Oral anticoagulation in patients with non-valvular atrial fibrillation and a CHA2DS2-VASc score of 1: a current opinion of the European Society of Cardiology Working Group on Cardiovascular Pharmacotherapy and European Society of Cardiology Council on Stroke

Oral anticoagulation in patients presenting with non-valvular atrial fibrillation and a CHA2DS2-VASc score of 1 (CHA2DS2-VASc of 2 in women) remains a challenging approach in clinical practice. Therapeutic decisions need to balance the individual benefit of reducing thromboembolic risk against the potential harm due to an increase in bleeding risk in this intermediate risk patient population. Within the current opinion statement of the European Society of Cardiology working group of cardiovascular pharmacotherapy and the European Society of Cardiology council on stroke the currently available evidence on the anti-thrombotic management in patients presenting with a CHA2DS2-VASc of 1 is summarized. Easily applicable tools for a personalized refinement of the individual thromboembolic risk in patients with atrial fibrillation and a CHA2DS2-VASc score of 1 that guide clinicians through the question whether to anticoagulate or not are provided.

Reasons for disparity in statin adherence rates between clinical trials and real-world observations: a review

With statins, the reported rate of adverse events differs widely between randomized clinical trials (RCTs) and observations in clinical practice, the rates being 1-2% in RCTs vs. 10-20% in the so-called real world. One possible explanation is the claim that RCTs mostly use a run-in period with a statin. This would exclude intolerant patients from remaining in the trial and therefore favour a bias towards lower rates of intolerance. We here review data from RCTs with more than 1000 participants with and without a run-in period, which were included in the Cholesterol Treatment Trialists Collaboration. Two major conclusions arise: (i) the majority of RCTs did not have a test dose of a statin in the run-in phase. (ii) A test dose in the run-in phase was not associated with a significantly improved adherence rate within that trial when compared to trials without a test dose. Taken together, the RCTs of statins reviewed here do not suggest a bias towards an artificially higher adherence rate because of a run-in period with a test dose of the statin. Other possible explanations for the apparent disparity between RCTs and real-world observations are also included in this review albeit mostly not supported by scientific data.

Decongestion in acute heart failure

Congestion is a major reason for hospitalization in acute heart failure (HF). Therapeutic strategies to manage congestion include diuretics, vasodilators, ultrafiltration, vasopressin antagonists, mineralocorticoid receptor antagonists, and potentially also novel therapies such as gut sequesterants and serelaxin. Uncertainty exists with respect to the appropriate decongestion strategy for an individual patient. In this review, we summarize the benefit and risk profiles for these decongestion strategies and provide guidance on selecting an appropriate approach for different patients. An evidence-based initial approach to congestion management involves high-dose i.v. diuretics with addition of vasodilators for dyspnoea relief if blood pressure allows. To enhance diuresis or overcome diuretic resistance, options include dual nephron blockade with thiazide diuretics or natriuretic doses of mineralocorticoid receptor antagonists. Vasopressin antagonists may improve aquaresis and relieve dyspnoea. If diuretic strategies are unsuccessful, then ultrafiltration may be considered. Ultrafiltration should be used with caution in the setting of worsening renal function. This review is based on discussions among scientists, clinical trialists, and regulatory representatives at the 9th Global Cardio Vascular Clinical Trialists Forum in Paris, France, from 30 November to 1 December 2012.

Potassium dynamics are attenuated in hyperkalemia and a determinant of QT adaptation in exercising hemodialysis patients

