Systolic function Flashcards
What are systolic time intervals
- Accurate to assess LV performance
o Better indicators of LV systolic function (vs FS%)
o Not indicator of contractility - Measure the sequential phases of ventricular systole
o LV ejection time (LVET): from start to end of ejection
o LV pre-ejection period (PEP): onset of QRS/depol => start of ejection
o Velocity of circumferential shortening (Vcf)
Reflect rate of LV shortening
o LV ejection to pre-ejection period ratio (LVET/PEP)
Calculated to decr HR influence
Combine in 1 parameter indicator of myocardial performance
o Total electromechanical systole: onset of QRS => AoV closure (2nd heart sound) = PEP + LVET
Insensitive to decr contractility, preload changes
Influenced by afterload
STIs will be affected by
by HR and loading conditions
o STI can be corrected for HR: STI x HR x (slope of regression of HR vs STI curve)
Short cycle length (incr HR): underestimate LV perform.
Formula for Vcf
LVIDd-LVIDs/LVIDd x LVET
Influence of contractility on STIs
- incr PEP => decr rate of pressure rise (dP/dt)
- incr PEP/LVET
- decr LVET
- Normal or decr Vcf
- Normal QAVC
STIs: incr preload
incr preload and decr afterload mimic
incr contractility => decr PEP, incr LVET => decr PEP/LVET
decr preload and incr afterload mimic
decr contractility => incr PEP, decr LVET => incr PEP/LVET
Effects of afterload and contractility on LVET
Incr of decr afterload => incr LVET
Incr or decr contractility => decr LVET
Less useful for eval of myocardial failure or effect of inotropic tx
STIs: incr afterload
incr PEP from incr heart work => longer time to reach pressure in LV before AoV open
STI decr afterload
: LV function is easier
decr PEP: force to reach pressure is shorter
incr VCF: rate at which the heart contract is faster
STI incr preload
volume in the heart => Starling mechanism => incr contractility
decr PEP, incr LVET
STI decr preload
not allow force to be generated = incr PEP
STIs effect of HR
inversely related to LVET, no/little effect on PEP
o incr HR => decr LVET + incr PEP
o decr HR => incr LVET + decr Vcf
STI MR
incr PEP
decr LVET
incr PEP/LVET
STI SAS
decr PEP
incr LVET
decr PEP/LVET
Catecholamines
incr contractility and HR
decr PEP
decr LVET
decr PEP/LVET
decr QAVC
incr Vcf
What prolongs PEP
decr preload
incr afterload
decr myocardial fct
neg inotropes
What shortens PEP
incr preload
decr afterload
positive inotropes
What prolong LVET
incr preload
incr afterload
decr afterload
decr HR
What shortens LVET
decr preload
positive inotrope
negative inotropes
incr HR
What incr PEP/LVET
decr preload
neg inotropes
decr myocardial fct
incr HR
What decr PEP/LVET
incr preload
decr afterload
decr HR
Positive inotropes
What prolong QAVC
decr HR
incr afterload
neg inotropes
What shortens QAVC
incr HR
pos inotropes
What incr Vcf
decr afterload
decr myocardial fct
incr HR
pos inotropes
What decr Vcf
incr afterload
decr HR
neg inotropes
STIs CM
incr PEP
decr LVET
incr PEP/LVET
normal QAVC
decr Vcf
STIs VSD
incr PEP
decr LVET
incr PEP/LVET
— QAVC
— Vcf
STIs R CHF
incr PEP
decr LVET
incr PEP/LVET
— QAVC
— Vcf
STI hypoT4
incr PEP
decr LVET
incr PEP/LVET
— QAVC
— Vcf
STIs hyperT4
decr PEP
incr LVET
decr PEP/LVET
— QAVC
— Vcf
STIs diabetes
incr PEP
decr LVET
incr PEP/LVET
— QAVC
— Vcf
STI digitalis
decr PEP
—- LVET
decr PEP/LVET
— QAVC
incr Vcf
STI propanolol
incr PEP
NA LVET
incr PEP/LVET
— QAVC
— Vcf
STI hydralazine
decr PEP
incr LVET
decr PEP/LVET
— QAVC
— Vcf
What is LV dp/dt
- Clinical index of contractility
- Rate of LV pressure rise: dp/dt
o Load independent measure of LV contractility
o Occur during IVCT = isovolumic period → after/preload constant
What affects LV dp/dt
o Intrinsic myocardial contractility
o Mechanical dyssynchrony may dp/dt
ie BBB
o ↑ preload can affect contractility fron Starling’s law
Measure of LV dp/dt
- Non invasively with MR jet
o LA pressure do not change significantly during IVCT
AoV + MV closed
Load independant
o Time from 1m/s => 3m/s divided by 32mmHg
Represent pressure change of 32mmHg according to Bernoulli equation
o Average dp/dt over that period
o Generally underestimated - Invasively by heart catheterazation
o Micromanometer tip KT in chamber
What affects ejection phase indices
