Sensitivity of isovolumic relaxation to hypothermia during myocardial infarction

Prediction of heart failure post myocardial infarction: comparison of ejection fraction, transmitral filling parameters, and the index of myocardial performance

Following an acute myocardial infarction (MI), the development of congestive heart failure (CHF) has been associated with a reduced ejection fraction (EF), pseudonormal or restrictive diastolic filling, and an increased index of myocardial performance (IMP).

STUDY OBJECTIVES

To determine the comparative predictive value of EF, transmitral filling parameters, and IMP for the development of CHF following a first MI.

DESIGN AND SETTING

A retrospective analysis of consecutive echocardiographic and Doppler studies in patients admitted for their first acute MI from the years 1988 through 1992. We studied 109 patients following their first MI with two-dimensional and Doppler within 24 hours of MI. We divided patients into those who developed CHF within 15 days (43 patients) and without CHF (66 patients).

RESULTS

Patients who developed CHF had greater LV dilatation, lower EF (27.7%+/- 10.2% vs 45.6%+/- 13.2%, P < 0.001), higher E/A, shorter deceleration times (DCT; 157 +/- 69 msec vs 248 +/- 105 msec, P < 0.001), and increased IMP. Utilizing multiple logistic regression, EF (strongest predictor), DCT, and IMP were predictive of CHF. Nineteen patients in the no CHF group developed late CHF and had lower EFs (30.5%+/- 13.1% vs 50.5%+/- 9.8%, P < 0.001), higher E/A and shorter DCTs (161 +/- 39 msec vs 283 +/- 103 msec, P < 0.001). EF, DCT, and E/A were predictive of late CHF in patients without initial CHF. For patients admitted with a first MI, the EF, DCT, and to a lesser extent IMP predicted who would ultimately develop CHF. An EF < 40% or a DCT < 200 msec correctly predicted CHF in 60 of 62 patients.

CONCLUSION

We conclude that the early and ultimate development of CHF following a first MI were associated with an moderately reduced EF < 40%, pseudonormal diastolic filling indices, and an increased IMP.

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 less than 0.05), a lower peak velocity (difference: 7.1 +/- 3.2 cm/sec, p less than 0.001), a shorter (difference: 26.9 +/- 16.2 msec, p less than 0.001) and more rapid deceleration (difference: 220.7 +/- 291.7 cm/sec2, p less than 0.005) of the late diastolic transmitral flow elicited by atrial systole. Stroke volume decreased (7.8 +/- 5.2%, p less than 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.

Computer analysis of physiologic signals in a cardiovascular research laboratory

A comprehensive computer program which provides immediate computation and feedback has been developed for data acquisition and analysis of signals in a cardiovascular animal laboratory. The system is based on a microcomputer equipped with analog-to-digital converter and supports function modules which digitize, filter, and differentiate up to 8 simultaneously sampled cardiovascular signals. The program detects, analyses, and plots incoming and averaged beats. Beat-by-beat signal averaging for each channel is performed and cardiac cycles are partitioned automatically. For each cardiac and average cycle the amplitude at 6 physiologic fiducial markers are measured and derived calculations are made. Channel vs channel plots and loop area measurements are also computed and displayed. The computer algorithms have been shown to give accurate, precise, and reproducible results when tested on canine cardiovascular data. Also, it has been demonstrated that signal averaging is an appropriate analysis technique for cardiovascular signals.

Abnormal cardiac function in the streptozotocin-diabetic rat. Changes in active and passive properties of the left ventricle

To provide an integrated assessment of changes in systolic and diastolic function in diabetic rats, we measured conscious hemodynamics and performed ex vivo analysis of left ventricular passive-elastic properties. Rats given streptozotocin (STZ) 65 mg/kg i.v. (n = 14) were compared with untreated age-matched controls (n = 15) and rats treated with insulin after administration of STZ (n = 11). After 7 d, diabetic rats exhibited decreases in heart rate and peak developed left ventricular (LV) pressure during aortic occlusion. After 26 d of diabetes there were significant decreases in resting LV systolic pressure, developed pressure, and maximal +dP/dt, whereas LV end-diastolic pressure increased and the time constant of LV relaxation was prolonged. The passive LV pressure-volume relationship was progressively shifted away from the pressure axis, and the overall chamber stiffness constant was decreased. However, "operating chamber stiffness" calculated at end-diastolic pressure was increased at 7 d, and unchanged at 26 d. LV cavity/wall volume and end-diastolic volume were increased after 26 d of diabetes. Myocardial stiffness was unchanged at both time intervals. All of the above abnormalities were reversed by the administration of insulin. We conclude that the hemodynamic and passive-elastic changes that occur in diabetic rats represent an early dilated cardiomyopathy which is reversible with insulin.

