Model-Based decomposition of myocardial strains:activation time and contractility mapping
Borut Kirn
Department of Biomedical EngineeringUniversity of MaastrichtThe Netherlands
In collaboration
Institute of PhysiologyUniversity of LjubljanaSlovenia
Detection of cardiac motion
MRI-tagging US - speckle tracking
Coordinated contraction
Circumferential strain (εcc)
Left bundle brench block (LBBB) and
Ischemia
Discoordinated contraction
LBBB
LBBB + Ischemia
Clinical problem
In cardiac resynchronization therapypatients are selected upon:
• QRS duration (LBBB)• Heart failure indices (LV dilatation, low EF)
30% of patients show no benefit + 20% no reduction of LV dilatation
Can we improve patients selection and PM positioning using mechanical indices?
Normal conduction
0 100 200 300 400
time [s]Time[ms]
P
Q
R
S
Short QRS duration
Conduction during LBBB
time [s]
0 100 200 300 400
Prolonged QRS duration
Time[ms]
P
Q
R
S
Ischemia
onset of shortening
Mechanical indices of asynchrony
• Onset of shortening time is not activation time
• Early activated regions are not detected
• Activation time is only one component of dyscoordination
However,
Aims
• Design of a model to simulate local circumferential shortening (εcc) for different
– activation time (Act) – contractility (Con)
• Mapping by inverse use of model fit to εcc
– map of Act– map of Con
CircAdapt model of heart and circulation
Dynamic(t)CompliancesInertiasNon-linear
Modeling of circulation- lumped model in modules: chambers, tubes, valves
Arts T et al. Am J Physiol. 2005;288:H1943-H1954
Adaptation of modules to load,i.e. wall mass, cavity size
Characteristics of CircAdapt
• Modular architecture
• Structured parameter data base
C i r c A d a p t
CavityMech
Tubes
SarcMech(Act, Con)
Timing
Valves
RepSarcSarcMech
(Act, Con)SarcMech(Act, Con)SarcMech
(Act, Con)SarcMech(Act, Con)SarcMech
(Act, Con)SarcMech(Act, Con)SarcMech
(Actn, Conn)
Act, Con Actn-2, Conn-2Actn-1, Conn-1
Actn, Conn
CircAdapt with Multi-segment myofiber
Sarcomere element:
PassiveActive
n
1
2
3
n-1
Assumption: Equal stress in all regions of ventricular wall
Solving inverse problem
INPUT PARAMETERS:
MODEL
RESULT:
Act1, Act2 … Act160
Con1, Con2 … Con160 εcc,1 , εcc,2 …. εcc,160
compare
measured εcc simulated εcc
MAPS:
Sar
com
ere
len
gth
Solution 1: 159 sarc.el. with Act=0; Con=1 1 sarc.el. with Act=?; Con=?
Influence of Activation time: Influence of Contractility:
time timeS
arco
mer
e le
ngt
hS
arc
om
ere
len
gth
tVtV)t(t ConnActnMn,M
Solution 2: linear decomposition
Reconstruction of maps, using MRI-tagging measurement on a dog model: ischemia induced by ligation
apex
base
sep
tum
anterior
2
1
0
Con
trac
tility
(n
orm
aliz
ed)
Reconstruction of maps, using MRI-tagging measurement on a dog model: ischemia induced by ligation
apex
base
sep
tum
anterior
10
30
50
70
Act
ivat
ion
time
[ms]
Activation time Contractility
Reconstruction of maps, using MRI-tagging measurement on human: LBBB
Activation time Contractility
Reconstruction of maps, using MRI-tagging measurement on human: LBBB + Ischemic cardiomyopathy
Activation time Contractility
Reconstruction of maps, using MRI-tagging measurement on human: healthy
healthy
+ischemia
+LBBB
Activation time Contractility
Reconstruction of maps, using MRI-tagging measurement on a dog model: healthy, +ischemia, +LBBB
Conclusions
• The circumferential strain as a function of time (εcc) in asynchronous contracting left ventricle (LV) was modelled as a long fibre around the LV, consisting of a series of fibre segments, each having its own activation time (Act) and contractility (Con).
• Applying the model inversely, the measured maps of regional εcc were converted to maps of activation time and contractility.
• Obtained maps were in agreement with clinical diagnosis of LBBB and ischemia in animal experiments and in patients.
Colaborators
Theo Arts, Joost Lumens,
Tammo Delhaas, Wilco Kroonand Frits Prinzen
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