bluuebunny/crossref_metadata_2025_split huggingface dataset:
Paroxysmal Cycle Length Shortening in the Pulmonary Veins During Atrial Fibrillation Correlates with Arrhythmogenic Triggering Foci in Sinus Rhythm
Authors: O'DONNELL DAVID , FURNISS STEVE S. , BOURKE JOHN P. 
Published: August 2003

Identifying Arrhythmogenic PVs in AF.
Introduction: The focal origin of atrial fibrillation (AF) is identified by recording atrial ectopic beats or the ectopic activity that precedes AF. We hypothesized that arrhythmogenic pulmonary veins (PVs) also could be identified during persistent AF. Methods and Results: Patients with persistent AF referred for focal ablation were enrolled prospectively. During AF, bipolar electrograms were recorded from each PV for a minimum of 120 seconds, as well as from the right atrium and coronary sinus. The cycle length of activity in each PV was measured during AF and plotted on a frequency histogram. Following cardioversion to sinus rhythm, arrhythmogenic PVs were identified from reinitiation of AF or from ectopic beats. Ten patients were enrolled and 37 PVs analyzed. During AF, 17 PVs demonstrated bimodal cycle length frequency histograms, with periods of paroxysmal short cycle length recording. Following cardioversion, 14 PVs were identified as arrhythmogenic as defined earlier. Each of these arrhythmogenic PVs showed paroxysmal short cycle length recording during AF. Sensitivity was 87%, specificity 91%, positive predictive value 87%, and negative predictive value 100%. Conclusion: The arrhythmogenic PVs responsible for the focal activity that triggers AF also demonstrate paroxysmal short cycle length recording during sustained AF. These results demonstrate that arrhythmogenic PVs still can be identified reliably, even during sustained AF.
Analysis of Troponin I Levels After Spontaneous Implantable Cardioverter Defibrillator Shocks
Authors: HASDEMIR CAN , SHAH NAYYAR , RAO ARUN P. , ACOSTA HELBERT , MATSUDAIRA KAGARI , NEAS BARBARA R. , REYNOLDS DWIGHT W. , PO SUNNY , LAZZARA RALPH , BECKMAN KAREN J. 
Published: August 2003

Troponin I Levels After Spontaneous ICD Shocks.
Introduction: Serum cardiac troponin I (cTnI) is a sensitive and specific marker for myocardial injury. Myocardial ischemia and/or injury can be a trigger for ventricular arrhythmias. The aim of this study was to assess the frequency and significance of elevated serum cTnI levels after spontaneous implantable cardioverter defibrillator (ICD) shocks. Methods and Results: Serial cTnI measurements and ECGs were performed in 35 patients with transvenous ICDs who were admitted after spontaneous ICD shocks. Elevated cTnI levels were found in 18 patients (51%). Acute coronary syndrome was diagnosed in 5 (22%) of 23 patients with known coronary artery disease. After excluding the patients with acute coronary syndrome, elevated cTnI levels were present in 13 (43%) of 30 patients: 18% of patients with < 3 shocks and 58% of patients with > 3 shocks. Patients with elevated cTnI levels received a higher number of shocks (16 ± 18 vs 5 ± 7; P < 0.05) and had higher total delivered energies (475 ± 538 J vs 128 ± 184 J; P < 0.05) compared with patients with normal cTnI. Patients with acute coronary syndrome had higher peak cTnI levels (18 ± 16 ng/mL) compared with patients with elevated cTnI without acute coronary syndrome (3.8 ± 4.3 ng/mL; P < 0.01). Conclusion: Serum cTnI rises occur in the majority of patients after multiple (> 3) spontaneous ICD discharges but are due to acute coronary syndrome only 14% of the time (22% of the time in patients with known coronary artery disease).
Excitability of Isolated Hearts from Rats During Postnatal Development
Authors: GOMES PAULO ALBERTO PAES , GALVÃO KLEBER DE MAGALHÃES , MATEUS EVANDRO FALLACI 
Published: August 2003