by contractility, pre and afterload
o incr preload => incr ejection phase indices (MR, AI, anemia…)
o decr afterload => decr ejection phase indices
What is assessed by ejection phase indices
- Not indicative of LV contractility
- Clinical measurement of LV systolic fct
Parameters of ejection phase indices
FS%
Thickening fraction
Vcf
EPSS
VTI of Ao flow
3D volumetric equivalents of ejection phase indices
- Ejection fraction (EF%): % of end diastolic volume ejected w each beat
o Normal <0.4, severe depression of LV function <0.2
EF (%) = (EDV - ESV)/EDV x 100
- Mean normalized ejection rate: indexes the EF to LVET
E rate = (EDV - ESV)/(EDV x ET)
- Cardiac output (CO):
o Insensitive indicator of cardiac performance => many compensatory mechanisms will aim to maintain CO in cardiac dz
o SV: estimated by calculating LV volumes (diastolic – systolic) or blood flow velocity in great vessels
CO = SV x HR
What is LV FS%
- Change in dimension from end diastole => end systole
- Normal values => dogs: 25-45%, cats: 30-55%
FS (%) = (LVIDd - LVIDs)/LVIDd x 100
What is thickening fraction
- % of change in LVFW or IVS thickness
- Useful when heterogenous myocardial performance
What is Vcf
Velocity of myocardial fiber shortening (Vcf)
* Rate of change in LV circumference
o End diastolic endocardial circumferential length end systolic
* Normal values: dogs: 1.6-1.8 circ/s
Vcf = (LVIDd - LVIDs)/(LVIDd x ET)
What is EPSS
Mitral E point to septal separation (EPSS)
* Max initial opening of MV => normal values = dogs: <6mm, cats: <4-5mm
o Inversely proportional to LA => LV flow
o Indicator of LV dysfunction
What is VTI Ao flow
- Area under the systolic ejection curve
- Correlates to SV if AoV diameter is constant
Major determinants of systolic function
Preload
Afterload
Contractility
HR
How does preload affect systolic fct
- Load before the contraction has started = force stretching the myocardium
- Provided by venous return
o incr preload => ventricular distension => incrSV
o Starling’s law: incr stretch of myocardial fibers => incr ventricular performance
incr contraction velocity and force
Optimal overlap of actin and myosin
Enhanced sensitization of actin-myosin to Ca2+ transient - Hypertrophy pattern: eccentric
How does afterload affect systolic fct
- Load after the ventricle starts to contract
- Determined by
o Arterial blood pressure
o Aortic compliance: Ao pressure/Ao flow
Varies throughout systole - incr afterload
o incr intraventricular pressure => incr wall stress
o stimulates sarcolemma stretch => incr intra¢ [Ca2+] - Wall stress: tension (force that tend to pull apart) applied to a CSA
o Law of Laplace: see figure
o incr wall thickness will compensate incr pressure/volume
o incr radius (chamber dilation) => incr wall stress - Peak force developed pressure: total # of cross bridges since start of systole=> depend on
o Initial fiber length
o Systolic Ca2+ incr
o Ca2+ responsiveness of myofilaments
o Myosin light chain phosphorylation
o Loading - Hypertrophy pattern: concentric
How does contractility affect systolic fct
- Inotropic state
- Important regulator of O2 uptake
- incr interaction of Ca2+ and contractile proteins
o incr Ca2+ transients
o Sensitization of contractile proteins to Ca2+ - Maximal velocity of contraction (Vmax or V0)
o incr with symp activation
o Proportional to:
Myosin ATPase activity
Rate limiting steps in cross bridge cycle
Rate of incr and peak level of cytosolic Ca2+ - Maximal tension (P0): related to # of attached cross bridges and peak Ca2+
How does HR affect systolic fct
- Acute regulation of contractile state (w Frank Starling and autonomic control)
- Determinant of myocardial O2 demand (w myocardial wall stress and contraction velocity)
o Force frequency relationship (= positive inotropic effect of activation)
Bowditch staircase or Treppe effect
incr HR => incr contractility and force of ventricular contraction
incr Na+ and Ca2+ influx => overwhelme Na+/K+ pump => incr [Na+] => activation of Na+/Ca2+ exchanger => Ca2+ influx => incr [Ca2+]
Particularities of RV systolic fct
- 3 systolic phases:
o Contraction of papillary muscles
o Mvt of RVFW => IVS
o Wringing of the RV 2nd to LV contraction - Contraction starts at the apex => thin walled/compliant upper region
