Adam P. Fitzpatrick

Tachycardia-induced cardiomyopathy: a review of animal models and clinical studies.

The increasing prevalence of congestive heart failure has focused importance on the search for potentially reversible etiologies of cardiomyopathy. The concept that incessant or chronic tachycardias can lead to ventricular dysfunction that is reversible is supported by both animal models of chronic rapid pacing as well as human studies documenting improvement in ventricular function with tachycardia rate or rhythm control. Sustained rapid pacing in experimental animal models can produce severe biventricular systolic dysfunction. Hemodynamic changes occur as soon as 24 h after rapid pacing, with continued deterioration in ventricular function for up to 3 to 5 weeks, resulting in end-stage heart failure. The recovery from pacing-induced cardiomyopathy demonstrates that the myopathic process associated with rapid heart rates is largely reversible. Within 48 h after termination of pacing, hemodynamic variables approach control levels, and left ventricular ejection fraction shows significant recovery with subsequent normalization after 1 to 2 weeks. In humans, descriptions of reversal of cardiomyopathy with rate or rhythm control of incessant or chronic tachycardias have been reported with atrial tachycardias, accessory pathway reciprocating tachycardias, atrioventricular (AV) node reentry and atrial fibrillation (AF) with rapid ventricular responses. Control of AF rapid ventricular responses has been demonstrated to improve ventricular dysfunction with cardioversion to sinus rhythm, pharmacologic ventricular rate control and AV junction ablation and permanent ventricular pacing. The investigation of potential tachycardia-induced cardiomyopathy in patients with heart failure requires further prospective confirmation in larger numbers of patients, with study of mechanisms, patient groups affected and optimal therapies.

Role of Right Atrial Endocardial Structures as Barriers to Conduction During Human Type I Atrial Flutter Activation and Entrainment Mapping Guided by Intracardiac Echocardiography

BACKGROUND The importance of barriers in atrial flutter has been demonstrated in animals. We used activation and entrainment mapping, guided by intracardiac echocardiography (ICE), to determine whether the crista terminalis (CT) and eustachian ridge (ER) are barriers to conduction during typical atrial flutter in humans. METHODS AND RESULTS In eight patients, ICE was used to guide the placement of 20-pole and octapolar catheters along the CT and interatrial septum and a roving catheter to nine sites: just posterior (1) and anterior (2) to the CT along the lateral right atrium, at the fossa ovalis (3), and just posterior and anterior to the ER at the low posterolateral (4 and 5), low posterior (6 and 7), and low posteromedial (8 and 9) right atrium. Entrainment was performed, and each site was considered within the flutter circuit if the postpacing interval-flutter cycle length (PPI-FCL) and the stimulus time-activation time (stim time-act time) were < 10 msec. Split potentials were recorded along the CT with components activated in a low-to-high pattern and a high-to-low pattern. Conduction times, as percentage of FCL, were significantly different at sites on either side of the CT and ER: site 1 (33 +/- 13%) and site 2 (43 +/- 12%) (P = .02), site 4 (48 +/- 24%) and site 5 (75 +/- 8.9%) (P = .02), and site 6 (22 +/- 10%) and site 7 (82 +/- 5.3%) (P = .0009). During entrainment, no surface fusion was observed at sites 5, 7, or 9. The PPI-FCL and stim time-act time were not significantly different than 0 at sites 2, 7, 5, or 9, indicating that they were within the flutter circuit, whereas sites 1, 3, 4, and 6 were not. CONCLUSIONS ICE enabled the correlation of functional electrophysiological properties with specific anatomic landmarks, identifying the CT and ER as barriers to conduction during human atrial flutter.

Radiofrequency catheter ablation of atrial arrhythmias. Results and mechanisms.

