Intermittent Capture Research Articles

Parallel Accelerated Fifth-Order WENO Scheme-Based Pipeline Transient Flow Solution Model

The water hammer phenomenon is the main problem in long-distance pipeline networks. The MOC (Method of characteristics) and finite difference methods lead to severe constraints on the mesh and Courant number, while the finite volume method of the second-order Godunov scheme has limited intermittent capture capability. These methods will produce severe numerical dissipation, affecting the computational efficiency at low Courant numbers. Based on the lax-Friedrichs flux splitting method, combined with the upstream and downstream virtual grid boundary conditions, this paper uses the high-precision fifth-order WENO scheme to reconstruct the interface flux and establishes a finite volume numerical model for solving the transient flow in the pipeline. The model adopts the GPU parallel acceleration technology to improve the program’s computational efficiency. The results show that the model maintains the excellent performance of intermittent excitation capture without spurious oscillations even at a low Courant number. Simultaneously, the model has a high degree of flexibility in meshing due to the high insensitivity to the Courant number. The number of grids in the model can be significantly reduced and higher computational efficiency can be obtained compared with MOC and the second-order Godunov scheme. Furthermore, this paper analyzes the acceleration effect in different grids. Accordingly, the acceleration effect of the GPU technique increases significantly with the increase in the number of computational grids. This model can support efficient and accurate fast simulation and prediction of non-constant transient processes in long-distance water pipeline systems.

What Is the Mechanism of This Cardiac Rhythm?

An 80-year-old man with syncope was admitted for evaluation. His clinical examination revealed nothing remarkable. He had no history of heart disease, his blood pressure and electrolyte levels were normal, and he was taking no medications known to cause bradyarrhythmia. Overnight telemetry revealed the electrocardiogram displayed below (Fig. 1).The rhythm strip suggests which diagnosis?D) Junctional escape and intermittent capture beatsThe telemetry strip displayed junctional rhythm, sinus capture after every second junctional rhythm, and right bundle branch block (RBBB) of the sinus-captured beat (Fig. 2). This rare phenomenon, wherein a sinus-captured beat occurs after 2 junctional escape beats, is termed escape-reentry-capture trigeminy.1In isorhythmic atrioventricular (AV) dissociation (Answer A), the atria and ventricles beat at the same rate but are dissociated from each other; here, however, the junctional beat with retrograde conduction to the atria rules out dissociation between competing rhythms. The lack of clear P waves preceding the QRS complexes and the absence of progressive PR prolongation makes Mobitz type I AV block (Answer B) unlikely. Premature ventricular contractions in trigeminy (Answer C) are unlikely because the wide complexes with RBBB morphology are preceded by a P wave, and the QRS pattern simulates a “typical” RBBB. The 2 junctional beats followed by P-wave capture makes premature atrial complexes in trigeminy (Answer E) unlikely.Escape-reentry-capture occurs in the presence of sinus nodal dysfunction (sick sinus syndrome) when the sinus impulse rate is slower than the junctional escape rate. The inverted P wave in Figure 2 (arrows) suggests that the first junctional beat was conducted retrograde to the atria, that the next junctional beat was not, and that the subsequent sinus beat was conducted with an RBBB. This aberrancy may be explained by the “long-short” sequence that prolongs the effective refractory period of the right bundle. Consequently, the sinus rate was apparently slow enough to be captured in a trigeminal pattern. Note also that the junctional rhythm did not affect the sinus rate. The patient was given a permanent pacemaker. This case illustrates the escape-reentry-capture phenomenon in a trigeminal pattern caused by sinus nodal dysfunction.Conflict of Interest Disclosure: NoneFunding/Support: None

Computational modeling of aberrant electrical activity following remuscularization with intramyocardially injected pluripotent stem cell-derived cardiomyocytes

