Shawn W. Robinson

Mechanisms of arrhythmogenic delayed and early afterdepolarizations in ferret ventricular muscle.

Drug-induced triggered arrhythmias in heart muscle involve oscillations of membrane potential known as delayed or early afterdepolarizations (DADs or EADs). We examined the mechanism of DADs and EADs in ferret ventricular muscle. Membrane potential, tension and aequorin luminescence were measured during exposure to elevated [Ca2+]0, strophanthidin and/or isoproterenol (to induce DADs), or cesium chloride (to induce EADs). Ryanodine (10(-9)-10(-6) M), an inhibitor of Ca2+ release from the sarcoplasmic reticulum, rapidly suppressed DADs and triggered arrhythmias. When cytoplasmic Ca2+-buffering capacity was enhanced by loading cells with the Ca2+ chelators BAPTA or quin2, DADs were similarly inhibited, as were contractile force and aequorin luminescence. In contrast to DADs, EADs induced by Cs were not suppressed by ryanodine or by loading with intracellular Ca2+ chelators. The possibility that transsarcolemmal Ca2+ entry might produce EADs was evaluated with highly specific dihydropyridine Ca channel agonists and antagonists. Bay K8644 (100-300 nM) potentiated EADs, whereas nitrendipine (3-20 microM) abolished EADs. We conclude that DADs and DAD-related triggered arrhythmias are activated by an increase in intracellular free Ca2+ concentration, whereas EADs do not require elevated [Ca2+]i but rather arise as a direct consequence of Ca2+ entry through sarcolemmal slow Ca channels.

Effects of exercise training on peak performance and quality of life in congestive heart failure patients.

BACKGROUND Exercise programs for patients with heart failure have often enrolled and evaluated relatively healthy, young patients. They also have not measured the impact of exercise performance on daily activities and quality of life. METHODS AND RESULTS We investigated the impact of a 6-month supervised and graded exercise program in 33 elderly patients with moderate to severe heart failure randomized to usual care or an exercise program. Six of 17 patients did not tolerate the exercise program. Of those who did, peak oxygen consumption increased by 2.4 +/- 2.8 mL/kg/min (P < .05) and 6-minute walk increased by 194 ft (P < .05). However, outpatient energy expenditure did not increase, as measured by either the doubly labeled water technique or Caltrac accelerometer. Perceived quality of life also did not improve, as measured by the Medical Outcomes Study, Functional Status Assessment, or Minnesota Living With Heart Failure questionnaires. CONCLUSION Elderly patients with severe heart failure can safely exercise, with an improvement in peak exercise tolerance. However, not all patients will benefit, and daily energy expenditure and quality of life do not improve to the same extent as peak exercise.

A Randomized, Controlled Trial of the Renal Effects of Ultrafiltration as Compared to Furosemide in Patients With Acute Decompensated Heart Failure

OBJECTIVES This study was designed to evaluate the consequences of ultrafiltration (UF) and standard intravenous diuretic (furosemide) therapy on glomerular filtration rate (GFR) and renal plasma flow in patients with acute decompensated heart failure. BACKGROUND It has been hypothesized that treatment with diuretics may worsen renal function as the result of systemic neurohormonal activation and direct renal vascular effects. UF also removes fluid, but its actions on intrarenal hemodynamics, and therefore renal function, are unknown. METHODS Patients hospitalized for acute decompensated heart failure with an ejection fraction less than 40% and two or more signs of hypervolemia were randomized to receive UF or intravenous diuretics. Urine output, GFR (as measured by iothalamate), and renal plasma flow (as measured by para-aminohippurate) were assessed before fluid removal and after 48 hours. RESULTS Nineteen patients (59 +/- 16 years, 68% were male) were randomized to receive UF (n = 9) or intravenous diuretics (n = 10). The change in GFR (-3.4 +/- 7.7 mL/min vs. -3.6 +/- 11.5 mL/min; P = .966), renal plasma flow (26.6 +/- 62.7 mL/min vs. 16.1 +/- 42.0 mL/min; P = .669), and filtration fraction (-6.9 +/- 13.6 mL/min vs. -3.9 +/- 13.6 mL/min; P = .644) after treatment were not significantly different between the UF and furosemide treatment groups, respectively. There was no significant difference in net 48-hour fluid removal between the groups (-3211 +/- 2345 mL for UF and -2725 +/- 2330 mL for furosemide, P = .682). UF removed 3666 +/- 2402 mL. Urine output during 48 hours was significantly greater in the furosemide group (5786 +/- 2587 mL) compared with the UF group (2286 +/- 915 mL, P < .001). CONCLUSIONS During a 48-hour period, UF did not cause any significant differences in renal hemodynamics compared with the standard treatment of intravenous diuretics.

