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Biomedical subjects

Richard Derksen

Publications and source records attributed to Richard Derksen.

10 recordsLinked to original sources
PubMed2006

Delayed paced ventricular activation in the long QT syndrome is associated with ventricular fibrillation.

BACKGROUND: LQTS may cause sudden cardiac death (SCD), but the mechanisms linking gene mutations to ventricular fibrillation (VF) are unclear. OBJECTIVE: To determine whether ventricular activation delays in congenital long QT syndrome (LQTS) are associated with VF and to describe these delays clinically by measuring activation through ventricular myocardium after a premature extrastimulus. METHODS: Forty-six patients with LQTS, including 16 with VF (LQTS VF) were investigated, and the results were compared with those from 24 patients with hypertrophic cardiomyopathy and VF (HCM VF). Electrograms in response to premature stimuli were analyzed for increases in electrogram duration (DeltaED) and the S1S2 coupling intervals at which electrogram latency starts to increase (S1S2(delay)). Two piecewise continuous straight line segments were fitted to the last electrogram deflection as a function of S1S2 interval in the LQTS and HCM VF populations, and the difference in their gradient (alpha) was taken as an index of the abruptness of the onset of this delay. RESULTS: Thirteen LQTS VF and six LQTS non-VF patients had values of DeltaED and S1S2(delay) comparable to those in HCM VF patients, while the remainder (three LQTS VF and 24 LQTS non-VF) had lower values (P<.001). There was only a weak correlation between delay and the corrected QT interval. The HCM and LQTS VF patients could be separated by the value of alpha (P<.01), with the LQTS patients having a more abrupt onset of delay. CONCLUSIONS: Large delays in ventricular activation after an extrastimulus occur in patients with the LQTS, especially those with VF. The change in delay is abrupt in the LQTS, indicating sudden block to activation creating a dynamic substrate for arrhythmogenesis.

Adolescent↗
PubMed2005

Where to draw the mitral isthmus line in catheter ablation of atrial fibrillation: histological analysis.

AIMS: A linear lesion between the left inferior pulmonary vein orifice and mitral annulus, the so-called mitral isthmus, may improve the success of catheter ablation for atrial fibrillation. Gaps in the lesion line, however, may facilitate left atrial flutter. The aim of the study was to determine the optimal location of the lesion line by serial sectioning of the isthmus area. METHODS AND RESULTS: In a post-mortem study of 16 patients with normal left atria, serial sections of the isthmus area from 10 mm superior to and 30 mm inferior to the isthmus were studied by light microscopy. The length of the isthmus was 35+/-7 mm. On average, the muscle sleeve around the coronary sinus ended 10 mm inferior to the isthmus. The prevalence of a ramus circumflexus <5 mm from the endocardial surface, decreased from 60% in the most superior section to 0% in the most inferior section. Atrial arteries were frequently present in all sections. CONCLUSIONS: The thickness of atrial myocardium, the ramus circumflexus sometimes very close to the endocardium, a myocardial sleeve around the coronary sinus, and local cooling by atrial arteries and veins may complicate the creation of conduction block in the mitral isthmus.

Atrial Fibrillation↗
PubMed2004

ICD: a qualitative study of patient experience the first year after implantation.

