JNM: PET/CT helps detect sign of hypertrophic cardiomyopathy

Short-axis representative PET images of two hypertrophic cardiomyopathy individuals, one with normal LVOTGs (5 and 12 mm Hg) and another with elevated gradients (97 and 135 mm Hg at rest and provocation, respectively). Source: J Nucl Med 2012;53(3):407-414.

Maximal wall thickness was identified through PET/CT exams as the strongest predictor of impaired dipyridamole-induced hyperemia and flow reserve, whereas outflow tract obstruction was not an independent determinant, according to a study in the March issue of the Journal of Nuclear Medicine.

Patients with obstructive hypertrophic cardiomyopathy (HCM) exhibit elevated left ventricular outflow tract gradients (LVOTGs) and appear to have a worse prognosis than those with non-obstructive HCM. As a result, through this study, Paco E. Bravo, MD, of the division of nuclear medicine in the Russell H. Morgan Department of Radiology and Radiological Science at Johns Hopkins Hospital in Baltimore, and colleagues sought to evaluate whether patients with obstruction, compared with non-obstructive HCM, demonstrate significant differences in PET parameters of microvascular function.

The researchers performed a PET exam on 33 symptomatic HCM patients at rest and during dipyridamole stress (peak) for the assessment of regional myocardial perfusion (rMP), left ventricular ejection fraction (LVEF), myocardial blood flow (MBF) and myocardial flow reserve (MFR). They also measured the myocardial wall thickness and LVOTG with an echocardiogram.

Patients were divided into the following groups:

• Group One: Non-obstructive (LVOTG less than 30 mm Hg at rest and after provocation test with amyl nitrite);
• Group Two: Obstructive (LVOTG at least 30 mm Hg at rest and with provocation); and
• Group Three: Latent HCM (LVOTG less than 30 at rest but at least 30 mm Hg with provocation).

Bravo et al classified 11 patients as non-obstructive (Group One), 12 as obstructive (Group Two) and 10 as latent HCM (Group Three). Except for age (42 years for Group One, 58 years for Group Two and 58 years for Group Three), all three groups had similar baseline characteristics, including maximal wall thickness (2.3 cm for Group One, 2.2 cm for Group Two and 2.1 cm for Group Three).

During peak flow, most patients in Groups One and Two, but fewer in Group Three, exhibited rMP defects (73 percent for Group One, 100 percent for Group Two and 40 percent for Group Three) and a drop in LVEF (73 percent for Group One, 92 percent for Group Two and 50 percent for Group Three), according to the study authors.

Also, peak MBF (1.58 mL/min/g for Group One, 1.72 mL/min/g for Group Two and 1.97 mL/min/g for Group Three) and MFR (1.62 for Group One, 1.90 for Group Two and 2.27 for Group Three) were lower in the non-obstructive and higher in the latent HCM group. They also pointed out that LVOTGs demonstrated no significant correlation with any flow dynamics.  

In their conclusion, the researchers noted that they found no significant correlation between LVOTGs and MBF, suggesting a lack of interdependency of these two prognostically useful markers. Therefore, they pointed to maximal wall thickness as the strongest predictor of impaired peak MBF and MFR. However, Bravo and colleagues said these findings should be considered “preliminary and need to be confirmed in larger studies.”