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Biomedical subjects

H Calkins

Publications and source records attributed to H Calkins.

At least 55 records · Page 3Linked to original sources
PubMed1998

Relation between impedance and electrode temperature during radiofrequency catheter ablation of accessory pathways and atrioventricular nodal reentrant tachycardia.

OBJECTIVES: Impedance monitoring has been proposed as a method to assess the adequacy of tissue heating during catheter ablation procedures. The purpose of this study was to evaluate the relation among initial impedance, fall in impedance, and electrode temperature during catheter ablation procedures. METHODS AND RESULTS: Data from 248 applications of radiofrequency energy in 45 consecutive patients (26 with accessory pathways and 19 with atrioventricular nodal reentrant tachycardia) referred for catheter ablation were analyzed. The initial impedance was higher during ablation of accessory pathways than during atrioventricular nodal reentrant tachycardia (116+/-66 versus 106+/-80 omega, P < .001). In both groups, a significant correlation was observed between the initial impedance and temperature (R = 0.98, P < .001). After accounting for differences between patients and ablation targets, an even closer correlation was observed (accessory pathways: R = 0.95, P < .0001; atrioventricular nodal reentrant tachycardia: R = 0.94, P < .0001). CONCLUSION: These data suggest that monitoring of the initial impedance and the fall in impedance during ablation procedures may provide clinically valuable information to assess the efficacy of tissue heating and lesion formation.

Adolescent↗
PubMed1998

Relationship Between Chronic Fatigue Syndrome and Neurally Mediated Hypotension.

Chronic fatigue syndrome is a chronic debilitating disease that afflicts 4/1000 of the general population. The pathophysiologic basis for this condition is unknown, and no known consistently effective therapy has been identified. Recent studies have reported a link between the chronic fatigue syndrome and neurally mediated hypotension, a common abnormality of blood pressure regulation. In nonrandomized studies, treatment directed at neurally mediated hypotension has been effective in treating the symptoms of the chronic fatigue syndrome in two-thirds of patients. Prospective randomized trials are now in progress.

Journal Article↗
PubMed1998

Relationship between the upper limit of vulnerability determined in normal sinus rhythm and the defibrillation threshold in patients with implantable cardioverter defibrillators.

The upper limit of vulnerability is the strength above which ventricular fibrillation is no longer inducible with a shock delivered during the vulnerable phase of the cardiac cycle. It has been demonstrated that the upper limit of vulnerability correlates with the defibrillation threshold in a paced rhythm. The purpose of this study is to evaluate the correlation of the upper limit of vulnerability determined in normal sinus rhythm with the defibrillation threshold using a simplified protocol in patients undergoing placement of an ICD. We studied 28 patients who underwent ICD implantation. CPI generators and Endotak leads were used in all patients. Device-based testing was used to determined the defibrillation threshold and the upper limit of vulnerability. The upper limit of vulnerability was tested with three shocks delivered at 0, 20, and 40 ms before the peak of the T wave during normal sinus rhythm. The defibrillation threshold was determined by a simple step up-down protocol. The upper limit of vulnerability (9.0 +/- 4.5 J) did not significantly differ from the defibrillation threshold (9.9 +/- 4.0 J), P = NS. A close correlation was present, correlation coefficient = 0.75, P < 0.0001. The upper limit of vulnerability was within 5 J of the defibrillation threshold in 27 (96%) of the 28 patients. The upper limit of vulnerability underestimated the defibrillation threshold by 10 J in one patient who had a defibrillation threshold of 15 J. The upper limit of vulnerability determined in normal sinus rhythm correlates significantly with the defibrillation threshold in patients undergoing ICD implantation. The protocol is simple and easily implemented clinically.

Anti-Arrhythmia Agents↗
PubMed1998

Prospective comparison of temperature guided microwave and radiofrequency catheter ablation in the swine heart.