BACKGROUND: The experiences of how patients live with an implantable cardioverter defibrillator are still poorly understood. Only a few qualitative studies have investigated this phenomenon. This paper was undertaken as part of a larger project to evaluate quality of life and psychological well-being in those survivors of cardiac arrest who have received an implantable cardioverter defibrillator. AIMS AND OBJECTIVES: The aim of this qualitative study was to explore how implantable cardioverter defibrillator recipients perceive their lives during the first year after implantation of the device. METHODS: A sample of 21 patients who received an implantable cardioverter defibrillator was interviewed during three consecutive periods: one, six and 12 months postdischarge from the hospital. The semi-structured interviews were based on insights gained from a literature review. The transcripts were subjected to content analysis. RESULTS: Analysis of the data revealed seven major categories: physical deterioration, cognitive changes, perceived social support, dependency, contact with the doctor, confrontation with mortality and uncertainty surrounding having a shock. Anxiety, uncertainty, disappointment, frustration, unexpected barriers, acceptance of and dependency on the implantable cardioverter defibrillator played a major role in the lives of implantable cardioverter defibrillator recipients. Well-being improved throughout the year. During the first months after discharge from the hospital the focus was on regaining physical health. During the early postimplantation period both the implantable cardioverter defibrillator recipient and family members had adapted to the situation. Reflection on the impact and consequences of the cardiac arrest was reported more often in the late postimplantation period. CONCLUSIONS: Content analysis is a resourceful approach giving answers to questions that have hardly been addressed within the domain of cardiology. Implantable cardioverter defibrillator recipients face a complex first year, especially the first 6 months. Cognitive deterioration and confrontation with mortality are problems that need to be researched further. RELEVANCE TO CLINICAL PRACTICE: Caregivers are able to explain to future patients what they can expect in the first year after implantation. Caregivers may become more receptive to physical, psychological and social limitations and to emotional and social problems that occur in implantable cardioverter defibrillator recipients, enabling them to act upon them.

Adult↗
PubMed2004

A geometric model of mortality and crop protection for insects feeding on discrete toxicant deposits.

Current theory governing the biological effectiveness of toxicants stresses the dose-response relationship and focuses on uniform toxicant distributions in the insect's environment. However, toxicants are seldom uniformly dispersed under field conditions. Toxicant distribution affects bioavailability, but the mechanics of such interactions is not well documented. We present a geometric model of the interactions between insects and heterogeneously distributed toxicants. From the model, we conclude the following: 1) There is an optimal droplet size, and droplets both smaller and larger than this optimum will decrease efficacy. 2) There is an ideal droplet distribution. Droplets should be spaced based on two criteria: calculate the allowable damage, double this quantity, and one lethal deposit should be placed in this area; and define the quantity of leaf the larva could eat before the toxicant decays below the lethal level and place one lethal deposit within this area. 3) Distributions of toxicant where deposits are sublethal will often be ineffective, but the application is wasteful if deposits contain more than a lethal dose. 4) Insect behavior both as individuals and collectively influences the level of crop production provided by an application. This conclusion has implications for both crop protection and natural plant-insect interactions. The effective utilization of new more environmentally sensitive toxicants may depend on how well we understand how heterogeneous toxicant distributions interact with insect behavior to determine the biological outcome.

Animals↗
PubMed2003

Tissue discontinuities affect conduction velocity restitution: a mechanism by which structural barriers may promote wave break.

BACKGROUND: The mechanism by which structural barriers promote wave break and fibrillation is unclear. Conduction velocity (CV) restitution is an important determinant of wave break. Abnormal CV restitution is associated with ventricular fibrillation in patients with heart disease and arises preferentially in fibrotic myocardium. We hypothesize that tissue discontinuities imposed by structural barriers cause abnormal CV restitution. METHODS AND RESULTS: Tissue discontinuities were simulated in cultures of neonatal rat heart cells grown in 8-armed star patterns. Premature stimulation was applied at the extremity of 1 arm (n=12) while extracellular electrograms were recorded at 24 sites throughout the star. Action potentials were recorded at the following 3 sites: in the stimulated arm and at the discontinuity both proximal to and distal from the star center. Extracellular recordings revealed progressive increases in activation delay (indicative for abnormal CV restitution) only at the discontinuity from arms proximal to the star center. The mean increase in delay was 0.81+/-0.41 ms/10 ms for recording sites proximal to and 3.13+/-0.58 ms/10 ms for sites distal from this discontinuity. Depolarizing currents were determined in single cells during premature stimulation and for voltage configurations similar to those arising at the discontinuity. Both voltage-clamp measurements and computer simulations showed that delay at the discontinuity was associated with biphasic, prolonged activation and delayed inactivation of depolarizing current. CONCLUSIONS: Tissue discontinuities cause abnormal CV restitution. Rapid increase in activation after an initial slow activation and delayed inactivation at the discontinuity lengthen the duration of depolarizing current and cause the abnormal restitution.

