Key points
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Gated SPECT perfusion imaging is useful in differentiating ischemic cardiomyopathy from dilated cardiomyopathy.
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Gated SPECT perfusion imaging and RNA are useful in differentiating patients with HF with normal LVEF (diastolic HF) from patients with HF with depressed LVEF (systolic HF).
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The RVEF measured by RNA, provides important prognostic information in patients with HF.
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The perfusion pattern in dilated cardiomyopathy is often normal at stress and rest, but perfusion abnormalities can be seen in one-third of patients. The LV size is increased and the EF is depressed. The perfusion abnormality is best described as “patchy” and does not involve an entire vascular territory. The abnormality could be fixed or reversible (or both).
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The perfusion pattern in ischemic cardiomyopathy shows large perfusion defects involving one or more vascular territories; they can be fixed or reversible (or both). The LV cavity is dilated and the EF is depressed.
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Patients with hypertrophic cardiomyopathy have septal hypertrophy, which can produce perfusion defects in the lateral wall due to down-scaling.
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Reversible and fixed defects can be seen in some patients with hypertrophic cardiomyopathy in the absence of CAD; such findings should not be labeled as false positive despite the temptation to do so!
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Alcohol septal ablation in hypertrophic cardiomyopathy is followed by a small perfusion defect seen at the base of the septum, which often decreases in size over time.
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Incorrect tracking of the endocardial contour can produce a falsely low EF by gated SPECT despite a vigorous contraction pattern with cavity obliteration by visual analysis. Be aware!
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Phase analysis of gated SPECT perfusion images and of RNA can be used to assess LV dyssynchrony.
Background
It is estimated that there are more than 5 million patients with HF in the United States and more than 500,000 new cases diagnosed each year. In 40% of these patients, the HF is due to diastolic dysfunction, known as diastolic HF or HF with preserved LVEF, and the remaining 60% have systolic HF with depressed EF (also known as HF with depressed EF). Most patients with HF also have CAD; by some estimates, as many as 90% (assessment of viability in patients with ICM is discussed in Chapter 15 ). Despite improvement in medical therapy and the use of ICDs and CRT, the morbidity and mortality in these patients remain high.
One of the classifications for HF is shown in Table 12-1 . Patients with CAD and systolic HF are often categorized as having an ICM (a misnomer since ischemia may not be present in all patients), while those without CAD are lumped together under DCM. These patients often have no identifiable causes and the HF is presumed to be caused by hypertension, myocarditis, or genetic causes. Over the past few decades, many tracers, such as Tc-99m pyrophosphate, In-111–labeled pentetreotide (a somatostatin analog), In-111 antimyosin, Tc-99m Annexin-V, and Tc-99m–labeled glucarate, have been used to detect inflammation/necrosis but none of these is approved or currently used consistently in the United States.
| Primary |
| Genetic |
| Hypertrophic cardiomyopathy |
| Arrythmogenic RV cardiomyopathy |
| LV non-compaction |
| Glycogen storage related |
| Ion channel disorders |
| Long QT syndromes |
| Brugada |
| Mixed |
| Dilated cardiomyopathy |
| Restrictive cardiomyopathy |
| Acquired |
| Inflammatory |
| Tako-tsubo |
| Peripartum |
| Secondary |
ICM versus DCM
Both DCM and ICM are characterized by a dilated LV cavity with wall motion/thickening abnormalities (WMAs) and a depressed EF. WMAs are often assumed to be regional in ICM and diffuse in DCM, but that distinction is often not reliable because, as the LV dilates, it also remodels and remote areas will exhibit WMAs as well. More often than not, the RV in DCM is also dilated and has a depressed EF because it is likely that the primary process (whatever it may be) that is affecting the LV, also affects the RV. However, this does not mean that RV function and size are always normal in ICM. On the contrary, it can also be abnormal in later stages of the disease when pulmonary hypertension and tricuspid regurgitation develop. Both MPI and RNA are quite helpful in these patients. MPI is used because these patients often have similar presentations, such as chest pain and shortness of breath on exertion. It also provides an incremental value in predicting new onset refractory HF.
