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