BACKGROUND Radio frequency catheter ablation is accepted therapy for patients with paroxysmal supraventricular tachycardia and has a low rate of complications. For patients with atrial arrhythmias, catheter ablation of the His bundle has been an option when drugs fail or produce untoward side effects. Although preventing rapid ventricular response, this procedure requires a permanent pacemaker and does not restore the atrium to normal rhythm. Therefore, we evaluated the safety and efficacy of radiofrequency ablation directed at the atrial substrate. METHODS AND RESULTS Thirty-seven patients with 42 atrial arrhythmias (mean +/- SD age, 41 +/- 24 years) who had failed a median of three drugs were enrolled. Diagnoses were automatic atrial tachycardia in 12, atypical atrial flutter in 1, typical atrial flutter in 18, reentrant atrial tachycardia in 8, and sinus node reentry in 3 patients. Sites for atrial flutter ablation were based on anatomic barriers in the floor of the right atrium. For automatic atrial tachycardia, the site of earliest activation before the P wave was sought. All with reentrant atrial tachycardia had previous surgery for congenital heart disease and reentry around a surgical scar, anatomic defect, or atriotomy incision and our goal was to identify a site of early activation in a zone of slow conduction. At target sites, 20 to 50 W of radiofrequency energy was delivered during tachycardia between the 4- or 5-mm catheter tip and a skin patch, except in 4 patients with atrial flutter, in whom a catheter with a 10-mm thermistor-embedded tip was used. Procedure end point was inability to reinduce tachycardia. Acute success was achieved in 11 of 12 (92%) with automatic atrial tachycardia, 17 of 18 (94%) with typical atrial flutter, 7 of 8 (88%) with reentrant atrial tachycardia, and 3 of 3 (100%) with sinus node reentry but not in the patient with atypical atrial flutter. For tachycardia involving reentry (reentrant atrial tachycardia and atrial flutter), successful ablation required severing an isthmus of slow conduction. For those with atrial flutter, this was between the tricuspid annulus and the coronary sinus os (10) or posterior (4) or posterolateral (3) between the inferior vena cava (2) or an atriotomy scar (1) and the tricuspid annulus. Deep venous thrombosis occurred in 1 patient. At mean follow-up of 290 +/- 40 days, the ablated arrhythmia recurred in 1 (9%) with automatic atrial tachycardia, 5 (29%) with atrial flutter, and 1 (14%) with reentrant atrial tachycardia, all of whom had successful repeat ablation. Previously undetected arrhythmias occurred in 2 patients who are either asymptomatic or controlled with medication. CONCLUSIONS Ablation of automatic and reentrant atrial tachycardia and atrial flutter had a high success rate and caused no complications from energy application. Repeat procedures may be required for long-term success, especially in patients with atrial flutter. The mechanism by which ablation is successful is similar for atrial flutter and other forms of atrial reentry and involves severing a critical isthmus of slow conduction bounded by anatomic or structural obstacles. Automatic arrhythmias are abolished by directing lesions at the focus of abnormal impulse formation.

METHODOLOGY OF HEAD-UP TILT TESTING IN PATIENTS WITH UNEXPLAINED SYNCOPE

Prolonged 60 degree head-up tilt has been shown to be valuable in the investigation of unexplained syncope, diagnosing neurally mediated bradycardia/hypotension or malignant vasovagal syndrome. To evaluate the methodology of tilt testing, the following were examined: reproducibility of results, tilt duration, angle of tilt, method of tilt support and effect of age in patients and control subjects. Seventy-one patients with recurrent unexplained syncope underwent 60 min of 60 degree tilt; 53 (75%) had an abnormal test with vasovagal syncope at 24 +/- 10 min (mean +/- SD). Tilting to 60 degrees resulted in an abnormal test in only 2 (7%) of 27 control subjects without cardiovascular symptoms (p less than 0.001); and 5 (15%) of 34 patients with syncope and documented conduction tissue disease (p less than 0.001). Of 15 youthful fainters, 3 (20%) had vasovagal reactions as did 1 (8%) of 12 asymptomatic youthful control subjects. These 12 control subjects also underwent tilting with a saddle support and 7 (67%) had vasovagal reactions. It is concluded that the duration of tilting at 60 degrees should be 45 min (mean time to syncope +2 x SD in the 53 patients with abnormal results). Twenty percent of patients with an abnormal tilt test may not demonstrate syncope with repeat tilting. Saddle tilt testing in unexplained syncope may result in a loss of specificity. Tilting at less than 60 degrees results in a loss of sensitivity. Head-up tilt may be less useful in youthful subjects with vasovagal syncope than in other subjects.

