Cardiac 123I-MIBG reflects left ventricular functional reserve in patients with nonobstructive hypertrophic cardiomyopathy.
Little is known about the relation between left ventricular (LV) functional reserve in response to exercise and cardiac sympathetic nervous function in patients with nonobstructive hypertrophic cardiomyopathy (HCM). We investigated whether an assessment of cardiac sympathetic nervous function by myocardial (123)I-metaiodobenzylguanidine ((123)I-MIBG) scintigraphy might provide a sign of an abnormal LV functional reserve in response to exercise-induced beta-adrenergic stimulation in patients with HCM.


METHODS
Thirty HCM patients underwent (123)I-MIBG scintigraphy and echocardiography at rest and subsequent biventricular cardiac catheterization at rest and during dynamic exercise. LV pressures were measured using a micromanometer-tipped catheter system. The early and delayed (123)I-MIBG images were quantified as a heart-to-mediastinum ratio (H/M). The plasma levels of brain natriuretic peptide (BNP) and norepinephrine (NE) were also measured.


RESULTS
Patients were divided into 2 groups according to the delayed (123)I-MIBG H/M: group I consisted of 12 patients with a delayed H/M of < or =1.8 and group II had 18 patients with a delayed H/M of >1.8. Both the percentage increase from rest to exercise in LV isovolumic contraction (LV dP/dt(max)) and the percentage shortening of LV pressure half-time (T(1/2)) as an index of isovolumic relaxation were significantly less in group I than in group II (P < 0.05, respectively). A significant linear correlation was observed between the percentage increase in LV dP/dt(max) and (123)I-MIBG H/Ms (early H/M: r = 0.49, P < 0.01; delayed H/M: r = 0.54, P < 0.005, respectively). A significant linear correlation was also observed between the percentage shortening in T(1/2) and (123)I-MIBG H/Ms (early H/M: r = 0.58, P < 0.001; delayed H/M: r = 0.64, P < 0.0005, respectively). The plasma NE levels were significantly higher in group I than in group II (P < 0.01), whereas the plasma BNP levels were comparable in the 2 HCM groups.


CONCLUSIONS
beta-Adrenergic enhancement of LV function during exercise may depend on the extent of cardiac sympathetic nervous innervation in HCM patients. Resting myocardial (123)I-MIBG scintigraphy can noninvasively evaluate LV functional reserve in response to exercise in patients with nonobstructive HCM.
Isobe
Satoshi
S
Department of Cardiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi 466-8550, Japan. sisobe@med.nagoya-u.ac.jp
Izawa
Hideo
H
Iwase
Mitsunori
M
Nanasato
Mamoru
M
Nonokawa
Makoto
M
Ando
Akitada
A
Ohshima
Satoru
S
Nagata
Kohzo
K
Kato
Katsuhiko
K
Nishizawa
Takao
T
Murohara
Toyoaki
T
Yokota
Mitsuhiro
M
D019797:3-Iodobenzylguanidine; D000328:Adult; D000368:Aged; D006328:Cardiac Catheterization; D002312:Cardiomyopathy, Hypertrophic / Q000000981:diagnostic imaging* / Q000503:physiopathology; D004452:Echocardiography; D005080:Exercise Test; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging* / Q000294:innervation / Q000503:physiopathology; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D020097:Natriuretic Peptide, Brain / Q000097:blood; D009638:Norepinephrine / Q000097:blood; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D013564:Sympathetic Nervous System / Q000503:physiopathology; D016277:Ventricular Function, Left
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D020097:Natriuretic Peptide, Brain; D019797:3-Iodobenzylguanidine; D009638:Norepinephrine