Microwave energy has been proposed as an alternative to radiofrequency energy for use during catheter ablation procedures. The purpose of this study was to prospectively compare, in an animal model, the lesion size associated with temperature guided catheter ablation using either microwave or radiofrequency energy. Eleven swine underwent catheter ablation with either radiofrequency (N = 4) or microwave energy (N = 7). In each animal catheter ablation was performed at 7-15 sites. At each site energy was delivered for 60 seconds using closed loop feedback temperature control to achieve a target temperature of 70 degrees C. Cardiac catheterization was performed before and after ablation. Animals were sacrificed approximately one month following the ablation procedure. Analysis of lesion size demonstrated that overall lesions created using radiofrequency energy were larger than those created using microwave energy. In the ventricle, lesions created using microwave energy were longer, but had a similar width and depth as those created using radiofrequency energy. An important relation was observed between the depth of lesions created using microwave energy and catheter stability, as evidenced by the temperature profile. Overall, lesions created using microwave energy are smaller than those created using radiofrequency energy. Catheter stability has an important impact on lesion size.

Animals↗
PubMed1998

Beat-to-beat repolarization lability identifies patients at risk for sudden cardiac death.

INTRODUCTION: Recent studies have implicated repolarization lability in the genesis of malignant ventricular arrhythmias. However, few data exist on assessment of temporal QT interval variability and its relation to arrhythmogenesis. We tested the ability of the QT variability index (QTVI), a measure of beat-to-beat QT interval fluctuations measured on a single ECG lead, to identify patients presenting with malignant ventricular arrhythmias and predict their subsequent occurrences. METHODS AND RESULTS: We measured the QTVI in 95 patients presenting for electrophysiologic study (EPS). The ability of the QTVI to identify patients with sudden cardiac death (SCD) or sustained monomorphic ventricular tachycardia (MVT) on presentation and during follow-up of 23.7+/-14.3 months was compared with spatial QT dispersion, T wave alternans ratio during atrial pacing, MVT inducibility at EPS, signal-averaged ECG, heart rate variability, and ejection fraction. The QTVI was higher in patients with heart disease than in controls (-0.7+/-0.7 vs -1.1+/-0.5, P < 0.05), and higher in patients presenting with SCD than in other patients with heart disease (0.0+/-0.6 vs -0.8+/-0.5, P < 0.05). The QTVI was the only clinical variable that identified patients who presented with SCD (P = 0.004, odds ratio = 12.5) on stepwise, logistic multiple regression. Fourteen patients had arrhythmic events during follow-up. In a Kaplan-Meier analysis of arrhythmic events, QTVI> or =0.1 was a discriminator for higher risk of arrhythmic events (P < 0.05). CONCLUSIONS: (1) This noninvasive measure of temporal repolarization lability identified patients with SCD and predicted arrhythmia-free survival. (2) Further studies are needed to determine the mechanisms that mediate beat-to-beat QT interval variability.

Death, Sudden, Cardiac↗
PubMed1997

Safety and effectiveness of placement of pacemaker and defibrillator leads in the axillary vein guided by contrast venography.

Despite evidence of an increased incidence of lead fracture, the infraclavicular subclavian approach remains the dominant approach for placement of pacemaker and implantable defibrillator leads. Although this complication can be prevented by lead placement in the cephalic vein or by recently described approaches for lead placement in the axillary vein, these approaches have not gained widespread acceptance. The purpose of this study was to evaluate the safety and efficacy of an alternative technique for lead placement that uses contrast-guided venipuncture of the axillary vein with a 5Fr micropuncture introducer set. A total of 50 patients underwent an attempt at placement of pacemaker or implantable defibrillator leads via the axillary vein using this new technique. Patients were randomized into 2 groups based on whether the initial attempt at axillary vein access was performed medial or lateral to the rib cage margin. Lead placement was successfully accomplished in 49 of the 50 patients using this technique. Initial success was achieved in each of 25 patients randomized to the medial approach compared with 18 of 24 patients randomized to the lateral approach to the axillary vein (75%). In each of the 6 patients in whom the initial technique failed, lead placement was subsequently achieved with the medial approach. In addition to a higher initial success rate, the medial approach was determined to be preferable as evidenced by a shorter lead placement time, a smaller number of contrast injections, and a reduced requirement for additional micropuncture guidewires. There were no major complications associated with either approach. Contrast-guided venipuncture of the axillary vein is a safe and effective approach to placement of endocardial leads.

Aged↗
PubMed1997

Beat-to-beat QT interval variability: novel evidence for repolarization lability in ischemic and nonischemic dilated cardiomyopathy.

