https://www.cell.com/cell/pdf/0092-8674(95)90340-2.pdf

A mechanistic link between an inherited and an acquird cardiac arrthytmia: HERG encodes the IKr potassium channel

Left ventricular hypertrophy (LVH) is the major risk factor associated with myocardial failure. An explanation for why a presumptive adaptation such as LVH would prove pathological has been elusive. Insights into the impairment in contractility of the hypertrophied myocardium have been sought in the biochemistry of cardiac myocyte contraction. Equally compelling is a consideration of abnormalities in myocardial structure that impair organ contractile function while preserving myocyte contractility. For example, in the LVH that accompanies hypertension, the extracellular space is frequently the site of an abnormal accumulation of fibrillar collagen. This reactive and progressive interstitial and perivascular fibrosis accounts for abnormal myocardial stiffness and ultimately ventricular dysfunction and is likely a result of cardiac fibroblast growth and enhanced collagen synthesis. The disproportionate involvement of this nonmyocyte cell, however, is not a uniform accompaniment to myocyte hypertrophy and LVH, suggesting that the growth of myocyte and nonmyocyte cells is independent of each other. This has now been demonstrated in in vivo studies of experimental hypertension in which the abnormal fibrous tissue response was found in the hypertensive, hypertrophied left ventricle as well as in the normotensive, nonhypertrophied right ventricle. These findings further suggest that a circulating substance that gained access to the common coronary circulation of the ventricles was involved. This hypothesis has been tested in various animal models in which plasma concentrations of angiotensin II and aldosterone were varied. Based on morphometric and morphological findings, it can be concluded that arterial hypertension (i.e., an elevation in coronary perfusion pressure) together with elevated circulating aldosterone are associated with cardiac fibroblast involvement and the resultant heterogeneity in tissue structure. Nonmyocyte cells of the cardiac interstitium represent an important determinant of pathological LVH. The mechanisms that invoke short- (e.g., collagen metabolism) and long-term (e.g., mitosis) responses of cardiac fibroblasts require further investigation and integration of in vitro with in vivo studies. The stage is set, however, to prevent pathological LVH resulting from myocardial fibrosis as well as to reverse it.

Pathological hypertrophy and cardiac interstitium. Fibrosis and renin-angiotensin-aldosterone system.

Smooth muscle cells in the walls of many organs are vital for most bodily functions, and their abnormalities contribute to a range of diseases. Although based on a sliding-filament mechanism similar to that of striated muscles, contraction of smooth muscle is regulated by pharmacomechanical as well as by electromechanical coupling mechanisms. Recent studies have revealed previously unrecognized contractile regulatory processes, such as G-protein-coupled inhibition of myosin light-chain phosphatase, regulation of myosin light-chain kinase by other kinases, and the functional effects of smooth muscle myosin isoforms. Abnormalities of these regulatory mechanisms and isoform variations may contribute to diseases of smooth muscle, and the G-protein-coupled inhibition of protein phosphatase is also likely to be impor-tant in regulating non-muscle cell functions mediated by cytoplasmic myosin II.

Signal transduction and regulation in smooth muscle

There is growing recognition that congestive heart failure (CHF) caused by a predominant abnormality in diastolic function (ie, diastolic heart failure) is both common and causes significant morbidity and mortality. However, there is continued controversy surrounding the definition of diastolic dysfunction and the diagnostic criteria for diastolic heart failure. As a result, clinical therapeutic trials have been slow to develop and difficult to design. Fortunately, these controversies are yielding to an emerging consensus. Recent clinical studies have provided sufficient data to develop standardized diagnostic criteria to define diastolic heart failure.1–4⇓⇓⇓ Experimental studies have provided increased insight into the mechanisms that cause diastolic heart failure.5–22⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓ Together, these clinical and experimental studies are being used to design targeted clinical trials to test effective treatments for diastolic heart failure. The purpose of this 2-part article is to provide a perspective on these issues, highlight new research, and introduce emerging ideas. Part 1 will focus on the criteria used to diagnose diastolic heart failure, the effects of diastolic heart failure on prognosis, and measurements used to assess diastolic function. Part 2 will describe the mechanisms that cause diastolic heart failure and discuss approaches to treatment.

### Differentiating Diastolic Dysfunction From Diastolic Heart Failure

Heart failure is a clinical syndrome characterized by symptoms and signs of increased tissue/organ water and decreased tissue/organ perfusion. Standardized criteria to diagnose heart failure have been developed, perhaps the best validated of which come from the Framingham Study.23 Definition of the mechanisms that cause this clinical syndrome requires measurement of both systolic and diastolic function. When heart failure is accompanied by a predominant or isolated abnormality in diastolic function, this clinical syndrome is called diastolic heart failure.

Diastolic dysfunction refers to a condition in which …

New Concepts in Diastolic Dysfunction and Diastolic Heart Failure: Part I Diagnosis, Prognosis, and Measurements of Diastolic Function

Rationale: Sleep-disordered breathing recurrent intermittent hypoxia and sympathetic nervous system activity surges provide the milieu for cardiac arrhythmia development.Objective: We postulate that the prevalence of nocturnal cardiac arrhythmias is higher among subjects with than without sleep-disordered breathing.Methods: The prevalence of arrhythmias was compared in two samples of participants from the Sleep Heart Health Study frequency-matched on age, sex, race/ethnicity, and body mass index: (1) 228 subjects with sleep-disordered breathing (respiratory disturbance index ⩾ 30) and (2) 338 subjects without sleep-disordered breathing (respiratory disturbance index < 5).Results: Atrial fibrillation, nonsustained ventricular tachycardia, and complex ventricular ectopy (nonsustained ventricular tachycardia or bigeminy or trigeminy or quadrigeminy) were more common in subjects with sleep-disordered breathing compared with those without sleep-disordered breathing: 4.8 versus 0.9% (p = 0.003) for atrial fibri...

/pdf/association-of-nocturnal-arrhythmias-with-sleep-disordered-43nsfi4v8z.pdf

Association of nocturnal arrhythmias with sleep-disordered breathing: The sleep heart health study

This book contains 72 chapters. Some of the chapter titles are: Nuclear Magnetic Resonance; Radionuclide Methods to Assess Cardiac Function, Perfusion Viability and Necrosis; NMR Imaging of the Cardiovascular System; Quantitative Angiographic Techniques; RNA Transcription in Heart Muscle; Reentry Rhythms; and Effect of Ischemia on Cardiac Electrophysiology.

E. Haber

Papers

The heart and cardiovascular system