Excitability of Developing Rat Hearts.
Introduction: After birth, cardiac myocytes undergo substantial growth and differentiation that affect their stimulation threshold. Cells from younger animals have a higher stimulation threshold than cells from adults. The aim of this work was to compare the excitability of isolated hearts of rats during postnatal development by measuring the stimulation threshold at several pulse durations. Methods and Results: Stimulation threshold of isolated hearts were measured at eight different pulse durations between 0.1 to 20 msec. For each heart, a strength‐duration curve was constructed and data were fitted using both Weiss‐Lapicque and Blair models. Analysis of variance showed significant age‐dependent differences in both rheobase field (Ereob) and chronaxie (c). Ereob decreased while c increased during development (Ereob was 0.21, 0.16, 0.13, 0.10, and 0.09 V/cm and c was 2.0, 2.2, 2.3, 2.7, and 3.2 msec for rats aged 1, 2, 4, 8, and 20 weeks, respectively). There was a decrease in the threshold field with heart weight between 0.1 and 0.7 g, whereas the threshold was almost constant in the range from 0.7 to 2.0 g. Estimation of the energy density needed to defibrillate the heart was performed and appeared to be higher for younger than for adult animals. Conclusion: Hearts from younger animals have higher stimulation threshold than those from adults. This probably is due to changes in the cellular threshold as a result of maturation. The smaller excitability of younger hearts can have consequences with regard to the energy levels required for younger patients.
Tight Mechanism Correlation Between Heart Rate Turbulence and Baroreflex Sensitivity: Sequential Autonomic Blockade Analysis
Authors: LIN LIAN‐YU , LAI LING‐PING , LIN JIUNN‐LEE , DU CHAO‐CHENG , SHAU WEN‐YI , CHAN HSIAO‐LUNG , TSENG YUNG‐ZU , HUANG SHOEI K. STEPHEN 
Published: August 2003

Heart Rate Turbulence and Baroreflex Sensitivity.
Introduction: Heart rate turbulence is a powerful de novo risk predictor for patients surviving acute myocardial infarction. However, little is known about its underlying physiologic mechanism. Methods and Results: Hypothesizing that heart rate turbulence is barorceptor reflex related, we studied heart rate and blood pressure fluctuations at rest and after systematically introduced ventricular premature beats in 16 patients without structural heart disease (10 men and 6 women; mean age 45 ± 17 years) before and after sequential sympathetic (esmolol 4‐mg bolus followed by 120 μg/kg/min intravenously), parasympathetic (atropine 0.04 mg/kg intravenously), and combined autonomic blockade (esmolol plus atropine). Turbulence onset (%) and turbulence slope (msec/beat) were averaged from 10 respective ventricular premature beats. Spontaneous baroreflex sensitivity (msec/mmHg) was calculated from 5 minutes of sinus rhythm recording. The results showed that turbulence slope decreased after atropine (0.71 ± 0.50 msec/beat vs 5.17 ± 3.96 msec/beat at baseline; P < 0.01) and combined autonomic blockade (1.23 ± 1.02 msec/beat; P < 0.01) but was unchanged after esmolol (4.53 ± 3.30 msec/beat; P > 0.05). Turbulence onset increased after atropine (0.32% ± 0.35% vs −0.45 ± 0.94 at baseline; P < 0.05) and combined sympathetic and parasympathetic blockade (0.58% ± 0.86%; P < 0.05) but was unchanged after esmolol (−0.62% ± 1.33%; P > 0.05). Turbulence slope was positively correlated with baroreflex sensitivity at baseline (r = 0.78, P < 0.01) and after esmolol (r = 0.8, P < 0.01), but dissociated after atropine (r = 0.16, P > 0.05) and combined autonomic blockade (r = 0.31, P > 0.05). Turbulence onset was negatively correlated with baroreflex sensitivity at baseline (r =−0.61, P < 0.05), after esmolol (r =−0.80, P < 0.01), and after atropine (r =−0.53, P < 0.05). Conclusion: Heart rate turbulence of turbulence onset and turbulence slope is critically vagal dependent and highly correlated with spontaneous baroreflex sensitivity, which underscores its clinical importance in cardiovascular risk stratification.
Discrimination of Ventricular Tachycardia from Supraventricular Tachycardia by a Downloaded Wavelet‐Transform Morphology Algorithm: A Paradigm for Development of Implantable Cardioverter Defibrillator Detection Algorithms
Authors: SWERDLOW CHARLES D. , BROWN MARK L. , LURIE KEITH , ZHANG JIANXIN , WOOD NICOLE M. , OLSON WALTER H. , GILLBERG JEFFREY M. 
Published: August 2003

