A Ronaszeki

Effect of superoxide dismutase on infarct size and postischemic recovery of myocardial contractility and metabolism in dogs

The effects of superoxide dismutase treatment on infarct size, postischemic recovery of contractile function and tissue content of high energy phosphates were examined in a canine model of myocardial ischemia and reperfusion. Ischemia was induced by thrombotic occlusion of a coronary artery and reperfusion was achieved by intravenous thrombolysis. Average duration of ischemia was 90 min. Fifty closed chest anesthetized dogs were randomized to receive either superoxide dismutase (34,000 IU/min intravenously) or placebo, starting approximately 30 min before and continuing for 30 min into the reperfusion phase. Left ventricular ejection fraction and regional segmental shortening of the postischemic area were calculated from contrast angiograms after 4 h, 48 h and 1 week of reperfusion. Tissue content of high energy phosphates was determined from transmural biopsy after 4 h and 1 week. Infarct size was measured by planimetry of dye-stained heart slices. In the superoxide dismutase and placebo-treated groups, respectively, the mortality rate was 25% and 16%, collateral flow 20 +/- 10 and 23 +/- 18 ml/min per 100 g, area at risk 25 +/- 6% and 26 +/- 7% of the left ventricle and infarct size 28 +/- 19% and 36 +/- 27% of the area at risk. Multiple regression analysis failed to show any beneficial effect of superoxide dismutase treatment on infarct size. Left ventricular ejection fraction, regional segmental shortening of the postischemic area and tissue content of high energy phosphates recovered to a similar extent and at a similar rate in both treated and placebo groups up to 1 week after reperfusion. Thus, in this model of coronary occlusion and reperfusion superoxide dismutase treatment is of no benefit.

Effect of Short Atrioventricular Delay on Cardiac Output

RONASZEKI, A., ET AL.: Effect of Short Atrioventricular Delay on Cardiac Output. Short atrioventricular (AV) delay modifies late diastolic filling dynamics. The effect of this change on cardiac output [CO) was studied in closed chest, AV blocked canine preparations (N: 10), during AV sequential pacing (80 bpm). CO (thermodilution technique) and transmitral flow velocity (TMFV, pulsed‐wave Doppler) were measured and compared (paired t‐test) on the basis of TMFV pattern, when atrial contraction (A wave) started just after early diastolic transmitral flow deceleration [PR:219 ± 25 ms, mean ± SD) and when A wave occurred at the end of late diastole and shortened due to the next ventricular contraction (PR: 56 ± 11 ms). The short AV delay resulted in 12.0 ± 5.9% decrease of CO, reflecting the interrupted late diastolic atrial transport. Properly timed atrial contraction is necessary for optimal AV sequential pacing.

Influence of short atrioventricular delay on late diastolic transmitral flow and stroke volume

Atrial transport function and the corresponding transmitral flow and stroke volume depend on the timing of atrial contraction. To study the influence of short atrioventricular delay (AVD) on these hemodynamic parameters, transmitral flow velocity (by pulsed wave Doppler) and aortic flow (by electromagnetic technique) were studied and compared (paired t test) during normal and short AVD at fixed rate DDD pacing (80 bpm) in AV-blocked, open-chest canine preparations (n:16). The short AVD resulted in a shorter acceleration (difference 4.1 ± 4.9 msec, mean ± SD, p<0.05), a lower peak velocity (difference: 7.1 ± 3.2 cm/sec, p < 0.001), a shorter (difference: 26.9 ± 16.2 msec, p<0.001) and more rapid deceleration (difference: 220.7 ± 291.7 cm/sec2, p < 0.005) of the late diastolic transmitral flow elicited by atrial systole. Stroke volume decreased (7.8 ± 5.2%, p < 0.001) during short AVD as a consequence of a reduced left ventricular filling due to the interruption of the active atrial transport by the onset of the ventricular contraction.

Relationship between diastolic atrio-ventricular pressure gradient and Doppler determined rapid inflow

The diastolic atrio-ventricular pressure gradient is one of the major determinants of ventricular inflow. The purpose of this study was to obtain very accurate pressure gradients across the mitral valve and compare these with peak early diastolic flow velocity from Doppler echocardiography. In 16 closed chest anesthetized mongrel dogs high gain left ventricular pressure and left atrial pressures were measured, digitized and the pressure gradient calculated. Simultaneously a Doppler tracing was obtained from a sample region between the mitral valve leaflets. The maximal positive and negative early diastolic pressure gradients were correlated with peak E and with peak positive and negative derivatives as well. Highly significant linear correlations were obtained between pressure and flow velocity variables.<<ETX>>

Comparison of Conventional and Laser Apexcardiogram in Healthy Young Men

The laser displacement technique is a new method to registrate low-frequency precordial movements. In 16 young healthy men, the apexcardiogram was obtained subsequently by the conventional and by the laser displacement technique. Basic differences in time intervals and amplitude relations were analysed with the paired t test