Intracardiac Pacing Research Articles

Analyses of Dynamic Beat‐to‐Beat QT–TQ Interval (ECG Restitution) Changes in Humans under Normal Sinus Rhythm and Prior to an Event of Torsades de Pointes during QT Prolongation Caused by Sotalol

Restitution through intracardiac pacing has been used to assess arrhythmia vulnerability. We examined whether analyses of sequential beat-to-beat QT and TQ interval measures can be used to quantify ECG restitution changes under normal sinus rhythm. The QT, R-R and TQ intervals were examined 22.5 hour Holter monitoring before and after oral sotalol in normal male and female volunteers. Additionally, comparisons were made to those observed in the time-matched dataset prior to torsades de pointes in a heart diseased patient that received a single dose of sotalol. Sotalol increased QT, R-R and TQ intervals 71, 101, and 125 ms after 160 mg (n = 38) and 194, 235, and 135 ms after 320 mg (n = 19) during maximum plasma concentrations, respectively. The percentage of beats with a QT/TQ ratio >1 was reduced 25% over the entire 22.5 hours after sotalol and the lower TQ interval boundary (5th quantile) was increased 22-30%. In contrast, 99% of the beats prior to torsades de pointes had a QT/TQ ratio > 1 and the median TQ interval was below the lower 98% confidence bounds of normals before and after sotalol. ECG restitution changes are quantifiable under varying states (nocturnally, beta-adrenergic blockade, QT prolongation) in healthy subjects.

Risk Factors for Mediastinitis Following Median Sternotomy in Children

Mediastinitis is a devastating complication of pediatric cardiothoracic surgery. However, risk factors for the development of mediastinitis are poorly characterized. The objective of this study was to identify risk factors for mediastinitis in a cohort of children undergoing cardiothoracic surgery at a tertiary care children's hospital. This case-control study included patients who underwent median sternotomy between January 1, 1995 and December 31, 2003. Univariate analyses, logistic regression, and multinomial regression were performed to determine the association between potential risk factors and the development of mediastinitis. Forty-three patients with mediastinitis and 184 patients without mediastinitis were included. One hundred and twelve (49%) patients were female. The median patient age was 128 days (interquartile range: 7 days-2.0 years). A known or possible genetic syndrome was present in 53 (24%) patients. The following factors were associated with the development of mediastinitis: presence of a known or possible genetic syndrome (adjusted odds ratio, OR: 4.5; 95% confidence interval, CI: 1.8-11.4); American Society of Anesthesiologists score >3 (adjusted OR: 3.4; 95% CI: 1.1-10.3); and presence of intracardiac pacing wires for >3 days (adjusted OR: 15.8; 95% CI: 2.0-127.2). The presence of a known or possible genetic syndrome, American Society of Anesthesiologists score >3, and the presence of intracardiac pacing wires for >3 days were each associated with the development of mediastinitis in children after median sternotomy.

25 years of insights into the mechanisms of supraventricular arrhythmias

The introduction of programmed electrical stimulation of the heart and intracardiac activation mapping 35 years ago made it possible to study the site of origin or pathway of a supraventricular tachycardia and to gain insight into the tachycardic mechanism. Information from these studies has been the basis for the development of new therapies, like arrhythmia surgery, antitachycardia pacing, and catheter ablation. The correlation of intracardiac findings with the 12-lead ECG during the tachycardia resulted in the recognition of characteristic ECG patterns for the different types of supraventricular tachycardias. Currently, gross localization of the site of origin of the arrhythmia is based on the 12-lead ECG during the arrhythmia with fine tuning using intracardiac activation mapping and pacing. These developments during the past 3 decades make accurate arrhythmia diagnosis possible and allow us to offer curative therapies to many of patients suffering from a supraventricular tachycardia.

