Preface - Ous-research.no

Integrated Cardiovascular Function
Furthermore, we have identified a new regional marker
for mechanical activation based on a segment’s first sign
of active force generation (onset AFG). Using onset AFG
we have been able to discriminate between electrical and
mechanical dyssynchrony because onset AFG accurately
reflect regional electrical activation (Fig1). This is important
when assessing patients for CRT since primary electrical
dyssynchrony is more likely to respond to the therapy. Our
experimental findings have been very promising and we
have now started patient based studies. Electrical activation
sequence also influences regional work distribution
in the LV. Using strain data (% myocardial deformation) by
echocardiography in combination with LV pressure allows
for assessment of regional work. We are currently working
on a new method to detect wasted work done during
Figure 2. Transmural mechanical dispersion in a symptomatic
LQTS patient. Shown are the longitudinal (left) and circumferential
(right) strain curves from a symptomatic LQTS patient. The
anterior basal septal segment from longitudinal strain (left, red
curve) shows a contraction duration of 460 milliseconds. From
circumferential strain, the contraction duration from the anterior
basal septal segment (right, yellow curve) is 360 milliseconds. Subendocardial
contraction duration (longitudinal strain) therefore
is markedly prolonged com- pared with midmyocardial contraction
duration (circumferential strain), indicating transmural
mechanical dispersion.
continue to investigate how LV myocardial mechanical dispersion
relates to risk for ventricular arrhythmias in ischemic
heart disease and in different types of cardiomyopathies.
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Figure 1. Assessment of onset active force generation (AFG) by
LV pressure and strain by speckle tracking echocardiography. Representative
traces from septal (thick lilac trace) and lateral (thin
green trace) segments during left bundle branch block (LBBB).
Strain measurements are performed in short axis view. Vertical
dotted line represents regional electrical activation by intramyocardial
electromyogram (IM-EMG). Aortic valve opening (AVO)
and closing (AVC) indicated by arrow.
LBBB, which can subsequently be reversed by bi-ventricular
pacing.
2. LV mechanical-electrical interactions: Evaluating patients
with susceptibility for cardiac arrhythmias and sudden
cardiac death is a major challenge in daily cardiology
practice. Electrophysiological studies have demonstrated
that damaged myocardium (e.g. infarcted or genetically
altered) provides the substrate for malignant arrhythmias.
Echocardiographic techniques can accurately quantify regional
myocardial function. There is limited insight into how
regional mechanical dysfunction may predict risk for ventricular
arrhythmias. We have recently demonstrated how
mechanical dispersion can predict ventricular arrhythmias
in patients with LQT syndrome and in myocardial infarction.
One study about mechanisms for ventricular arrhythmias in
LQT syndrome was published in Circulation (Fig 2). We will
3. Diastolic dysfunction: Left ventricular function has traditionally
been evaluated non-invasively in terms of ejection
fraction (LVEF). The assessment of LVEF is important for
diagnostics, prognosis and selection of treatment. Many patients
with symptoms of heart failure have, however, normal
ejection fraction and appear to have diastolic heart failure.
In this patient group there is need for other measures than
ejection fraction. We are studying LV diastolic lengthening
rate and LV untwisting rate and how these indices may be
used as markers of LV diastolic dysfunction. In addition to
experimental models we utilize mathematical heart modeling
to explore our ideas. This includes finite element simulation
to interpret measurements of myocardial wall deformation
under normal and diseased conditions. The recently
introduced method speckle tracking echocardiography
represents a simplified, objective and angle-independent
modality for quantification of regional myocardial deformation.
The software utilizes conventional grayscale B-mode
recordings, and tracks myocardial speckles which serve as
natural acoustic markers. Radial and longitudinal myocardial
deformation can be measured simultaneously from longaxis
recordings, radial and circumferential deformation from
short-axis recordings and LV torsion from assessment of
apical and basal short-axis rotation.
Patients with acute decompensated heart failure (ADHF)
suffer from increased morbidity and mortality. The hemodynamic
assessment of ADHF offers the potential of tailored
therapy. However, the invasive gold standard is not without
risks. Accordingly the non-invasive assessment by Doppler