Acute engraftment arrhythmias (EAs) remain a serious complication of remuscularization therapy. Preliminary evidence suggests that a focal source underlies these EAs stemming from the automaticity of immature pluripotent stem cell-derived cardiomyocytes (PSC-CMs) in nascent myocardial grafts. How these EAs arise though during early engraftment remains unclear. In a series of in silico experiments, we probed the origin of EAs—exploring aspects of altered impulse formation and altered impulse propagation within nascent PSC-CM grafts and at the host-graft interface. To account for poor gap junctional coupling during early PSC-CM engraftment, the voltage dependence of gap junctions and the possibility of ephaptic coupling were incorporated. Inspired by cardiac development, we also studied the contributions of another feature of immature PSC-CMs, circumferential sodium channel (NaCh) distribution in PSC-CMs. Ectopic propagations emerged from nascent grafts of immature PSC-CMs at a rate of <96 bpm. Source-sink effects dictated this rate and contributed to intermittent capture between host and graft. Moreover, ectopic beats emerged from dynamically changing sites along the host-graft interface. The latter arose in part because circumferential NaCh distribution in PSC-CMs contributed to preferential conduction slowing and block of electrical impulses from host to graft myocardium. We conclude that additional mechanisms, in addition to focal ones, contribute to EAs and recognize that their relative contributions are dynamic across the engraftment process.

Catheter Ablation of Ventricular Tachycardia Guided by Substrate Electrical Inexcitability.

Catheter Ablation of Ventricular Tachycardia Guided by Substrate Electrical Inexcitability.

The radiofrequency interference on CRT-D functioning during AV node ablation: An educational case.

We have described some unusual findings of radiofrequency interference with ICD functioning during AV nodal ablation, guiding the reader to the possible explanation of the phenomena.

Stochastic modelling and analysis of harvesting model: Application to "summer fishing moratorium" by intermittent control

As we all know, summer fishing moratorium is an internationally recognized management measure of fishery, which can protect stock of fish and promote the balance of marine ecology. In this paper, control is used to simulate this management strategy, which is the first attempt in theoretical analysis and the intermittence fits perfectly the moratorium. As an application, a stochastic two-prey one-predator Lotka-Volterra model with intermittent capture is considered. Modeling ideas and analytical skills in this paper can also be used to other stochastic models. In order to deal with intermittent capture in stochastic model, a new time-averaged objective function is proposed. Besides, the corresponding optimal harvesting strategies are obtained by using the equivalent method (equivalency between time-average and expectation). Theoretical results show that intermittent capture can affect the optimal harvesting effort, but it cannot change the corresponding optimal time-averaged yield, which are accord with observations. Finally, the results are illustrated by practical examples of marine fisheries and numerical simulations.

Relationship between left atrium catheter contact force and pacing threshold.

The purpose of this study is to analyze the relationship between contact force (CF) and pacing threshold in left atrium (LA). Six to ten LA sites were studied in 28 consecutive patients with atrial fibrillation undergoing pulmonary vein isolation. Median CF, bipolar and unipolar electrogram voltage, impedance, and bipolar and unipolar thresholds for consistent constant capture and for consistent intermittent capture were measured at each site. Pacing threshold measurements were performed at 188 LA sites. Both unipolar and bipolar pacing thresholds correlated significantly with median CF; however, unipolar pacing threshold correlated better (unipolar: Pearson R -0.45; p<0.001; Spearman Rho -0.62; p<0.001, bipolar: Pearson R -0.39; p<0.001; Spearman Rho -0.52; p<0.001). Consistent constant capture threshold had better correlation with median CF than consistent intermittent capture threshold for both unipolar and bipolar pacing (Pearson R -0.45; p<0.001 and Spearman Rho -0.62; p<0.001 vs. Pearson R -0.35; p<0.001; Spearman Rho -0.52; p<0.001). The best pacing threshold cutoff point to detect a good CF (>10g) was 3.25mA for unipolar pacing with 69% specificity and 73% sensitivity. Both increased to 80% specificity and 74% sensitivity for sites with normal bipolar voltage and a pacing threshold cutoff value of 2.85mA. Pacing thresholds correlate with CF in human not previously ablated LA. Since the combination of a normal bipolar voltage and a unipolar pacing threshold <2.85mA provide reasonable parameters of validity, pacing threshold could be of interest as a surrogate for CF in LA.

Intermittent Capture of the Left Bundle With Permanent His Bundle Pacing: Mechanistic Insights and Implications for an Emerging Field.