Physiological early diastolic intraventricular pressure gradient is lost during acute myocardial ischemia

A consistent pattern of intraventricular regional pressure gradients exists under physiological conditions during the rapid filling phase of diastole in the normal dog left ventricle. We hypothesized that this pressure gradient pattern is caused, in part, by early diastolic recoil of the left ventricular walls in conjunction with release of elastic potential energy stored during systole, generating suction and thus contributing to diastolic filling. If so, any condition that interferes with normal regional systolic function might be expected to modify the pattern of the normal early diastolic intraventricular pressure gradients. Accordingly, the present study was designed to determine whether acutely induced regional systolic left ventricular mechanical dysfunction is accompanied by changes in the pattern of the early diastolic intraventricular pressure gradients. Acute myocardial ischemia was induced by balloon occlusion of the left anterior descending coronary artery (LAD) in nine anesthetized closed-chest dogs. The maximum early diastolic intraventricular pressure gradient (MIVP) was measured between the mid-left ventricle and apex with a dual-sensor micromanometer (3-cm spacing between the sensors) before and 20 minutes after LAD occlusion. Ejection fraction (EF) and number of dyskinetic chords (DChords) were measured from left ventricular contrast ventriculograms. Twenty minutes after LAD occlusion, the nine dogs evidenced significant changes in EF (56 +/- 10% to 37 +/- 8%), DChords (0 +/- 0 to 17 +/- 16 chords), left ventricular minimum pressure (-1.7 +/- 0.5 to 0.0 +/- 1.5 mm Hg), left ventricular end-diastolic pressure (4.2 +/- 1.2 to 5.9 +/- 2.2 mm Hg), and heart rate (90 +/- 17 to 103 +/- 18 beats/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of different pacing modes on left ventricular relaxation in closed-chest dogs

Ventricular relaxation is an important determinant of ventricular filling; impaired relaxation may decrease cardiac output and stroke volume. Relaxation has been shown to occur more quickly following beats with an increased extent of systolic fiber shortening. Since cardiac output and stroke volume are greater during atrioventricular (AV) sequential pacing than during ventricular pacing at identical heart rates, we reasoned that AV sequential pacing would improve relaxation. To assess this hypothesis we studied 11 dogs with chronic (1-3 months) complete heart block (CHB) induced by radiofrequency catheter ablation of the His bundle. Right and left heart pressures, thermodilution cardiac output, and single plane ventriculography were recorded during baseline rhythm (CHB), and VVI, and AV sequential pacing at a heart rate greater than the sinus rate. None had ventriculoatrial conduction. During AV sequential pacing, the AV interval was set at 150 msec. Cardiac output and stroke volume were significantly increased in the AV sequential compared to the VVI pacing mode. Left ventricular pressures, maximal positive and negative dP/dt, and the time constant (T) of isovolumic pressure decay were not different in the two modes. We conclude that despite increased stroke volume in the AV sequential pacing mode, relaxation is unchanged. We believe the lack of change in relaxation is due to nonuniform ventricular activation when depolarization is initiated at the right ventricular apex.

The transmitral pressure-flow velocity relation. Effect of abrupt preload reduction

Although recent animal and clinical studies suggest that Doppler-derived indexes may be useful for the characterization of ventricular diastolic behavior, the hemodynamic basis for the preload dependency of these indexes has not previously been fully elucidated. Accordingly, effects of reduction of left atrial load on the pressure-flow velocity relation were characterized in 10 anesthetized, closed-chest dogs during transient inferior vena caval occlusion by means of simultaneously recorded left atrial and left ventricular micromanometric pressure measurement and transesophageal Doppler echocardiograms. Within four or five beats after inferior vena caval balloon occlusion, left atrial loading was reduced as evidenced by a decrease in the slope of the left atrial v wave from 21 +/- 4 to 13 +/- 4 mm Hg/sec (p less than 0.001) and by a decrease in the first crossover point of left atrial and left ventricular pressures from 5.6 +/- 1.1 to 2.9 +/- 1.5 mm Hg (p less than 0.001). This decrease in left atrial loading resulted in reductions during early diastole of minimum left ventricular pressure (from 1.0 +/- 0.8 to -0.4 +/- 1.2 mm Hg, p less than 0.001), the maximum early forward (i.e., left atrial pressure greater than left ventricular pressure) transmitral pressure gradient (from 2.8 +/- 0.8 to 2.4 +/- 0.5 mm Hg, p less than 0.01); the slope of the rapid filling pressure wave (from 44 +/- 11 to 38 +/- 10 mm Hg/sec, p less than 0.025); and the area of the reversed (i.e., left ventricular pressure greater than left atrial pressure) transmitral pressure gradient (from 79 +/- 42 to 53 +/- 33 mm Hg.msec, p less than 0.05). During late diastole, both the heights and slopes of the left atrial and left ventricular a waves fell, resulting in a decrease in the maximum late transmitral pressure gradient (from 1.2 +/- 0.7 to 0.9 +/- 0.5 mm Hg, p less than 0.05). Vena caval occlusion also altered Doppler transmitral velocity profiles during both the early and late phases of diastole. Peak velocity of the E wave decreased (from 50 +/- 11 to 41 +/- 7 cm/sec, p less than 0.01) as did acceleration (from 880 +/- 222 to 757 +/- 258 cm/sec2, p less than 0.025) and deceleration (from 597 +/- 260 to 429 +/- 197 cm/sec2, p less than 0.025). Peak velocity of the A wave also fell (from 29 +/- 9 to 22 +/- 5 cm/sec, p less than 0.005). Abrupt inferior vena caval occlusion did not significantly change heart rate or mean aortic pressure.(ABSTRACT TRUNCATED AT 400 WORDS)