Apical Plasma Membrane Mispolarization of NaK-ATPase in Polycystic Kidney Disease Epithelia Is Associated with Aberrant Expression of the β2 Isoform

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease of the kidney, characterized by cystic enlargement of renal tubules, aberrant epithelial proliferation, and ion and fluid secretion into the lumen. Previous studies have shown abnormalities in polarization of membrane proteins, including mislocalization of the NaK-ATPase to the apical plasma membranes of cystic epithelia. Apically located NaK-ATPase has previously been shown to be fully functional in vivo and in membrane-grown ADPKD epithelial cells in vitro, where basal-to-apical (22)Na transport was inhibited by application of ouabain to the apical membrane compartment. Studies were conducted with polymerase chain reaction-generated specific riboprobes and polyclonal peptide antibodies against human sequences of alpha1, alpha3, beta1, and beta2 subunits of NaK-ATPase. High levels of expression of alpha1 and beta1 messenger RNA were detected in ADPKD and age-matched normal adult kidneys in vivo, whereas beta2 messenger RNA was detected only in ADPKD kidneys. Western blot analysis and immunocytochemical studies showed that, in normal adult kidneys, peptide subunit-specific antibodies against alpha1 and beta1 localized to the basolateral membranes of normal renal tubules, predominantly thick ascending limbs of Henles loop. In ADPKD kidneys, alpha1 and beta2 subunits were localized to the apical epithelial cell membranes, whereas beta1 was distributed throughout the cytoplasm and predominantly in the endoplasmic reticulum, but was not seen associated with cystic epithelial cell membranes or in cell membrane fractions. Polarizing, renal-derived epithelial Madin Darby canine kidney cells, stably expressing normal or N-terminally truncated chicken beta1 subunits, showed selective accumulation in the basolateral Madin Darby canine kidney cell surface, whereas c-myc epitope-tagged chicken beta2 or human beta2 subunits accumulated selectively in the apical cell surface. Similarly, human ADPKD epithelial cell lines, which endogenously expressed alpha1 and beta2 NaK-ATPase subunits, showed colocalization at the apical cell surface and coassociation by immunoprecipitation analysis. These results are consistent with a model in which the additional transcription and translation of the beta2 subunit of NaK-ATPase may result in the apical mislocalization of NaK-ATPase in ADPKD cystic epithelia.

Renal response to indomethacin in congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy.

