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Role of Nuclear Imaging in The Evaluvation of Non Coronary
334
Artery Disease

performed to differentiate ischemic cardiomyopathy Frais et al. demonstrated utility of phase
from non-ischemic cardiomyopathy. Absence of per- analysis of gated ERNA in assessment of
fusion defect in stress and rest studies in a patient
with cardiomyopathy reliably ruled out possibilities of cardiac mechanical dyssynchrony [2]. The
coronary artery disease as a cause of heart failure. phase image analysis is based on the first
However false negative results may happen in a case Fourier harmonic fit of the blood pool time
of balanced ischemia where presence of triple vessel vs. radioactive curve to measure the magni-
disease mask the difference between perfusion of tude and sequence of ventricular contraction
different segments and falsely considered as normal
studies. However careful evaluation of studies will in each pixel of the image. A phase angle is
reveal presence of transient ischemic dilatation and assigned between 0º-360º depending on the
stress induced dysfunction in these cases. With ad- relative time delay from the R-wave to the
vent of PET perfusion radiotracer such as 13N-Ammo- start of the cardiac cycle for each pixel. A
nia and 82- Rubidium this problem can be completely phase histogram is constructed correspond-
solved since PET tracers give actual assessment of
myocardial blood flow (coronary flow reserve) to in- ing to the sequence of ventricular contration
dividual segments.
during cardiac cycle. Mean & Standard devi-
Determining the therapeutic options ation (SD) of phase histogram is calculated
The therapeutic decision for patients with cardiomy- for each ventricle separately. Intraventricular
opathy is crucial. The determination of left venricu- dyssynchrony is measured by Standard de-
lar ejection fraction (LVEF) to its exact value is im- viation of the mean phase angle (SD mPA)
portant for decision regarding performing a surgical for left ventricle (LV) & right ventricle (RV)
procedure or managing the patients conservatively. and interventricular dyssynchrony (IVD) is
ERNA, commonly known as MUGA study (Multigated
acquisition) being the most reliable and reproducible calculated as the difference between LV
methodology to determine the LVEF with minimal in- and RV mean phase angles (LV-RVmPA), in
ter-observer variation, is the method of choice. Due milliseconds (ms) and/or degree (°). Mukher-
to its reliability and repeatability it is also performed jee et al. in their study of 32 patients with
frequently to assess LVEF during follow up.
non-ischemic cardiomyopathy noted that
Identifying candidates suitable for device therapy both intra left ventricular dyssynchrony

Implantable cardiac defibrillator (ICD) and cardiac re- (ILVD) and IVD were significantly larger in
synchronization therapy (CRT) are exciting treatment responders vs. non responders. Reciever op-
options for patients with drug refractory HF [1]. How- erating curve (ROC) curve analysis showed
ever despite selecting the patient according the con-
ventional criteria, approximately one third of patients an optimal sensitivity of 95% and specific-
who receive CRT will not have an improvement in LV ity of 80% at cut-off value of 30° for ILVD
function or symptoms and are called nonresponders. & an optimal sensitivity of 81% & specificity
It has been suggested that ‘lack of a correctable form of 80% at cut-off value of 23˚ for IVD for
of mechanical dyssynchrony’ may be the prime rea- prediction of response to CRT. However, on
son behind the lack of response to CRT. Therefore,
assessment of cardiac mechanical dyssynchrony has multivariate analysis, ILVD was found to be
gained considerable attention in recent years with most important independent predictor for
the aim to distinguish CRT responders from non-re- response to CRT [3].
sponders with a high degree of accuracy.
Quantitative softwares for assessment of
In recent years, many studies have been published cardiac dyssynchrony on GMPS are com-
demonstrating role of nuclear imaging techniques in
predicting response to CRT. Most of these studies mercially available providing objective pa-
are performed using ERNA and GMPS. Limited stud- rameters for assessment of intraventricular
ies have also demonstrated the role of GBPS, gated dyssynchrony [4]. The two parameters com-
myocardial PET and myocardial autonomic imaging monly used to assess cardiac dyssynchro-
in prediction of response to CRT. ny on GMPS are Phase Standard Deviation

GCDC 2017