Left ventricular function evaluation
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This document discusses techniques for evaluating left ventricular function in patients with ischemic cardiomyopathy, including multigated angiography (MUGA), myocardial perfusion scintigraphy using thallium-201 or technetium-99m tracers, gated cardiac single photon emission computed tomography (SPECT), and positron emission tomography (PET). SPECT and PET can assess myocardial perfusion, function, volumes, and viability. Segmental analysis of wall motion and calculations of ejection fraction from gated imaging provide prognostic information. The identification of viable but ischemic tissue has implications for the potential benefits of revascularization.
Left ventricular function evaluation
- 2. Left ventricular function evaluation of patients with ischemic cardiomyopathy. By Mostafa Sayed Mostafa Prof. of Nuclear Medicine Assiut University-Egypt.
- 3. Many forms of cardiomyopathy exist, but by far the most common category is dilated cardiomyopathy. The most common cause of dilated cardiomyopathy is extensive coronary artery disease(Jay,2001).
- 4. Coronary artery disease (CAD) results in an inadequate blood supply to the heart muscle, which leads to injury and death of heart muscle. As a result, the heart cannot pump as forcefully. The dead heart muscle is finally replaced by fibrous tissue. The remaining uninjured heart muscle then stretches and thickens to compensate for the lost pumping action. The more the heart muscle is stretched, the more forcefully it contracts or pumps but only up to a point. After that point, the stretching and thickening do not adequately compensate, and dilated cardiomyopathy with heart failure develops( Michael etal.,2001).
- 5. An ischemic dilated cardiomyopathy is present when myocardial infarction of left ventricle experiences remodeling and a drop in ejection fraction occurs . Dilatation of the LV and a decrease in ejection fraction (EF) occurs in 15-40% of subjects within 12-24 months following an anterior MI and in a smaller percentage of subjects following an inferior MI( Michael etal.,2001).
- 6. It is now well established that impaired left ventricular function does not necessarily represent irreversible tissue injury, because contractile performance can improve after revascularization . So ,assessment of left ventricular function must couple with assessment of residual viable myocardium (Christoph et al., 2002).
- 7. Various imaging techniques, including Single photon emission computed tomography (SPECT), positron emission tomography (PET) echocardiography, and magnetic resonance imaging (MRI), have been mostly employed to determine and localize the extent of irreversible myocardial injury. Many of these techniques are affected by a number of limitations. These include difficulties in detecting small infarcts, inability to separate infracted from dysfunctional but viable myocardium, and relatively poor spatial resolution (Gibbson et al.,2000).
- 8. Radionuclide techniques used in evaluation of left ventricular function (A) Multigated study (MUGA) (B) Myocardial perfusion scintigraphy (C) Gated cardiac SPECT (D) Positron Emission Tomography
- 9. (A) Multigated study (MUGA): Conventionally, ventricular function is evaluated by multigated acquisition studies (MUGA) with either Tc-99m-labeled red blood cells or human serum albumin. Gating is the technique that links the acquisition of the image data to the cardiac cycle, the ECG is the most convenient and is universally used. The accuracy of the gate depends on the QRS complex recognition scheme used by the computer and the qualities of the ECG signal (Sugihara et al., 2001).
- 10. (B) Myocardial perfusion scintigraphy Usually employed for the evaluation of muscle cell viability, using tracers that are markers of perfusion. Study of the myocardial distribution of the radiopharmaceutical after stress and at rest provides information on myocardial viability and inducible perfusion abnormalities. SPECT imaging is preferred over planar imaging because of the three dimensional nature of the images and their superior contrast resolution (Anagnostopoulos et al., 2004).
- 11. Thallium-201 is the common radiopharmaceutical used to assess viability and perfusion abnormalities, initially distributed after intravenous injection to the myocardium according to myocardial viability and perfusion. Technetium-99m MIBI and Tc-99m tetrofosmin have been used for myocardial perfusion imaging especially with SPECT studies (Anagnostopoulos et al., 2004).
- 12. The role of stress myocardial perfusion imaging techniques in the functional evaluation of ischemic cardiomyopathy is to assess the presence of myocardial viability in patients with significant systolic dysfunction and to determine the extent of CAD as well as infarct-related area.
- 13. TI-201 stress-redistribution SPECT study show, stress induced cardiac dilatation, irreversible perfusion defects at most of Lt. ventricular wall.
- 14. (C) Gated cardiac SPECT: Gated myocardial perfusion single photon emission computed tomography (g SPECT) has been used to assess myocardial perfusion and left ventricular function and volumes through one study. Technetium-99m MIBI and tetrofosmin, after intravenous injection are distributed within the myocardium according to myocardial perfusion and permit ECG gating, which gives additional functional information (Anagnostopoulos et al., 2004).
