Impact of obstructive and central apneas on ventricular repolarisation: lessons learned from studies in man and pigs.

BACKGROUND: Sleep apnea (SA) is associated with sudden cardiac death. Compared to central apneas, obstructive apneas are associated with negative intrathoracic pressure swings inducing autonomic imbalance, which may disturb ventricular repolarisation resulting in arrhythmias. OBJECTIVES: To identify the influence of obstructive apneas versus central apneas on ventricular repolarisation. METHODS: In 14 patients with SA, duration (RT-intervals) and dispersion of ventricular repolarisation [Tpeak-to-Tend-interval (TpTe)] were determined during central apneas compared to obstructive apneas. To identify mechanisms, hypoxia alone or hypoxia with applied negative thoracic pressure was applied in a pig model for SA before and after atropine (n = 7), atenolol (n = 5) and sympathetic renal denervation (RDN, n = 7). RESULTS: In patients with SA, obstructive apneas during sleep were always associated with a prolongation of RT- as well as TpTe intervals. By contrast central apneas did not affect ventricular repolarisation significantly in the same patients. In the pig model for SA, 2 min of acute tracheal occlusion with applied negative thoracic pressure resulted in a prolongation in RT- and TpTe-interval. These changes in ventricular repolarisation could be inhibited by atenolol as well as by RDN and were not influenced by parasympathetic blockade by atropine. By contrast hypoxia alone did not affect ventricular repolarisation. CONCLUSIONS: Intrathoracic pressure swings during obstructive apneas contribute to changes in ventricular repolarisation, which are not observed with central apneas. These changes are mainly driven by sympathetic activation and may represent mechanisms for increased occurrence of sudden cardiac death in obstructive SA.

A background Ca2+ entry pathway mediated by TRPC1/TRPC4 is critical for development of pathological cardiac remodelling.

AIMS: Pathological cardiac hypertrophy is a major predictor for the development of cardiac diseases. It is associated with chronic neurohumoral stimulation and with altered cardiac Ca(2+) signalling in cardiomyocytes. TRPC proteins form agonist-induced cation channels, but their functional role for Ca(2+) homeostasis in cardiomyocytes during fast cytosolic Ca(2+) cycling and neurohumoral stimulation leading to hypertrophy is unknown. METHODS AND RESULTS: In a systematic analysis of multiple knockout mice using fluorescence imaging of electrically paced adult ventricular cardiomyocytes and Mn(2+)-quench microfluorimetry, we identified a background Ca(2+) entry (BGCE) pathway that critically depends on TRPC1/C4 proteins but not others such as TRPC3/C6. Reduction of BGCE in TRPC1/C4-deficient cardiomyocytes lowers diastolic and systolic Ca(2+) concentrations both, under basal conditions and under neurohumoral stimulation without affecting cardiac contractility measured in isolated hearts and in vivo. Neurohumoral-induced cardiac hypertrophy as well as the expression of foetal genes (ANP, BNP) and genes regulated by Ca(2+)-dependent signalling (RCAN1-4, myomaxin) was reduced in TRPC1/C4 knockout (DKO), but not in TRPC1- or TRPC4-single knockout mice. Pressure overload-induced hypertrophy and interstitial fibrosis were both ameliorated in TRPC1/C4-DKO mice, whereas they did not show alterations in other cardiovascular parameters contributing to systemic neurohumoral-induced hypertrophy such as renin secretion and blood pressure. CONCLUSIONS: The constitutively active TRPC1/C4-dependent BGCE fine-tunes Ca(2+) cycling in beating adult cardiomyocytes. TRPC1/C4-gene inactivation protects against development of maladaptive cardiac remodelling without altering cardiac or extracardiac functions contributing to this pathogenesis.

Relationship between heart rate and mortality and morbidity in the irbesartan patients with heart failure and preserved systolic function trial (I-Preserve).

