Citations

Myofiber passive stiffness is lowered by phosphorylation of the giant sarcomeric protein titin, with beneficial effects on diastolic function. Titin can be phosphorylated by cGMP-activated protein kinase (PK)G, a pathway stimulated by B-type natriuretic peptide (BNP) or PDE-5A inhibitor (sildenafil). Whether titin phosphorylation and stiffness are affected by PKG activation in vivo had not been studied. Here we examined how dogs with experimental hypertension and diastolic dysfunction, induced by renal wrapping, respond to treatment with β-blockers, sildenafil, and BNP, in terms of altered titin phosphorylation and passive stiffness. Isolated permeabilized cardiomyocytes from left ventricular (LV) biopsies untreated (n=5), treated with β-blockers (n=7), followed by sildenafil (n=7) and BNP (n=7) were attached to a force transducer and the passive length tension relation (F pas ) was measured between 1.8 and 2.4µm sarcomere length (SL) before and after PKA and PKG administration. We also assessed phosphorylation of myofilament proteins including titin, cMyBPC, desmin, cTnT, cTnI and MLC2 by gel electrophoresis (SYPRO Ruby and ProQ Diamond stain) and expression of titin PEVK, phospho-PEVK, cTnI, phospho-cTnI (at Ser 23/24), PKCα and phospho-PKCα by Western blotting. Compared to untreated cardiomyocytes, F pas was unaltered with β-blocker therapy, but significantly reduced with sildenafil; with BNP F pas did not change further. Ex-vivo administration of PKG lowered F pas of untreated and β-blocker cardiomyocytes to the levels measured in sildenafil and BNP samples, and additional administration of PKA did not further change F pas . Total titin phosphorylation was low in untreated samples and with β-blockade, but significantly increased with sildenafil and BNP. Total cTnI phosphorylation and phospho-cTnI at Ser 23/24 were low in untreated compared to treated samples but were similar between β-blocker, sildenafil and BNP groups. Phospho-PEVK and phospho-PKCα were high in untreated samples and with β-blockade, but reduced with sildenafil and BNP. Acute cGMP enhancing therapy with sildenafil and BNP improves LV diastolic function through correction of a titin phosphorylation deficit, thereby reducing cardiomyocyte passive stiffness.

Introduction: The physiologic relevance of myocardial bridging (MB) that is found on invasive (ICA) and CT coronary angiography (CTA) is not known. Myocardial perfusion imaging (MPI) may be useful in objectively assessing altered myocardial blood flow associated with MB. We studied the prevalence of ischemia on MPI and mortality among patients with MB. Methods: Patients with MPI studies within 6 months of MB identified on ICAs (2002-2014) or CTAs (2005-2014) at the Mayo Clinic were retrospectively studied. Exclusion criteria included a history of myocardial infarction (MI), coronary artery bypass grafting and hemodynamically significant coronary artery disease (CAD, coronary artery stenosis ≥ 50%) were excluded. Results: 1116 individuals had MB on ICA out of which 300 had MPI studies. 511 individuals had MB on CTA out of which 63 had MPI studies. After excluding patients with CAD, 114 patients with MB identified on ICA and 31 patients with MB identified on CTA remained for analysis. Patients in the ICA and CTA cohort were the same age (60±13 years for ICA vs 60±12 years for CTA cohort, p=0.9). The ICA cohort was likely to include smokers (47 vs 26%, p=0.03) and those with hyperlipidemia (67 vs 45%, p=0.03). The prevalence of ischemia on MPI was similar in the ICA and CTA cohorts (42 vs. 44%, p=0.5). After a median follow-up of 1166 days, the ICA cohort had 12 patient deaths (8%). There was no death in the CTA cohort. The presence of ischemia on MPI was not associated with increased mortality on long-term follow-up (Log Rank p=0.9). Conclusions: Ischemia on MPI is commonly found in patients with MB who do not have significant CAD. While patients with MB identified on ICA are more likely to have traditional CAD risk factors, the prevalence of ischemia on MPI was similar when compared to patients with MB on CTA. In this small retrospective study, ischemia identified on MPI was not associated with increased mortality.

Confirmation of the presence and magnitude of left ventricular outflow tract (LVOT) obstruction is a critical component of the evaluation of symptoms in patients with hypertrophic cardiomyopathy (HCM). The presence of LVOT obstruction in patients with severe symptoms refractory to pharmacologic therapy identifies a subgroup of HCM patients who may benefit from septal reduction therapy. Two‐dimensional echocardiography with continuous wave Doppler is the main tool for confirming the presence and severity of LVOT obstruction in HCM. However, when uncertainty remains following non‐invasive evaluation, invasive hemodynamics studies are required to confirm and quantify LVOT obstruction. In this manuscript we describe a series of 6 cases in which hemodynamic catheterization is instrumental in supplementing non‐invasive imaging in the assessment of LVOT obstruction in HCM. © 2015 Wiley Periodicals, Inc.

Background— In vitro studies suggest that phosphorylation of titin reduces myocyte/myofiber stiffness. Titin can be phosphorylated by cGMP-activated protein kinase. Intracellular cGMP production is stimulated by B-type natriuretic peptide (BNP) and degraded by phosphodiesterases, including phosphodiesterase-5A. We hypothesized that a phosphodiesterase-5A inhibitor (sildenafil) alone or in combination with BNP would increase left ventricular diastolic distensibility by phosphorylating titin. Methods and Results— Eight elderly dogs with experimental hypertension and 4 young normal dogs underwent measurement of the end-diastolic pressure-volume relationship during caval occlusion at baseline, after sildenafil, and BNP infusion. To assess diastolic distensibility independently of load/extrinsic forces, the end-diastolic volume at a common end-diastolic pressure on the sequential end-diastolic pressure-volume relationships was measured (left ventricular capacitance). In a separate group of dogs (n=7 old hypertensive and 7 young normal), serial full-thickness left ventricular biopsies were harvested from the beating heart during identical infusions to measure myofilament protein phosphorylation. Plasma cGMP increased with sildenafil and further with BNP (7.31±2.37 to 26.9±10.3 to 70.3±8.1 pmol/mL; P <0.001). Left ventricular diastolic capacitance increased with sildenafil and further with BNP (51.4±16.9 to 53.7±16.8 to 60.0±19.4 mL; P <0.001). Changes were similar in old hypertensive and young normal dogs. There were no effects on phosphorylation of troponin I, troponin T, phospholamban, or myosin light chain-1 or -2. Titin phosphorylation increased with sildenafil and BNP, whereas titin-based cardiomyocyte stiffness decreased. Conclusion— Short-term cGMP-enhancing treatment with sildenafil and BNP improves left ventricular diastolic distensibility in vivo, in part by phosphorylating titin.