We present a case of a patient with elevated His lead capture thresholds and intermittent recruitment of the left bundle. The patient underwent a noninvasive electrophysiology study and was determined to have a left bundle branch block due to postrepolarization refractoriness. The nature of bundle branch block can have important implications for optimal patient selection and device programming in the emerging field of His bundle pacing.

Intermittent capture of the right ventricular outflow tract by atrial pacing in a patient with a dual-chamber pacemaker

We describe a previously unreported phenomenon of intermittent outflow right ventricular tract capture from the atrial lead of a dual-chamber pacemaker. This was more obvious at slower paced atrial rates and disappeared by decreasing the atrial pulses voltage. Electroanatomical mapping showed that the onset of activation was nearly simultaneous at the insertion site of the atrial lead and at an intermediate level of the right ventricular outflow tract. This exceptional finding might be erroneously diagnosed as due to pseudo-pseudo fusion beats.

Kinetics of Atrial Repolarization Alternans in a Free‐Behaving Ovine Model

Kinetics of Atrial Repolarization Alternans. Repolarization alternans (Re-ALT), a beat-to-beat alternation in action potential repolarization, promotes dispersion of repolarization, wavebreaks, and reentry. Recently, Re-ALT has been shown to play an important role in the transition from rapid pacing to atrial fibrillation (AF) in humans. The detailed kinetics of atrial Re-ALT, however, has not been reported so far. We developed a chronic free-behaving ovine pacing model to study the kinetics of atrial Re-ALT as a function of pacing rate. Thirteen sheep were chronically implanted with 2 pacemakers for the recording of broadband right atrial unipolar electrograms and delivery of rapid pacing protocols. Beat-to-beat differences in the atrial T-wave apex amplitude as a measure of Re-ALT and activation time were analyzed at incremental pacing rates until the effective refractory period (ERP) defined as stable 2:1 capture. Atrial Re-ALT appeared intermittently but without periodicity, and increased in amplitude as a function of pacing rate until ERP. Intermittent 2:1 atrial capture was observed at pacing cycle lengths 40 ms above ERP, and increased in duration as a function of pacing rate. Episodes of rapid pacing-induced AF were rare, and were preceded by Re-ALT or complex oscillations of atrial repolarization, but without intermittent capture. We show in vivo that atrial Re-ALT developed and increased in magnitude with rate until stable 2:1 capture. In rare instances where capture failure did not occur, Re-ALT and complex oscillations of repolarization surged and preceded AF initiation. (J Cardiovasc Electrophysiol, Vol. 23, pp. 1003-1012, September 2012).

254 Comparison of Chest Position and Distance to the Heart in the Induction of Cardiac Stimulation From an Electronic Control Device Using Steel versus Carbon Fiber Darts in Pigs

254 Comparison of Chest Position and Distance to the Heart in the Induction of Cardiac Stimulation From an Electronic Control Device Using Steel versus Carbon Fiber Darts in Pigs

Severely malfunctioning defibrillator with cardiac resynchronization therapy showing no abnormalities during testing with the programming head in place

In June 2005, a 78-year-old man with complete AV block and junctional escape rhythm in the setting of idiopathic cardiomyopathy with NYHA class III symptoms underwent a pectoral implantation of a Model InSync Maximo 7303 (Medtronic, Inc., Minneapolis, MN, USA) dual chamber implantable cardioverter defibrillator with cardiac resynchronization therapy (CRT-D). The LV lead was placed in the great cardiac vein. In June 2007 at a clinic visit, the Cardiac Compass Trends Report showed that an abrupt change had taken place on 1 December 2006 (see August 2007 Cardiac Compass Trends Report, Figure 1 ). From only a few per cent previously, atrial pacing was now 100%, resulting in DDD pacing at a constant rate of 60 bpm, and based upon the activity indicator, a decline in patient activity. The patient was complaining of fatigue and dyspnoea on exertion, but no dizziness or syncope. A decision to turn rate responsiveness on resulted in a return to the previous level of physical activity and an increase in the heart rate as evidence of at least intermittent ventricular capture. The daily automatic impedance measurements were all normal and stable, but there were no P wave amplitude measurements after 1 December 2006. Whether atrial pacing (competing with spontaneous sinus rhythm) was intermittently captured …

