Clinical outcomes and programming strategies of implantable cardioverter-defibrillator devices in paediatric hypertrophic cardiomyopathy: a UK National Cohort Study

AIMS

Sudden cardiac death (SCD) is the most common mode of death in paediatric hypertrophic cardiomyopathy (HCM). This study describes the implant and programming strategies with clinical outcomes following implantable cardioverter-defibrillator (ICD) insertion in a well-characterized national paediatric HCM cohort.

METHODS AND RESULTS

Data from 90 patients undergoing ICD insertion at a median age 13 (±3.5) for primary (n = 67, 74%) or secondary prevention (n = 23, 26%) were collected from a retrospective, longitudinal multi-centre cohort of children (<16 years) with HCM from the UK. Seventy-six (84%) had an endovascular system [14 (18%) dual coil], 3 (3%) epicardial, and 11 (12%) subcutaneous system. Defibrillation threshold (DFT) testing was performed at implant in 68 (76%). Inadequate DFT in four led to implant adjustment in three patients. Over a median follow-up of 54 months (interquartile range 28-111), 25 (28%) patients had 53 appropriate therapies [ICD shock n = 45, anti-tachycardia pacing (ATP) n = 8], incidence rate 4.7 per 100 patient years (95% CI 2.9-7.6). Eight inappropriate therapies occurred in 7 (8%) patients (ICD shock n = 4, ATP n = 4), incidence rate 1.1/100 patient years (95% CI 0.4-2.5). Three patients (3%) died following arrhythmic events, despite a functioning device. Other device complications were seen in 28 patients (31%), including lead-related complications (n = 15) and infection (n = 10). No clinical, device, or programming characteristics predicted time to inappropriate therapy or lead complication.

CONCLUSION

In a large national cohort of paediatric HCM patients with an ICD, device and programming strategies varied widely. No particular strategy was associated with inappropriate therapies, missed/delayed therapies, or lead complications.

Patent Ductus Arteriosus in Extreme Prematurity: Role of Echocar-diography and Other Imaging Techniques

Clinical signs alone are unreliable in the diagnosis of patent ductus arteriosus (PDA) in preterm infants, and therefore echocardiography remains the mainstay of diagnosis of this common condition. Echocardiography also facilitates understanding of the hemodynamic effects of a PDA, and thus aids in management decisions. Several echocardiographic parameters, including duct size, maximum ductal velocity, left atrial: aorta ratio, mitral inflow E:A ratio, and isovolumic relaxation time, have been utilized in the assessment of PDA, but no single measurement can be used in isolation to inform clinical judgement. Therefore, it is important that echocardiographers on the neonatal unit have a comprehensive understanding of available methods and their limitations. Newer echocardiographic techniques, such as 3 Dimensional echocardiography, tissue Doppler imaging and strain imaging, are now providing insights into myocardial function in the adaptation of preterm infants to extra-uterine life, and into the effects of a PDA causing systemic-to-pulmonary artery shunting. Magnetic resonance imaging delivers excellent diagnostic information and accurate hemodynamic evaluation; however this modality is not easily accessible for most preterm infants, in comparison to echocardiography, which is readily available at the cotside in most neonatal units. Further developments in echocardiography may further refine the contribution it makes to individualized clinical decisionmaking in the management of premature infants with PDA.

Thirty-four cases of esophageal perforation: the experience of a district general hospital in the UK

Esophageal perforation is uncommon and traditionally has a high rate of morbidity and mortality. Our aim was to perform a 13-year retrospective review of the cases managed in our district general hospital. Thirty-four cases of esophageal perforation diagnosed between 1995 and 2008 were retrospectively analyzed. There were 20 males and 14 females with a median age of 64 (range 23-86) years. The etiology of the perforations were Boerhaave's syndrome (n= 19), therapeutic endoscopy (n= 9), diagnostic endoscopy (n= 2), gastric lavage injury (n= 1), foreign body (n= 1), blunt chest trauma (n= 1), and spontaneous tumor perforation (n= 1). Only 11 cases (32%) had evidence of surgical emphysema upon examination. In 50% of cases, another clinical diagnosis was initially suspected. Twenty-four were treated surgically and 10 cases managed non-operatively. Surgical treatment included thoracotomy with primary repair (n= 9), T-tube drainage (n= 7), emergency esophagectomy (n= 1), or intra-operative stent insertion (n= 1). Four cases had primary repair and fundal wrap via abdominal approach without thoracotomy. Two patients were treated with washout and drainage only. Eight patients died overall (in-hospital mortality 23.5%). Esophageal perforations are often initially misdiagnosed and the majority do not have surgical emphysema. There are a wide variety of methods to manage esophageal perforation. Management tailored to the location and size of perforation, degree of contamination, and underlying cause appears to result in a reasonable prognosis.

