Improvement of afterload mismatch of left atrial booster pump function with positive inotropic agent.
ABSTRACT The objective of this study was to examine the hypothesis that a positive inotropic agent improves left ventricular (LV) filling during left atrial (LA) contraction in the presence of markedly elevated LV filling pressure.
In patients with old myocardial infarction (MI), an increase in the operational LV chamber stiffness reduces LV filling during the LA contraction, resulting from an "afterload mismatch" of the LA booster pump function.
We investigated the effect of dobutamine infusion (3 microg/kg/min) on the LA pump function in the presence of elevated LV filling pressure induced by aortic constriction (Aoc) during acute MI in 10 dogs. Transmitral flow velocity was determined by transesophageal echocardiography, LV pressure by a micromanometer and LV volume by a conductance catheter. We measured the early (E) and late (A) diastolic peak transmitral flow velocities (cm/s) and LV chamber stiffness (deltaP/deltaV: mm Hg/ml; where deltaP is developed pressure and deltaV is the absolute filling volume during LA contraction).
When the deltaP/deltaV was increased by Aoc during MI (from 1.1 +/- 0.8 to 3.1 +/- 2.6 mm Hg/ml, p < 0.01), A decreased significantly (from 30 +/- 5 to 22 +/- 8 cm/s, p < 0.01), and the ratio of E to A increased (from 1.0 +/- 0.3 to 1.4 +/- 0.8, p < 0.05) compared with MI without Aoc, showing the pseudonormal transmitral flow pattern, the so called "LA afterload mismatch." Dobutamine under this condition significantly reduced the deltaP/deltaV (to 1.7 +/- 1.2 mm Hg/ml, p < 0.05), resulting in an increase in A (to 31 +/- 8 cm/s, p < 0.01) and a decrease in E/A (to 1.0 +/- 0.3, p < 0.05), and the transmitral flow became a prolonged relaxation pattern as in MI without Aoc in all dogs. There was an inverse correlation between the deltaP/deltaV and the time-velocity integral of A (r = -0.70, p < 0.01).
Dobutamine improved the afterload mismatch of the LA booster pump function. This effect may have been due to the reduction in LV operational chamber stiffness, resulting in an increase in the LA forward ejection into the LV.
Article: Doppler echocardiographic assessment of left atrial appendage flow velocities in normal cats.[show abstract] [hide abstract]
ABSTRACT: The use of transthoracic Doppler echocardiography (TTDE) to evaluate the patterns and technique of measuring of left atrial appendage (LAA) flow velocities in normal cats. Left atrial enlargement and dysfunction are characteristic features of feline cardiomyopathy that may cause blood stasis in the left atrium (LA). This low flow state may be associated with hypercoagulability and thrombus formation. Left atrial enlargement, spontaneous echocardiographic contrast, and decreased velocity of LAA flow may be early indicators of thromboembolic risk. Little is known about the patterns and determination of LAA flow in normal cats. Transthoracic Doppler echocardiography was used to evaluate LAA flow in 47 normal cats and to assess the effects of age, body weight, sex, heart rate, arterial blood pressure, and echocardiographic indices of LA and LV size and function on LAA flow variables. Adequate LAA flow signals could be recorded in 43 (92%) cats. Polyphasic LAA flow profiles were obtained in all cats, consisting of two (79%), three (16%), or four (5%) flow waves. Maximum LAA flow velocity (mean+/-SD) was 0.47+/-0.20m/s (range 0.24-1.00) and average LAA flow velocity was 0.42+/-0.17m/s (0.22-0.93). There was a weak correlation between LAA flow velocity and LA size based on maximum LA diameter (r=0.36, p=0.018) and maximum LA area (r=0.44, p=0.004). There was no association between LAA flow velocity and any other independent variable evaluated. LAA flow may be recorded by use of TTDE in cats. The results of this study can be used for comparison with LAA flow patterns found in disease states.Journal of veterinary cardiology: the official journal of the European Society of Veterinary Cardiology 06/2005; 7(1):15-25.
Article: Assessment of left atrial appendage flow velocity and its relation to spontaneous echocardiographic contrast in 89 cats with myocardial disease.[show abstract] [hide abstract]
ABSTRACT: The hypotheses of this prospective study were that (1) left atrial appendage (LAA) blood flow velocities can be recorded in cats with myocardial disease by transthoracic Doppler echocardiography, (2) LA enlargement, LA mechanical dysfunction, and left ventricular (LV) diastolic abnormalities are associated with decreased LAA flow velocities, and (3) low LAA flow velocities predict the appearance of spontaneous echocardiographic contrast in cats with cardiomyopathy. Transthoracic 2-dimensional, M-mode, and Doppler echocardiographic studies were performed in 89 cats with hypertrophic, restrictive, dilated, or unclassified cardiomyopathy or with hyperthyroid heart disease. Maximal LAA flow velocity (LAAmax) was decreased (P < .001) in cats with cardiomyopathy (median, 0.28 m/s; range, 0.08-1.35) compared to normal cats. Associated with decreased LAA flow velocities were increased LA size, decreased LA function, increased severity of LV diastolic dysfunction, and the presence of congestive heart failure. Multivariate logistic regression analysis detected an LAAmax <0.20 m/s as the only independent variable to predict LA spontaneous echocardiographic contrast (odds ratio, 30.1; 95% confidence interval [CI], 4.1 222.3; P < .001). Receiver operating characteristic analysis performed to predict spontaneous echocardiographic contrast indicated an area under the curve of 0.88 (95% CI, 0.80-0.95; P < .001) with sensitivities of 100 and 74% and specificities of 69 and 83% for LAAmax <0.25 and <0.20 m/s, respectively. Thus, low LAA flow velocities identified a subgroup of patients at increased risk of spontaneous echocardiographic contrast and possible thromboembolism. These findings may have important clinical implications for anticoagulation therapy and prognostication in cats with cardiomyopathy.Journal of Veterinary Internal Medicine 20(1):120-30. · 1.99 Impact Factor