Misdiagnosis of Epilepsy: Many Seizure-Like Attacks Have a Cardiovascular Cause

OBJECTIVES We sought to investigate the value of cardiovascular tests to diagnose convulsive syncope in patients with apparent treatment-resistant epilepsy. BACKGROUND As many as 20% to 30% of epileptics may have been misdiagnosed. Many of these patients may have cardiovascular syncope, with abnormal movements due to cerebral hypoxia, which may be difficult to differentiate from epilepsy on clinical grounds. METHODS Seventy-four patients (33 men, mean age 38.9 +/- 18 years [range 16 to 77]) who were previously diagnosed with epilepsy were studied. Inclusion criteria included continued attacks despite adequate anticonvulsant drug treatment (n = 36) or uncertainty about the diagnosis of epilepsy, on the basis of the clinical description of the seizures (n = 38). Each patient underwent a head-up tilt test and carotid sinus massage during continuous electrocardiography, electroencephalography and blood pressure monitoring. Ten patients subsequently underwent long-term electrocardiographic (ECG) monitoring with an implantable loop recorder. RESULTS In total, an alternative diagnosis was found in 31 patients (41.9%), including 13 (36.1%) of 36 patients taking an anticonvulsant medication. Nineteen patients (25.7%) developed profound hypotension or bradycardia during the head-up tilt test, confirming the diagnosis of vasovagal syncope. One other patient had a typical vasovagal reaction during intravenous cannulation. Two patients developed psychogenic symptoms during the head-up tilt test. Seven patients (9.5%) had significant ECG pauses during carotid sinus massage. In two patients, episodes of prolonged bradycardia correlated precisely with seizures according to the insertable ECG recorder. CONCLUSIONS A simple, noninvasive cardiovascular evaluation may identify an alternative diagnosis in many patients with apparent epilepsy and should be considered early in the management of patients with convulsive blackouts.

Use of P wave configuration during atrial tachycardia to predict site of origin

OBJECTIVES This study sought to construct an algorithm to differentiate left atrial from right atrial tachycardia foci on the basis of surface electrocardiograms (ECGs). BACKGROUND Atrial tachycardia is an uncommon form of supraventricular tachycardia, often resistant to drug therapy. METHODS A total of 31 consecutive patients with atrial tachycardia due to either abnormal automaticity or triggered rhythm underwent detailed atrial endocardial mapping and successful radiofrequency catheter ablation of a single atrial focus. P wave configuration was analyzed from 12-lead ECGs during tachycardia during either spontaneous or pharmacologically induced atrioventricular block. P waves inscribed above the isoelectric line (TP interval) were classified as positive, below as negative, above and below (or conversely, below and above) as biphasic and flat P waves as isoelectric (0). In 17 patients the tachycardia was located in the right atrium: crista terminalis (n = 4); right atrial appendage (n = 4); lateral wall (n = 4); posteroinferior right atrium (n = 3); tricuspid annulus (n = 1); and near the coronary sinus (n = 1). In 14 patients, atrial tachycardia was located in the left atrium: at the entrance of the right (n = 6) or left (n = 4) superior pulmonary veins; left inferior pulmonary vein (n = 1); inferior left atrium (n = 1); base of left atrial appendage (n = 1); and high lateral left atrium (n = 1). RESULTS There were no differences in P wave vectors between sites at the right atrial lateral wall versus the right atrial appendage or between sites at the entrance of right versus left superior pulmonary veins. However, analysis of P wave configuration showed that leads aVL and V1 were most helpful in distinguishing right atrial from left atrial foci. The sensitivity and specificity of using a positive or biphasic P wave in lead aVL to predict a right atrial focus was 88% and 79%, respectively. The sensitivity and specificity of a positive P wave in lead V1 in predicting a left atrial focus was 93% and 88%, respectively. CONCLUSIONS 1) Analyses of surface P wave configuration proved to be reasonably good in differentiating right atrial from left atrial tachycardia foci. 2) Leads II, III and aVF were helpful in providing clues for differentiating superior from inferior foci.

