Diastolic function Flashcards
What is tau
Indicator of ventricular compliance: time constant for relaxation
* Tau (T): duration (ms) for ventricular pressure to fall 1/3 (63%) from its initial value at MV opening to the most negative pressure
o Most accurate method to measure ventricular compliance
o = 1/compliance
Describe ventricular relaxation process. How does it pertain to Tau?
- Ventricular relaxation = active process
o Ca2+ removed from cytosol against [gradient]
o Relaxation rate determine the rate of pressure fall in the ventricle
Rapidity of this drop = time constant Tau
* Tau ↓ → good relaxation
* Tau ↑ → reduced relaxation
o Delayed relaxation = prolong Tau
Measured during IVRT: no change in loading conditions
Other indicators of ventricular compliance
o Ratio or end diastolic volume to end diastolic pressure
o Rate of fall of ventricular pressure (-dP/dt) during IVRT
o Slope of curve from ventricular volume and pressure during diastole
Goal of diastolic fct
allows heart to fill appropriately at normal filling pressures
Diastolic dysfct leads to
myocardial alterations leading to incr resistance to filling and incr LVP
- With age, LV becomes stiffer and relaxes more slowly
Define diastolic period
- Correspond to closure of semilunar valves to closure of AV valves
o T wave => start of QRS
Phases of diastole
1) Isovolumic relaxation phase
o Rapid energy dependant relaxation of LV myocardium => decr LVP
o Require ATP for Ca2+ uptake by SR = active process
o Rate of early diastolic LV relaxation
incr w impaired ralaxation
decr w incr LAP
2) Rapid/early filling => 80% of ventricular filling
o Peak flow velocity proportional to the pressure gradient LA => LV
LV suction effect: LVP continues to decr
o LVP decr < LAP
3) Slow filling/diastasis => 5%
o LVP incr to = LAP
4) Atrial contraction => 15%
o incr LAP > LVP
Cellular factors influencing relaxation
- decr intra¢ [Ca2+]: SR uptake of Ca2+ require =
o ATP
o Pi of phospholamban - Pi of troponin I => incr rate of relaxation
- Inherent viscoelastic properties of myocardium
- Systolic load: incr systolic load => incr rate of relaxation
o Rate of decr in Ca2+ is greater - Others: pericardium, atrial function, ventricular interaction and afterload
How does ventricular interaction influence myocardial relaxation
o RV & LV fct = intimately linked
CO of LV must equate RV
Except if imbalance, ie. Acute LV failure and pulmonary edema
o Pressure work from RV < LV.
RV has normally thin walls
LV hypertrophy include IVS => can incr RV work => RV hypertrophy = systolic ventricular interaction
o Bernheim effect: large LV can compress RV
Impair RV filling
Diastolic function determinants
- Active relaxation of the myocardium
- Compliance of the LV
- Pump function of the LA and PVs
- HR
- Age
What is a feature of atrial function
Atrial contraction: Presystolic contraction = booster function = helps to complete LV filling
o Smaller myo¢
o Shorter AP: incr outward K+ currents (KAch + ITO)
o Fetal myosin phenotype
LA volume is indicator of
useful indicator of presence, chronicity and severity of diastolic dysfct
* In diastolic dysfct: compensatory incr in atrial contraction
o incr A wave on Doppler mitral filling pattern
Brainbridge reflex
incr venous return => mechanoR => incr SA node d/c rate => tachycardia
How does pericardium influence diastolic fct
- Pericardium and endocardium
o Restraining effect on diastolic properties of ventricles, especially RV
o W/o pericardium: RV would dilate by 40%, RA by 70% - Pericardial disease: effusive or constrictive
o Acute volume incr => intrapericarial pressure > RA/RVP => decr venous filling
Diastolic volume : influenced by
o Loading conditions
o Elastic properties: ability to recover normal shape after removal of systolic stress
Compliance curve
- Compliance: relationship btw change in stress and resultant strain => curvilinear
o Gentle initial slope
o As pressure incr => volume increase less
o Considerable incr in pressure for small incr volume
o Influence Starling curve + pressure-volume loop + early diastolic filling
decr compliance => lower Starling curve
incr upward baseline on pressure-volume loop = incr LAP for early filling required
Parameters of diastolic fct on echo
- 2D and M-mode
o LA size
o B-bump: late diastolic reopening of MV - Doppler flow patterns
o IVRT
o Transmitral valve flow: peak E, A waves, Edec, E:A, DTe - Color M mode: Vp
- PV flow: S/D ratio
o Flow reversal seen during Akick → A: Ar
o High velocity reversed flow - MR: -dP/dT
- Invasive methods
o Tau: rate of fall of LV pressure during IVRT
o -dP/dT
o Diastolic pressure-volume relationships
Diastolic dysfct can be 2nd to
- Impaired relaxation
o incr early diastolic LVP => delayed LV filling => incr atrial contraction contribution to filling
o Hypertorphy, ischemia - Decreased LV compliance
o Stiff LV = pressure incr rapidly as LV fill
o Larger role in late diastole when LV is partially filled
o Fibrosis, infiltrative process, hypertrophy, structural abnormalities - Forward failure => decr volume 2nd to decr filling
- Backward failure => incr LV filling pressure => incr LAP
E wave
rapid early filling
o Peak E wave: reflect LA=> LV pressure gradient at beginning of diastole
o E wave deceleration: reflect time for equilibration of pressures
i proportional to stiffness
A wave
reflect LA => LV pressure gradient at end of diastole
o Small amount of filling
o Normally smaller vs E wave
Factors affecting E/A waves
tachycardia, 1˚AVB, Afib
E’ wave
brisk motion of mitral annulus as chamber expands
* Less dependent on preload
Changes in spectral Doppler w/ diastolic dysfct
- decr E wave, incr deceleration time
- incr A wave, decr E/A ratio
- incr IVRT
- decr E’
- incr E/E’ ratio (at any stage of diastolic failure)
Stages of diastolic dysfct
Delayed relaxation
Pseudonormal
Restrictive physiology
