Thomas S. Klitzner

Cardiovascular health supervision for individuals affected by duchenne or becker muscular dystrophy

Duchenne muscular dystrophy is the most common and severe form of the childhood muscular dystrophies. The disease is typically diagnosed between 3 and 7 years of age and follows a predictable clinical course marked by progressive skeletal muscle weakness with loss of ambulation by 12 years of age. Death occurs in early adulthood secondary to respiratory or cardiac failure. Becker muscular dystrophy is less common and has a milder clinical course but also results in respiratory and cardiac failure. The natural history of the cardiomyopathy in these diseases has not been well established. As a result, patients traditionally present for cardiac evaluation only after clinical symptoms become evident. The purpose of this policy statement is to provide recommendations for optimal cardiovascular evaluation to health care specialists caring for individuals in whom the diagnosis of Duchenne or Becker muscular dystrophy has been confirmed.

Developmental changes in membrane Ca2+ and K+ currents in fetal, neonatal, and adult rabbit ventricular myocytes

Whole-cell calcium current (ICa) and inwardly rectifying potassium current (IK1) were studied in 21-day fetal, 28-day fetal (total gestation, 31 days), 2-5-day neonatal, and adult rabbit ventricular myocytes isolated by enzymatic dissociation. Whole-cell peak ICa and IK1 at -100 mV increased significantly after birth. Cell size approximated from cell membrane capacitance also increased with age, with the most significant increase occurring after birth. When normalized to cell surface area, peak ICa density increased from day 21 of gestation to the neonate and then increased again from neonate to adult. In all age groups, peak ICa occurred at a test potential of +10 mV, and the shape of the Ca2+ current-voltage relation did not change with age. These findings suggest that there are no significant developmental changes in the voltage dependence of ICa. Therefore, the measured age-related increase in Ca2+ current density may result from increased channel expression. IK1 also exhibited a pattern of increasing current density with age. For IK1, the increase in current density was most rapid between day 21 and the perinatal period and much slower after birth. These results demonstrate that ICa and IK1 undergo significant changes during late fetal and postnatal development.

Fractionated endocardial electrograms are associated with slow conduction in humans: evidence from pace-mapping.

Fractionated ventricular electrograms recorded during catheter mapping may arise from areas of asynchronous depolarization associated with slow conduction, the substrate for reentrant ventricular tachycardia, but can also be a nonspecific abnormality or even artifact. To determine whether fractionated sinus rhythm electrograms are associated with slow conduction in humans, the results of endocardial catheter mapping and pacing at 133 endocardial sites in 13 patients were analyzed. Eleven patients had sustained monomorphic ventricular tachycardia and two patients had old myocardial infarction without ventricular tachycardia. Functional evidence of slow conduction at the recording site was assessed by pacing at that site and measuring the interval between the stimulus artifact (S) and the onset of the QRS complex in the 12 lead electrocardiogram (ECG). During pacing at 89 of 90 sites without fractionated sinus rhythm electrograms, the S-QRS interval was less than 40 ms, a value consistent with rapid propagation of the stimulated wave front away from the pacing site. During pacing at 21 (49%) of 43 sites with fractionated sinus rhythm electrograms, the S-QRS interval was greater than 40 ms (range 40 to 140), consistent with slow conduction at the pacing site (p less than 0.001 versus nonfractionated sites). In 9 of the 11 patients with ventricular tachycardia analysis of the paced QRS configuration, electrograms during induced ventricular tachycardia or programmed stimulation during tachycardia suggested that a site with a long S-QRS interval during pacing was located at or near a ventricular tachycardia circuit. Therefore, fractionated sinus rhythm electrograms are often associated with slow conduction, which may be the substrate for reentrant ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Databases for assessing the outcomes of the treatment of patients with congenital and paediatric cardiac disease - the perspective of cardiology

This review includes a brief discussion, from the perspective of cardiac surgeons, of the rationale for creation and maintenance of multi-institutional databases of outcomes of congenital heart surgery, together with a history of the evolution of such databases, a description of the current state of the art, and a discussion of areas for improvement and future expansion of the concept. Five fundamental areas are reviewed: nomenclature, mechanism of data collection and storage, mechanisms for the evaluation and comparison of the complexity of operations and stratification of risk, mechanisms to ensure the completeness and accuracy of the data, and mechanisms for expansion of the current capabilities of databases to include comparison and sharing of data between medical subspecialties. This review briefly describes several European and North American initiatives related to databases for pediatric and congenital cardiac surgery the Congenital Database of The European Association for Cardio-Thoracic Surgery, the Congenital Database of The Society of Thoracic Surgeons, the Pediatric Cardiac Care Consortium, and the Central Cardiac Audit Database in the United Kingdom. Potential means of approaching the ultimate goal of acquisition of long-term follow-up data, and input of this data over the life of the patient, are also considered.