Quality of life and outcomes after radiofrequency His-bundle catheter ablation and permanent pacemaker implantation : Impact of treatment in paroxysmal and established atrial fibrillation

One hundred seven patients underwent atrioventricular (AV)-junctional ablation and pacing for atrial fibrillation, and 90 were alive 2.3 +/- 1.2 years later. Quality of life index (1.9 +/- 1.2 to 3.6 +/- 1.1; 3.6 +/- 1.1; p<0.001) and ease of activities of daily living (2 +/- 0.4 to 2.4 +/- 0.3; p<0.001) were significantly improved. Doctor visits (10 +/- 13 to 5.06 +/-7; p<0.03), hospital admissions (2.8 +/- 6.8 vs 0.17 +/- 0.54; p<0.03, and antiarrhythmic drug trials (6.2 +/- 4 to 0.46 +/- 1.5; p<0.001) decreased significantly after treatment. Congestive heart failure episodes decreased from 18 before to 8 afterward. Twenty-eight of 36 patients with dual-chamber pacemakers remained in a dual-chamber mode at follow-up. Radiofrequency AV-junctional catheter ablation and pacing is a highly successful form of treatment for medically refractory atrial fibrillation.

New algorithm for the localization of accessory atrioventricular connections using a baseline electrocardiogram

OBJECTIVES In this study, we propose a new algorithm for accessory atrioventricular pathway localization using a 12-lead electrocardiogram (ECG). BACKGROUND Radiofrequency catheter ablation produces a very discrete lesion, and ECG localization based on surgical dissection is obsolete. METHODS Stepwise discriminant analysis was used to assess the relation of 18 pre-excited ECG (QRS duration > 100 ms) variables to the site of successful ablation in 93 patients. The most discriminating variables were combined to form rules for each location. The ECGs were retested by these rules to determine predictive accuracy. RESULTS If the precordial QRS transition was at or before lead V1, the pathway had been ablated on the left side. If it was after lead V2, the pathway had been ablated on the right side. If the QRS transition was between leads V1 and V2 or at lead V2, then if the R wave amplitude in lead I was greater than the S wave by > or = 1.0 mV, it was right-sided; otherwise, it was left-sided (p < 0.0001, sensitivity 100%, specificity 97%). Right-side pathways. If the QRS transition was between leads V2 and V3, the pathway was right septal; if after lead V4, it was right lateral. If it was between leads V3 and V4, then if the delta wave amplitude in lead II was > or = 1.0 mV, it was right septal; otherwise, it was right lateral (p < 0.0001, sensitivity 97%, specificity 95%). In right lateral locations, if the delta wave frontal axis was > or = 0 degrees, or if it was < 0 degrees but the R wave amplitude in lead III was > or = 0 mV, it was anterolateral; otherwise, it was posterolateral (p < 0.0001, sensitivity 100%, specificity 87.3%). Anteroseptal pathways had a sum of delta wave polarities in leads II, III and aVF > or = +2(p < 0.0001, sensitivity 100%, specificity 100%). Posteroseptal pathways (inferior delta wave sum < or = -2) were less well discriminated from right midseptal pathways (inferior delta wave sum < or = 1 > or = -1) (p < 0.0001, sensitivity 76.5%, specificity 71%) [corrected]. Left-sided pathways. Two or more positive delta waves in the inferior leads or the presence of an S wave amplitude in lead aVL greater than the R wave, or both, discriminated left anterolateral pathways from posterior pathways (p < 0.001, sensitivity and specificity 100%). If the R wave in lead I was greater than the S wave by > or = 0.8 mV, and the sum of inferior delta wave polarities was negative, the location was posteroseptal; otherwise, it was posterolateral (p < 0.05, sensitivity 71.4%, specificity 100%). CONCLUSIONS Using the algorithm derived, a right-sided accessory pathway can be reliably distinguished from one that is left-sided, right free wall from right septal, right anterolateral from posterolateral and anteroseptal from other right septal pathways. Left anterolateral pathways can be distinguished from left posterior pathways and left posterolateral pathways from left posteroseptal pathways.

Radiofrequency catheter ablation guided by intracardiac echocardiography.