Tumor suppressor p53 is a negative regulator in thyroid hormone receptor signaling pathways

Thyroid hormone nuclear receptors (TRs) are ligand-dependent transcription factors which regulate growth, differentiation, and development. The molecular mechanisms by which TRs mediate these diverse effects are unclear. One emerging hypothesis suggests that TRs could mediate these diverse effects via cooperation with different transcription factors/receptors. Indeed, we have recently shown that the human TR subtype beta1 (h-TRbeta1) interacts with the tumor suppressor p53. p53 is a transcription factor that plays a critical role in cell cycle regulation and tumor development. To assess the physiological relevance of the interaction of h-TRbeta1 with p53, the present study addressed the question as to whether the functions of h-TRbeta1 could be modulated by p53. We first compared the h-TRbeta1-mediated transcriptional activity in two pairs of isogenic cell lines, RKO/RKO E6 and MCF-7/MCF-7 E6. RKO and MCF-7 cells are colon and breast carcinoma cell lines, respectively, that contain p53 but lack TRbeta1. The isogenic RKO E6 and MCF-7 E6 cells are stable clones expressing high levels of papillomavirus type 16 E6 protein. In these cells, the level of p53 protein was lower than the parental cells. The impairment of p53 functions in these E6-containing cells led to an activation of TRbeta1-mediated transcriptional activity. Furthermore, in a growth hormone-producing cell line in which the expression of the growth hormone gene is positively regulated by TRs, overexpression of the wild-type p53 led to repression in the expression of the growth hormone gene. Thus, TRs could cross-talk with p53 in its signaling pathways to regulate gene regulatory functions. The present findings further strengthen the hypothesis that mediation of the pleiotropic effects of T3 requires the cooperation of TRs with a large network of transcription factors.

Modulation of hormone-dependent transcriptional activity of the glucocorticoid receptor by the tumor suppressor p53

The glucocorticoid receptor (GR) is a ligand-dependent transcription factor which regulates growth, development and metabolic functions. To test the hypothesis that the pleiotropic effect of the GR could be mediated by other transcription factors/oncogenes, the present study assessed its interaction with the tumor suppressor p53. p53 is a transcription factor which is involved in cell cycle regulation and apoptosis. We found that the wild-type p53 physically interacted with the GR and repressed the glucocorticoid-dependent transcriptional activity. In contrast, mutant p53 had no or a lesser effect depending on the type of p53 mutant. These findings raised the possibility that p53 may play an important role in modulating the activities of glucocorticoids in cells.

Modulation of the transcriptional activity of thyroid hormone receptors by the tumor suppressor p53

Thyroid hormone nuclear receptors (TRs) are ligand-dependent transcriptional factors that regulate growth, differentiation, and development. The molecular mechanisms by which TRs mediate these effects are unclear. One prevailing hypothesis suggests that TRs may cooperate with other transcriptional factors to mediate their biological effects. In this study, we tested this hypothesis by examining whether the activity of TRs is modulated by the tumor suppressor p53. p53 is a nuclear protein that regulates gene expression via sequence-specific DNA binding and/or direct protein-protein interaction. We found that the human TR subtype beta 1 (h-TR beta 1) physically interacted with p53 via its DNA binding domain. As a result of this physical interaction, binding of h-TR beta 1 to its hormone response elements either as homodimer or as a heterodimer with the retinoic X receptor was inhibited by p53 in a concentration-dependent manner. In transfected cells, wild-type p53 repressed the hormone-dependent transcriptional activation of h-TR beta 1. In contrast, mutant p53 either had no effect or activated the transcriptional activity of h-TR beta 1 depending on the type of hormone response elements. These results indicate the gene regulating activity of TRs was modulated by p53, suggesting that the cross talk between these two transcriptional factors may play an important role in the biology of normal and cancer cells.