Magnetic guidance system for cardiac electrophysiology: a prospective trial of safety and efficacy in humans

ObjectivesWe evaluated in humans the safety and efficacy of a novel magnetic guidance system (MGS) for electrophysiological mapping, pacing, and ablation. BackgroundCatheter ablation of atrial fibrillation and other complex arrhythmias requires precise catheter manipulation and stabilization. We have shown in animals that the MGS can precisely manipulate a mapping catheter within the heart with an external magnetic field rather than manual catheter control. MethodsThirty-one adults referred for diagnostic electrophysiology studies were enrolled in a prospective trial of the MGS. The magnetic catheter was navigated to preselected sites in the right atrium (RA) and right ventricle (RV) in the first 20 patients. Electrograms were recorded at each target site, and pacing thresholds were measured. In a subset of five patients, RA and RV electrograms and stimulation thresholds were recorded with both a standard ablation catheter and the magnetic catheter. Eleven additional patients were recruited for supraventricular tachycardia (SVT) mapping, and seven of these underwent ablation. ResultsNavigation was successful in 200 of 202 predetermined right-sided navigation targets and 13 of 13 targets in the left atria. Pacing thresholds and electrogram amplitudes in the RA and RV were not significantly different between the standard and magnetic catheters. The SVT mapping with the magnetic catheter was successful in 13 patients, including 4 with left-sided accessory pathways. The MGS was used for successful ablation of SVT in seven of seven patients. There were no procedural complications. ConclusionsThese results demonstrate that the MGS can be used for intracardiac mapping, pacing, and ablation safely and effectively.

Twenty-five years of insights into the mechanisms of supraventricular arrhythmias.

The introduction of programmed electrical stimulation of the heart and intracardiac activation mapping 35 years ago made it possible to study the site of origin or the pathway of a supraventricular tachycardia and to obtain insight into the mechanism of the tachycardia. Information from these studies has been the basis for the development of new therapies, such as arrhythmia surgery, antitachycardia pacing, and catheter ablation. Correlation of intracardiac findings with the 12-lead ECG recorded during the tachycardia resulted in the recognition of ECG patterns characteristic of the different types of supraventricular tachycardias. Currently, gross localization of the site of origin of the arrhythmia is based on the 12-lead ECG recorded during the arrhythmia, with fine-tuning using intracardiac activation mapping and pacing. These developments during the past 3 decades have made accurate arrhythmia diagnosis possible and allow us to offer curative therapies to many of our patients with a supraventricular tachycardia.

25 years of insights into the mechanisms of supraventricular arrhythmias.

The introduction of programmed electrical stimulation of the heart and intracardiac activation mapping 35 years ago made it possible to study the site of origin or pathway of a supraventricular tachycardia and to gain insight into the tachycardic mechanism. Information from these studies has been the basis for the development of new therapies, like arrhythmia surgery, antitachycardia pacing, and catheter ablation. The correlation of intracardiac findings with the 12-lead ECG during the tachycardia resulted in the recognition of characteristic ECG patterns for the different types of supraventricular tachycardias. Currently, gross localization of the site of origin of the arrhythmia is based on the 12-lead ECG during the arrhythmia with fine tuning using intracardiac activation mapping and pacing. These developments during the past 3 decades make accurate arrhythmia diagnosis possible and allow us to offer curative therapies to many of patients suffering from a supraventricular tachycardia.

Right atrial lymphoma in a patient with hypoxemia

SYMPTOMS OF hypoxemia often complicate the early period after myocardial infarction, with complications of third-degree heart block, which is treated with intracardiac dual-chamber pacing. The usual differential diagnosis must exclude the worsening of heart failure, pulmonary embolism, and malfunction of the pacemaker. Investigations including echocardiography and pulmonary angiography may be needed to find the cause of the symptoms. This case shows that right atrial lymphoma may cause isolated symptoms of hypoxemia. Transesophageal echocardiography may be needed to establish the correct diagnosis.