Development of a pediatric cardiology quality improvement collaborative: From inception to implementation. From the joint council on congenital heart disease quality Improvement task force

While clinical outcomes in pediatric cardiac disease have improved in recent years, marked institutional and individual cardiology practice variability exists. Quality improvement science has demonstrated that reducing process variation leads to more favorable outcomes, safer practices, cost savings, and improved operating efficiency. This report describes the process undertaken to develop the first collaborative quality improvement project of the Joint Council on Congenital Heart Disease. The project chosen aims to reduce mortality and improve the quality of life of infants with hypoplastic left heart syndrome during the interstage period between discharge from the Norwood procedure and admission for the bidirectional Glenn procedure. The objective of this special article is to inform the pediatric cardiology and cardiac surgery communities of the project to help ensure that the early work by the project pilot participants will spread to clinicians caring for children with cardiovascular disease. It is anticipated that this project will add to our understanding of care for this challenging group of children with hypoplastic left heart syndrome, identifying clinical care changes with the potential to lead to improvements in outcome. It will also introduce the field of pediatric cardiology to the science of collaborative quality improvement and assist in reducing clinical process variation and improving patient outcomes across centers. Finally, it will establish an ongoing network of pediatric cardiologists and their teams linked through a longitudinal data set and collaboration for improvement and research.

Patient- and Family-Centered Care Coordination: A Framework for Integrating Care for Children and Youth Across Multiple Systems

Understanding a care coordination framework, its functions, and its effects on children and families is critical for patients and families themselves, as well as for pediatricians, pediatric medical subspecialists/surgical specialists, and anyone providing services to children and families. Care coordination is an essential element of a transformed American health care delivery system that emphasizes optimal quality and cost outcomes, addresses family-centered care, and calls for partnership across various settings and communities. High-quality, cost-effective health care requires that the delivery system include elements for the provision of services supporting the coordination of care across settings and professionals. This requirement of supporting coordination of care is generally true for health systems providing care for all children and youth but especially for those with special health care needs. At the foundation of an efficient and effective system of care delivery is the patient-/family-centered medical home. From its inception, the medical home has had care coordination as a core element. In general, optimal outcomes for children and youth, especially those with special health care needs, require interfacing among multiple care systems and individuals, including the following: medical, social, and behavioral professionals; the educational system; payers; medical equipment providers; home care agencies; advocacy groups; needed supportive therapies/services; and families. Coordination of care across settings permits an integration of services that is centered on the comprehensive needs of the patient and family, leading to decreased health care costs, reduction in fragmented care, and improvement in the patient/family experience of care.

Developmental changes in cardiac myocyte calcium regulation.

Developmental changes in the contributions of transsarcolemmal Ca2+ influx and Ca2+ release from intracellular storage sites to myocardial contraction were evaluated in isolated ventricular myocytes from neonatal (aged 1-7 days) and adult (aged 8-10 weeks) New Zealand White rabbits. Contractions ceased in one beat when extracellular Ca2+ was decreased from 1mM to micromolar levels using a rapid perfusion technique. On reperfusion with 1 mM Ca2+, recovery of control contraction amplitude occurred after significantly fewer beats in neonatal myocytes compared with adult myocytes, and after 1 minute compared with 5 minutes of reduced Ca2+. After 15 minutes of perfusion with either 1 or 10 microM ryanodine, contraction amplitude decreased in both age groups, but the decrease was significantly greater in adults than in neonates. These experiments indicate that isolated ventricular myocytes may be used in the study of developmental changes in intracellular Ca2+ regulation. Results suggest that cardiac contraction in neonates is relatively more dependent on transsarcolemmal Ca2+ influx. Furthermore, although Ca2+ release from intracellular storage sites is present in both neonates and adults, its role in cardiac contraction is more significant in adults.

