A 63-year-old woman was referred for pre-operative cardiology evaluation prior to elective cholecystectomy. She was experiencing palpitations lasting five to 10 minutes associated with lightheadedness, periodic – sometimes exertional back pain – and had an abnormal electrocardiogram (ECG) (see Figure 1). ECG findings were consistent with:
- normal sinus rhythm;
- left atrial enlargement;
- left ventricular hypertrophy; and
- non-specific ST and T wave abnormalities.
A pharmacologic single photon emission computed tomography (SPECT) study was ordered. This was carried out with a low-dose 8mCi, followed by a high-dose 32mCi, Tc-99m sestamibi one-day protocol with regadenoson stress.
The RegEx protocol was used.1 The patient walked for four minutes at zero percent grade with 0.4mg of regadenoson administered intravenously over 10 seconds at the 1.5-minute mark. Sestamibi was administered at two minutes. The patient experienced lightheadedness and dyspnea, which was reversed five minutes into the study with 100mg intravenous aminophyline over 30 seconds. Baseline non-specific ST and T wave changes worsened with the development of 3mm ST segment depression in the inferolateral leads. Arrhythmias did not occur.
Myocardial perfusion imaging-gated SPECT images were performed as per the American Society of Nuclear Cardiology guidelines.2 These images are shown in Figure 2. Markedly increased septal thickness is noted, with consequent increased tracer uptake resulting in an apparent fixed defect in the inferolateral wall.
Hypertrophic cardiomyopathy (HCM) was suspected and echocardiography was ordered. Septal thickness by echocardiography was up to 3cm, with a mean echocardiographic outflow tract gradient of 90mm (see Figure 3) Ejection fraction was normal, with moderate left atrial enlargement.
Subsequently a more detailed family history documented a father and an aunt with HCM.
HCM has been recognized during myocardial perfusion imaging, but has not been well characterized. If septal hypertrophy is marked, as in this case report, its recognition is not difficult. Milder forms are less recognizable.
While this patient did not have reversible defects, Cannon and colleagues and others have demonstrated that exercise-induced reversible perfusion defects are not uncommon in HCM patients without obstructive coronary artery disease.3,4 The ischemic etiology of these defects in the study by Cannon et al. was confirmed by myocardial lactate extraction measurement in the great cardiac vein.
Whether ischemia is caused by systolic compression of myocardial arterioles, outstripping of the blood supply, endothelial dysfunction, or other etiologies is not known.5