Chapter 68: Pathophysiology of Heart Failure
Which of the following is true of heart failure with preserved ejection fraction (HFpEF)?
A. HFpEF only affects a minority of patients with heart failure
B. HFpEF is defined as having a left ventricular ejection fraction (LVEF) > 55%
C. Therapies that are effective for heart failure with reduced ejection fraction (HFrEF) are not as effective for HFpEF
D. Diagnostic criteria for HFpEF are well defined
E. None of the above are true
The answer is C. (Hurst’s The Heart, 14th Edition, Chap. 68) Approximately half of heart failure (HF) patients have HFrEF and half have HFpEF (option A). A diagnosis of HFpEF is typically based on the ejection fraction of the left ventricle (LV) on cardiac imaging. The cutoff LVEF by which to distinguish HFrEF from HFpEF is not well established, but clinical trials (the same trials that have either supported or refuted a specific HF therapy for use) have used LVEF ≤ 35% to 40% to define HFrEF and LVEF ≥ 40% to 50% to define HFpEF (options B and D).1-8 It is important to distinguish between HFpEF and HFrEF because therapies that have a proven mortality and morbidity benefit in patients with HFrEF do not appear to be effective in patients with HFpEF, and to some extent these conditions may have fundamentally different pathophysiologic mechanisms and phenotypes (option C).4,5,7,9,10
Which of the following molecular changes are associated with a failing heart?
A. α-MHC is upregulated and β-MHC is downregulated
B. Action potential duration is shortened in patients with HF
C. Ca2+ uptake and release are dysregulated
D. Oxidative phosphorylation is increased
The answer is C. (Hurst’s The Heart, 14th Edition, Chap. 68) Two myosin heavy-chain (MHC) isoforms are present in the mammalian heart, α- and β-MHC. The α-MHC is cardiac specific and is more enzymatically active. The less active β-MHC is present in the heart and in slow-twitch skeletal muscle. The distribution of α- and β-MHC is developmentally and hormonally regulated. Mechanical stress, such as pressure overload, induces an α- to β-MHC transition in the ventricles of experimental animals, thus imparting a slower but more economical type of work for the overloaded heart (option A). A common feature of both animal and human models of HF is prolongation of the action potential (option B). Both decreased sodium influx ...