Anatomic and electrophysiologic relation between the coronary sinus and mitral annulus: Implications for ablation of left-sided accessory pathways

To determine whether precise left-sided accessory pathway localization is possible from the coronary sinus, electrocardiogram (ECG) characteristics from the coronary sinus pair demonstrating earliest activation via the accessory pathway were compared to simultaneous mitral annular ablation catheter ECGs at successful ablation sites in 48 patients. To define the coronary sinus-mitral annular relation, the coronary sinus to mitral annulus distance (D) was measured at sequential distances from the coronary sinus os in 10 cadaver hearts. Mitral annular ECGs demonstrated earliest activation via the accessory pathway more frequently than the earliest coronary sinus pair (p < 0.001), more frequent continuous electrical activity (p < 0.001), and more frequent accessory pathway potentials (p < 0.01). D was >10 mm at 20, 40, and 60 mm, respectively, from the coronary sinus os. Coronary sinus ECGs do not precisely localize left-sided accessory pathways, which may be due in part to an average anatomic separation of more than 10 mm between the coronary sinus and accessory pathways bridging the mitral annulus.

Resetting of ventricular tachycardia: Implications for localizing the area of slow conduction

Analysis of local endocardial electrograms recorded during reentrant ventricular tachycardia does not provide direct information as to the participation of the recording site in the tachycardia circuit. To determine if programmed electrical stimulation at the recording site can assist in localizing areas of slow conduction that are participating in the tachycardia circuit, seven patients with sustained monomorphic ventricular tachycardia were studied. The cardiac cycle was scanned with single stimuli delivered during ventricular tachycardia at multiple endocardial sites. In four patients, an endocardial site was identified at which stimuli advanced the tachycardia with marked conduction delay and without alteration of the ventricular activation sequence, as indicated by a lack of change in the configuration of the QRS complex and endocardial electrograms distant from the stimulation site. This finding was seen only during stimulation at sites displaying abnormal electrograms and is consistent with premature depolarization of an area of slow conduction within the tachycardia focus by stimuli delivered at or near that area. Attempted endocardial catheter ablation at or adjacent to these sites in three patients was followed by persistent noninducibility of ventricular tachycardia in one patient, marked modification of the configuration and cycle length of inducible tachycardia in one patient and transient noninducibility of tachycardia in one patient. Programmed electrical stimulation during ventricular tachycardia at sites with abnormal electrograms may provide information about the proximity of the stimulation site to the tachycardia circuit.

Developmental cardiac electrophysiology. Recent advances in cellular physiology

This overview of cardiac ion channel development does not suggest any particular theme underlying the expression or regulation of all channel subtypes. Calcium and potassium channels generally exhibit increased expression in more mature hearts. However, this increase in channel number or activity as determined under voltage clamp conditions may not be translated into increased activity in vivo. Concomitant changes in other physiological factors such as local intracellular Ca2+ accumulation, increased resting membrane potential and decreased heart rate in mature heart may inhibit or augment channel activity. Na(+)-Ca2+ exchange activity appears to decrease with development, possibly reflecting its decreasing role in both systolic and diastolic Ca2+ regulation. Na+ channel activity follows a middle course, exhibiting little change in channel conductance. The reported shift in the voltage dependence of channel inactivation toward more negative membrane potentials may reflect a concomitant shift in the resting membrane potential in mature heart. However, this change is in the direction opposite to that reported for L-type Ca2+ channel inactivation, suggesting that the regulation of these channels is not modulated by a common factor such as membrane surface charge. A detailed characterization of multiple channel subtypes in mature myocardium has resulted in significant advances in models of the cardiac action potential and excitation-contraction coupling. Recently, developmental changes in ion channel physiology have been described, setting the stage for a comparable elucidation of the ontogeny of the cardiac action potential. Ca2+ and K+ channel currents generally become more prominent with development. In contrast, developmental changes in Na+ currents are less dramatic and Na(+)-Ca2+ exchange currents appear to decrease with age. These changes may, in part, be reflected by the increasingly important role of transsarcolemmal Ca2+ influx in triggering Ca2+ release from the SR in mature heart as compared to its direct role of providing Ca2+ for cell contraction in immature heart. These developmental changes in ion channel expression and function are likely to have a significant effect on the generation of the action potential in individual myocytes. Developmental changes in the characteristics of the action potential may then have a major influence on the initiation, propagation and termination of autonomic, triggered, and re-entrant arrhythmias. Progress in this area provides an essential foundation for the evolution of a systematic approach to pediatric arrhythmias comparable to that under development for mature heart [3].