Sinoatrial node reentrant tachycardia in infants with congenital heart disease

T exact nature of sinoatrial node reentrant tachycardia (SANRT) is debated, but has been reported to occur as a clinical entity in 1.8% to 16.9% of adults undergoing electrophysiologic evaluation for supraventricular tachycardia (SVT). Although SANRT has been occasionally mentioned in reports of pediatric SVT, the reports are few in number and sparse in data. –11 SANRT has electrocardiographic features that are similar to sinus tachycardia, and it may be easily misdiagnosed, particularly when there is a high likelihood of sympathetic and/or catecholaminergic stimulation. Because SANRT has a high association with structural heart disease and has been noted to cause hemodynamic embarrassment, situations may arise when the diagnosis of SANRT rather than sinus tachycardia may be critical for patient management (e.g., after surgery for congenital heart disease). The purpose of this study was to assess the relative incidence and clinical characteristics of SANRT in a pediatric population. • • • The pediatric electrophysiologic study database at the Medical University of South Carolina was reviewed for cases of SANRT in children 0 to 18 years of age diagnosed by intracardiac, transesophageal, or epicardial pacing wire electrophysiologic study performed to investigate a previously documented clinical SVT between January 1999 and November 2000. Studies were performed before initiation of any antiarrhythmic therapy or after therapy had begun. Studies were generally performed on an elective basis unless they were performed for postoperative arrhythmia evaluation, in which case they were performed as close to presentation as possible. Transesophageal electrophysiologic studies were performed with administration of midazolam and/or fentanyl. Intracardiac studies were usually performed with the patient under deep sedation or general anesthesia, and epicardial pacing wire studies were typically performed without sedation. All studies were performed in the fasting state. Study protocols consisted of single and double atrial extrastimuli after either sensed atrial rhythm and/or a fixed atrial drive train (500 and 400 ms, if underlying rhythm permitting, or 30 ms below baseline rhythm cycle length), followed by rapid atrial pacing. Ventricular stimulation was used when possible to investigate retrograde conduction. Because all of the studies were not intracardiac, all previously described criteria of SANRT could not be demonstrated (Table 1). 3–6,9 Thus, for the purposes of this study, SANRT was defined as a paroxysmal or reproducibly inducible and terminable tachycardia, with a P-wave axis and morphology in all 12 surface leads nearly identical to sinus rhythm. The reentrant mechanism of the tachycardia was confirmed by the ability to initiate the tachycardia with programmed atrial stimulation. Tachycardia response to adenosine, when available, was used to support the diagnosis of an atrial arrhythmia. Demographic and electrophysiologic variables as well as short-term management and follow-up are noted in the review. Because of the small number of subjects, variables are described as median and range unless otherwise noted. Group comparisons are made with Yates’ coefficient. Of the 106 patients, aged 1 day to 18 years, who underwent electrophysiologic study for documented SVT during the study period, 7 male patients (6.6%) met this study’s criteria for SANRT (Figures 1A and 1B). All identified patients were infants with structural heart disease (Table 2). Of the 6 patients with congenital heart disease, 5 had undergone surgical repair or palliation within the past 0 to 11 days (median 5) before presentation, 4 of those for palliation of hypoplastic left heart syndrome. One patient had a dilated cardiomyopathy. The incidence of structural heart disease and congenital heart disease was much greater in those with SANRT than in the remaining 99 patients with other SVT mechanisms (100% vs 26%, p 0.0003; 86% vs 24%, p 0.002, respectively). However, if only infants are considered, differences between the SANRT and non-SANRT groups in the incidence of structural heart disease and congenital heart disease do not reach statistical significance (100% vs 60%, p 0.14; 86% vs 53%, p 0.3, respectively). This may be a reflection of the fact that the proportion of infants in the SANRT group was From the Children’s Heart Program of South Carolina–Medical University of South Carolina, Charleston, South Carolina. Dr. Blaufox is supported by National Institutes of Health Training Grant T32 HL07710-06, Bethesda, Maryland. Dr. Blaufox’s address is: Children’s Heart Program of South Carolina–MUSC, 165 Ashley Avenue, PO Box 250915, Charleston, South Carolina 29425. E-mail: Blaufoad@musc.edu. Manuscript received April 25, 2001; revised manuscript received and accepted June 21, 2001. TABLE 1 Previously Described Criteria for SANRT

Magnetic navigation system for intracardiac pacing and mapping: Safety and equivalence study Mitchell N. Faddis, Andrew F. Hall, Michael Talcott, Jennifer Dehne, John C. Rauch, Jon C. Sell, Bruce D. Lindsay. Washington University School of Medicine, St. Louis, MO, Stereotaxis, Inc, St. Louis, MO