Disturbances in plasma potassium concentration (pK) are well known risk factors for the development of cardiac arrhythmia. The aims of the present study were to evaluate the effect of hemodialysis on exercise pK dynamics and QT hysteresis, and whether QT hysteresis is associated with the pK decrease following exercise. Twenty-two end-stage renal disease patients exercised on a cycle ergometer with incremental work load before and after hemodialysis. ECG was recorded and pK was measured during exercise and recovery. During exercise, pK increased from 5.1 ± 0.2 to 6.1 ± 0.2 mM (mean ± SE; P < 0.0001) before hemodialysis and from 3.8 ± 0.1 to 5.1 ± 0.1 mM (P < 0.0001) after hemodialysis. After 2 min of recovery, pK had decreased to 5.0 ± 0.2 mM and 4.1 ± 0.1 mM (P < 0.0001) before and after hemodialysis, respectively. pK increase during exercise was accentuated after hemodialysis. The pK increase was negatively linearly correlated with pK before exercise (β = -0.21, R(2) = 0.23, P = 0.001). QT hysteresis was negatively linearly correlated with the decrease in pK during recovery (β = -28 ms/mM, R(2) = 0.36, P = 0.006). Thus, during recovery, low pK was associated with relatively longer QT interval. In conclusion, new major findings are an accentuated increase in pK during exercise after hemodialysis, an attenuated increase in pK in hyperkalemia, and an association between pK and QT interval adaptation during recovery. The acute pK shift after exercise may modulate QT interval adaptation and trigger cardiac arrhythmias.

Hypokalemia and sudden cardiac death

Worldwide, approximately three million people suffer sudden cardiac death annually. These deaths often emerge from a complex interplay of substrates and triggers. Disturbed potassium homeostasis among heart cells is an example of such a trigger. Thus, hypokalemia and, also, more transient reductions in plasma potassium concentration are of importance. Hypokalemia is present in 7% to 17% of patients with cardiovascular disease. Furthermore, up to 20% of hospitalized patients and up to 40% of patients on diuretics suffer from hypokalemia. Importantly, inadequate management of hypokalemia was found in 24% of hospitalized patients. Hypokalemia is associated with increased risk of arrhythmia in patients with cardiovascular disease, as well as increased all-cause mortality, cardiovascular mortality and heart failure mortality by up to 10-fold. Long-term potassium homeostasis depends on renal potassium excretion. However, skeletal muscles play an important role in short-term potassium homeostasis, primarily because skeletal muscles contain the largest single pool of potassium in the body. Moreover, due to the large number of Na(+)/K(+) pumps and K(+) channels, the skeletal muscles possess a huge capacity for potassium exchange. In cardiovascular patients, hypokalemia is often caused by nonpotassium-sparing diuretics, insufficient potassium intake and a shift of potassium into stores by increased potassium uptake stimulated by catecholamines, beta-adrenoceptor agonists and insulin. Interestingly, drugs with a proven significant positive effect on mortality and morbidity rates in heart failure patients all increase plasma potassium concentration. Thus, it may prove beneficial to pay more attention to hypokalemia and to maintain plasma potassium levels in the upper normal range. The more at risk of fatal arrhythmia and sudden cardiac death a patient is, the more attention should be given to the potassium homeostasis.

Atrial Na,K-ATPase increase and potassium dysregulation accentuate the risk of postoperative atrial fibrillation

BACKGROUND

Postoperative atrial fibrillation is a common complication to cardiac surgery. Na,K-ATPase is of major importance for the resting membrane potential and action potential. The purpose of the present study was to evaluate the importance of Na,K-ATPase concentrations in human atrial biopsies and plasma potassium concentrations for the development of atrial fibrillation.

METHODS

Atrial myocardial biopsies were obtained from 67 patients undergoing open chest cardiac surgery. Na,K-ATPase was quantified using vanadate-facilitated 3H-ouabain binding. Plasma potassium concentration was measured with ion-selective electrode.

RESULTS

In patients with preoperative sinus rhythm, 3H-ouabain-binding site concentration was 16% higher in patients developing postoperative atrial fibrillation compared to patients maintaining sinus rhythm [302 +/- 15 pmol/g wet weight (n = 20) vs. 261 +/- 11 mmol/g wet weight (n = 33), p = 0.03]. Also with multivariable analysis, 3H-ouabain-binding site concentration was significantly associated with the development of atrial fibrillation. High increase in plasma potassium concentration during the perioperative period and surgery was associated with postoperative atrial fibrillation.

CONCLUSIONS

The present study supports the increasing evidence of dysregulation of the potassium homeostasis as an important factor in the development of cardiac arrhythmias. High atrial Na,K-ATPase and sudden plasma potassium concentration increase may contribute to precipitate atrial fibrillation.

