Simultaneous assessment of right ventricular function and hypertrophy by Tc-99m MIBI

The role of nuclear imaging in pulmonary hypertension

Pulmonary hypertension (PH) is a disease characterized by a chronic elevation of pulmonary artery pressure from various causes. Pulmonary artery hypertension (PAH) is one of subtype which results in premature death often as a result of right ventricular (RV) dysfunction. In spite of the recent progress in novel cardiac imaging techniques and new drugs for PAH, there remain significant unresolved issues including a need for earlier diagnosis, refinement of risk stratification, and monitoring the effects of treatment. Cardiac and pulmonary imaging with transthoracic echocardiography (TTE) with Doppler, magnetic resonance imaging (MRI), and computed tomography (CT) are done routinely in many clinical centers. However, routine and emerging nuclear techniques may have a pivotal role of assessment of the patient with PH, and is currently the subject of significant research. Potential Roles for Nuclear Imaging in the Evaluation of the PH Patient: (1) Evaluation of cardiac structure and function (RNA) (non-nuclear techniques would include TTE, CT, and MRI). (2) Functional imaging. This includes the use of ventilation-perfusion scintigraphy (V/Q scan) to diagnose chronic thromboembolic pulmonary hypertension (CTEPH), 123l-metaiodobenzylguanidine (MIBG) imaging to evaluate the cardiac sympathetic nervous system (non-nuclear techniques include invasive right heart catheterization and TTE). (3) Measurement of RV perfusion (with gated SPECT studies). (4) Evaluation of cardiac and pulmonary metabolism (PET scans). This review article will summarize the pathophysiology, classification, natural history, and diagnostic approach of PH. Current and emerging nuclear techniques will be discussed under the four themes of evaluation of structure, functional imaging, flow, and metabolism. These will be compared to current and emerging nuclear and non-nuclear diagnostic tests in the evaluation and management of patients with PH. We will also discuss research applications exploring new insights into flow and metabolism in the right heart and lung and the application of new radioligands.

Right ventricular wall "ischemia" findings using a dual isotope protocol

A 74-year-old man with a history of diabetes and arterial hypertension, presented with right ventricular failure, remarkable jugular venous distension, hepatomegaly, and swelling of the lower extremities. He was complaining of atypical chest pain and was referred for an echocardiogram and a myocardial perfusion SPECT imaging study. The echocardiogram showed normal left ventricular function with a dilated right atrium and right ventricle, severe tricuspid regurgitation, pulmonary hypertension, and an atrial septal defect with bidirectional shunt. The SPECT images showed normal left ventricular function with no areas of induced ischemia but an impressive right ventricle with severe dilatation and hypertrophy. A right ventricular "perfusion abnormality," consistent with ischemic changes, seen on stress but less evident on rest images was demonstrated on the dual isotope (Tl-201 rest/Tc-99m MIBI stress) protocol but not seen on the single isotope study (rest/stressTc-99m MIBI). Coronary angiogram showed diffuse coronary atherosclerosis but without significant obstruction.

Assessment of right and left ventricular perfusion in patients with right bundle branch block

BACKGROUND

Patients with conduction abnormalities may have abnormal images on perfusion scintigraphy without evidence of coronary artery disease (CAD). Based on the presence of left ventricular perfusion abnormalities in left bundle branch block and taking advantage of the Tc-99m sestamibi for the assessment of myocardial perfusion of both ventricles, we aimed to evaluate right (RV) and left (LV) myocardial perfusion in patients with right bundle branch block (RBBB).

METHODS

This study included 21 patients with RBBB and 21 control subjects without conduction abnormality. None had previous myocardial infarction, known CAD, left ventricular hypertrophy, LVEF <55%, congenital, pulmonary or valvular heart disease. Rest and stress SPECT images were obtained using 1-d Tc-99m sestamibi SPECT protocol. Regional perfusion of LV and RV myocardium was semiquantitatively evaluated. Also, RV/LV uptake ratio was calculated in two different ways.

RESULTS

In patients with RBBB, the normality ratios of RV and LV myocardial perfusion were very high (both 90.5%) and not different from those of patients with normal intraventricular conduction. In the comparison of RV/LV uptake ratios, no significant difference was found between the RBBB and control groups.

CONCLUSIONS

LV perfusion, RV perfusion or R-to-L perfusion ratio were not significantly influenced by the conduction abnormality in this selected patient population with RBBB. Tc-99m sestamibi myocardial scintigraphy could help in the exclusion of myocardial ischemia in patients with RBBB.