Magnetic navigation system for intracardiac pacing and mapping: Safety and equivalence study Mitchell N. Faddis, Andrew F. Hall, Michael Talcott, Jennifer Dehne, John C. Rauch, Jon C. Sell, Bruce D. Lindsay. Washington University School of Medicine, St. Louis, MO, Stereotaxis, Inc, St. Louis, MO

Tachycardia Alone Fails To Change the Myocardial Pharmacokinetics and Dynamics of Lidocaine, Thiopental, and Verapamil after Intravenous Bolus Administration in Sheep

Previous reports have suggested that tachycardia alone can increase the rate of myocardial uptake of some drugs. As part of a systematic study of the determinants of the myocardial uptake and effects of drugs in critical illness, the effect of tachycardia induced by intracardiac pacing on the myocardial disposition and effects of lidocaine, verapamil, and thiopental were studied in chronically instrumented sheep. For each drug, seven sheep received either 100mg of lidocaine, 10mg of verapamil, or 750mg of thiopental over 2min in unpaced and paced (140 beats/min) states on separate occasions and in random order. Arterial and coronary sinus (effluent from the heart) blood samples were taken at regular intervals for 30min, and the maximum rate of change of left ventricular pressure (LV dP/dtmax) was measured as an index of myocardial contractility. There were no differences between unpaced and paced studies in the time courses of arterial and coronary sinus concentrations, or the time-courses of myocardial contractility and blood flow, after bolus iv injections of these drugs. Tachycardia alone does not appear to influence the myocardial kinetics or dynamics of lipophilic drugs that can rapidly diffuse into the heart.

Intracardiac overdrive pacing as a treatment of atrial flutter in a horse

A five-year-old warmblood mare with atrial fibrillation was treated with quinidine sulphate. The atrial rhythm changed to atrial flutter and, because there were toxic effects, the treatment was discontinued. Seven...

In utero pacing for fetal congenital heart block.

We report what we believe is the first percutaneous transvenous intracardiac cardiac pacing of a fetus. The case is important because it demonstrates that transvenous fetal cardiac pacing is technically possible and provides a basis for development of the technology.

Diagnostic and therapeutic use of transesophageal atrial pacing in children

Transesophageal atrial pacing was used in 29 consecutive patients aged 1 day to 16.5 years (mean 8.04 years) to replace the following procedures: intracardiac electrophysiologic study in patients with selected arrhythmias (21 patients), intracardiac overdrive or synchronized direct current cardioversion of supraventricular tachyarrhythmias or drug administration in patients with acute reciprocating supraventricular tachycardia (9 patients). Atrial capture was achieved without discomfort in 27 patients (93.1%). The diagnostic or therapeutic goal of the procedure was achieved in 26 children (89.7%). Transesophageal atrial pacing may replace intracardiac pacing procedures, direct current cardioversion and drug administration in patients with selected cardiac arrhythmias and has proved appropriate as a first diagnostic or therapeutic step.

Percutaneous Nd:YAG Laser Coagulation of Ventricular Myocardium in Dogs Using a Special Electrode Laser Catheter

A novel catheter system was used for intracardiac electrogram recordings, ventricular pacing and continuous-wave Nd:YAG laser (1,064 nm) irradiation of ventricular myocardium in eight dogs. Radiation at a power of 10 W for 3, 5, and 10 seconds was delivered through a 400 microns optical fiber. Power density was 15 W/mm2. A total of 96 laser injuries (12 per dog) were produced in selected sites in both the right and the left normal canine ventricle. Ventricular arrhythmias were noted during 12 of 96 (12.5%) laser pulses. Programmed electrical stimulation performed during control study immediately (all dogs) at 2 days (two dogs), and 4 months (4 dogs) following the experiments showed no episodes of sustained or nonsustained ventricular tachycardia. Radiation energies up to 50 J (10 W over 5 s) caused focal injuries of homogeneous coagulation/fibrosis localized to the target area, without vaporizing tissue and forming craters. Morphometrically and histologically there was a direct relationship between the energy of radiation delivered, and the extent and severity of the injury produced. The maximum size of lesions measured 7/11 mm (diameter/depth). Using a special catheter system laser coagulation of myocardium can be accomplished percutaneously. This method can create controlled subendocardial injuries without major side effects and appears to overcome most disadvantages of transcatheter high energy direct-current shocks when used as a regular course of procedure in ablation of arrhythmogenic tissue in the heart.