o Slow and continuous blood flow into lungs - Shorter IVRT/IVCT
- Longer ET
Clinical indices of myocardial contractility
Isovolumic indices: dP/dt
Load sensitive indices:
- EF% FS%
-Vcf
End systolic indices
End systolic volume
end syst PV relationship
end syst wall stress
PV loops
TDI: IVCT
Clinical indices of myocardial contractility
LV fct curves
Maximal rate of LV pressure generation
Ejection phase indices
Volumetric flow
Myocardial performance index
Tissue Doppler indices
Invasive assessment of systolic fct
- KT based methods: end systolic elastance (Es), +dT/dP
- Indicator dilution methods: thermodilution, indocyanine green, Fick, lithium dilution
- Imaging: SPECT, cineangiography, radionuclide angiography, MRI, SPECT
Non invasive assessment of systolic fct
- M-mode/2D
o LVIDd, EPSS
o LV volume: SMOD
o Load dependent indices: FS, EF, Vcf, SV, CO
o Wall stress - Doppler
o E wave: decr if decr CO
o dP/dT of MR
o Tei index: (IVCT-IVRT)/ET
o LV dP/dT
o STIs : PEP, LVET, PEP/ET - TDI
o Pulse wave S wave
o Strain, strain rate
o Speckle tracking - RV function
o Tricuspid annular motion
o Myocardial performance indices
o CaVC imaging
o TR => PAPs
Left ventricular function curves
- Obtain with IV infusion => vary end diastolic volume => repetitive measures
o Swan-Ganz KT: pulmonary wedge pressure as surrogate of heart volume/end diastolic fiber length - Based on Starling relationship
- Pressure volume loops:
o As preload incr => volume incr => incr contractility =>icnr SV => decr end systolic volume at similar end systolic pressure
o incr slope of end systolic pressure volume relationship
Maximal rate of LV pressure generation
- During IVCT: constant preload/afterload
o Maximal rate of pressure generation = index of inotropic state
o Inotropic index = max dP/dt - Preload can still influence by incr contractile state with incr length activation
- LV KT necessary (transducer tipped KT)
o If MR present => can assess LA/LV pressure gradient
Ejection phase indices
EF
FS
Vcf
Ejection phase indices
MV and TV annular motion
Calculation of EF
relates stroke volume to end diastolic volume
o Index of the extent of LV fiber shortening
o Relates systolic emptying of the end diastolic volume, but no information about this volume
Does not imply forward SV
Measure of volume leaving LV (MR, shunt…)
o Determined by volume measurements
Teicholz method: assume LV as an ellipse
* LV overload => changes LV geometry to more spherical shape
* Normal according to BSA:
o Systolic <30ml/m2
o Diastolic <100ml/m2
Simpson’s rule: best correlation w actual LV volumes
* Unaffected by changes in geometry
* Computerized calculation of volume from stack of discs from LAX planes in systole and diastole
* Volume = 0.85 A2/L
* Normal according to BSA: systolic <30ml/m2 , diastolic <70ml/m2
Bullet methods: assume bullet shaped ventricle
* Transverse images at level of chordae + length on LAX
* LVV = 5/6 x area x length
Calculation of FS
% of change of LV chamber size in systole
o Measure of contractility, not function
o Factors affecting: contractility, afterload, preload
decrFS% => decr contractility, decr preload, incr afterload
Calculate Vcf
velocity of circumference change in systole
o Minor axis: distance from the L side of IVS => LVFW
o incr afterload => decr Vcf: slower contraction rate
MV and TV annular motion
o Correlated to EF%: decr if decr EF
o Normal in dogs:0.46 to 1.74cm
Influenced by BW => can be indexed on BSA
o TAPSE: TV
Poorer px in Hu w L-CHF 2nd to DCM or PH
Volumetric flow
- Continuity equation: volume in = volume out
o Flow profile: area under the curve = VTI
o Area of the vessel
VTI = (Velocity x ET)/2
CSA = πr2
SV = VTI x CSA
Myocardial performance index
- Global myocardial function => correlates w diastolic + systolic fct
- Preload and BP independent
- Affected by acute changes in loading conditions
MPI = (IVRT - IVCT)/ET
Tissue Doppler
- Systolic wave (S’) and diastolic waves (E’ and A’)
- Q-S’: time from start of QRS => S’
Contrast contractility vs. systolic function, what is the difference?
- Contractility is an inherent property of the myocardium
- Systolic function is the performance of the myocardium, and can be affected by several factors