BACKGROUND: Higher heart rate is associated with poorer outcomes in patients with heart failure and reduced ejection fraction (HF-REF). Less is known about the association between heart rate and outcomes in patients with heart failure and preserved ejection fraction (HF-PEF). Therefore, we examined the relationship between heart rate and outcomes in the irbesartan in patients with heart failure and preserved systolic function trial (I-Preserve) in patients with an ejection fraction >45% aged >60 years. METHODS AND RESULTS: Heart rate was analysed as both a categorical (tertiles) and continuous variable. Patients in sinus rhythm (n = 3271) and atrial fibrillation (n = 696) were analysed separately. The outcomes examined were the primary endpoint of the trial (all-cause death or cardiovascular hospitalization), the composite of cardiovascular death or heart failure hospitalization (and its components) and all-cause death alone. Higher heart rate was associated with a significantly higher risk of all outcomes studied for patients in sinus rhythm, even after adjustment for other prognostic variables, including N-terminal pro-B-type natriuretic peptide. Each standard deviation (12.4 bpm) increase in heart rate was associated with an increase in risk of 13% for cardiovascular death or heart failure hospitalization (P = 0.002). No relationship between heart rate and outcomes was observed for patients in atrial fibrillation. Beta-blocker treatment did not reduce the heart rate-risk relationship. CONCLUSIONS: In patients with heart failure and preserved ejection fraction, heart rate is in sinus rhythm an independent predictor of adverse clinical outcomes and might be a therapeutic target in this syndrome. Clinical Trial Registration - URL http://www.clinicaltrials.gov. Unique identifier: NCT 0095238.

Renal denervation: a novel non-pharmacological approach in heart failure.

Heart failure is associated with activation of the sympathetic nervous system which presumably results in a progression of the syndrome and thereby in poor outcome. Renal denervation has shown to be effective in conditions with enhanced sympathetic activity like resistant hypertension and metabolic syndrome associated with sleep apnea. The first pilot trials assessing the effect of renal denervation on signs and symptoms of heart failure in patients with both preserved and reduced left ventricular ejection fraction are presently ongoing. The results of these studies will determine whether to proceed with larger prospective outcome trials. Altogether, renal denervation is a promising novel technique that may improve the outcome of patients with sympathetic hyperactivity and cardiovascular diseases.

Therapeutic potential of renal sympathetic denervation in patients with chronic heart failure.

Chronic heart failure is associated with sympathetic activation characterised by elevated circulating norepinephrine levels linked to cardiovascular morbidity and mortality. Norepinephrine induces phenotype changes of the cardiomyocyte, fibrosis and ß-adrenergic signal transduction defects implicated in the dysregulation of contractility. Renal denervation reduces left ventricular hypertrophy and improves diastolic dysfunction, partly blood pressure independently. Also, exercise tolerance and cardiac arrhythmias are positively influenced. Furthermore, there is evidence that common comorbidities like sleep apnoea, metabolic disease and microalbuminuria are improved following renal denervation. The available evidence suggests performing randomised controlled trials to scrutinise whether renal sympathetic denervation might be able to improve morbidity and mortality in chronic heart failure with preserved or reduced ejection fraction.

Overview of the i-SEARCH Global Study : Cardiovascular Risk Factors and Microalbuminuria in Hypertensive Individuals.

Microalbuminuria (MAU) is a highly predictive, sensitive, inexpensive and easily repeatable marker of cardiovascular risk and all-cause mortality in hypertensive patients. The international, observational, practice-based study i-SEARCH (Survey for Evaluating Microalbuminuria Routinely by Cardiologists in patients with Hypertension) was designed to assess the frequency with which MAU occurred in a large outpatient population who were currently treated or newly diagnosed with hypertension and were under professional care. The primary aim of the study was to define the prevalence of MAU in hypertensive outpatients attending a cardiologist or internist (i-SEARCH A) and to compare hypertensive outpatients with or without coronary artery disease (i-SEARCH B). A secondary objective was to establish a correlation between MAU and known cardiovascular risk factors. A total of 21 050 patients from 26 countries were included in the primary analysis. Overall, this study demonstrated a very high worldwide prevalence (58.4%) of MAU in high-risk cardiovascular patients, but with a considerable variation across countries. MAU was more prevalent in patients with coronary artery disease than in those without. It was also significantly related to the presence of specific predictors, including male gender, abnormally high waist circumference, increased blood pressure levels (systolic ≥120 mmHg, diastolic ≥100 mmHg), creatinine clearance ≥50 mL/min, or clinical conditions such as diabetes mellitus, congestive heart failure, history of cerebral pathology, and peripheral arterial disease. Since the presence of MAU reflects long-term detrimental effects on the cardiovascular system, these results indicate the high, and in many cases hidden, burden of cardiovascular diseases among the hypertensive patients seen by cardiologists. This article discusses the main results of the study and the potential implications of ongoing analyses included in the core clinical study programme.