The impact of nonsteroidal anti-inflammatory drugs (NSAIDs) on renal function has not been evaluated in patients with congestive heart failure. Therefore, the renal effects of indomethacin were examined in patients with chronic heart failure, and the relation between the changes in glomerular filtration rate and renal plasma flow after indomethacin administration was assessed. Twenty-five patients with congestive heart failure and an ejection fraction less than 40% were evaluated. At baseline, renal plasma flow and glomerular filtration rate were measured, using disappearance from the serum of intravenously injected 131I-orthodihippurate and urinary accumulation of intravenously injected technetium-99m diethylenetriamine pentaacetic acid, respectively. After 3 days, 75 mg of sustained release indomethacin were administered, and repeat renal function tests were performed. Mean glomerular filtration rate decreased from 40 +/- 21 to 32 +/- 16 ml/min/1.73 m2 (p less than 0.05), and mean renal plasma flow decreased from 242 +/- 122 to 222 +/- 110 ml/min/1.73 m2 (p less than 0.05). There was no correlation between the changes in glomerular filtration rate and renal plasma flow after indomethacin administration. It is concluded that 1 dose of an NSAID may cause marked and clinically important alterations in renal function in patients with heart failure. However, the decrease in glomerular filtration rate does not merely reflect a decrease in renal plasma flow, but probably the effects of NSAIDs on the intraglomerular actions of prostaglandins.

Hypertrophy-associated polymorphisms ascertained in a founder cohort applied to heart failure risk and mortality.

A three‐stage approach was undertaken using genome‐wide, case‐control, and case‐only association studies to identify genetic variants associated with heart failure mortality. In an Amish founder population (n = 851), cardiac hypertrophy, a trait integral to the adaptive response to failure, was found to be heritable (h2= 0.28, p = 0.0002) and GWAS revealed 21 candidate hypertrophy SNPs. In a case (n = 1,610)‐control (n = 463) study in unrelated Caucasians, one of the SNPs associated with hypertrophy (rs2207418, p = 8 × 10−6), was associated with heart failure, RR = 1.85(1.25–2.73, p = 0.0019). In heart failure cases rs2207418 was associated with increased mortality, HR = 1.51(1.20–1.97, p = 0.0004). There was consistency between studies, with the GG allele being associated with increased ventricular mass (˜13 g/m2) in the Amish, heart failure risk, and heart failure mortality. This SNP is in a gene desert of chromosome 20p12. Five genes are within 2.0 mbp of rs2207418 but with low LD between their SNPs and rs2207418. A region near this SNP is highly conserved in multiple vertebrates (lod score = 1,208). This conservation and the internal consistency across studies suggests that this region has biologic importance in heart failure, potentially acting as an enhancer or repressor element. rs2207418 may be useful for predicting a more progressive form of heart failure that may require aggressive therapy. Clin Trans Sci 2011; Volume 4: 17–23

Determinants of the renal response to ACE inhibition in patients with congestive heart failure

The objective of the present study was to determine whether pretreatment neurohormonal and renal hemodynamic parameters predict the change in renal function with the administration of quinapril, a new angiotensin-converting enzyme (ACE) inhibitor. Twenty patients with New York Heart Association (NYHA) class III and IV heart failure were evaluated. Following pretreatment determination of renal function and plasma neurohormones, patients were treated daily with 10 mg of quinapril. Measurements of glomerular filtration rate (GFR) and renal plasma flow (RPF) were repeated after 7 weeks to assess changes in function (delta GFR and delta RPF). Mean GFR increased from 49 +/- 6 to 56 +/- 7 ml/min/1.73 m2 (p = 0.10), but decreased in five patients. Mean RPF increased from 235 +/- 23 to 252 +/- 23 ml/min/1.73 m2 (p = 0.08), but decreased in five patients. There was no relation between delta GFR and baseline determinations of GFR, RPF, plasma renin activity, plasma angiotensin II, or serum Na. Only a high filtration fraction (GFR/RPF) predicted a decreased GFR (r = 0.61, p less than 0.005). In contrast, no baseline renal hemodynamic parameter correlated with delta RPF. We conclude that poor renal function does not increase the risk of renal deterioration with quinapril. However, dependence of renal function upon the renin-angiotensin system may be predicted by a high filtration fraction.