Mannan-binding lectin is a determinant of survival in infective endocarditis

Mannan-binding lectin (MBL) is a collectin plasma protein activating the lectin pathway of the complement system, enhancing opsonophagocytosis and modulating the cytokine response to inflammation. Deficiency of MBL, caused by structural mutations or promoter polymorphisms in the MBL2 gene, has been associated with increased susceptibility to infection and autoimmune disease. Thus, as infective endocarditis remains a severe disease requiring intensive and long-term treatment with antibiotics, we examined whether there was an association between MBL and clinical outcome in 39 well-characterized patients with infective endocarditis. Five patients (13%) had MBL concentrations < 100 microg/l and were considered MBL-deficient. This proportion was similar to that in a healthy control group of blood donors. Mortality 3 months after diagnosis was 20% in patients with MBL-deficiency and 9% in patients with normal MBL. The 5-year mortality was 80% and 25%, respectively. MBL-deficiency was on univariate survival statistics associated with significantly higher mortality on follow-up (P=0 x 03). In conclusion, this is the first report of an association between MBL-deficiency and survival in infective endocarditis. The present observation is important, as replacement therapy in MBL-deficient patients is possible. For certain high-risk subgroups, it opens new perspectives for improvement of treatment and outcome in infective endocarditis.

Mutations in the Kv1.5 channel gene KCNA5 in cardiac arrest patients

Mutations in one of the ion channels shaping the cardiac action potential can lead to action potential prolongation. However, only in a minority of cardiac arrest cases mutations in the known arrhythmia-related genes can be identified. In two patients with arrhythmia and cardiac arrest, we identified the point mutations P91L and E33V in the KCNA5 gene encoding the Kv1.5 potassium channel that has not previously been associated with arrhythmia. We functionally characterized the mutations in HEK293 cells. The mutated channels behaved similarly to the wild-type with respect to biophysical characteristics and drug sensitivity. Both patients also carried a D85N polymorphism in KCNE1, which was neither found to influence the Kv1.5 nor the Kv7.1 channel activity. We conclude that although the two N-terminal Kv1.5 mutations did not show any apparent electrophysiological phenotype, it is possible that they may influence other cellular mechanisms responsible for proper electrical behaviour of native cardiomyocytes.

Endocarditis at a tertiary hospital: reduced acute mortality but poor long term prognosis

The outcome in 132 patients with infective endocarditis diagnosed in accordance with the Duke criteria at a tertiary hospital in Denmark in the period 1998-2000 is reported. The total in-hospital mortality was 15%. Indications are that in-hospital mortality over the last decade has been reduced by around a quarter. Mortality after 3 months was 17% (CI 29%), after 3 years 32% (CI 16-47%) and after 5 years 39% (CI 22-55%). This 5-years mortality was 5 times that of an age and gender matched background population. After follow-up for 5-8 y, mortality was highest for prosthetic valve endocarditis (63% vs. 39%, p = 0.05). Heart surgery was performed in 51% of the cases. Patients who underwent surgery had a lower mortality at follow-up (36% vs. 52%, p = 0.04). The 5-year mortality was 30% (CI 9-52%) for patients treated with surgery and 48% (CI 23-72%) for patients treated without surgery. In multivariable analysis surgery was not an independent predictor for lower long-term mortality. Surgery was however an independent predictor for lower intermediate-term mortality. It is concluded that surgery may be associated with lower short- and intermediate-term mortality, while the effect might decline in the long-term. High age, prosthetic valve endocarditis, and Staphylococcus aureus endocarditis were independent predictors for high mortality. Although improvements have occurred over recent years, infective endocarditis is still a high mortality disease.

A proficient mentor is a must when starting up with research

Modern research is highly competitive, with a demand for publications soon after the start of a research career. Thus, a proficient mentor - a supervisor - is now recognized to be essential for success when starting up with research. A proficient mentor may introduce an individual to the crucial points in a particular field of research, which cannot simply be identified by a novice by reading background literature. Influential and sustained mentorship enhances research activity and a researcher's career.The present paper provides a guide on how to make an informed, rational decision about which qualities to seek in a prospective mentor. An individual should seek a mentor with a research field of interest and with the potential of being a proficient mentor. Which questions must the novice in research always consider before committing himself or herself to a mentor? A mentor should be evaluated on the basis of insight and knowledge, time for supervision and productivity. Furthermore, a mentor's reputation as supervisor must be taken into account. Aim early at obtaining an appointment for a meeting with a prospective mentor and show up prepared by having read relevant information. Be aware that the mentor will also continuously evaluate the apprentice's qualifications. It is important that the apprentice's expectations regarding the mentor's input - and vice versa - are well defined at an early stage. When both parties decide to give it a go, start by creating a research plan. This plan will serve as a written commitment between apprentice and mentor.