ECG-gated 99mTc single-photon emission CT for assessment of right ventricular structure and function: is the information provided similar to echocardiography?

STUDY OBJECTIVE

(99m)Tc single-photon emission CT (SPECT) and ECG-gated SPECT can visualize well the right ventricle (RV) in most patients, but their utility for assessment of the RV has not been formally evaluated. We examined whether (99m)Tc SPECT/ECG-gated SPECT provide similar information to transthoracic two-dimensional Doppler echocardiography (2D-ECHO) regarding RV cavity size, wall thickness, and systolic function.

DESIGN

Retrospective analysis.

SETTING

A major university teaching hospital.

PATIENTS

A consecutive series of 194 patients with good quality stress SPECT and 2D-ECHO studies performed within 1 day of each other and no significant interim cardiac events.

MEASUREMENTS AND RESULTS

RV size and function were visually assessed by SPECT/ECG-gated SPECT and 2D-ECHO. RV wall thickness was visually assessed by SPECT and measured in mm in end-diastole by 2D-ECHO. Of 142 patients with normal RV cavity size by SPECT, 134 patients (94%) had normal RV cavity size by 2D-ECHO. However, of 52 patients with RV dilation by SPECT, only 9 patients (17%) had RV dilation by 2D-ECHO. A perfusion abnormality in the right coronary artery territory was significantly associated with RV dilation by SPECT (p < 0.005) and 2D-ECHO (p < 0.05). Among 150 patients with ECG-gated SPECT, only 2 patients had abnormal RV systolic function, as compared with 18 patients by 2D-ECHO. RV wall thickness measurements by SPECT and 2D-ECHO did not correlate.

CONCLUSIONS

For normal interpretations regarding RV cavity size, wall thickness, and systolic function, there is good agreement between (99m)Tc stress SPECT/ECG-gated SPECT and 2D-ECHO. However, there is poor overall agreement between gated SPECT/ECG-gated SPECT and 2D-ECHO regarding the presence of RV dilation, hypertrophy, and systolic dysfunction.

Functional assessment of the right ventricle with gated myocardial perfusion SPECT

BACKGROUND

The evaluation of right ventricular function can provide valuable information in a variety of cardiac and noncardiac conditions. Functional assessment of the right ventricle is difficult because of its anatomy and geometry. The authors describe a method for assessing right ventricular function using gated myocardial perfusion SPECT.

METHODS

In 20 patients, right and left ventricular ejection fractions (RVEF, LVEF) were determined using gated blood-pool scintigraphy (GBPS) and gated myocardial perfusion SPECT (GSPECT). To avoid contamination with right atrial activity, the two-frame method was adopted for gated blood-pool data when RVEF was measured. In nine patients with normal right ventricles, an index of wall thickening for the right ventricle was derived from the peak systolic and diastolic counts in the free wall.

RESULTS

Linear correlation between the two methods adopted for calculation of LVEF and RVEF was good. Bland-Altman analysis revealed good agreement between the two methods with no specific bias. The mean LVEF was 47.9 +/- 12% (GBPS) and 47.3 +/- 12.4 (GSPECT). The mean RVEF was 43.2 +/- 9.6% (GBPS) and 44.2 +/- 8.5% (GSPECT). In both cases, the values were not significantly different. The mean wall motion index was 35%. There was no correlation between the wall thickness index and ejection fraction, but the index was greater in patients with a normal right ventricle compared with those with reduced RVEF.

CONCLUSIONS

Gated SPECT offers an alternative to GBPS for the functional assessment of the right ventricle. Using GSPECT will allow the simultaneous assessment of both the right and left ventricles.

Quantitative assessment of right ventricular structural abnormalities by right ventricular polar mapping of single photon emission computed tomogram

The identification of right ventricular (RV) abnormalities is clinically important in the evaluation of arrhythmogenic substrates in right ventricular-originated ventricular tachycardia (RVT). The purpose of this study was to determine the diagnostic benefit of quantitative analysis in RV single photon emission computed tomography (SPECT) imaging with (99m)Tc-tetrofosmin/sestamibi in patients with RVT. Thirty patients with RVT (15 with idiopathic RVT and 15 with arrhythmogenic right ventricular cardiomyopathy (ARVC)) were compared with 27 control subjects (including 11 with right bundle branch block) with regard to the semiquantitative RV uptake score in each of six segments and the quantitative RV extent score in polar coordinate map displays by SPECT imaging. The RV total score and RV extent score were compared with the RV global function. Perfusion abnormalities were more frequently detected (P = 0.0001) in the ARVC group (59/90, 65.6%) than in the idiopathic RVT group (4/90, 4.4%) or controls (1/162, 0.6%). The RV extent score in the ARVC group (53.0 +/- 24.8) was significantly higher than that in the idiopathic RVT group (8.4 +/- 10.1) or controls (1.2 +/- 4.9). The RV extent score correlated well with the regional RV perfusion score (P < 0.0001) and with the RV ejection fraction (P < 0.0001). Non-invasive RV perfusion mapping using a (99m)Tc-labelled tracer is useful for the quantitative evaluation of RV substrates in patients with ARVC.