- 15. The most important information provided by gated myocardial perfusion tomography g SPECT (which can be done with stress and rest) includes the following: 1) LVEF, which can be performed serially to monitor cardiac function; 2) Wall motion impairment, which usually correlates with regional myocardial damage; 3) Volume of the ventricle; and overall quality of contractions ; 4) Pulmonary activity (Andrewet al.,2000).
- 16. (1)value of left ventricular ejection fraction(LVEF): If wide regional dysfunction is present, global left ventricular ejection fraction can be markedly depressed which is the most frequently calculated quantitative parameter of ventricular function. Gated SPECT, unaffected by attenuation or chamber overlap, is more accurate than planar imaging.
- 17. During exercise, a normal increase for LVEF has been accepted to be 5% or more over a normal resting value . In patients with LV dysfunction the recent data have shown that stress radionuclide- determined LVEF of 40% carry possibility of mortality in range of 5% in 1-2 years, while LVEF less than 30 % carry mortality rate about 25 % in 1-2 years (Gordon et al., 2001)
- 18. In patients with left ventricular ejection fractions (LVEF's) below 30% and predominant heart failure symptoms, coronary revascularization can improve LV function, heart failure symptoms, and long-term prognosis when compared with medical treatment alone. Because post-operative improvement in LVEF has been related to the preoperative identification of viable myocardial tissue, viability is a crucial factor when considering chronic ischemic heart failure patients for coronary artery bypass grafting.
- 19. (2) Wall motion analysis: One of the principal clinical applications of g SPECT was the evaluation of regional ventricular function and wall motion abnormalities. Multislice cine displays have proven highly effective and readily demonstrate the diagnostic efficacy of g SPECT imaging in comparison to contrast ventriculography and planar blood pool imaging.
- 20. The left ventricle is subdivided anatomically into multiple segments according to standard definitions. Each segment is graded on four point scale : 1) normal, 2) hypokinesia ,abnormal areas demonstrating diminished contraction , 3) akinesia ,complete absence of wall motion , 4) dyskinesia , a dyskinetic wall segment is one that passively bulges outward while the surrounding ventricular segments contract inward.
- 21. (3) Left ventricular volume: It is an important determinant of diagnosis and prognosis in patients with heart disease. In patients with old myocardial infarction, the left ventricular mass index was significantly lower, and the magnitude was closely related to the severity of the perfusion defect on the resting SPECT images.
- 22. The evaluation of the chamber size difference between stress and rest images is of great importance . Scintigraphic evidence of left ventricular dilatation with stress is an indirect indicator of extensive coronary artery disease . There is a strong correlation (sensitivity 60%, specificity 95%) between LV stress dilatation and the presence of multivessel CAD. (Patrick et al., 2003).
- 23. Gated Tc-99m MIBI myocardial perfusion SPECT shows diminished perfusion, wall thickness, LVEF and impaired wall motion (From Noor Eldeeen et al.,2003).
- 24. (4) Pulmonary activity on stress imaging: An increase in Tc99m MIBI lung uptake on stress imaging is a marker for severe underlying coronary artery disease. A lung to heart ratio of greater than 33% is suggestive of underlying severe CAD (Choy & Leslie 2001). In thallium-201 myocardial perfusion imaging, abnormally high lung uptake due to prolonged lung transit time and increased capillary wedge pressure correlates with left ventricular dysfunction at exercise and usually indicates multivessel CAD and identifies patients with poor prognosis (Saber et al.,1997).
- 25. Positron Emission Tomography (PET): PET is known to accurately identify viable myocardium in patients with CAD. It can be performed with ECG gating. The pharmacological stress imaging can also be done. Compared with SPECT, PET offers high sensitivity, superior resolution, possibilities of attenuation correction and allows absolute quantification of regional tracer uptake. But on the other hand, PET has not been used on a wide scale due to the limited availability of PET system and difficulties in the production of its tracers.
- 26. Segments with reduced perfusion in SPECT studies but preserved FDG uptake in PET study (Perfusion-FDG mismatch) are classified as viable. The extent of mismatch as assessed by PET correlates closely with improvement of global LV function after revascularization . On contrast, segments with proportionate reduction in perfusion and FDG uptake (Perfusion-FDG match) are considered as non viable tissue and frequently do not show improved ventricular function following revascularization (George et al 2000).
- 27. Using FDG PET has been demonstrating that 36- 47% of myocardium with irreversible perfusion defects according to both TI-201 stress- redistribution and Tc99m MIBI stress-rest imaging, are metabolically active and hence viable , so can benefit from revascularization surgery. Because the resolution of FDG PET is much higher than that of g SPECT , using gated FDG PET provides a more sensitive and accurate method for the calculation of left ventricular ejection fraction (LVEF) and wall motion abnormalities in patients with ischemic heart disease (Yoshinaga et al.,2002).