Mutations in the HERG K+-ion channel: a novel link between long QT syndrome and sudden infant death syndrome

In a 7-week-old infant who experienced sudden infant death syndrome (SIDS), a novel missense mutation was identified in KCNH2, causing a lysine-to-glutamic acid amino acid substitution at position 101 (K101E). KCNH2 codes for the HERG ion channel and mutations in the gene are associated with congenital long-QT syndrome (LQTS), and in the family of this case of SIDS, the mutation was associated with Torsades de pointes tachycardia, making SIDS the most likely outcome of congenital LQTS.

Genetic and phenotypic characterization of mutations in myosin-binding protein C (MYBPC3) in 81 families with familial hypertrophic cardiomyopathy: total or partial haploinsufficiency

Mutations in the MYBPC3 gene, encoding the sarcomere protein myosin-binding protein C, are among the most frequent causes of autosomal dominant familial hypertrophic cardiomyopathy (FHC). We studied the frequency, type, and pathogenetic mechanism of MYBPC3 mutations in an unselected cohort of 81 FHC families, consecutively enrolled at a tertiary referral center. Nine mutations, six of which were novel, were found in 10 (12.3%) of the families using single-strand conformation polymorphism and DNA sequencing. A frameshift mutation in exon 2 clearly suggests that haploinsufficiency is a pathogenetic mechanism in FHC. In addition, splice site mutations in exon 6 and intron 31, a deletion in exon 13, and a nonsense mutation in exon 25, all lead to premature termination codons, most likely causing loss of function and haploinsufficiency. Furthermore, there were two missense mutations (D228N and A833 T) and one in-frame deletion (DeltaLys813). A considerable intrafamilial variation in phenotypic expression of MYBPC3-based FHC was noted, and we suggest that mutations influencing stability of mRNA could play a role in the variable penetrance and expressivity of the disease, perhaps via partial haploinsuffciency.

Does KCNE5 play a role in long QT syndrome?

BACKGROUND

Long QT syndrome [LQTS] is a congenital cardiac disease characterised by prolonged QTC-time, syncopes and sudden cardiac death. LQTS is caused by mutations in genes coding for ion channels involved in the action potential. KCNE5 codes for a novel beta-subunit of the ion channel conducting the delayed rectifier repolarizing current IKs. As KCNE5 is expressed in the human heart and suppresses the IKs current in heterologous systems, it is a candidate gene that may be mutated in LQTS families where no causative mutations in known LQTS associated genes have been found. We examined whether this was the case.

METHODS

Genomic DNA from LQTS patients [n=88] and normal controls [n=90] was screened for mutations in KCNE5 by endonuclease-enhanced single strand conformation polymorphism analysis [EE-SSCP], and DNA sequencing of aberrant conformers. Mutations in other LQTS associated ion channels were excluded by SSCP.

RESULTS

No mutations were found in the coding region of the KCNE5 gene in LQTS patients. One polymorphism, a T-to-C transition at nucleotide 97, causing an amino acid polymorphism P33S, was present in 16 persons, nine heterozygotes and seven homozygotes. The T-allele frequency was 0.13 in LQTS patients and 0.10 in controls.