Morphology Download.
Introduction: Present implantable cardioverter defibrillators (ICDs) have algorithms that discriminate supraventricular tachycardia (SVT) from ventricular tachycardia (VT). One type of algorithm is based on differences in morphology of ventricular electrograms during VT and SVT. Prior SVT‐VT discrimination algorithms have not undergone real‐time evaluation in ambulatory patients until they were incorporated permanently into ICDs. This approach may result in incomplete testing of electrogram morphology algorithms because they are influenced by posture, activity, and electrogram maturation. We downloaded software into implanted ICDs to study a novel algorithm that compares morphologies of baseline and tachycardia electrograms based on differences between corresponding coefficients of their wavelet transforms. This comparison is expressed as a match‐percent score. Methods and Results: In 23 patients, we downloaded the wavelet algorithm into implanted ICDs to assess the temporal and postural stability of baseline electrograms as measured by this algorithm and its accuracy for SVT‐VT discrimination. Median follow‐up was 6 months. Software was downloaded into all ICDs without altering other device functions. With few exceptions, percent template match in baseline rhythm was stable with changes in body position, rest versus walking, isometric exercise, and over time (1 and 3 months). Using the nominal match‐percent threshold of 70%, sensitivity for detection of 38 VTs was 100%. Specificity for rejection of 65 SVTs was 78%. SVTs were rejected for a total of 2.7 hours. Inappropriate detections of SVT as VT were caused by electrogram truncation, myopotential interference with low‐amplitude electrograms, waveform alignment error, and rate‐dependent aberrancy. The first three accounted for 69% of inappropriate detections and could have been prevented by optimal programming. The optimal match‐percent threshold was 60% to 70% based on a receiver‐operator characteristic curve. After shocks, the median time for baseline electrogram morphology to normalize was 85 seconds. Conclusion: The wavelet morphology algorithm has high sensitivity for VT detection. Inappropriate detections of SVT as VT may be reduced by optimal programming. Downloadable software permits evaluation of new algorithms in implanted ICDs.
Analysis of the Chronotropic Effect of Acetylcholine on Sinoatrial Node Cells
Authors: ZHANG HENGGUI , HOLDEN ARUN V. , NOBLE DENIS , BOYETT MARK R. 
Published: August 2003

Analysis of Chronotropic Effect of ACh.
Introduction: The ionic basis underlying the negative chronotropic effect of acetylcholine (ACh) on sinoatrial (SA) node cells is unresolved and controversial. In the present study, mathematical modeling was used to address this issue. Methods and Results: The known concentration‐dependent effects of ACh on iK,ACh, iCa,L, and if were introduced into models of rabbit central and peripheral SA node cells. In the central and peripheral models, 9 × 10−8 and 14 × 10−8 M ACh, respectively, caused a 50% decrease in pacemaking rate, whereas in rabbit SA node ˜ 7.4 × 10−8 M ACh caused such a decrease. In the models, iK,ACh was primarily responsible for the decrease and actions of ACh on iCa,L or if alone caused a negligible effect. Although the inhibition of if did not directly contribute to the chronotropic effect, it was indirectly important, because it minimized the opposition by if to the decrease of rate caused by activation of iK,ACh. The central model was more sensitive to ACh than the peripheral model. Conclusion: The chronotropic effect of ACh is principally the result of activation of iK,ACh, and inhibition of iCa,L plays little or no role. Inhibition of if and possible inhibition of ib,Na play an important facilitative role by reducing the ability of if and ib,Na to curtail the chronotropic effect caused by activation of iK,ACh.
Atrial Fibrillation After DDDR Pacemaker Implantation
Authors: GILLIS ANNE M. , MORCK MARGARET 
Published: August 2003