BACKGROUND: Dilated cardiomyopathy (DCM) is associated with a high incidence of malignant ventricular arrhythmias and sudden death. Abnormalities in repolarization of ventricular myocardium have been implicated in the development of these arrhythmias. Spatial heterogeneity in repolarization has been studied in DCM, but temporal fluctuations in repolarization in this setting have been largely ignored. We sought to test the hypothesis that beat-to-beat QT interval variability is increased in DCM patients compared with control subjects. METHODS AND RESULTS: Eighty-three patients with ischemic and nonischemic DCM and 60 control subjects served as the study population. Beat-to-beat QT interval variability was measured by automated analysis on the basis of 256-second records of the surface ECG. A QT variability index (QTVI) was calculated for each subject as the logarithm of the ratio of normalized QT variance to heart rate variance. The coherence between heart rate and QT interval fluctuations was determined by spectral analysis. In patients, ejection fractions were assessed by echocardiography or ventriculography, and spatial QT dispersion was determined from the standard 12-lead ECG. DCM patients had greater QT variance than control subjects (60.4+/-63.1 versus 25.7+/-24.8 ms2, P<.0001) despite reduced heart rate variance (6.7+/-7.8 versus 10.5+/-10.4 bpm2, P=.01). The QTVI was higher in DCM patients than in control subjects, with a high degree of significance (-0.43+/-0.71 versus -1.29+/-0.51, P<10[-12]). QTVI did not correlate with ejection fraction or spatial QT dispersion but did depend on New York Heart Association functional class. QTVI did not differ between DCM patients with ischemic and those with nonischemic origin. Coherence between heart rate and QT interval fluctuations at physiological frequencies was lower in DCM patients compared with control subjects (0.28+/-0.14 versus 0.39+/-0.18, P<.0001). CONCLUSIONS: DCM is associated with beat-to-beat fluctuations in QT interval that are larger than normal and uncoupled from variations in heart rate. QT interval variability increases with worsening functional class but is independent of ejection fraction. These data indicate that DCM leads to temporal lability in ventricular repolarization.

Adult↗
PubMed1997

Dispersion of ventricular activation and refractoriness in patients with idiopathic dilated cardiomyopathy.

We sought to evaluate the electrophysiologic substrate for ventricular arrhythmias and sudden cardiac death in patients with idiopathic dilated cardiomyopathy. When compared with controls, patients with cardiomyopathy had prolonged activation times, increased dispersion of activation and recovery, and prolonged duration of monophasic action potential recordings at 70%, but not at 90%, of repolarization.

Cardiac Catheterization↗
PubMed1997

Comparison of heart rate variability in patients with chronic fatigue syndrome and controls.

Recent studies have reported a close association between chronic fatigue syndrome and neurally mediated hypotension. We hypothesized that this association may result from an abnormality in autonomic function among patients with chronic fatigue syndrome, which may be detectable using an analysis of heart rate variability. We prospectively studied 19 patients who fulfilled the Centers for Disease Control criteria for chronic fatigue syndrome and 11 controls. Each subject underwent a two-stage tilt-table test while wearing a Holter monitor. Heart rate variability was assessed in the supine baseline position and during upright tilt using frequency domain parameters. In the baseline supine position, high frequency (HF) power, low frequency (LF) power, and the ratio of low frequency power to high frequency power (LF/HF ratio) were similar. In both patient groups, upright tilt resulted in a similar decrease in HF power, increase in LF power, and increase in the LH/HF ratio. In conclusion, autonomic function, as assessed using an analysis of heart rate variability, does not differ in the baseline supine state, nor in response to upright tilt among patients with chronic fatigue syndrome and healthy controls.

Adult↗
PubMed1997

Acute radiation dermatitis following radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia.

Radiation exposure during fluoroscopic imaging poses potential risks to patients and physicians, especially during protracted cardiovascular or radiological interventional procedures. We describe a woman with refractory paroxysmal supraventricular tachycardia who underwent radiofrequency catheter ablation of the slow pathway involved in atrioventricular nodal reentrant tachycardia. The patient subsequently returned 4 weeks later with acute radiation dermatitis that was retrospectively attributed to a malfunction in the fluoroscopy unit that lacked a maximum current output cut-off switch. Using dose reconstruction studies and her estimated biological response, we determined that she received between 15 and 20 Gy (1 Gy = 100 rads) to the skin on her back during the procedure. The exposure will result in an increase in her lifelong risk of skin and lung cancer. This article underscores the potential for radiation-induced injury during lengthy therapeutic procedures using x-ray equipment.