Severe intracellular magnesium and potassium depletion in patients after treatment with cisplatin

The purpose of this study is (1) to evaluate skeletal muscle magnesium (Mg) and potassium (K) during treatment with cisplatin; (2) to evaluate the predictive value of plasma (P)-Mg for intracellular Mg during cisplatin treatment; and (3) to evaluate whether changes in intracellular K influence skeletal muscle Na,K-ATPase. In all, 65 patients had a needle muscle biopsy obtained before and 26 patients both before and after cisplatin treatment. Biopsies were analysed for Mg, K, and Na,K-ATPase concentrations, and P-Mg and P-K determined. Treatment with a total dose of ≈500 mg (270 mg m⁻² surface area) cisplatin over 80 days was associated with reductions in muscle [Mg] (95% CI) (8.95 (8.23–9.63) to 7.76 (7.34–8.18) μmol g⁻¹ wet wt. (P<0.01), and muscle [K] (90.81 (83.29–98.34) to 82.87 (78.74–87.00) μmol g⁻¹ wet wt. (P<0.05), as well as in P-Mg 0.82 (0.80–0.85) to 0.68 (0.64–0.73) mmol l⁻¹ (P<0.01 but not in P-K (4.0 (3.8–4.1) vs 3.8 (3.7–4.0) mmol l⁻¹). No simple correlations were observed between P-Mg and muscle [Mg], or between P-K and muscle [K], either before (n=65) or after (n=26) treatment with cisplatin. The changes in [Mg] and [K] were not associated with changes in the muscle Na,K-ATPase concentration. Following treatment with cisplatin, an ≈15% decline in P-Mg was accompanied by an ≈15% loss of muscle [Mg], as well as an ≈10% reduction of muscle [K] and fatigue and muscle weakness previously ascribed to hypomagnesaemia may therefore also be well explained by muscle K depletion observed despite normal levels of P-K. There was no correlation between P-Mg and SM-Mg or between P-K and SM-K. Thus, P-Mg and P-K are not reliable indicators for Mg and K depletion during treatment with cisplatin. However, the majority of patients will present Mg and K depletion after cisplatin therapy and of these only very few patients will present a low P-Mg or P-K. Therefore, routine supplementation should be considered in all patients receiving cisplatin.

Impaired muscle Ca2+ and K+ regulation contribute to poor exercise performance post-lung transplantation

Lung transplant recipients (LTx) exhibit marked peripheral limitations to exercise. We investigated whether skeletal muscle Ca2+ and K+ regulation might be abnormal in eight LTx and eight healthy controls. Peak oxygen consumption and arterialized venous plasma [K+] (where brackets denote concentration) were measured during incremental exercise. Vastus lateralis muscle was biopsied at rest and analyzed for sarcoplasmic reticulum Ca2+ release, Ca2+ uptake, and Ca2+-ATPase activity rates; fiber composition; Na+-K+-ATPase (K+-stimulated 3-O-methylfluorescein phosphatase) activity and content ([3H]ouabain binding sites); as well as for [H+] and H+-buffering capacity. Peak oxygen consumption was 47% less in LTx (P < 0.05). LTx had lower Ca2+ release (34%), Ca2+ uptake (31%), and Ca2+-ATPase activity (25%) than controls (P < 0.05), despite their higher type II fiber proportion (LTx, 75.0 +/- 5.8%; controls, 43.5 +/- 2.1%). Muscle [H+] was elevated in LTx (P < 0.01), but buffering capacity was similar to controls. Muscle 3-O-methylfluorescein phosphatase activity was 31% higher in LTx (P < 0.05), but [3H]ouabain binding content did not differ significantly. However, during exercise, the rise in plasma [K+]-to-work ratio was 2.6-fold greater in LTx (P < 0.05), indicating impaired K+ regulation. Thus grossly subnormal muscle calcium regulation, with impaired potassium regulation, may contribute to poor muscular performance in LTx.

Diabetes- and semi-starvation-induced changes in metabolism and regulation of Na,K-ATPase in rat heart

AIMS/HYPOTHESIS

In comparison with healthy controls, rats with streptozotocin-induced diabetes exhibit retarded gain in body weight. This is generally attributed to lowered protein synthesis resulting from abnormal metabolism. Furthermore, decreased abundance and activity of Na,K-ATPase in heart and skeletal muscle has been described. However, decreased gain in body weight per se is accompanied by a down-regulation of skeletal muscle Na,K-ATPase. Thus, the aim of the present study was to evaluate cardiac Na,K-ATPase in semi-starvation and diabetes.

METHODS

Diabetes was induced in male Wistar rats with streptozotocin. In healthy parallel running control rats body weight gain was kept reduced by limited food intake.