Technetium-99m sestamibi/tetrofosmin myocardial perfusion scanning in cardiac and noncardiac sarcoidosis

Left ventricular (LV) and right ventricular (RV) involvement in sarcoidosis must be firmly confirmed to determine patients' prognosis. We examined whether myocardial perfusion images using technetium-99m single photon emission computed tomography (SPECT) have a diagnostic benefit in the evaluation of biventricular involvement. Sixteen patients with sarcoidosis, aged 21-78 (54 +/- 12) years old, 5 males and 11 females, complicated with cardiac disease (cardiac sarcoidosis, n = 6) including tachyarrhythmias of ventricular origin (n = 5), atrioventricular block (n = 4), and congestive heart failure (NYHA > or = II, n = 1), were enrolled in this study. Myocardial SPECT using technetium-99m sestamibi or tetrofosmin was performed and semiquantitatively scored for comparison with 25 control subjects. Perfusion abnormalities were more frequently recognized in sarcoidosis (LV 5/16, 31% and RV 14/16, 88% vs. LV 0/25, 0% and RV 8/25, 32% in controls). LV involvement had a close correlation with atrioventricular block and with congestive heart failure, and multiple sites of RV involvement correlated with ventricular tachyarrhythmia of RV origin. Total number of defect segments were highest in cardiac sarcoidosis (18/30, 60% vs. 19/60, 32% in noncardiac sarcoidosis, and 11/150, 7% in controls, p = 0.0001), and semiquantitatively evaluated total LV and RV scores (ranging from 0 to 18) were higher than those of controls (15.1 +/- 1.8 vs. 11.4 +/- 3.0 in noncardiac sarcoidosis, and 9.0 +/- 5.0 in cardiac sarcoidosis) and exhibited a significant positive linear correlation with the RV ejection fraction (y = 19.8 + 1.83x, r = 0.786, p = 0.001). Biventricular SPECT using technetium-99m is clinically useful for the noninvasive evaluation of both ventricular involvements in sarcoidosis.

Right ventricular abnormalities assessed by myocardial single-photon emission computed tomography using technetium-99m sestamibi/tetrofosmin in right ventricle-originated ventricular tachyarrhythmias

OBJECTIVES

We sought to determine whether right ventricular (RV) perfusion imaging with technetium-99m (Tc-99m) sestamibi or tetrofosmin single-photon emission computed tomography has diagnostic benefit for RV-originated ventricular tachyarrhythmias (RVT).

BACKGROUND

Identification of RV abnormalities is clinically important to establish RVT etiology.

METHODS

Forty-seven patients with RVT (23 with idiopathic and 24 with organic RVT due to arrhythmogenic RV or dilated cardiomyopathy, cardiac sarcoidosis or myocarditis) were compared to 25 control subjects. Right ventricular uptake score, as assessed by modified tomographic imaging, and regional RV count relative to peak left ventricular (LV) count (RV/LV count ratio) were compared with RV regional and global function.

RESULTS

Regional RV uptake score correlated well with the RV/LV count ratio, and segmental abnormality was more frequently (p = 0.001) detected in the organic RVT group (22 [92%] of 24 patients) than in the idiopathic RVT group (4 [17%] of 23 patients) or the control group (8 [32%] of 25 patients). The total RV score (8.4+/-3.8) in the organic RVT group was significantly lower than that in the idiopathic RVT group (15.6+/-1.6) or the control group (15.1+/-1.8). The total RV score correlated with RV EF (r = 0.702, p<0.001). A total RV score <12 differentiated the organic RVT group from the other two groups, with a sensitivity of 79% and a specificity of 100%. The asynergic RV regions had a significantly lower RV/LV count ratio and RV score as compared with the nonasynergic regions and were identified by RV assessment, with a sensitivity of 76.1% and a specificity of 76.6%.

CONCLUSIONS

Right ventricular perfusion tomography using a Tc-99m-labeled tracer is clinically useful for the noninvasive detection of RV myocardial damage in patients with RVT and for differentiating organic from idiopathic RVT.