New Methods
Time to Onset of Regional Relaxation: Feasibility,
Variability and Utility of a Novel Index of
Regional Myocardial Function by Strain Rate Imaging
Theodore P. Abraham, MD,* Marek Belohlavek, MD, P
H
D, FACC,*† Helen L. Thomson, MBBS,*
Cristina Pislaru, MD,† Bijoy Khandheria, MD, FACC,* James B. Seward, MD, FACC,*
Patricia A. Pellikka, MD, FACC*
Rochester, Minnesota
OBJECTIVES Time to onset of regional relaxation (T
R
) has been proposed as a novel index of regional
myocardial function. This study sought to prospectively establish the feasibility and variability
of T
R
in healthy volunteers (CONTROL) and to examine its utility in patients with inducible
ischemia (PATIENT).
BACKGROUND Strain rate imaging (SRI) depicts myocardial deformation and enables quantitation of
regional myocardial function with high temporal and spatial resolution. Thus, regional
mechanical events can be accurately timed with SRI. The time point of regional transition
from contraction to relaxation is altered in pathologic states.
METHODS Resting mean segmental T
R
was determined in 60 subjects: 20 in the CONTROL group and
40 in the PATIENT group. T
R
was also measured at peak dobutamine stress in the
PATIENT group. An automated image analysis program determined the time point of
transition from regional contraction to relaxation activity, and calculated T
R
, defined as the
time, in milliseconds, from the electrocardiogram R-wave to this transition point.
RESULTS Automated T
R
measurements were feasible in more than 90% of the segments in CON
-
TROL and PATIENT groups. Mean T
R
was 353 Ϯ 24 ms and was shorter in the mid
segments compared to apical and basal segments. Intra- and interobserver variability were low
(6% and 9%, respectively). In the PATIENT group, the percent decrease in T
R
during
dobutamine stress was significantly higher in normal compared to ischemic segments (30% vs.
19%, respectively, p ϭ 0.01). A percent change Ͼ20% in T
R
identified patients with an
ischemic response during dobutamine infusion (sensitivity 92%, specificity 75%).
CONCLUSIONS T
R
, a novel quantitative index of regional myocardial function, can be determined with low
variability and satisfactory feasibility in routine clinical settings. Percent change in T
R
identifies ischemic segments during dobutamine stress echocardiography (DSE) and may
allow quantitative assessment of DSE. (J Am Coll Cardiol 2002;39:1531–7) © 2002 by the
American College of Cardiology Foundation
Quantitation of regional myocardial function would greatly
enhance the value of the current echocardiographic exami-
nation. Tissue Doppler imaging (TDI), which tracks local
myocardial tissue velocities with high temporal and spatial
resolution, has enabled online quantitation of regional
myocardial function (1–5). However, TDI can be adversely
influenced by translational motion of the heart and may not
distinguish between contracting and tethered myocardium.
Strain rate imaging (SRI) uses tissue velocity data to
calculate regional deformation rates and is less influenced by
translational motion or tethering (6–9). Thus, SRI may be
superior to TDI in regional function analysis. However,
Doppler parameters are influenced by the insonating angle,
lack target tracking and have low volume resolution. There-
fore, high-resolution regional tracking of temporal events,
which are less affected by these limitations, appear promis-
ing. Angiocardiography and radionuclide angiography,
techniques also used for quantitative cardiac function anal-
ysis, lack the temporal and spatial resolution necessary to
track the rapid events of the cardiac cycle. In contrast, SRI
can reliably track regional myocardial contraction and re-
laxation activity with high temporal resolution.
The initiation of diastole is a sensitive, energy-dependent
phase of the cardiac cycle (10). The transition from systole
to diastole is negatively influenced by the lack of adenosine
triphosphate (ATP), which delays the onset and rate of
relaxation in conditions such as ischemia. Ischemia-induced
diastolic asynchrony or delay in the onset of regional
relaxation has been demonstrated in animal and clinical
models (11–15). We have recently demonstrated a quanti-
fiable delay in the time to onset of regional relaxation by
SRI in an animal model of coronary occlusion (16,17).
We have proposed time to onset of regional relaxation
(T
R
) as a novel parameter of regional myocardial function
(18). To extend the application of this parameter, we
prospectively established feasibility and variability of T
R
in
From the *Division of Cardiovascular Diseases and †Department of Physiology and
Biophysics, Mayo Clinic, Rochester, Minnesota.
Manuscript received February 23, 2001; revised manuscript received January 17,
2002, accepted February 5, 2002.
Journal of the American College of Cardiology Vol. 39, No. 9, 2002
© 2002 by the American College of Cardiology Foundation ISSN 0735-1097/02/$22.00
Published by Elsevier Science Inc. PII S0735-1097(02)01768-0