RESULTS

Semi-starved and diabetic rats demonstrated 18 and 16% (p < 0.05) retarded gain in body weight after 63 days. As compared to semi-starved rats, diabetic animals exhibited a 59-273% (p < 0.05) increase in glucose, glycohaemoglobin, triglyceride and cholesterol plasma levels. Activity of heart K-pNPPase, reflecting Na,K-ATPase, in crude membrane homogenates was reduced by 29 and 10% (p < 0.05) by diabetes and semi-starvation. The age-dependent reduction in heart K-pNPPase in normal controls was 6%. After subtracting the age-dependent change, the reductions were 25 and 4% in diabetes and semi-starvation, respectively. After subtracting the semi-starvation-associated change, the diabetes-induced reduction was 22-27%. The reduction was in accord with measurements of Na,K-ATPase activities in partially purified membranes, Na,K-ATPase isoforms and cytochemical evaluations. Expressed per heart, the reduction in Na,K-ATPase was 30%.

CONCLUSIONS/INTERPRETATION

Streptozotocin-induced diabetes selectively reduces heart Na,K-ATPase concentration by around 1/4, which reduces the capacity of the heart for maintaining K- and Ca-homeostasis. This may pose a risk of arrhythmias and may be associated with heart failure in diabetic cardiomyopathy.

Myocardial Na,K-ATPase and digoxin therapy in human heart failure

The specific binding of digitalis glycosides to the Na,K-ATPase is used as a tool for Na,K-ATPase quantification with high accuracy and precision. In myocardial biopsies from patients with heart failure, total Na,K-ATPase concentration is decreased, and the decrease in Na,K-ATPase concentration correlates with a decrease in heart function. During digitalization, a fraction of remaining pumps are occupied by digoxin. No evidence for an endogenous digitalis-like factor of any clinical importance was obtained. It is recommended that digoxin be administered to heart failure patients who still have dyspnea after institution of mortality-reducing therapy.

Endotoxemia stimulates skeletal muscle Na+-K+-ATPase and raises blood lactate under aerobic conditions in humans

We assessed the hypothesis that the epinephrine surge present during sepsis accelerates aerobic glycolysis and lactate production by increasing activity of skeletal muscle Na(+)-K(+)-ATPase. Healthy volunteers received an intravenous bolus of endotoxin or placebo in a randomized order on two different days. Endotoxemia induced a response resembling sepsis. Endotoxemia increased plasma epinephrine to a maximum at t = 2 h of 0.7 +/- 0.1 vs. 0.3 +/- 0.1 nmol/l (P < 0.05, n = 6-7). Endotoxemia reduced plasma K(+) reaching a nadir at t = 5 h of 3.3 +/- 0.1 vs. 3.8 +/- 0.1 mmol/l (P < 0.01, n = 6-7), followed by an increase to placebo level at t = 7-8 h. During the declining plasma K(+), a relative accumulation of K(+) was seen reaching a maximum at t = 6 h of 8.7 +/- 3.8 mmol/leg (P < 0.05). Plasma lactate increased to a maximum at t = 1 h of 2.5 +/- 0.5 vs. 0.9 +/- 0.1 mmol/l (P < 0.05, n = 8) in association with increased release of lactate from the legs. These changes were not associated with hypoperfusion or hypoxia. During the first 24 h after endotoxin infusion, renal K(+) excretion was 27 +/- 7 mmol, i.e., 58% higher than after placebo. Combination of the well-known stimulatory effect of catecholamines on skeletal muscle Na(+)-K(+)-ATPase activity, with the present confirmation of an expected Na(+)-K(+)- ATPase-induced decline in plasma K(+), suggests that the increased lactate release was due to increased Na(+)-K(+)-ATPase activity, supporting our hypothesis. Thus increased lactate levels in acutely and severely ill patients should not be managed only from the point of view that it reflects hypoxia.

Outcome of clinical versus genetic family screening in hypertrophic cardiomyopathy with focus on cardiac beta-myosin gene mutations

OBJECTIVE

Familial hypertrophic cardiomyopathy (FHC) is caused by mutations in genes encoding cardiac sarcomere proteins. Although available, genetic analyses are generally not used clinically. In the present study, we evaluated the outcome of clinical vs. genetic screening of family members with specific focus on mutations in the cardiac beta-myosin heavy chain (MYH7) gene.

