Key points
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Current guidelines do not recommend routine screening with stress MPI in asymptomatic individuals. Obviously, some exceptions are expected.
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Although patients with DM are considered at high risk for cardiovascular events, there is a spectrum of risk in these patients and MPI is a useful tool for risk stratification in this population. Recent data from prospective studies show that the risk of cardiac events is actually small in asymptomatic but well-treated patients.
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Patients with CKD are also a subgroup at high risk for cardiac events. LV hypertrophy, especially septal hypertrophy, is common and may affect the perfusion pattern by downscaling of the lateral wall.
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Perfusion pattern and LVEF on MPI are powerful predictors of outcome in patients with ESRD being considered for renal transplantation.
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Women have unique characteristics that need to be recognized, such as atypical clinical presentations, small hearts, breast attenuation, a greater need for vasodilator stress testing, smaller coronary vessels, and more microvascular disease. Women with an ischemic ECG response during stress but normal perfusion tend to have a benign course.
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Vasodilator stress testing might be the stress test modality of choice in elderly patients, who are more likely than younger patients to fail to achieve target heart rates during treadmill exercise testing.
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In patients with LBBB, the rest MPI should be normal in the absence of prior myocardial infarction (MI). The exercise (or dobutamine or any other stress agent that is associated with high heart rate) MPI might show reversible defects that mimic LAD disease, even in the absence of angiographic LAD disease, in about 40% of patients. These are not seen with vasodilator stress where the heart rate is not high. Any abnormality outside the LAD zone should not be ascribed to LBBB. Vasodilator stress, rather than exercise or dobutamine, should therefore be the stress modality of choice in such patients.
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In patients with LBBB, the gated images often show abnormal septal wall motion but normal thickening. The presence of the wall-thickening abnormality together with a perfusion defect suggests that the septal scar is responsible for the LBBB and not the reverse.
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In morbidly obese patients, a higher tracer dose and a longer imaging time could ensure high-quality images. Otherwise, the images would be of poor quality and difficult to interpret.
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Some, but not all, arrhythmias can interfere with gating and produce falsely low LVEF. This is another reason why gating should be done on both the rest and stress images.
Background
Certain groups of patients might pose challenges in the performance and interpretation of MPI. Most, if not all, of the groups discussed in this chapter are not “zebras” that are encountered every now and then, but rather are part and parcel of everyday practice. These patient groups include asymptomatic patients, those with DM, CKD (especially those at end-stage on dialysis [ESRD]), women, the elderly, morbidly obese patients, and patients with LBBB, and arrhythmias. Some of their unique features are discussed in this chapter.
Case 11-1
Stress Testing in a Patient With Diabetes and Shortness of Breath ( Figure 11-1 )
A 74-year-old woman with type 2 DM for more than 30 years but no past medical history of CAD, is referred for stress MPI because of a recent history of progressive shortness of breath and unusual fatigue. She also has chronic obstructive pulmonary disease, dyslipidemia, hypertension, and osteoporosis, and has had hip surgery in the past. There is a strong family history of CAD. Adenosine/rest gated SPECT MPI showed a large area of reversible perfusion abnormality ( Figure 11-1, A, B ). Coronary angiography subsequently revealed severe stenosis in the LAD with occlusion of the LCX. The LVEF was normal ( Figure 11-1, C ). Mature collaterals to the LCX were evident. She was treated with a drug-eluting stent to the LAD plus optimization of medical therapy. Her symptoms resolved.
Comments
Although it is widely acknowledged that DM constitutes a CAD-equivalent based on studies that demonstrated that DM patients without known CAD have an equivalent cardiac risk to patients without DM but with prior MI, there is a spectrum of risk for DM patients and the presence of CAD increases cardiovascular risk substantially. As a general rule, the diagnostic accuracy of MPI is similar in patients with and without DM. The presence and extent of myocardial ischemia is a powerful predictor of future cardiovascular events. Nevertheless, there is a residual risk associated with DM such that patients with DM with an abnormal MPI have a higher cardiovascular risk than patients without DM with an abnormal MPI. More significantly, patients with DM with a normal MPI are also at higher risk than patients without DM with normal results. Recent data from the BARI2D trial showed that residual ischemia is decreased following coronary revascularization with the addition of optimal medical management compared to optimal medical management alone. DM also affects LV function; the LV volume is higher and the EF is slightly lower in patients with DM compared to those without DM. Abnormalities in diastolic LV function are even more common and may occur earlier.
Case 11-2
Stress Testing in a Patient With Severe CKD ( Figure 11-2 )
A 60-year-old man with stage IV CKD secondary to long-standing uncontrolled hypertension is referred for stress MPI prior to high-risk peripheral vascular surgery. The rest ECG showed severe LVH. The perfusion pattern after regadenoson was normal, but there was marked septal hypertrophy producing downscaling of the lateral wall on both the stress and rest images ( Figure 11-2 , only stress images are shown). The gated images showed normal EF and wall motion/thickening. He underwent surgery with no complications.
Comments
CKD is increasingly being recognized as an important risk factor for cardiovascular disease, and current guidelines consider patients with CKD to be in the highest CAD risk category for risk factor management. The risk of cardiovascular events is known to increase with progressively decreasing eGFR. Moreover, most patients with CKD succumb to cardiovascular death before initiating hemodialysis (stage 5 CKD). The presence and extent of perfusion abnormalities on MPI have been shown to be predictive of risk, but those with a normal MPI are at a higher risk than patients without CKD and a normal MPI. This could be due to the effect of CKD on cardiac structure and function that are independent of coronary perfusion. By the time the renal function deteriorates to stage V, most patients would already have developed LVH and/or LV dysfunction. The LVH in ESRD involves the septum more than the lateral wall. The reasons are not known, but we believe that the LV diastolic dysfunction (due to LVH) produces pulmonary hypertension and this, together with volume overload, produces right ventricular hypertrophy. Thus, the septum is subjected to both LVH and right ventricular hypertrophy/volume overload. This unique feature (also seen in patients with hypertrophic cardiomyopathy) may give the appearance of a lateral wall perfusion abnormality on MPI and misdiagnosis of LCX scar or ischemia. As in patients with severe hypertrophy, the EF might be underestimated because of improper tracking of the endocardial borders. Analysis of the cine slices often show cavity obliteration and should be interpreted as normal.
Case 11-3
Stress Testing Before Renal Transplantation in a Patient With Known Heart Disease ( Figure 11-3 )
A 61-year-old man with ESRD secondary to IgA nephropathy is referred for stress MPI before renal transplantation. He underwent coronary artery bypass grafting and aortic valve replacement a year ago and has been on hemodialysis for 6 years. Adenosine MPI showed a large mixed (scar and ischemia) perfusion abnormality ( Figure 11-3, A, B ). The LVEF was severely depressed on the gated images ( Figure 11-3, C ). Coronary angiography revealed severe CAD and poor runoff. He was denied renal transplantation and continued on hemodialysis.