AF After Pacemaker Implantation.
Introduction: Newer implantable pulse generators have data storage capabilities that permit detection of multiple episodes of atrial fibrillation (AF). This study evaluated the clinical predictors and time course of AF development in a general pacemaker population. Methods and Results: Patients (n = 231) received DDDR pacemakers with features that permit detection and storage of information about the date, time of onset, and duration of multiple, sequential episodes of AF. Patients were followed for 718 ± 383 days. Time to first occurrence of AF, interval between first and second episode of AF, and total AF burden were determined at each follow‐up visit. AF occurred more often in patients (68%) with sinus node disease than in patients with AV block (37%; P < 0.001). Time to first occurrence of AF was 21.2 days (95% confidence interval [CI] 14.7 to 30.6 days) after pacemaker implantation. AF burden initially decreased significantly in patients (0.8 hours/day, 95% CI 0.7 to 0.9 at 8 weeks after implant vs 0.6 hours/day, 95% CI 0.4 to 0.8 at 12 months after implant; P = 0.005) but then increased significantly during long‐term follow‐up (2.0 hours/day, 95% CI 1.0 to 3.7 at 48 months after implant; P = 0.008). The long‐term increase in AF burden was seen predominantly in patients with sinus node disease. A prior history of AF and the duration of follow‐up were independent predictors of AF occurrence. Conclusion: AF develops frequently after dual‐chamber pacemaker implantation. AF burden increases progressively over the long term.
Outcome of Women Versus Men with Ventricular Tachyarrhythmias Treated with the Implantable Cardioverter Defibrillator
Authors: PIRES LUIS A. , SETHURAMAN BARATHI , GUDUGUNTLA VAMSHIDHAR D. , TODD KATRINA M. , YAMASAKI HIROSHI , RAVI SRIHARI 
Published: August 2003

Gender and ICD Therapy.
Introduction: Important sex differences in the incidence and outcome of patients with ischemic heart disease, the leading cause of ventricular tachyarrhythmias, have been identified. Implantable cardioverter defibrillator (ICD) therapy has become the treatment of choice for patients with ventricular tachycardia (VT) and ventricular fibrillation (VF), but little is known about gender differences in the outcome of ICD‐treated patients. Methods and Results: In this retrospective study, we compared arrhythmic events and survival of 376 women and 1,654 men treated with an ICD as part of prospective evaluations of transvenous devices or lead systems. Women were younger (62 ± 14 years vs 65 ± 12 years, P = 0.0005), had higher left ventricular ejection fraction (0.36 ± 0.15 vs 0.32 ± 0.13, P < 0.0001), were more likely to present with VF (34% vs 19%, P < 0.001), and had lower implantation defibrillation threshold (11 ± 6 vs 13 ± 6 J, P < 0.0001). Implant complication rates were similar in men and women (2.6% vs 3.5%, P = 0.46). The 1‐year and 2‐year cumulative rates of appropriate ICD therapies were 31.4% and 38.4% for men and 32.6% and 40.8% for women, respectively (P = 0.63). The unadjusted 1‐year and 2‐year cumulative survival rates were 95.6% and 93.7% for men and 95.7% and 94.3% for women, respectively (P = 0.98). Adjusted total (P = 0.61), sudden (P = 0.82), and cardiac (P = 0.34) death‐free survivals also were similar in men and women. Conclusion: Despite clinical differences suggesting women are at lower risk than men, men and women with VT/VF who are treated with an ICD have similar arrhythmic event and survival rates. These factors should be considered when determining risk and prescription of ICD therapy for women.
Short‐Term Rapid Atrial Pacing Produces Electrical Remodeling of Sinus Node Function in Humans
Authors: HADIAN DJAVID , ZIPES DOUGLAS P. , OLGIN JEFFREY E. , MILLER JOHN M. 
Published: August 2003