Impedance to Transesophageal Atrial Pacing: Significance Regarding Power Sources

Transesophageal stimulation is an expeditious method of atrial pacing. Using pulse widths of 10 msec results in reduction of current requirement to values that are usually less than 15 mA. An unknown variable in transesophageal atrial pacing has been impedance. In this study, we investigated the impedance to transesophageal atrial pacing in ten patients using a stimulator with a 63 V power source capable of delivering constant current to 20 mA against an impedance of 2,000 ohms. A bipolar electrode was used to deliver stimuli with a current of 15 mA. Voltage across a known resistance and current were measured on an oscilloscope and the impedance was calculated. Pacing thresholds were also performed and ranged from 6.2 to 16.5 mA (mean 9.4 +/- 2.9 mA, SD). Impedance varied between 720 and 2,670 ohms (mean 1,750 +/- 540 ohms). The stimulator used to measure impedance in man and two other commercially available stimulators were bench tested against known resistances of 500 to 2,000 ohms. The other stimulators with power sources of 12.5 and 15 V had attenuation of the delivered current at resistances of between 1,000 and 2,000 ohms. Thus, this study has demonstrated that transesophageal atrial pacing incurs impedances two to five times greater than incurred with intracardiac pacing leads. Therefore stimulators with high power sources are required to deliver the programmed current against these impedances.

Effects of repeated increments in right atrial pressure on secretion of atrial natriuretic factor

I t has been demonstrated that an acute increase in right atria1 (RA) pressure and paroxysmal supraventricular tachycardias induce the release of atria1 natriuretic factor (ANF).*-4 In a previous study that allowed a selective or combined increase in heart rate and RA pressure by intracardiac pacing, we showed that acute increment in RA pressure is the determinant factor for ANF secretion.5 Hollister et al3 demonstrated that, in subjects with elevated ANF levels due to a high salt diet, ANF release caused by atria1 pressure increment was higher compared with subjects with normal baseline ANF. These data suggest that under chronically stimulated ANF secretion, there might be a higher sensitivity of ANF release to additional secretory stimuli. However, it is unknown whether there is an adaptation of the ANF release to repetitive secretion stimuli. We therefore investigated the ANF response to repeated identical atria1 pressure increments.

Cardiovascular manifestations of systemic lupus erythematosus: Current perspective

