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ABSTRACT

Introduction: Left bundle branch block (LBBB), affects septal wall thickening during systole, due to abnormal polarization pattern. However, in patients with LBBB, frequent septal perfusion defects are reported in Myocardial Perfusion SPECT even when there is no coronary stenosis on angiography. GATED Myocardial Perfusion SPECT (Single Photon Emission Tomography) is an accurate indicator and has shown high sensitivity and specificity to diagnose CAD. Septal perfusion defects in patients with LBBB is intensified during stress perfusion scintigraphy due to abnormal systolic phase in the septum, and abnormal conduction which gives a false appearance of reduced perfusion during the systolic phase.

Patients and Method: Stress-rest Gated Myocardial Perfusion SPECT using Tc99m myoview was performed in 20 subjects with LBBB with probability of CAD. Visual analyses of the slice images and revision results of Gated SPECT study were done on end diastolic (ED), end systolic (ES) images, regional wall motion and wall thickness for evaluation of the perfusion of septum.

Results: Visual analysis of stress-rest slices: 1) Reversible septal hypoperfusion was noted in 13 (65%) patients. 2) Fixed septal defects in 4 (20%). 3) Three patients (15%) had normal septal perfusion.

Quantitative analysis of gated study: 1) Out of the 13 patients with reversible hypoperfusion, 8 (40%) show normal findings on Gated SPECT and only the remaining 5 (25 %) patients had true reversible hypoperfusion. 2) The 4 patients with fixed septal defects show normal findings on Gated SPECT

Conclusion: The use of Gated myocardial perfusion scintigraphy particularly end-diastolic images can help in the evaluation of septal perfusion, wall motion and thickening and hence differentiate true perfusion defects from false patterns in cases of LBBB. Heart Views. 2008;9(2): 56-60. © Gulf Heart Association 2008.

Keywords: Myocardial perfusion SPECT ¨ Left Bundle Branch Block ¨ Coronary disease

Introduction

     Left bundle branch block (LBBB) is a conduction abnormality, which results in an abnormal polarization pattern and abnormal systolic phase in the septum, which affects the extent of septal wall thickening during systole1.
    In stress Myocardial Perfusion SPECT studies using Tc99m Myoview, reversible septal perfusion defects may occur in patients with LBBB. Decreased coronary flow reserve, a shortened diastolic filling time, and thinned septum as part of a LBBB process mimicking exercise-induced ischemia in about 30% to 90% of cases depending on whether visual or quantitative (Gated) analysis is applied4.
     Perfusion images in routine MPS are the sum of frames of all the phases of cardiac cycle. Abnormal systolic phase “pollutes” perfusion images in patient with LBBB4.
     Septal perfusion defects have been observed at stress perfusion scintigraphy in patients with LBBB and normal coronary arteries on angiography due to asynchronous relaxation of the septum, which is out of phase with diastolic filling of the reminder of the ventricle, during which coronary perfusion is maximal. At higher heart rates the degree of septal asynchrony relative to the R-R interval is greater than at rest, making septal perfusion defects appear as reversible ischemia5.
   These false positive results may be avoided by using ECG gated myocardial perfusion SPECT technique. As evaluation of ECG Gated Myocardial Perfusion Scintigraphy has improved the field of nuclear cardiology, making simultaneous assessments of myocardial perfusion status in different phases of the cardiac cycle, regional wall motion, thickness and pumping function of heart3.


Purpose

     To evaluate the value of Gated myocardial perfusion SPECT technique for enhancing the accuracy in reporting myocardial perfusion defects in LBBB patients.

Fig. 1A: Stress and Fig. 1B rest non gated images show a fixed perfusion defect affecting the septum.1

Fig. 1C: End diastolic polar map demonstrate normal perfusion.