Action Potentials↗
PubMed2003

Sudden death in noncoronary heart disease is associated with delayed paced ventricular activation.

BACKGROUND: Slowed or delayed myocardial activation and dispersed refractoriness predispose to reentrant excitation that may lead to ventricular fibrillation (VF). Increased ventricular electrogram duration (DeltaED) in response to extrastimuli and increased S1S2 coupling intervals at which electrogram duration starts to increase (S1S2delay) are seen both in hypertrophic cardiomyopathy (HCM) in those at risk of VF and in patients with idiopathic VF (IVF). METHODS AND RESULTS: DeltaED and S1S2delay have been measured using paced electrogram fractionation analysis in 266 patients with noncoronary heart disease. Of these, one group of 61 patients had a history of VF and included 21 HCM, 17 IVF, 13 long-QT syndrome (LQTS), 5 dilated cardiomyopathy (DCM), and 5 others. These were compared with 205 patients with similar diseases with no VF history (non-VF group) and a control group (n=12) without heart disease. Results from HCM VF patients (DeltaED, 19+/-3.3 ms; S1S2delay, 350+/-9.7 ms) differed sharply from observations in HCM non-VF patients (DeltaED, 7.3+/-1.35 ms; S1S2delay, 312+/-6.7 ms; P<0.001). DCM VF patients had longer delays (DeltaED, 14.3+/-5.9; S1S2delay, 344+/-11.2) than DCM non-VF patients (DeltaED, 5.8+/-1.87 ms; S1S2delay, 311+/-5.7 ms; P<0.001), with major differences also seen comparing LQTS VF (DeltaED, 12.4+/-5.3 ms; S1S2delay, 343+/-13.8 ms) and LQTS non-VF patients (DeltaED, 11.0+/-2.7 ms; S1S2delay, 320+/-5.4 ms; P<0.001). IVF patients had both severely abnormal and normal areas of myocardium. CONCLUSIONS: Slowed or delayed myocardial activation is a common feature in patients with noncoronary heart disease with a history of VF, and its assessment may allow the prospective prediction of VF risk in these patients.

Cardiac Pacing, Artificial↗
PubMed2003

Pulmonary vein ostium geometry: analysis by magnetic resonance angiography.

BACKGROUND: During a catheter ablation procedure for selective electrical isolation of pulmonary vein (PV) ostia, the size of these ostia is usually estimated using fluoroscopic angiography. This measurement may be misleading, however, because only the projected supero/inferior ostium diameters can be measured. In this study, we analyzed 3-dimensional magnetic resonance angiographic (MRA) images to measure the minimal and maximal cross-sectional diameter of PV ostia in relation to the diameter that would have been projected on fluoroscopic angiograms during a catheter ablation procedure. METHODS AND RESULTS: In 42 patients with idiopathic atrial fibrillation who were scheduled for selective electrical isolation of PV ostia, the minimal and maximal diameters of these ostia were measured from 3-dimensional MRA images. Thereafter, these images were oriented in a 45 degrees right or left anterior oblique direction and the projected diameter of the PV ostia were measured again. The average ratio between maximal and minimal diameter was 1.5+/-0.4 for the left and 1.2+/-0.1 for the right pulmonary vein ostia. Because of the orientation and oval shape of especially the left pulmonary vein ostia, their minimal diameters were significantly smaller than the projected diameters. CONCLUSION: Pulmonary vein ostia, especially those at the left, are oval with the short axis oriented approximately in the antero/posterior direction. Consequently, PV ostia may sometimes be very narrow despite a rather normal appearance on angiographic images obtained during a catheter ablation procedure.

Atrial Fibrillation↗
PubMed2003

Radiofrequency catheter ablation of junctional ectopic tachycardia with preservation of atrioventricular conduction.

Junctional ectopic tachycardia is a relatively rare disorder, frequently refractory to drug therapy, and with a poor prognosis in childhood. This report describes a successful radiofrequency catheter ablation of the focus of this arrhythmia in a 9-year-old girl with preservation of normal atrioventricular conduction, using precise catheter navigation with the LocaLisa system and carefully titrated RF delivery.

Atrioventricular Node↗