Diastolic stiffening induced by acute myocardial infarction is reduced by early reperfusion

Reperfusion early during myocardial infarction improves ejection fraction and this improvement may represent myocardial salvage in the injured segment. Alternatively, reperfusion of injured myocardium may cause intramyocardial hemorrhage with resultant increased stiffness causing a dyskinetic segment to become akinetic, thus improving ejection fraction without concomitant myocardial salvage. To evaluate this possibility, diastolic stiffness was assessed in a closed chest, anesthetized, normothermic dog model immediately after a 1 or 3 h occlusion of the left anterior descending coronary artery and during the 4 weeks after occlusion. Acute myocardial infarction in experimental dogs was accompanied by a fivefold increase in the chamber stiffness constant, a threefold increase in the myocardial stiffness constant and a significant increase in elastic stiffness and end-diastolic pressure. These changes occurred contemporaneously with a marked decline in ejection fraction. Early reperfusion (1 h occlusion) resulted in improvement of the ejection fraction accompanied by simultaneous resolution of the previously increased stiffness. Late reperfusion (3 h occlusion) resulted in permanent depression of ejection fraction with permanent elevation of stiffness. These results indicate that the improved systolic function observed after early reperfusion reflects a process other than increased stiffness, perhaps salvage of jeopardized myocardium.

Transmitral pressure-flow velocity relation. Importance of regional pressure gradients in the left ventricle during diastole

Effects of regional diastolic pressure differences within the left ventricle on the measured transmitral pressure-flow relation were determined by simultaneous micromanometric left atrial (LAP) and left ventricular pressure (LVP) measurements, and Doppler echocardiograms in 11 anesthetized, closed-chest dogs. Intraventricular pressure recordings at sites that were 2, 4, and 6 cm from the apex were obtained. Profound differences between these sites were noted in the transmitral pressure relation during early (preatrial) diastolic filling. In measurements from apex to base, minimum LVP increased (1.6 +/- 0.7 to 3.1 +/- 0.8 mm Hg, mean +/- SD); the time interval between the first crossover of transmitral pressures and minimum LVP increased (31 +/- 3 to 50 +/- 17 msec); the slope of the rapid-filling LVP wave decreased (74 +/- 13 to 26 +/- 5 mm Hg/sec); the maximum forward (i.e., LAP greater than LVP) transmitral pressure gradient decreased (3.6 +/- 1.3 to 2.1 +/- 0.7 mm Hg); the time interval between the first and second points of transmitral pressure crossover increased (71 +/- 9 to 96 +/- 13 msec); and the area of reversed (i.e., LVP greater than LAP) gradient between the second and third points of transmitral pressure crossover decreased (101 +/- 41 to 40 +/- 33 mm Hg.msec). During atrial contraction, significant regional ventricular apex-to-base gradients were also noted. The slope of the LV A wave decreased (26 +/- 10 to 16 +/- 4 mm Hg/sec); LV end-diastolic pressure decreased (8.1 +/- 2.0 to 7.4 +/- 2.0 mm Hg), and the upstroke of the LV A wave near the base was recorded earlier than near the apex. All differences were significant at the 0.05 level. Simultaneous transmitral Doppler velocity profiles and transmitral pressures were measured at the 4-cm intraventricular site. The average interval between the first and second points of pressure crossover and between the onset of early rapid filling and maximum E-wave velocity were statistically similar (81 +/- 13 vs. 85 +/- 12 msec; NS); and the average area of the forward transmitral pressure gradient associated with acceleration of early flow was significantly greater than the area of reversed gradient associated with deceleration of early flow (133 +/- 36 vs. 80 +/- 46 msec.mm Hg; p less than 0.025).(ABSTRACT TRUNCATED AT 400 WORDS)