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Biomedical subjects

Kenneth C Bilchick

Publications and source records attributed to Kenneth C Bilchick.

8 recordsLinked to original sources
PubMed2006

Heart failure-associated alterations in troponin I phosphorylation impair ventricular relaxation-afterload and force-frequency responses and systolic function.

Recent studies have found that selective stimulation of troponin (Tn)I protein kinase A (PKA) phosphorylation enhances heart rate-dependent inotropy and blunts relaxation delay coupled to increased afterload. However, in failing hearts, TnI phosphorylation by PKA declines while protein kinase C (PKC) activity is enhanced, potentially augmenting TnI PKC phosphorylation. Accordingly, we hypothesized that these site-specific changes deleteriously affect both rate-responsive cardiac function and afterload dependence of relaxation, both prominent phenotypic features of the failing heart. A transgenic (TG) mouse model was generated in which PKA-TnI sites were mutated to mimic partial dephosphorylation (Ser22 to Ala; Ser23 to Asp) and dominant PKC sites were mutated to mimic constitutive phosphorylation (Ser42 and Ser44 to Asp). The two highest-expressing lines were further characterized. TG mice had reduced fractional shortening of 34.7 +/- 1.4% vs. 41.3 +/- 2.0% (P = 0.018) and slight chamber dilation on echocardiography. In vivo cardiac pressure-volume studies revealed near doubling of isovolumic relaxation prolongation with increasing afterload in TG animals (P < 0.001), and this remained elevated despite isoproterenol infusion (PKA stimulation). Increasing heart rate from 400 to 700 beats/min elevated contractility 13% in TG hearts, nearly half the response observed in nontransgenic animals (P = 0.005). This blunted frequency response was normalized by isoproterenol infusion. Abnormal TnI phosphorylation observed in cardiac failure may explain exacerbated relaxation delay in response to increased afterload and contribute to blunted chronotropic reserve.

Animals↗
PubMed2006

Differential regional gene expression from cardiac dyssynchrony induced by chronic right ventricular free wall pacing in the mouse.

Routine clinical right ventricular pacing generates left ventricular dyssynchrony manifested by early septal shortening followed by late lateral contraction, which, in turn, reciprocally stretches the septum. Dyssynchrony is disadvantageous to cardiac mechanoenergetics and worsens clinical prognosis, yet little is known about its molecular consequences. Here, we report the influence of cardiac dyssynchrony on regional cardiac gene expression in mice. Mice were implanted with a custom-designed miniature cardiac pacemaker and subjected to 1-wk overdrive right ventricular free wall pacing (720 beats/min, baseline heart rate 520-620 beats/min) to generate dyssynchrony (pacemaker: 3-V lithium battery, rate programmable, 1.5 g, bipolar lead). Electrical capture was confirmed by pulsed-wave Doppler and dyssynchrony by echocardiography. Gene expression from the left ventricular septal and lateral wall myocardium was assessed by microarray (dual-dye method, Agilent) using oligonucleotide probes and dye swap. Identical analysis was applied to four synchronously contracting controls. Of the 22,000 genes surveyed, only 18 genes displayed significant (P < 0.01) differential expression between septal/lateral walls >1.5 times that in synchronous controls. Gene changes were confirmed by quantitative PCR with excellent correlations. Most of the genes (n = 16) showed greater septal expression. Of particular interest were seven genes coding proteins involved with stretch responses, matrix remodeling, stem cell differentiation to myocyte lineage, and Purkinje fiber differentiation. One week of iatrogenic cardiac dyssynchrony triggered regional differential expression in relatively few select genes. Such analysis using a murine implantable pacemaker should facilitate molecular studies of cardiac dyssynchrony and help elucidate novel mechanisms by which stress/stretch stimuli due to dyssynchrony impact the normal and failing heart.

Animals↗
PubMed2006

Use of a coronary sinus lead and biventricular ICD to correct a sensing abnormality in a patient with arrhythmogenic right ventricular dysplasia/cardiomyopathy.

Implantable cardioverter defibrillators (ICDs) are frequently offered to patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). Yet ICDs in these patients may be complicated by poor sensed amplitudes resulting from fatty and fibrous tissue replacement of right ventricular myocardium. We present the case of a patient with ARVD/C who had inappropriate detection of ventricular tachycardia with a single-chamber ICD due to poor sensed right ventricular amplitudes. We discuss how the use of a bipolar coronary sinus lead and a biventricular ICD generator with a novel header configuration solved the problem.

Adult↗
PubMed2004

Treatment of hyperlipidemia in cardiac transplant recipients.

Of the 60,000 patients receiving heart transplants between 1982 and 2001, approximately 12,000 are currently alive. The high incidence of hyperlipidemia and coronary disease (also known as accelerated graft atherosclerosis, or AGA) in these patients warrants early prophylaxis soon after transplantation with 3-hydroxy-3-methylglutaryl (HMG) Co-A reductase inhibitors (statins). Immunosuppressive agents such as prednisone, cyclosporine, mycophenylate mofetil, and sirolimus are associated with hyperlipidemia. Statins, in addition to lowering cholesterol levels, also benefit cardiac transplant recipients via effects on the immune system and endothelial function. Recent data have demonstrated that statins decrease AGA and mortality rates. Furthermore, greater benefits are seen when statins are started early. The 2 statins shown to decrease mortality in patients after cardiac transplantation are pravastatin and simvastatin, which differ in their metabolism (pravastatin is the only statin with non-cytochrome metabolism) and lipophilicity (pravastatin is less lipophilic). Although the benefit of simvastatin has been shown to extend to 8 years after transplantation, increased adverse effects in other studies with higher doses of simvastatin have resulted in new prescribing recommendations, which state that the dose of simvastatin should probably not exceed 10 mg with cyclosporine or gemfibrozil and 20 mg with amiodarone or verapamil. The evidence for potential benefits, interactions, and adverse effects of other potential lipid-lowering drugs for this patient population, such as fibrates, niacin, fish oil, cholestyramine, and ezetimibe, are also discussed. A summary algorithm is proposed, including approaches to patients with statin-associated musculoskeletal symptoms and patients with inadequate results after initial statin therapy.

Algorithms↗
PubMed2002

Prognostic value of heart rate variability in chronic congestive heart failure (Veterans Affairs' Survival Trial of Antiarrhythmic Therapy in Congestive Heart Failure).

Although the value of heart rate variability (HRV) for risk stratification after acute myocardial infarction has been demonstrated, the value of low HRV as a predictor of sudden cardiac death in patients with ischemic cardiomyopathy has not been shown convincingly to date. We retrospectively analyzed electrocardiographic data from 179 patients in the Veterans Affairs' Survival Trial of Antiarrhythmic Therapy in Congestive Heart Failure to determine if HRV (expressed as the SD of the normal-to-normal RR intervals [SDNN]) would be useful as a predictor of overall mortality and sudden death. Because our goal was to identify high-risk patients, we compared patients in the lowest quartile of HRV with the remaining patients. Among the 127 patients meeting inclusion criteria, SDNN <65.3 ms (the lowest quartile) was the sole independent factor predictive of survival in a multivariate model (p = 0.0001). A Cox proportional-hazards model revealed that each increase of 10 ms in SDNN conferred a 20% decrease in risk of mortality (p = 0.0001). Furthermore, patients with SDNN <65.3 ms had a significantly increased risk of sudden death (p = 0.016). Thus, HRV was the sole independent predictor of overall mortality and was significantly associated with sudden death in this population.

Aged↗