Page 7 - CBAC Newsletter 2015

the meaning oF ‘diastoliC FunCtion’!

By sándor kováCs, m.d., Ph.d.

Department of Medicine, Cardiovascular Division
Washington University School of Medicine, St. Louis, MO

There is currently an epidemic of heart failure (2, 13, It therefore follows that LVEF is affected by heart size
22), in particular, diastolic heart failure (1, 12, 14), or and load, and indeed it is used to classify HF into low EF
heart failure with preserved ejection fraction (HFpEF), vs. preserved EF categories. No simple, dimensionless
whose molecular mechanisms, clinical features and parameter of diastolic function analogous to LVEF for
therapies have been recently reviewed (38). Therefore, it systolic function/contractility has been
is more important than ever to understand the derived or proposed. Importantly, a key distinction
physiology of diastole, or, the mechanism by which all between ‘congestive heart failure’ usually due to
hearts fill and therefore, the meaning of ‘diastolic impaired ejection fraction (LVEF < 35%) and HFpEF is
function.’ Usually the phrase ‘diastolic function’ is that impairment of cardiac output is not a key causal
interpreted as some metric or index or number that determinant of HFpEF. To appreciate the meaning of
conveys filling function. For a practicing clinician, ‘diastolic function’ the elegant and curious multiscale
‘diastolic function’ is relevant in assessing clinical physiology of how all hearts work when they fill merits
history and symptoms. Clinically, diastolic dysfunction consideration in detail.
tends to manifest initially as breathlessness associated
with activities of daily living or minimal exertion. Often, Common misconceptions remain about the filling
the causal mechanism of transient diastolic dysfunction process. Diastolic function can be better understood
such as ischemia induced impaired relaxation, is when one considers the basic principles that govern it.
amenable to pharmacologic therapy (38). In other
circumstances adverse chamber remodeling (increased These principles are:
stiffness, fibrosis) due to hypertension, chronic atrial
fibrillation etc. results in symptomatic diastolic 1) The four-chambered heart is (within 5%) a
dysfunction (40) where treatment is guided by relief of constant-volume pump, and
symptoms rather than based on understanding and 2) all LVs (and RVs) initiate filling by being mechanical
reversing the underlying cause. suction pumps,
3) the volume at diastasis is the in-vivo equilibrium
By analogy, the term ‘systolic function’ or ‘contractility’ volume of the LV, and
is usually interpreted in terms of left ventricular ejection 4) all four heart chambers are primarily volume-pumps
26 NEWS & ANNOUNCEMENTS fraction (LVEF) where the dimensionless, normal for the entire cardiac cycle, except for the LV, which is a
29 CBAC 10 ANNIVERSARY LVEF = (stroke volume)/(end-diastolic volume) falls in the pressure-volume pump only in systole.
TH
1
50% or greater range.
SYMPOSIUM Constant-volume pumping physiology
32 PUBLICATIONS 1 The fact that LVEF is also an index of diastolic function is not Leonardo da Vinci (1452 to 1519) observed that

46 LECTURES & PRESENTATIONS taught, nor generally appreciated. Consider the definition of ejec- — “the atria or filling chambers contract together while
tion fraction: LVEF=SV/LVEDV= (E-wave VTI + A-wave VTI)/(diastatic
the pumping chambers or ventricles are relaxing and
52 CBAC MEMBER LISTING volume + A-wave VTI). When written in this way, using only diastolic vice versa”. This description of constant-volume pump-
function indexes, it explicitly reveals the critical physiologic impor-
55 CBAC 2015-2016 SEMINAR tance of the volume at diastasis (the chamber’s equilibrium vol- ing means that when the ventricles eject, the atria simul-
taneously fill, because the apical aspect and
ume) as the volume relative to which the LV oscillates as a volume
SCHEDULE pump! So, LVEF is indeed a diastolic function index!

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