Sinus Node Remodeling in Man.
Introduction: Depression of sinus node function occurs in dogs and in patients after cessation of atrial flutter and fibrillation. We tested whether transient atrial pacing might produce similar changes in humans. Methods and Results: We studied the impact of short‐term rapid atrial pacing, simulating atrial tachyarrhythmias, on sinoatrial conduction time (SACT) and corrected sinus node recovery time (CSNRT) in 10 patients undergoing electrophysiologic study. None had recognizable structural heart disease, history of atrial fibrillation or flutter, autonomic dysfunction, or any tachycardia for at least 24 hours before study. All cardiac drugs were discontinued > 5 half‐lives prior to study. No patient had significant hypotension during atrial stimulation. SACT and CSNRT were measured at baseline, and sinus node reset zone was determined. Right atrial pacing was performed for 10 to 15 minutes, after which SACT and CSNRT were measured again. Both parameters increased significantly, from 423 ± 208 msec to 491 ± 214 msec and from 80 ± 50 msec to 96 ± 53 msec, respectively (P = 0.02 and P < 0.001, respectively). Conclusion: Rapid atrial pacing for only 10 to 15 minutes, simulating transient atrial tachyarrhythmias, alters sinus node function in humans. Additional studies are needed to evaluate the mechanism, but the clinical implication is that even transient episodes of atrial tachyarrhythmias can cause sinus node remodeling in patients.
Intrapericardial Therapeutics: A Pharmacodynamic and Pharmacokinetic Comparison Between Pericardial and Intravenous Procainamide Delivery
Authors: UJHELYI MICHAEL R. , HADSALL KELLY Z. , EULER DAVID E. , MEHRA RAHUL 
Published: August 2003

Pericardial Procainamide Delivery.
Introduction: Procainamide delivery into the pericardial space may produce a greater and more prolonged electrophysiologic effect, particularly in thin superficial atrial tissue, compared with intravenous delivery. Methods and Results: Swine were randomized to sequential procainamide doses delivered intravenously (n = 6) or into the pericardial space (n = 7). The cumulative pericardial doses were 0.5, 1.5, and 3.5 mg/kg, and the intravenous doses were 2, 10, and 26 mg/kg. Pericardial procainamide prolonged right atrial effective refractory period from baseline by 22% (P < 0.01) but only at the 3.5 mg/kg cumulative dose. This dose slowed interatrial conduction time by 14% (P < 0.05) and raised atrial fibrillation threshold by 70 mA (P < 0.05). Pericardial procainamide had minimal effect on ventricular electrophysiology. Similar results occurred with a single 2 mg/kg pericardial dose in a closed chest model. Intravenous 10 and 26 mg/kg cumulative doses prolonged atrial effective refractory period from baseline by 24% and 18% (P < 0.01), respectively. The 26 mg/kg cumulative intravenous dose slowed interatrial and atrial‐ventricular conduction times by 27% and 17%, respectively (P < 0.05), raised atrial fibrillation threshold, and slowed ventricular conduction time by 29% (P < 0.05). Pericardial procainamide produced pericardial fluid concentrations ranging from 250 to 1,500 μg/mL, but plasma concentrations were < 1 μg/mL. Intravenous procainamide doses produced pericardial fluid concentrations similar to plasma trough concentrations 0 to 12 μg/mL. Conclusion: The single 2 mg/kg and 3.5 mg/kg cumulative pericardial procainamide doses prolonged atrial refractoriness and raised atrial fibrillation threshold similar to the 26 mg/kg cumulative intravenous dose, but the duration of effect was similar between delivery methods. Pericardial procainamide did not affect global or endocardial ventricular electrophysiology nor was it associated with ventricular proarrhythmia.
Short‐Term Reproducibility of T Wave Alternans Measurement
Authors: TURITTO GIOIA , MIRANDI ANTHONY P. , PEDALINO RONALD P. , URETSKY SCOTT , EL‐SHERIF NABIL 
Published: August 2003

