Identifying Features of Cardiac Disease Phenotypes Based on Mechanical Function in a Catecholaminergic Polymorphic Ventricular Tachycardia Model.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is characterized by an arrhythmogenic mechanism involving disruption of calcium handling. This genetic disease can lead to sudden death in children and young adults during physical or emotional stress. Prior CPVT studies have focused on calcium handling, but mechanical functionality has rarely been investigated in vitro. In this research we combine stem cell-derived cardiomyocytes from a CPVT patient (RyR2-H2464D mutation) and a healthy familial control with an engineered culture platform to evaluate mechanical function of cardiomyocytes. Substrates with Young's modulus ranging from 10 to 50 kPa were used in conjunction with microcontact printing of ECM proteins into defined patterns for subsequent attachment. Digital Image Correlation (DIC) was used to evaluate collections of contracting cells. The amplitude of contractile strain was utilized as a quantitative indicator of functionality and disease severity. We found statistically significant differences: the maximum contractile strain was consistently higher in patient samples compared to control samples on all substrate stiffnesses. Additionally, the patient cell line had a statistically significantly slower intrinsic contraction rate than the control, which agrees with prior literature. Differences in mechanical strain have not been previously reported, and hypercontractility is not a known characteristic of CPVT. However, functional changes can occur as the disease progresses, thus this observation may not represent behavior observed in adolescent and adult patients. These results add to the limited studies of mechanical function of CPVT CMs reported in literature and identify functional differences that should be further explored.

Pediatric digital echocardiography: a study of the analog-to-digital transition.

Limited information is available that describes the practical conversion of a pediatric echocardiography laboratory from videotape to a primarily digital format. To help pediatric echocardiographers begin to make the analog-to-digital transition, we report our pediatric digital acquisition protocol and the acquisition and storage parameters of 1000 unselected, consecutive digitally acquired studies of pediatric patients with known or suspected congenital or acquired heart disease. With the use of our acquisition protocol, a complete normal study requires 46 moving clips and 12 still-frame images. Five hundred consecutive patient studies acquired with "high" JPEG (Joint Photographers Experts Group) compression (group 1) were compared with the next 500 examinations acquired using "medium" JPEG compression (group 2) for number of moving clips, still images, and megabytes of storage space. No intergroup difference was found in the number of moving clips or still images. When JPEG compression was decreased from high to medium, the average clip storage requirement per patient increased, and the number of patients stored per 230-MB magneto optical disk decreased significantly. Non-ECG-triggered timed single-plane clips and still images required significantly more storage space than ECG-triggered single-beat clips and still images. The frequency of multiplane sweeps was.03% and was independent of diagnosis. With the use of high JPEG compression, the digital storage cost per patient was $1.90, which was 6.0 times greater than that for simultaneously recorded 120-minute VHS videotape. Many features of the digital paradigm, including decreased MOD storage space, enhanced serial study comparisons, random image access, and improved image quality, mitigate this cost differential.

The relationship between temperature and calcium in acute cell damage after exposure to radiofrequency or thermal energy in isolated neonatal and adult rabbit cardiac myocytes.

Radiofrequency (RF) ablation is a nonsurgical technique using catheter-directed RF energy for treating cardiac arrhythmias in children and adults. Previous reports have suggested that sequestration of calcium (Ca2+) by the sarcoplasmic reticulum may partially protect mature cardiac myocytes from the effects of RF energy. The purposes of this study were to determine whether differences exist between neonatal and adult myocyte responses to RF energy and if myocyte damage is a Ca2+-dependent process. Because immature myocardium is functionally deficient in sarcoplasmic reticulum, we hypothesized that immature myocytes would be more susceptible to damage induced by RF energy. Isolated ventricular myocytes were obtained from neonatal and adult New Zealand White rabbits by enzymatic dissociation, then placed in a perfusion chamber designed to deliver RF energy or a heated perfusate solution. Measurements of bath temperature, cell morphology, and contractile response to electrical stimuli were recorded. RF energy application associated with increased perfusate temperature resulted in cell death, but not when the temperature rise was inhibited. Thus, the acute damage to cells exposed to RF energy appears to be mediated by thermal energy. After exposure to thermal energy, neonatal cells underwent contracture at lower temperatures than did adult cells. Perfusion with solutions containing low Ca2+ concentrations, comparable to intracellular diastolic Ca2+ levels, had a protective effect for both neonatal and adult myocytes. These findings indicate that acute cell damage after exposure to RF energy is mediated by a Ca2+-dependent process. Furthermore, immature myocardium is particularly susceptible to RF-mediated cell damage, possibly secondary to reduced Ca2+ sequestration by the sarcoplasmic reticulum.