Assessment of regional early diastolic function using cine magnetic resonance imaging in patients with hypertrophic cardiomyopathy

Comparison of myocardial contrast enhancement via cardiac magnetic resonance imaging in healthy cats and cats with hypertrophic cardiomyopathy

OBJECTIVE

To quantify myocardial contrast enhancement (MCE) of the left ventricle (LV) by use of cardiac magnetic resonance imaging (CMRI) in healthy cats and cats with hypertrophic cardiomyopathy (HCM) and to compare MCE between the 2 groups.

ANIMALS

10 healthy cats and 26 Maine Coon cats with moderate to severe HCM but without clinical evidence of congestive heart failure.

PROCEDURE

Anesthetized cats underwent gradient echo CMRI examination. Short-axis images of the LV were acquired before and 7 minutes after IV administration of gadolinium dimeglumine. Regions of interest were manually traced in the quadrants of 5 mid-LV slices acquired at end systole, and the MCE percentage was calculated from summed weight-averaged data from all slices. Doppler tissue imaging echocardiography was performed to measure the early diastolic myocardial velocity (Em) as an index of diastolic function. Three-way repeated-measures ANOVA was used to determine differences in MCE between cats with HCM and healthy cats. Simple linear regression was used to assess whether MCE was correlated with LV mass, LV mass index (LVMI), or Em. A Student t test was used to compare the SDs of the postcontrast myocardial signal intensity between the 2 groups.

RESULTS

There was no difference in MCE between cats with HCM and healthy cats. There was no correlation of MCE with LV mass, LVMI, or Em. There was no difference in heterogeneity of signal intensities of LV myocardium between the 2 groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Contrast-enhancement CMRI was not useful in detecting diffuse myocardial fibrosis in cats with HCM.

Does the progression of myocardial fibrosis lead to atrial fibrillation in patients with hypertrophic cardiomyopathy?

The majority of left ventricular (LV) inflow volumes in hypertrophic cardiomyopathy (HCM) depend on atrial contraction because of impaired LV relaxation. If HCM is complicated by atrial fibrillation (AF), heart failure can develop because of the loss of atrial contraction. The purpose of this study was to determine the relationship between the development of AF and myocardial fibrosis or intramyocardial small artery (IMSA) stenosis in autopsied hearts with HCM. Studies were performed in five HCM hearts with AF (AF group) and five HCM hearts without AF (non-AF group). LV specimens were divided into the inner (IT), middle (MT), and outer (OT) thirds. We selected at random 120 fields and 20 IMSAs from each layer and assessed them quantitatively using an image analyzer. We determined the extent of fibrosis (%F) and the degree of stenosis of each IMSA (%L). The %F in the AF group was greater than in the non-AF group (P<.01). In the AF group, the %F of the IT was greater than in the MT and the OT (P<.01). In the non-AF group, the %F of the IT was greater than in the MT (P<.05), and the %F of the MT was greater than in the OT (P<.01). The %L was similar in the AF and non-AF groups. In both groups, the %L of the IT was lower than in the MT (P<.01), which was lower than that of the OT (P<.05). LV fibrosis is more severe in patients with HCM and AF than in those without AF. Therefore, myocardial fibrosis might impair LV relaxation, resulting in hemodynamic intolerance to AF.

Left ventricular diastolic function in the elderly

Previous studies using pulsed Doppler echocardiography have demonstrated a pattern of abnormal left ventricular relaxation associated with increasing age. Specifically, aging is associated with decreased peak velocity of early diastolic mitral inflow, increased peak velocity of late diastolic inflow, increased isovolumic relaxation time, and early diastolic deceleration time. Abnormal relaxation can progress to significantly elevated left atrial pressure--characterized by increased early peak velocity and shortened isovolumic relaxation time and deceleration time--as part of the disease processes. Left ventricular diastolic dysfunction is highly prevalent, occurring in one half to two thirds of elderly patients with congestive heart failure, in association with normal systolic function. Left ventricular hypertrophy, which is commonly related to systemic arterial hypertension, and ischemic heart disease are the two major causes of abnormal left ventricular diastolic function in the elderly. Recently, newer echocardiographic techniques have been described that allow more accurate evaluation of left ventricular diastolic function. Treatments for left ventricular diastolic dysfunction should focus on the underlying disease etiology as well as on the derangement in left ventricular diastolic function. Although calcium channel blockers and angiotensin-converting enzyme inhibitors have been used clinically to treat diastolic dysfunction, their effects on prognosis remain unproven.

Effect of regional myocardial perfusion abnormalities on regional myocardial early diastolic function in patients with hypertrophic cardiomyopathy

Nonuniform hypertrophy of the left ventricle is an important factor in regional diastolic dysfunction in patients with hypertrophic cardiomyopathy (HCM). However, the effect of myocardial perfusion abnormalities on regional diastolic dysfunction has not been established in patients with HCM. We investigated the relationship between regional myocardial perfusion abnormalities and regional early diastolic function in 31 patients with HCM and 8 control patients. Short-axis images of the left ventricle recorded by cine magnetic resonance imaging were divided into ten blocks. The time-to-peak-wall-thickness-thinning rate (TPWR) and the wall thickness were measured in each block. Of the 310 blocks from the patients with HCM, 242 (78%) showed normal thallium-201 uptake (group 1), 40 (13%) showed slightly decreased uptake (group 2), and 28 (9%) showed markedly decreased uptake (group 3). There was no difference in the regional wall thickness among the three groups. The TPWR was longer in patients with HCM than in control patients. It was significantly longer in group 3 (190+/-45ms) than in group 1 (167+/-36 ms) and group 2 (160+/-31 ms). (P < 0.01). The linear regression slope of the relationship between the TPWR and the regional wall thickness was significantly steeper in group 3 than in groups 1 and 2 (P < 0.05). In conclusion, abnormalities in regional myocardial perfusion, in addition to regional hypertrophy, contributed to the regional early diastolic dysfunction in patients with HCM.