T Wave Alternans Reproducibility.
Introduction: Microvolt T wave alternans (TWA) has been proposed as a strong independent predictor of malignant ventricular tachyarrhythmias and sudden cardiac death. TWA reproducibility during bicycle stress test has not been previously investigated. We sought to assess the short‐term reproducibility of TWA, as well as heart rate (HR) threshold for TWA, and its spatial distribution and magnitude. Methods and Results: The study enrolled 42 patients who were able to complete two bicycle stress tests with HR at peak exercise > 110 beats/min within 4 hours of each other and who had technically adequate recordings for TWA analysis during both tests. Concordant results for TWA determination were obtained in 39 (93%) of 42 cases. TWA was present during both tests in 23 patients and was absent during both tests in 16 patients. In the 23 patients with two positive tests, HR at the onset of TWA was not significantly different during the two tests. Further, the number of leads showing TWA and the magnitude of TWA were not significantly different between the two tests. Conclusion: TWA is characterized by satisfactory short‐term reproducibility and, when present, by high temporal and spatial stability.
Repolarization Dynamics in Patients with Long QT Syndrome
Authors: PERKIÖMÄKI JUHA S. , ZAREBA WOJCIECH , NOMURA ATSUNOBU , ANDREWS MARK , KAUFMAN ELIZABETH S. , MOSS ARTHUR J. 
Published: August 2003

Repolarization Dynamics in LQTS.
Introduction: Dynamics of ventricular repolarization may contribute to cardiac arrhythmias in subjects with the long QT syndrome (LQTS). The aim of the present study was to assess the dynamics of repolarization duration and the dynamics of repolarization complexity in LQTS patients and their unaffected family members. Methods and Results: Twelve‐lead 24‐hour ambulatory ECG recordings were obtained from LQTS patients (n = 38) and unaffected family members (n = 20). The 24‐hour dynamics of the QT interval, T wave complexity (TWC) index measured by principal component analysis, and the RR interval were analyzed using standard deviation (SD) and square root of the mean squared differences of successive values of the parameters (RMSSD). QT variability, mean TWC, and TWC variability were increased in the LQTS patients compared with unaffected family members (QT‐SD: 38 ± 20 msec vs 19 ± 7 msec, P = 0.0001; QT‐RMSSD: 36 ± 20 msec vs 14 ± 8 msec, P = 0.0001; TWC: 27.7% ± 11.1% vs 20.4% ± 6.7%, P = 0.003; TWC‐SD: 6.7% ± 2.8% vs 4.6% ± 1.8%, P = 0.003; TWC‐RMSSD: 5.3% ± 2.8% vs 3.7% ± 1.2%, P = 0.004, respectively). At the same time, the measures of heart rate variability were similar between the affected and unaffected LQTS subjects (SD of normal‐to‐normal RR intervals [SDNN]: 94 ± 25 msec vs 89 ± 37 ms, P = 0.56; RMSSD: 49 ± 26 msec vs 49 ± 34 ms, P = 0.97, respectively). Conclusion: Despite similar heart rate variability, QT variability and the variability of TWC are significantly increased in LQTS patients compared with unaffected family members, suggesting that disturbances in temporal dynamics of repolarization and repolarization complexity in LQTS patients possibly increase vulnerability to arrhythmias.