Patients and Methods

     This study was performed in the Nuclear Medicine department of Kuwait Heart center (CHEST HOSPITAL). It included 20 patients who presented with a history of chest pain, and LBBB on ECG. Their ages ranged from 41-63 years with a mean ± standard deviation (SD) of 51.3 ± 5.6.
      We did two days protocol stress/rest gated myocardial perfusion SPECT for each patient using Tc99m myoview in a dose ranging from 23 to 30 mCi for each study depending on patient weight. For stress we used dipyridamole infusion in a dose of 0.56mg/kg after the radiotracer was injected.
      We used a general electrical SPECT scintillation camera, the patient was supine with arms raised. The matrix size was 128 x 128 and the imaging from 45° right anterior oblique, to 135°left posterior oblique. Butterworth prefilter and Ramp filter were utilized for reconstruction and back projection, respectively using order5, and frequency 0.4.
     Visual analyses of the slice images in short axis, horizontal long axis, and vertical long axis using five regions were evaluated: anterior, apical, septal, inferior, and lateral.
     Then revision of results of Gated SPECT study were done using QGS protocol on end diastolic (ED) images. Reconstructed gated SPECT short axis images were displayed on the screen to determine the end systolic slice, which has the smallest cavity (often fourth or fifth frame)and also we looked to end systolic (ES) images, as well as revision of regional wall motion and wall thickness for evaluation of the perfusion defects in the myocardium.

Results

Stress-rest (nongated) SPECT slices and end-diastolic and end-systolic gated SPECT images were evaluated for each patient.

Fig. 2: (a) Stress and (b) rest non-gated images show partial reversibility of septal ischemia, (c) end systolic and (d) end diastolic images also partial improvement in septum, denoting a true perfusion lesion.

Stress-rest (nongated) SPECT imaging slices revealed


   1) Reversible septal hypo-perfusion was noted in 13 (65%) patients.
   2) Fixed septal defect in 4 (20%).
   3) Three patients (15%) had normal septal perfusion.

Perfusion findings	Non Gated	Gated
Reversible	13	5
Fixed	4	0
Normal	3	15
Total	20	20

Table 1: Nongated and Gated perfusion findings

Analysis of Gated Study Revealed

1) Out of the 13 patients with reversible hypo perfusion,8 (40 %) show normal findings on Gated SPECT and only the remaining 5 (25 %) patients had true reversible hypo perfusion.

    2) The 4 patients with fixed septal defects show normal finding on Gated SPECT.

Discussion


    The accuracy of commonly used noninvasive techniques such as SPECT images for the detection of CAD in patients with LBBB is confounded by the heterogeneous effects of LBBB on myocardial structure, function, and perfusion, resulting in a high incidence of anteroseptal and septal perfusion defects in the absence of CAD. Alternative approaches, including the use of coronary vasodilators as stress agents in place of exercise or dobutamine and the application of different gated image interpretation algorithms such as QGS and Emory protocols have reduced but not eliminated the incidence of false-positive results8.
    Despite sufficient perfusion, defects can be seen in the septum on nongated SPECT images if they do not show a count increase from end-diastole to end-systole as a result of segmental contraction abnormality. Septal perfusion defects are therefore common on nongated SPECT slices in patients with LBBB, even in the absence of coronary artery disease.2
     SABAHAT et al., found that eleven of 14 patients who underwent a dipyridamole stress test had hypoactivity in the left anterior descending (LAD) artery territory in the ungated (summed) stress-rest images (abnormality ratio, 78%). On the ungated images, the abnormality was completely reversible in one patient (9%), partially reversible in five patients (46%), irreversible in two patients (18%), and reverse perfusion was identified in three patients (27%).2
     Other authors' also showed perfusion abnormalities in LBBB patients both in the septal region and in other areas. They also showed that the severity of impaired septal perfusion was associated with the severity of septal wall motion abnormalities and global LV function.7
   Gated SPECT imaging was recommended to avoid the effects of wall motion abnormalities on gamma camera imaging by separately recording end-systolic and end-diastolic images. Increased counts from end-diastole to end-systole on gated SPECT slices corresponds to the degree of wall thickening, help in assessing wall thickening by comparing end-systolic and end-diastolic images.6
     Our preliminary data indicate that end-diastolic images can significantly reduce artifactual defects in patients with LBBB. These finding coincident with that found by other researchers.

Conclusion


    The use of Gated SPECT myocardial perfusion scintigraphy particularly end-diastolic images can help in the evaluation of septal perfusion, wall motion and thickening and hence differentiate true perfusion defects from false patterns in cases of LBBB.¨

References:

1. *Septal Perfusion and Wall Thickening in Patients with Left Bundle Branch Block Assessed by Technetium-99m-Sestamibi Gated Tomography.

