Afterload mismatch in patients with hypertrophic nonobstructive cardiomyopathy
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11st Department of Internal Medicine, Kobe University School of Medicine, Japan.
Insights
Hypertrophic nonobstructive cardiomyopathy (HNCM) patients with impaired cardiac reserve show reduced forward ejection under stress. This is linked to left ventricular stiffness and myocardial fibrosis, impacting cardiac function.
Area of Science:
- Cardiology
- Cardiovascular Physiology
Background:
- Hypertrophic nonobstructive cardiomyopathy (HNCM) is characterized by left ventricular hypertrophy without significant outflow tract obstruction.
- Assessing cardiac reserve in HNCM is crucial for understanding disease progression and prognosis.
Purpose of the Study:
- To investigate the cardiac reserve and response to afterload stress in patients with HNCM.
- To identify echocardiographic and clinical factors associated with impaired cardiac reserve in HNCM.
Main Methods:
- An echocardiographic study was conducted on 22 HNCM patients and 8 controls during angiotensin II loading.
- Parameters measured included left ventricular end-diastolic dimension (LVDd) and time velocity integral (Ie) at the aortic annulus.
- Patients were categorized into two groups based on the decrease in Ie during stress; clinical and biopsy findings were compared.
Main Results:
- HNCM patients were divided into Group I (Ie decrease >15%) and Group II (Ie decrease <15%).
- Group I exhibited a smaller increase in LVDd, higher incidence of ventricular tachycardia, lower maximal oxygen consumption, and elevated LV end-diastolic pressure compared to Group II.
- Group I also showed more severe myocardial fibrosis and disarray on right ventricular biopsy.
Conclusions:
- Some HNCM patients demonstrate an impaired ability to maintain forward ejection under afterload stress.
- This impairment is associated with reduced preload reserve, increased left ventricular stiffness, and significant myocardial lesions.
- These findings highlight the importance of assessing cardiac reserve in HNCM management.
Abstract:
To investigate the cardiac reserve of hypertrophic nonobstructive cardiomyopathy (HNCM), an echocardiographic study was performed before and during angiotensin II loading in 22 HNCM patients without left ventricular (LV) systolic dysfunction at rest and 8 normal subjects. LV end-diastolic dimension (LVDd) and time velocity integral (Ie) at aortic annulus were obtained as parameters of preload and forward ejection respectively. Responses of these indices to afterload stress were compared with clinical findings and right ventricular biopsy findings. Based on the reserve of forward ejection characteristics to afterload stress, 22 HNCM patients were divided into 2 groups; Group I: 9 cases with more than 15% decrease of Ie which corresponded to the value of mean - 1SD in normal subjects, Group II: 13 cases with a decrease of Ie less than 15%. There were no significant differences in echocardiographic findings between Group I and II before angiotensin II loading. On the other hand, Group I had a smaller increase of LVDd (p less than 0.05) to afterload stress, a higher incidence of ventricular tachycardia on a Holter electrocardiogram (p less than 0.05), lower maximal oxygen consumption with treadmil exercise test (p less than 0.01), and a larger value of LV end-diastolic pressure (p less than 0.05) than those in Group II, respectively. Although no difference in myocyte diameter was found between the 2 groups, myocardial fibrosis was more severe (p less than 0.001) and the incidence of moderate or severe disarray was higher (p less than 0.05) in Group I than in Group II. Thus, some HNCM patients cannot maintain forward ejection to afterload stress because of impaired preload reserve attributable to a greater stiffness of the left ventricle with severe myocardial lesion.