Metabolic Cardiomyopathy and Mitochondrial Disorders in the Pediatric Intensive Care Unit

ur patient, a 10 year-old boy with a past medical history significant for Pearson’s anemia, Addison’s disease, retinitis pigmentosa, ataxia, and sensorineural hearing loss, came to the pediatric intensive care unit with cardiogenic shock. He was born at 34 weeks gestational age with an uneventful delivery and had mild developmental delay. There was o family history for cardiac or genetic abnormalities. Pearson’s anemia was diagnosed when he was 4 months old, and he equired chronic transfusion therapy and monthly erythropoietin injections until age 3 years, when his disorder went into pontaneous remission. When he was 4 years old, Addison’s disease was diagnosed after a hospitalization for diarrhea and yponatremia. With the exception of an appendectomy for acute appendicitis, he had no other surgical history. His home edications included sodium bicarbonate, magnesium, calcium, potassium, enalapril, and spironolactone for his renal disorder; e was maintained on physiologic doses of prednisone for his Addison’s disease. On the day of admission, he was found unresponsive in his bed with labored breathing and generalized pallor. Paramedics ound the child unresponsive to painful stimuli. Rhythm strip revealed bradycardia and complete heart block. He was started on n isoproterenol infusion because of bradycardia and was then transported to the pediatric intensive care unit. On arrival, he was ound to be tachypneic with a Kussmal breathing pattern and bradycardic. His skin was pale and lips were dry. Results of an bdominal examination were significant for hepatomegaly with liver edge palpable 4 cm below the right costal margin. Capillary efill time was prolonged to 4 seconds with weak distal pulses. His mental status was significant for intermittent moaning, asking or his mother, and requesting water. Mildly enlarged cardiac shadow with bilateral alveolar infiltrates was demonstrated with chest radiography. An electroardiogram was performed (Figure), and moderate left ventricular dilation with reduced systolic function and mild tricuspid and itral valve regurgitation were demonstrated. Laboratory evaluation results were significant for arterial blood gas pH of 7.22, aCO2 5.2 torr, with a base deficit of 25. The serum chemistry results showed a serum bicarbonate level of 5.3 mEq/L, a lucose level of 245 mg/dL, a lactate level of 12 meq/L, and an ammonia level of 53 mol/L. Urine testing results were positive or ketones and glucose. The results of the remainder of laboratory studies, including complete blood count, liver enzymes, ilirubin, and coagulation studies, were normal. In the next several hours, he progressed to respiratory failure from pulmonary edema, requiring intubation and mechanical entilation. He was started on stress-dose steroids because of home steroid use and multiple inotropic agents to augment cardiac utput. Transcutaneous pacing was attempted, and intermittent capture was achieved at ventricular rates of 80, 90, and 100 beats er minute; however, there was no significant improvement in his hemodynamic condition. With further titration of his cardiac edications, including isoproterenol, milrinone, epinephrine, and dobutamine, his heodynamics improved in the subsequent 24 hours of hospitalization. Temporary transvenous ventricular pacing was initiated, which facilitated weaning off ll inotropes, and he was successfully extubated. Coenzyme Q10 and carnitine supplementaions were added, and a muscle biopsy was sent for mitochondrial analysis. Despite being etabolically stable, he remained in complete heart block, requiring placement of a permanent ransvenous dual-chamber pacemaker. His home medications were resumed, and he was ischarged to home at his neurologic baseline.

Surgical Electrocautery and the Runaway Pacemaker Syndrome

A case of a unipolar surgical electrocautery-induced runaway pacemaker is described. The single chamber ventricular pacemaker began firing at 140 beats/min with intermittent capture and the abnormal rhythm persisted after cessation of the electrocautery. Emergent explanation of the pulse generator was required.

A Quantitative Review of the Performance of Implanted Cardiac Pacemakers, Medtronic Model No. 5944

One of the service functions of the Sir Charles Gairdner Hospital Department of Biophysics since 1972 has been the routine performance testing of pacemakers implanted by the Hospital's Cardiologists. This service was set up to measure pacemaker pulse parameters with a view to detecting battery depletion. It was also found to be of great help in showing lead insulation deterioration, intermittent capture and movement of the catheter tip within the right ventricle, information that is frequently of help to the Cardiologists in planning acute or elective pacemaker replacement.