2. Hideki Sugihara, Nagara Tamaki, Masato Nozawa, Tomoko Ohmura, Yasuhiko Inamoto, Yoshimitsu Taniguchi, Etsuo Aoki, Kenichi Mitsunami and Masahiko Kinoshita

3. Takashima General Hospital; Department of Nuclear Medicine, Hokkaido University; First Department of Internal Medicine, Shiga University of Medical Science, Shiga-ken, Japan. The Journal of NuclearMedicine Vol. 38 No. 4 April 1997

4. *Tc-99m Sestamibi Gated SPECT in Patients with Left Bundle Branch Block SABAHAT INANIR, M.D.,* OGUZ CAYMAZ, M.D.,† TUGRUL OKAY, M.D.,‡ FUAT DEDE, M.D.,*AHMET OKTAY, M.D.,† MERAL DEGER,, M.SC.,* AND H. TURGUT TUROGLU, M.D., M.SC.* From the Departments of Nuclear Medicine* and Cardiology,† Marmara University, School of Medicine, and the Department of Cardiology,‡ International Hospital, Istanbul, Turkey. Clinical Nuclear Medicine, October 2001

5. *Clinical Validation of Technetium-99m MIBI-Gated Single-Photon Emission Computed Tomography (SPECT) for Avoiding False Positive Results in Patients with Left Bundle-Branch Block: Comparison with Stress-Rest Nongated SPECT, Hakandemir, M.D., GÜNERERBAY, M.D., K. METINKIR, M.D., KENANOMURLU, M.D.,* FATMABERK, M.D., M.SC.,† CUMALIAKTOLUN, M.D., M.SC.† Ankara University School of Medicine, Department of Nuclear Medicine; *Ankara University School of Medicine, Department of Cardiology, Ankara; †Kocaeli University School of Medicine, Department of Nuclear Medicine, Kocaeli, Turkey. Clin. Cardiol. 26, 182-187 (2003)

6. *Technetium-99m-Sestamibi SPECT Myocardial Perfusion Imaging in Patients with Complete Left Bundle Branch Block Erick Alexa´nderson,a,b Finn Mannting,c Diana Go´mez-Martý´n,a Salomon Fermona and Aloha Meaveb aUnidad PET_Ciclotro´n, Facultad de Medicina, Universidad Nacional Auto´noma de Me´xico (UNAM), Mexico City, Mexico bDepartamento de Medicina Nuclear y Resonancia Magne´tica, Instituto Nacional de Cardiologý´a Ignacio Cha´vez, Mexico City, Mexico cDivision of Nuclear Medicine, Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA, Archives of Medical Research 35 (2004) 150-156

7. Comparison of myocardial contrast echocardiography with SPECT in the evaluation of coronary artery disease in asymptomatic patients with LBBB Apostolos I. Karavidas, Evangellos P. Matsakas, George A. Lazaros *, Paris S. Brestas, Dimitrios A. Avramidis, Achilleas Ap. Zacharoulis, Ioannis N. Fotiadis, Dimitrios A. Korres, Apostolos Ach. Zacharoulis International Journal of Cardiology 112 (2006) 334 - 340

8. Left bundle-branch block artifact on single photon emission computed tomography with technetium Tc 99m (Tc-99m) agents: Mechanisms and a method to decrease false-positive interpretations John P. Higgins, MD, MPhil,a Gethin Williams, MBBS, PhD,b James S. Nagel, MD,c and Johanna A. Higgins, MDd Boston, MA. American Heart Journal October 2006

9. Prognostic value of gated SPECT in patients with left bundle branch block Yves G. C. J. America, MD,a Jeroen J. Bax, MD, PhD,a Eric Boersma, MSc, PhD,b Marcel Stokkel, MD, PhD,c and Ernst E. van der Wall, MD, PhDa. Journal of Nuclear Cardiology January/February 2007

10. Effects of Left Bundle-Branch Block on Cardiac Structure, Function, Perfusion, and Perfusion Reserve Implications for Myocardial Contrast Echocardiography Versus Radionuclide Perfusion Imaging for the Detection of Coronary Artery Disease S.A. Hayat, MBChB, MRCP; G. Dwivedi, MD, DM, MRCP; A. Jacobsen, MD; T.K. Lim, MD;C. Kinsey, HND; R. Senior, MD, DM, FRCP, FESC.

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   MULTIPLE ASDs

Multiplane transesophageal echocardiography in the 90° view showing an atrial septal aneurysm with fenestrations (A, arrows) and clearly seen with color Doppler (B, arrows). LA = left atrium; RA = right atrium.