An Antisense Oligonucleotide Against H1 Inhibits the Classical Sodium Current but not ICa(TTX) in Rat Ventricular Cells

I Ca(TTX) is a sodium current component, functionally distinct from the main body of sodium current, seen in cardiac and other cells. To determine if ICa(TTX) channels are a separate isoform from the classical cardiac sodium channels, we exposed rat ventricular cells in primary culture to an antisense oligonucleotide (AON) directed against rH1 (rNav1.5): 5′‐CTCCTCATACCCTCT‐3′. The homologous human sequence has been identified (and confirmed by us on HEK 293 cells) as effective against hH1 expressed heterologously. Scrambled sequence (5′‐CCCCCCTTATCTACT‐3′) controls were also included. The AON (10 μm; day 2 of exposure) reduced the classical sodium current by 69.6 % compared to untreated and 60.8 % compared to scrambled sequence (10 μm; day 2 of exposure) controls (mean ±s.e.m. maximum peak inward current density of −8.23 ± 0.60 pA pF−1, 18 cells, for untreated; −6.37 ± 0.79 pA pF−1, 16 cells, for scrambled sequence; and −2.50 ± 0.31 pA pF−1, 18 cells, for AON‐treated cells). The two control groups are not significantly different from each other, but are both significantly different from the AON‐treated group (P < 0.001). The inhibition was specific for sodium channels, with no significant AON effect on the L‐type calcium current. This confirms that H1 generates the classical cardiac sodium current. This same AON at the same concentration and time of exposure had no significant effect on ICa(TTX) (mean of −4.72 ± 0.55, 15 cells; −5.47 ± 0.53, 13 cells; and −5.04 ± 0.63 pA pF−1, 15 cells, for untreated controls, scrambled controls and AON treated, respectively). Hence, ICa(TTX), which is functionally distinct from the classical cardiac sodium current, is encoded by a distinct gene.

Surgical and Transcatheter Mitral Valve Repair for Severe Chronic Mitral Regurgitation: A Review of Clinical Indications and Patient Assessment.

Significant mitral regurgitation (MR) is an increasingly common disorder affecting nearly 10% of the US population aged >75 years and is associated with increased morbidity and mortality in the setting of left ventricular (LV) dysfunction and heart failure symptoms. Mitral valve repair or

I(Ca(TTX)) channels are distinct from those generating the classical cardiac Na(+) current.

The Na(+) current component I(Ca(TTX)) is functionally distinct from the main body of Na(+) current, I(Na). It was proposed that I(Ca(TTX)) channels are I(Na) channels that were altered by bathing media containing Ca(2+), but no, or very little, Na(+). It is known that Na(+)-free conditions are not required to demonstrate I(Ca(TTX).) We show here that Ca(2+) is also not required. Whole-cell, tetrodotoxin-blockable currents from fresh adult rat ventricular cells in 65 mm Cs(+) and no Ca(2+) were compared to those in 3 mM Ca(2+) and no Cs(+) (i.e., I(Ca(TTX))). I(Ca(TTX)) parameters were shifted to more positive voltages than those for Cs(+). The Cs(+) conductance-voltage curve slope factor (mean, -4.68 mV; range, -3.63 to -5.72 mV, eight cells) is indistinguishable from that reported for I(Ca(TTX)) (mean, -4.49 mV; range, -3.95 to -5.49 mV). Cs(+) current and I(Ca(TTX)) time courses were superimposable after accounting for the voltage shift. Inactivation time constants as functions of potential for the Cs(+) current and I(Ca(TTX)) also superimposed after voltage shifting, as did the inactivation curves. Neither of the proposed conditions for conversion of I(Na) into I(Ca(TTX)) channels is required to demonstrate I(Ca(TTX)). Moreover, we find that cardiac Na(+) (H1) channels expressed heterologously in HEK 293 cells are not converted to I(Ca(TTX)) channels by Na(+)-free, Ca(2+)-containing bathing media. The gating properties of the Na(+) current through H1 and those of Ca(2+) current through H1 are identical. All observations are consistent with two non-interconvertable Na(+) channel populations: a larger that expresses little Ca(2+) permeability and a smaller that is appreciably Ca(2+)-permeable.