METHODS

A consecutive cohort of 68 FHC probands and their families (395 persons) of Danish origin was evaluated including patient- and family histories, physical examinations, electrocardiogram and echocardiography. Mutation screening was performed by a combination of single strand conformation/heteroduplex analysis and direct sequencing.

RESULTS

Eight different MYH7 gene mutations were identified in nine (13%) families (96 persons). In eight (89%) of the families, major cardiac events had occurred. Myectomy or percutaneous septal alcohol ablation had been performed in a higher number of MYH7 probands i.e. in five of nine (56%) as compared to 10 of 59 (17%) (P<0.05) non-MYH7 mutation probands. Neither echocardiographic nor ECG findings were useful to distinguish MYH7 from non-MYH7 probands. Between adult MYH7 mutation-carriers (n=38) and their non-carrier relatives (n=39), low sensitivity and specificity of the clinical diagnostic criteria tested were observed and minor clinical diagnostic criteria alone were not useful for identification of mutation carriers. By genetic screening of relatives with no or only minor hypertrophy on echocardiography, i.e. a priori possible mutation-carriers normally recommended clinical follow-up-the diagnosis was excluded in 52 (83%) persons. In addition, six relatives with secondary hypertrophy were identified as non-carriers.

CONCLUSION

Neither echocardiographic nor ECG findings were useful to distinguish MYH7 from non-MYH7 probands. Extension of screening to include genetic analyses offered a marked diagnostic advantage as compared to clinical screening alone in FHC families.

Myocardial Na,K-ATPase: Clinical aspects

The specific binding of digitalis glycosides to Na,K-ATPase is used as a tool for Na,K-ATPase quantification with high accuracy and precision. In myocardial biopsies from patients with heart failure, total Na,K-ATPase concentration is decreased by around 40%; a correlation exists between a decrease in heart function and a decrease in Na,K-ATPase concentration. During digitalization, around 30% of remaining pumps are occupied by digoxin. Myocardial Na,K-ATPase is also influenced by other drugs used for the treatment of heart failure. Thus, potassium loss during diuretic therapy has been found to reduce myocardial Na,K-ATPase, whereas angiotensin-converting enzyme inhibitors may stimulate Na,K pump activity. Furthermore, hyperaldosteronism induced by heart failure has been found to decrease Na,K-ATPase activity. Accordingly, treatment with the aldosterone antagonist, spironolactone, may also influence Na,K-ATPase activity. The importance of Na,K pump modulation with heart disease, inhibition in digitalization and other effects of medication should be considered in the context of sodium, potassium and calcium regulation. It is recommended that digoxin be administered to heart failure patients who, after institution of mortality-reducing therapy, still have heart failure symptoms, and that the therapy be continued if symptoms are revealed or reduced. Digitalis glycosides are the only safe inotropic drugs for oral use that improve hemodynamics in heart failure.An important aspect of myocardial Na,K pump affection in heart disease is its influence on extracellular potassium (K(e)) homeostasis. Two important aspects should be considered: potassium handling among myocytes, and effects of potassium entering the extracellular space of the heart via the bloodstream. It should be noted that both of these aspects of K(e) homeostasis are affected by regulatory aspects, eg, regulation of the Na,K pump by physiological and pathophysiological conditions, as well as by medical treatments. Digitalization has been shown to affect both parameters. Furthermore, in experimental animals, potassium loading and depletion are found to significantly affect K(e) handling. The effects of potassium depletion are of special interest because this condition often occurs in patients treated with diuretics. In human congenital long QT syndrome caused by mutations in genes coding for potassium channels, exercise and potassium depletion are well known for their potential to elicit arrhythmias and sudden death. There is a need for further evaluation of the dynamic aspects of potassium handling in the heart, as well as in the periphery. It is recommended that resting plasma potassium be maintained at around 4 mmol/L.

