Importance of Gated Imaging in Both Phases of Myocardial Perfusion SPECT: Myocardial Stunning After Dipyridamole Infusion
Vahidreza Dabbagh Kakhki, Seyed Rasoul Zakavi, Ramin Sadeghi and Ahmad Yousefi Department of Nuclear Medicine, Emam Reza Hospital, Mashad University of Medical Sciences, Mashad, Iran
Correspondence: For correspondence or reprints contact: Vahidreza Dabbagh Kakhki, Department of Nuclear Medicine, Emam Reza Hospital, Mashad University of Medical Sciences, Mashad, Iran. E-mail: dvdkakh@yahoo.com
 | ABSTRACT |
We present the case report of a 72-y-old woman who underwent
99mTc-sestamibi gated myocardial perfusion SPECT with a 2-d
protocol. SPECT images revealed ischemia of the apical, anteroapical,
apicoseptal, and septal walls. Postdipyridamole gated SPECT
revealed significant deterioration in the left ventricular ejection
fraction (LVEF), wall motion, and systolic wall thickening relative
to the findings obtained with rest gated SPECT. Myocardial stunning
is a lingering contractile dysfunction that occurs after a brief
ischemic insult. Myocardial stunning after dynamic exercise
or pharmacologic stress tests has been demonstrated. Thus, the
use of gated SPECT in both phases of perfusion studies may add
useful information about cardiac function, as a poststress study
alone probably reflects stunned myocardium in some patients
undergoing ischemic stress tests. The difference between poststress
LVEF and rest LVEF may have a powerful impact on prognosis,
as it seems to depend on the extent and severity of induced
ischemia.
Key Words: myocardial stunning; gated SPECT; dipyridamole; myocardial perfusion
| INTRODUCTION |
The term "stunned myocardium" has been used to describe myocardium
with persistent contractile dysfunction despite the restoration
of perfusion after a period of ischemia; this condition usually
improves with time (
1).
Electrocardiography (ECG)-gated SPECT myocardial perfusion imaging can be used for the simultaneous assessment of myocardial perfusion and left ventricular function (2,3). This integrated approach has already proved useful clinically for tissue characterization and prediction of prognosis (4).
| CASE REPORT |
A 72-y-old woman with a history of atypical chest pain and exertional
dyspnea was referred for gated myocardial perfusion SPECT. Cardiac
risk factors included hypertension, diabetes mellitus for 10
y, hypercholesterolemia, and age. The results of resting ECG
were normal. The patient underwent myocardial perfusion SPECT
with a 2-d protocol. On the first day, 740 MBq of
99mTc-sestamibi
were injected intravenously 4 min after the infusion of dipyridamole
at 0.568 mg/kg. At 90 min after the injection of
99mTc-sestamibi,
gated perfusion imaging was performed in the supine position
by use of a dual-head
-camera in the 90° setting (Dual-Head
Variable-Angle E.CAM; Siemens) and equipped with high-resolution,
low-energy collimators. After dipyridamole injection, the patient
experienced no chest pain; ECG showed ST depression in the precordial
leads. On the next day, at 10 min after the oral administration
of a trinitroglycerin (NTG) pearl, 740 MBq of
99mTc-sestamibi
were injected, and rest images were acquired with the same protocol.
The images were stored in a 64 x 64 matrix in the computer and reconstructed by filtered backprojection with a Butterworth filter (order = 5, cutoff frequency = 0.4). Gated SPECT data were analyzed with Quantitative Gated SPECT software (Cedars Cardiac Quantification; Cedars-Sinai Medical Center) for end-diastolic volume (EDV), end-systolic volume (ESV), and left ventricular ejection fraction (LVEF). Myocardial perfusion was assessed visually and semiquantitatively. A 17-segment 5-point scoring system was used for the semiquantitative assessment of myocardial perfusion.
Reversible defects (myocardial ischemia) were noted in the apical, anteroapical, apicoseptal, and anteroseptal walls (Figs. 1 and 2). The summed stress score, summed rest score, and summed difference score were 11, 5, and 6, respectively.
The rest gated images displayed in 2-dimensional and 3-dimensional
(
Fig. 3) formats revealed normal left ventricular wall motion
and systolic wall thickening. EDV, ESV, and LVEF calculated
from the rest gated images were 53 mL, 17 mL, and 68%, respectively.
The stress gated images acquired after dipyridamole injection
(
Fig. 3) revealed akinesia in the apicoseptal region as well
as hypokinesia in the apical, anteroapical, anteroseptal, and
septal walls. Calculated EDV, ESV, and LVEF were 69 mL, 46 mL,
and 33%, respectively.
Dipyridamole gated
99mTc-sestamibi SPECT revealed significant
deterioration in systolic myocardial function (decreased LVEF)
as well as remarkable wall motion and systolic wall thickening
abnormalities (myocardial stunning) in the regions of reversible
defects relative to the findings obtained with rest gated SPECT.
| DISCUSSION |
Myocardial stunning is a lingering contractile dysfunction that
occurs after a brief ischemic insult, even in the absence of
necrosis, and persists for some time after the restoration of
adequate blood flow (
1). The histologic appearance of the stunned
myocardium is normal, so there is no permanent damage and contractile
function is able to recover gradually with time (
5). Although
in some instances full recovery may occur within a few minutes
after the recovery of myocardial perfusion, in some cases it
may take hours, days, or even weeks, depending on the severity
of the ischemic episode (
6). A variety of hypotheses have been
postulated as mechanisms for myocardial stunning; these include
insufficient energy production by mitochondria, impaired energy
use by myofibrils, reduced myofilament responsiveness to calcium,
reduced contractile protein activation, calcium overload, and
generation of free radicals (
6,7). Reperfusion through the restoration
of the oxygen supply, which is beneficial and protective for
the ischemic myocardium, induces at the same time a burst of
oxygen-free radicals, complicated by intracellular Ca
2+ overload,
which is harmful for contractile proteins (
7).
Well-documented clinical settings in which myocardial stunning can occur include percutaneous transluminal coronary angioplasty, unstable and variant angina, acute myocardial infarction with early reperfusion, cardiac surgery, and cardiac transplantation (8,
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