BACKGROUND Radiofrequency catheter ablation requires precise positioning of the ablation electrode. Fluoroscopically guided catheter manipulation has limitations, and there are risks of radiation exposure. The purpose of this study was to examine the feasibility of guiding catheter ablation within the right atrium with catheter-based intracardiac echocardiography. METHODS AND RESULTS A 10F, 10-MHz intracardiac imaging catheter was used to direct an ablation electrode at four or five anatomic landmarks in the right atrium. Thirty-eight radiofrequency energy applications were performed in nine anesthetized dogs, and 38 lesions were identified on pathological examination. Lesions were created a mean of 1.9 +/- 2.1 mm from the ultrasound-guided site. Twenty-six of 38 lesions (68%) were less than 2.2 mm from the imaged site. Intracardiac echocardiography also was used to confirm stable electrode-endocardial contact in 37 energy applications (97%) and identified catheter movement in 9 energy applications (24%). Discrete lesions, microcavitations, and thrombi were observed in 13 (34%), 23 (61%), and 19 (50%) of 38 energy applications, respectively. Microcavitations predicted the appearance of thrombus. Fluoroscopy time required to create four or five lesions decreased from 23 minutes in the first study to less than 2 minutes in the last five studies. CONCLUSIONS Catheter-based intracardiac echocardiography can accurately guide catheter ablation directed at anatomic landmarks and potentially reduced ionizing radiation exposure. Intracardiac imaging can be used to confirm endocardial contact, identify electrode movement, and directly visualize lesions. Intracardiac echocardiography also can be used to identify microcavitations, which predict thrombus formation during radiofrequency energy applications.

Biophysical characteristics of radiofrequency lesion formation in vivo: Dynamics of catheter tip–tissue contact evaluated by intracardiac echocardiography

During clinical radiofrequency catheter ablation a wide range of delivered power may be necessary to achieve success despite an apparently stable catheter position on fluoroscopy. The purpose of this study was to use intracardiac echocardiography to characterize the relation between catheter tip-tissue contact and the efficiency of heating during applications of radiofrequency energy in vivo and to determine whether intracardiac echocardiography could be used prospectively to improve tissue contact. A closed-loop temperature feedback control system was used during radio-frequency applications at five anatomic regions in the right atrium of 15 anesthetized dogs to ensure achievement of a predetermined temperature (70 degrees C) at the catheter tip thermistor by automatic adjustment of delivered power (maximum 100 W). The efficiency-of-heating index was defined as the ratio of steady-state temperature (degrees Celsius) to power (watts). Two-dimensional intracardiac echocardiography was used to evaluate movement of the catheter tip relative to the endocardium. Perpendicular contact was scored as good, average, or poor and lateral catheter sliding as < 2, 2 to 5, or > 5 mm. Two groups of animals were included: group 1, in which tissue contact was guided by fluoroscopic and electrographic criteria for stability of contact, with intracardiac echocardiography used simply to observe the application; and group 2, in which tissue contact was guided by intracardiac echocardiography. Of 66 applications, 18 (27.3%) had poor perpendicular contact on echocardiography, and 12 (18.2%) demonstrated lateral sliding of > 5 mm even though they had been considered to have good tissue contact by fluoroscopic and electrographic criteria. Perpendicular catheter contact and anatomic location were shown to be independently related to the efficiency-of-heating index. Applications with good perpendicular contact had a significantly higher efficiency-of-heating index and a significantly greater lesion size than those with average or poor contact. The percentage of applications having good perpendicular tissue contact and the lesion size were significantly greater when tissue contact was guided by intracardiac echocardiography compared with fluoroscopic and electrographic guidance. This study demonstrates that variations in catheter tip-tissue contact account for differences in the efficiency of tissue heating, independently of the anatomic site of the application. Poor tissue contact was observed by intracardiac echocardiography and confirmed by indexes of tissue heating in approximately one third of radiofrequency applications despite a fluoroscopic appearance and electrographic morphologic appearance suggestive of good tissue contact. There was a significant correlation between echocardiographic evaluation of tissue contact, parameters of tissue heating (efficiency-of-heating index), and lesion size. In addition, intracardiac echocardiography could be used prospectively to improve the percentage of good contact applications and increase the lesion size.