Cardiovascular manifestations develop in the majority of SLE patients at some time during the course of their illness, the most common being acute fibrinous pericarditis and pericardial effusion. Echocardiography has demonstrated an increased incidence of pericardial effusion, even in those who have minimal symptoms. Chronic adhesive pericarditis, pericardial tamponade, and constrictive pericarditis occur rarely. While myocarditis is commonly noted at autopsy, it is often silent clinically. Diagnosis during life can be confirmed only by endomyocardial biopsy. Electrocardiographic changes are often nonspecific. Endocarditis with superimposed nonbacterial verrucous vegetations (Libman-Sacks) is noted in more than 40% of hearts at autopsy, but is rarely diagnosed during life. Valve dysfunctions, such as aortic stenosis, aortic insufficiency, mitral stenosis, and mitral insufficiency, occasionally manifest during life and rarely may necessitate surgery. Atrial and ventricular arrhythmias, first degree AV block, and acquired CHB occur in association with pericarditis, myocarditis, vasculitis, and myocardial fibrosis, respectively. CCHB developing in newborns of mothers with SLE, particularly those who have an antibody to soluble tissue ribonuclear protein RO(SS-A), is increasingly being appreciated by both pediatric cardiologists and rheumatologists. Recently, severe coronary atherosclerosis resulting in angina pectoris and/or myocardial infarction in young adults has been noted, particularly in those who had developed risk factors such as hypertension and hyperlipidemia while receiving prolonged corticosteroid therapy. Rarely, coronary arteritis may produce similar symptoms. Congestive heart failure of either single or multiple etiologies carries an ominous prognosis. It remains a cause of high morbidity and mortality unless recognized early and treated properly. Extracardiac vascular manifestations of SLE include telangiectasia, vasculitis, livedo reticularis, Raynaud's phenomena, and thrombophlebitis, all of which may occur either alone or in different combinations. Evidence is now slowly accumulating that substantiates that immune complex deposition, complement activation and subsequent inflammatory reaction is responsible for the majority of the cardiovascular manifestations of SLE, for example, pericarditis, myocarditis, endocarditis, coronary arteritis, coronary atherosclerosis, and systemic and pulmonary vasculitis. For the pathogenesis of CCHB, a maternal antibody to the soluble tissue ribonuclear protein RO(SS-A), which crosses the placenta during the early stage of gestation and either interferes with the development or afflicts a degenerating process in the developing conduction system, is being incriminated. Corticosteroid therapy remains the cornerstone for the management of pericarditis, myocarditis, vasculitis, and coronary arteritis. However, nonsteroidal inflammatory agents, antiarrhythmic drugs, antihypertensive agents, vasodilator drugs, intensive endocarditis prophylaxis, and rarely, intracardiac pacing when indicated also play an important role in the overall management of cardiovascular manifestations of SLE. Renal failure, lupus cerebritis, and infections are still the three most common causes of death in patients with SLE. However, recently increased cardiac mortality as a result of hypertension, congestive heart failure, coronary atherosclerosis, and thrombosis, the latter particularly in young women, has been recognized. Mortality of infants with CCHB born to mothers with SLE remains significant despite intracardiac pacing.

Atrial Overdrive Pacing for Conversion of Atrial Flutter in Children

Twenty-three successive patients with 27 different episodes of sustained atrial flutter were treated with atrial pacing for conversion of the tachyarrhythmia; 15 patients with 16 episodes of atrial flutter underwent intracardiac right atrial pacing and eight patients with 11 episodes of atrial flutter were treated with transesophageal atrial pacing. Ten of sixteen episodes (63%) and eight of 11 episodes (73%) were successfully converted using intracardiac and transesophageal techniques, respectively. Mean flutter cycle length for all 27 episodes was 219 ms (mean heart rate 274 beats per minute); successful pacing conversion cycle length (n = 15) was 72% of the flutter cycle length. Hemodynamic, electrophysiologic, and roentgenographic data were not predictive of conversion by either technique. Induction of localized atrial fibrillation or failure to meet critical pacing criteria may explain pacing failures. Based on this experience, a trial of transesophageal atrial pacing for acute conversion of any episode of atrial flutter in children prior to direct current cardioversion is recommended.

Refractory Supraventricular Tachycardia in the Neonate: Treatment With Temporary Antitachycardial Pacing

Although intracardiac antitachycardial pacing techniques are frequently used to terminate reentrant supraventricular tachycardia in adults, this approach has rarely been used in neonates. We describe two neonates, both of whom were in circulatory shock due to recurrent paroxysmal supraventricular tachycardia, who were treated with temporary antiatachycardial pacing. This approach allows repeated termination of the tachycardia at the bedside until an adequate therapeutic concentration of an effective drug regimen is achieved and obviates repeated direct-current cardioversion.

Conversion of atrial flutter: rapid atrial pacing as a bedside technique.

Eleven patients with atrial flutter underwent intracardiac right atrial pacing at bedside in an attempt to terminate this dysrhythmia. Nine of the eleven patients were converted to sinus rhythm; the remaining two patients were converted to atrial fibrillation with a slower ventricular rate. There were no complications. The potential hazards of direct current cardioversion (anesthesia, fractures, muscle strain, myocardial injury, etc.) were avoided. In contrast to rapid atrial pacing in the electrophysiology laboratory, the bedside technique did not require a special laboratory setting, electronic or x-ray equipment, or technical personnel. Transportation of critically ill patients was obviated. Atrial flutter can be converted at the bedside to a more favorable rhythm; the expediency, safety, and low cost of this bedside cardioversion technique not only makes it feasible, but also it is often the procedure of choice.