Fatigue depresses maximal in vitro skeletal muscle Na(+)-K(+)-ATPase activity in untrained and trained individuals

This study investigated whether fatiguing dynamic exercise depresses maximal in vitro Na(+)-K(+)-ATPase activity and whether any depression is attenuated with chronic training. Eight untrained (UT), eight resistance-trained (RT), and eight endurance-trained (ET) subjects performed a quadriceps fatigue test, comprising 50 maximal isokinetic contractions (180 degrees /s, 0.5 Hz). Muscle biopsies (vastus lateralis) were taken before and immediately after exercise and were analyzed for maximal in vitro Na(+)-K(+)-ATPase (K(+)-stimulated 3-O-methylfluoroscein phosphatase) activity. Resting samples were analyzed for [(3)H]ouabain binding site content, which was 16.6 and 18.3% higher (P < 0.05) in ET than RT and UT, respectively (UT 311 +/- 41, RT 302 +/- 52, ET 357 +/- 29 pmol/g wet wt). 3-O-methylfluoroscein phosphatase activity was depressed at fatigue by -13.8 +/- 4.1% (P < 0.05), with no differences between groups (UT -13 +/- 4, RT -9 +/- 6, ET -22 +/- 6%). During incremental exercise, ET had a lower ratio of rise in plasma K(+) concentration to work than UT (P < 0.05) and tended (P = 0.09) to be lower than RT (UT 18.5 +/- 2.3, RT 16.2 +/- 2.2, ET 11.8 +/- 0.4 nmol. l(-1). J(-1)). In conclusion, maximal in vitro Na(+)-K(+)-ATPase activity was depressed with fatigue, regardless of training state, suggesting that this may be an important determinant of fatigue.

Potassium depletion increases potassium clearance capacity in skeletal muscles in vivo during acute repletion

Muscular K uptake depends on skeletal muscle Na-K-ATPase concentration and activity. Reduced K uptake is observed in vitro in K-depleted rats. We evaluated skeletal muscle K clearance capacity in vivo in rats K depleted for 14 days. [(3)H]ouabain binding, alpha(1) and alpha(2) Na-K-ATPase isoform abundance, and K, Na, and Mg content were measured in skeletal muscles. Skeletal muscle K, Na, and Mg and plasma K were measured in relation to intravenous KCl infusion that continued until animals died, i.e., maximum KCl dose was administered. In soleus, extensor digitorum longus (EDL), and gastrocnemius muscles K depletion significantly reduced K content by 18%, 15%, and 19%, [(3)H]ouabain binding by 36%, 41%, and 68%, and alpha(2) isoform abundance by 34%, 44%, and 70%, respectively. No significant change was observed in alpha(1) isoform abundance. In EDL and gastrocnemius muscles K depletion significantly increased Na (48% and 59%) and Mg (10% and 17%) content, but only tendencies to increase were observed in soleus muscle. K-depleted rats tolerated up to a fourfold higher KCl dose. This was associated with a reduced rate of increase in plasma K and increases in soleus, EDL, and gastrocnemius muscle K of 56%, 42%, and 41%, respectively, but only tendencies to increase in controls. However, whereas K uptake was highest in K-depleted animals, the K uptake rate was highest in controls. In vivo K depletion is associated with markedly increased K tolerance and K clearance despite significantly reduced skeletal muscle Na-K-ATPase concentration. The concern of an increased risk for K intoxication during K repletion seems unwarranted.

Myocardial Na,K-ATPase: the molecular basis for the hemodynamic effect of digoxin therapy in congestive heart failure

Congestive heart failure may be deemed the epidemic of cardiology in the 21st century in the industrialized part of the world. Although new therapies improving morbidity and mortality from chronic heart failure have emerged it is likely that there is a growing role for digoxin. Thus, digoxin treatment is known to control symptoms of congestive heart failure when added to standard therapy. In this setting, we review the prevailing knowledge of the Na,K-ATPase, the cellular receptor for the inotropic action of digitalis glycosides, in relation to the hemodynamic effect of digoxin. It is concluded that if improvement of hemodynamics is needed in congestive heart failure, this knowledge should be taken into account and in many cases digoxin should be added to standard therapy. Digoxin is still the only safe inotropic drug for oral use that improves hemodynamics. Digoxin should be used to heart failure patients in sinus rhythm when they after institution of mortality reducing treatment still have heart failure symptoms, and to patients intolerant to heart failure mortality reducing drugs. Digoxin should probably in heart failure patients with sinus rhythm be given in the lowest possible dose that relieves symptoms sufficiently.