Acute Disease↗
PubMed1997

High dose neostigmine treatment of malignant sinus tachycardia.

Sinus tachycardia caused by circulating catecholamines in the setting of congestive heart failure may impair systemic perfusion because of decreased diastolic filling time. We report the case of a patient with Wolff-Parkinson-White syndrome with angina and cardiogenic shock who improved dramatically following administration of neostigmine. Cardiac output, blood pressure, and stroke volume increased as heart rate was reduced. A previous attempt at heart rate control, in the same patient, using a low dose beta-antagonist, precipitated hemodynamic collapse. The remarkable recovery of our patient suggests that acetylcholinesterase inhibitors may warrant further investigation in patients with severe sinus tachycardia.

Adult↗
PubMed1997

Tissue magnesium levels and the arrhythmic substrate in humans.

INTRODUCTION: Magnesium deficiency has been implicated in the pathogenesis of sudden death, but the investigation of arrhythmic mechanisms has been hindered by difficulties in measuring cellular tissue magnesium stores. METHODS AND RESULTS: To see if magnesium deficiency is associated with a propensity toward triggered arrhythmias, we measured tissue magnesium levels and QT interval dispersion (as an index of repolarization dispersion) in 40 patients with arrhythmic complaints. Magnesium was measured in sublingual epithelium using X-ray dispersive analysis. QT interval dispersion was assessed on 12-lead surface ECGs in all patients, and programmed stimulation was performed in 28. The sublingual epithelial magnesium level ([Mg]1), but the not the serum level, correlated inversely with QT interval dispersion in 40 patients (r = 0.58, P < 0.005); in 12 patients undergoing repeat testing on therapy, the change in magnesium also correlated inversely with the change in QT dispersion (r = 0.61, P < 0.05). Patients with left ventricular ejection fractions > 40% had significantly higher tissue magnesium and lower QT dispersion (34.5 +/- 0.5 mEq/L, 81 +/- 8 msec) than those with left ventricular ejection fractions < 40% (32.7 +/- 0.5 mEq/L, P < 0.01, and 114 +/- 9 msec, P < 0.05). There was no difference in either [Mg]1 or QT dispersion in the 16 patients with inducible monomorphic ventricular tachycardia versus the 12 noninducible patients. CONCLUSION: Reduced tissue magnesium stores may represent a significant risk factor for arrhythmias associated with abnormal repolarization, particularly in patients with poor left ventricular systolic function, but may not represent a risk for excitable gap arrhythmias associated with a fixed anatomic substrate (e.g., monomorphic ventricular tachycardia).

Adult↗
PubMed1997

Signal-averaged intracardiac electrograms: a new method to detect kent potentials.

INTRODUCTION: In patients with manifest accessory pathways, Kent potentials are often difficult to identify even at sites of successful catheter ablation, due largely to signal noise and catheter instability. We hypothesized that signal averaging the intracardiac electrogram recorded from the ablation catheter over a number of beats would improve the signal-to-noise ratio of the electrogram and aid in the detection of Kent potentials at accessory pathway locations. METHODS AND RESULTS: We retrospectively analyzed distal-pair electrograms recorded from 9 successful, 6 transiently successful, and 10 failed ablation sites in 10 patients with manifest accessory pathways who underwent catheter ablation. We developed custom software to finely align 20 to 30 consecutive sinus beats and compute the signal average of the electrogram (SAE) for each site. Kent potentials were classified as probable, possible, or absent in the raw ablation site electrogram and the SAE base on morphologic criteria. A measure of beat-to-beat signal instability, the variability quotient (VQ), was also computed for each site. Probable Kent potentials were found in the raw ablation site electrogram at only 2 of the 15 successful and transiently successful sites, but were found in the SAE at 10 of these sites (P = 0.008). Eight of the 9 successful sites had VQ < 0.2, suggesting stable catheter-tissue contact, while 3 of the 6 transiently successful sites had VQ > 0.2, indicating unstable contact. CONCLUSIONS: Signal averaging the intracardiac ablation site electrogram enhances detection of Kent potentials at accessory pathway locations. Catheter instability can be quantified by signal variability analysis and, when high, may predict lack of successful ablation even at sites where Kent potentials are present.