Case 12-1
Patient With Dilated Cardiomyopathy and Shortness of Breath ( Figure 12-1 )
A 55-year-old woman presents with chest pain, exertional dyspnea, and lack of energy of 1-year duration. She has hypertension, which is not well controlled. Her mother died of heart disease at the age of 50. The physical examination is unremarkable except for a BP of 145/95 mm Hg. The ECG shows nonspecific T-wave changes.
She exercised on the treadmill but became short of breath after 2 minutes and the stress test was switched to adenosine. The images are shown in Figure 12-1 . Cardiac catheterizations showed LV end-diastolic pressure of 25 mm Hg and a normal coronary angiogram.
Case 12-2
Patient With Dilated Cardiomyopathy and Chest Pains ( Figure 12-2 )
A 44-year-old man was referred for stress testing because of chest pain and shortness of breath on exertion that had occurred for 2 years, but had worsened in the past 6 months. He was recently seen in the ED of another hospital for the same symptoms and was discharged home after evaluation showed no evidence of acute MI. He smokes and has hypertension. Physical examination is normal. The ECG shows left anterior hemiblock. He exercised for 6 minutes on the Bruce protocol and stopped because of shortness of breath at 80% of maximum predicted heart rate response. The images are shown in Figure 12-2 . Subsequent cardiac catheterization showed elevated LV filling pressure, mild pulmonary hypertension, and 30% stenosis in the RCA.
Comments ( Cases 12-1 and 12-2 )
The images in these two patients illustrate part of the spectrum of perfusion patterns in patients with DCM. The perfusion pattern could be normal or show fixed or reversible defects (or both). Often attenuation abnormalities appear more prominent because of wall thinning and partial volume effect. Perfusion defects, when present, often involve small areas in multiple vascular territories consistent with the diffuse nature of the disease. The defects, therefore, are generally different from those seen in patients with CAD. Also, the decreases in EF and LV dilatation are out of proportion to the degree of the perfusion abnormality. Studies using positron emission tomography have shown a decrease in hyperemic MBF, as well as alteration in myocardial substrate utilization in such patients, even in the presence of normal coronary angiograms. Clearly, such abnormalities reflect microvascular dysfunction and microscarring.
Studies have linked such abnormalities to poor outcomes in these patients. In general, 70% of these patients will have a normal perfusion pattern, and the remaining 30% an abnormal pattern. It is improper to call these abnormalities false-positive scans because the epicardial arteries are normal. Both patients subsequently underwent coronary angiography, a not uncommon practice based on the premise that identification of CAD and coronary revascularization can alter the outcome in these patients. Based on the preceding discussion, one can make a good case for reserving coronary angiography for patients with an abnormal perfusion pattern. Skeptics might argue that balanced ischemia due to left main disease can go undetected in those with a normal perfusion pattern. This argument has a stronger appeal in patients with a small LV size and normal EF (see Chapter 6 ) than in patients with a dilated and poorly functioning LV. In patients with normal coronary angiograms, a rest study alone might be sufficient to exclude the possibility of prior MI due to occlusion and spontaneous recanalization of an otherwise normal coronary artery.
Case 12-3
Patient With Ischemic Cardiomyopathy ( Figure 12-3 )
A 79-year-old man presented with long-standing shortness of breath, which had progressively worsened in the last year. He had left leg pain with ambulation, which had also gotten progressively worse. The physical examination showed a displaced apical impulse with the soft murmur of mitral regurgitation and an S 3 gallop. The ECG showed LBBB. He underwent stress testing with adenosine without incident. The images are shown in Figure 12-3 .
Cases 12-4 and 12-5
Patient With Ischemic Cardiomyopathy ( Figures 12-4 and 12-5 )
A 60-year-old woman presents with chest pain, shortness of breath, and a syncopal episode. She was previously diagnosed with HF, but has not seen a physician in years. She is obese (210 lbs) and has hypertension. She underwent stress and rest sestamibi imaging on two separate days, using adenosine as the stress agent. The images are shown in Figure 12-4 .
