AFL; no hemodynamic alteration is required. Injury to the crista terminalis is a significant risk factor in this model, which suggests that a modification of the suture line might reduce the incidence of AFL in patients following this operation.