Adolescent↗
PubMed1996

Temperature monitoring during radiofrequency ablation.

Thermal injury is the primary mechanism of lesion formation during radiofrequency catheter ablation procedures. Irreversible tissue injury requires heating to approximately 50 degrees C. Temperatures above 100 degrees C result in coagulum formation. Because of this importance of temperature during radiofrequency catheter ablation procedures, temperature monitoring has been proposed as a tool to facilitate catheter ablation procedures. The results of recent clinical studies demonstrate that electrode temperatures do not differ at successful and failed ablation sites, electrode temperature does not predict or eliminate the possibility of arrhythmia recurrence, and closed-loop temperature control decreases but does not eliminate the development of coagulum nor guarantees that target temperatures will be achieved. These observations are due in large part to the important distinctions between electrode temperature, the temperature at the electrode-tissue interface, and the temperature at the ablation target. Nonetheless, temperature monitoring and temperature control are valuable tools during radiofrequency ablation procedures as they provide important information regarding the adequacy of tissue heating, minimize the development of coagulum, and maximize lesion size.

Animals↗
PubMed1996

Catheter ablation of coexistent bundle branch and interfascicular reentrant ventricular tachycardias.

INTRODUCTION: Bundle branch reentry and interfascicular reentry are potential mechanisms of ventricular tachycardia in the setting of a dilated cardiomyopathy. We report a patient with myotonic dystrophy who presented with near syncope, in whom both of these mechanisms were present, leading to two different wide complex tachycardias. METHODS AND RESULTS: Electrophysiologic study demonstrated infra-Hisian conduction system disease and inducible bundle branch reentrant ventricular tachycardia. Catheter ablation of the right bundle eliminated bundle branch reentry. However, following this, the patient had inducible interfascicular reentry, which subsequently occurred spontaneously while still hospitalized. Catheter ablation of the left posterior fascicle successfully eliminated this second tachycardia, and the patient has had no further arrhythmias. CONCLUSIONS: This report is of an unusual patient with coexistent bundle branch reentry and interfascicular reentry producing two different forms of sustained ventricular tachycardia. This is the first report of catheter ablation of the left posterior fascicle for elimination of conduction system reentry.

Adult↗
PubMed1996

Recurrence of conduction following radiofrequency catheter ablation procedures: relationship to ablation target and electrode temperature. The Atakr Multicenter Investigators Group.

INTRODUCTION: More than 1 in 10 patients may develop recurrence of conduction after undergoing a successful radiofrequency catheter ablation procedure. The physiologic basis for recurrence following successful ablation procedures remains uncertain. The purpose of this study was to evaluate the role of electrode temperature as a predictor of recurrence following radiofrequency catheter ablation procedures. METHODS AND RESULTS: The subjects of this study were 538 patients who underwent a successful attempt at radiofrequency catheter ablation of AV nodal reentrant tachycardia, an accessory pathway, and/or the AV junction. Patients were followed for a mean of 215 +/- 138 days. Conduction recurred in 35 (6.5%) of the 538 patients. Recurrence of conduction occurred in 25 (9.3%) of 270 patients undergoing ablation of an accessory pathway, 7 (3.5%) of 201 patients undergoing ablation of AV nodal reentrant tachycardia, and in 3 (4.5%) of 67 patients undergoing ablation of the AV junction. The electrode temperature achieved at successful sites associated with recurrence was not different from the temperature achieved at successful sites without recurrence (61.1 +/- 8.9 vs 61.6 +/- 9.1; P = 0.8). The likelihood of developing a recurrence was higher following ablation of accessory pathways than following ablation of AV nodal reentrant tachycardia or the AV junction (P = 0.03). Patients experiencing a recurrence following ablation of an accessory pathway had longer procedure durations (P = 0.0001). Ablation of left free-wall pathways was associated with a lower incidence of recurrence as compared with all other locations (P = 0.008). CONCLUSION: The results of this study suggest that electrode temperature at the successful ablation site cannot be used to identify patients at highest risk of recurrence.

Adolescent↗