- 28. Another approach employs quantitative estimates of regional myocardial glucose utilization as a predictor of LV function. A threshold value of 0.25 u mol/min/gm has been proposed to distinguish between reversibility and irreversibility of regional LV function after revascularization. Use of this threshold in a study offered a sensitivity of 99% for predicting an improvement in LV function (Bax et al.,2001).
- 29. Rubidium perfusion and FDG PET viability study. Rubidium images (top row) performed with dobutamine stress , show a perfusion defect in the apex and lateral wall (arrows). FDG images (bottom row) show normal metabolism in those regions (open arrows) indicating myocardial viability. (From Andrew et al ., 2000.)
- 30. ECHOCARDIOGRAPHY In ischemic heart diseases echocardiography is indicated to: – detect deterioration of left ventricular function; – follow the behavior of left ventricular expansion, show aneurysm formation and thrombus after institution of therapy; – detect reversible ischemia by stress echocardiography.
- 31. The echocardiographic hallmark of ischemic heart disease is regional loss of systolic wall thickening and motion abnormalities. The geometry of the left ventricle in patients with cardiomyopathy is often sub-optimal for 2-dimensional ultrasound when assessing left ventricular (LV) function and localized abnormalities such as a ventricular aneurysm. So, some investigators prefer using of real- time 3-D echocardiography for evaluating patients with cardiomyopathy (Shiota et al., 1999).
- 32. Dobutamine stress echocardiography assesses the ability of myocardium to increase its contraction in response to an adrenergic stimulus. It has been routinely employed for evaluation of patients with ischemic heart disease by means of detection of wall motion abnormalities under pharmacologic stress. Evaluation of wall thickening by echo during low- dose dobutamine infusion can also be used to determine reversible left ventricular dysfunction in patients with ischemic heart disease (Scott et al.,2001).
- 33. Magnetic Resonance Imaging Recently, MRI has demonstrated its potential for showing the structure , the function of the heart muscles, the thickness of the chambers, and determine the extend of damage caused by a heart attack or progressive heart disease. MRI, creates images of the beating heart that can be used to diagnose a variety of cardiovascular problems. Depending on how many images are needed, the exam will generally take from 15 to 45 minutes (Radiology Info, 2003).
- 34. Cardiac magnetic resonance imaging (CMRI) has been performed early as non gated images, and then gated cardiac study was introduced using chest ECG leads. The images acquired during the multiple phases of the cardiac cycle can be viewed in a cine loop, thereby displaying the contracting heart (William & Bradley2003).
- 35. Dobutamine stress CMRI assesses the induction of ischemia by evaluation of regional wall motion during progressively increased doses of IV dobutamine. Ischemic cardiomyopathy can be evaluated on the basis of perfusion or wall motion abnormalities, comparing rest and stress imaging. Normal myocardium is bright, and nonperfused myocardium is dark. Ischemia results in a new or worsening wall motion abnormality compared with the baseline study.
- 36. A new technique known as “delayed hyper enhancement” is proving to be extremely sensitive and specific for the diagnosis and quantitation of myocardial infarction. Normal myocardium is dark 20 to 30 minutes following injection of (Gd-DTPA), a commonly used paramagnetic contrast agent, because the Gd has washed out and infracted myocardium is bright. Use of contrast agents has enhanced the ability of MRI to distinguish infracted from viable myocardium and so detect cases which may get benefit from further treatment (Simonetti et al.,2001).
- 37. Perfusion imaging demonstrating hypoperfusion of a posterolateral wall infarction.( A) Preinjection study shows thinning of the posterolateral wall (arrow). (B) Following the injection of gadolinium, all normal myocardium enhances; the infarcted posterolateral wall does not (arrow). from (William & Bradley, 2003).
- 38. SUMMARY Various imaging techniques, including Single photon emission computed tomography (SPECT), Positron emission tomography (PET), echocardiography and magnetic resonance imaging (MRI), have been mostly employed to determine and localize the extent of myocardial injury and left ventricular dysfunction. All these investigations can be done during rest and stress to determine the residual myocardial reserve. The most important items in evaluation of lt.vent. function are evaluation of its perfusion ,EF. and wall motion.
- 39. Conclusion Perfusion radionuclide imaging is essential to distinguish ischemic cardiomyopathy from other causes of dilated cardiomyopathy. Both stress gated SPECT and stress echocardiography with dobutamine can assess wall motion abnormalities especially dyskinetic with aneurysm. Myocardial viability assessment using TI-201 or F18- FDG is essential to stratify patients with good or poor prognosis and those who benefit from revascularization process.