Regional nonischemic performance as assessed by end-systolic measures of shortening and thickening

Stimulation of A2A-adenosine receptors after myocardial infarction suppresses inflammatory activation and attenuates contractile dysfunction in the remote left ventricle

Following myocardial infarction (MI), contractile dysfunction develops not only in the infarct zone but also in noninfarcted regions of the left ventricle remote from the infarct zone. Inflammatory activation secondary to MI stimulates inducible nitric oxide synthase (iNOS) induction with excess production of nitric oxide. We hypothesized that the anti-inflammatory effects of selective A2A-adenosine receptor (A2AAR) stimulation would suppress inflammation and preserve cardiac function in the remote zone early after MI. A total of 53 mice underwent 60 min of coronary occlusion followed by 24 h of reperfusion. The A2AAR agonist (ATL146e, 2.4 μg/kg) was administered intraperitoneally 1, 3, and 6 h postreperfusion. Because of the 1-h delay in treatment after MI, ATL146e had no effect on infarct size, as demonstrated by contrast-enhanced cardiac MRI ( n = 18) performed 24 h post-MI. ATL146e did however preserve global cardiac function at that time by limiting contractile dysfunction in remote regions [left ventricle wall thickening: 51 ± 4% in treated ( n = 9) vs. 29 ± 3% in nontreated groups ( n = 9), P < 0.01]. RT-PCR, immunohistochemistry, and Western blot analysis indicated that iNOS mRNA and protein expression were significantly reduced by ATL146e treatment in both infarcted and noninfarcted zones. Similarly, elevations in plasma nitrate-nitrite after MI were substantially blunted by ATL146e ( P < 0.01). Finally, treatment with ATL146e reduced NF-κB activation in the myocardium by over 50%, not only in the infarct zone but also in noninfarcted regions ( P < 0.05). In conclusion, A2AAR stimulation after MI suppresses inflammatory activation and preserves cardiac function, suggesting the potential utility of A2AAR agonists against acute heart failure in the immediate post-MI period.

Validation of in vivo myocardial strain measurement by magnetic resonance tagging with sonomicrometry

OBJECTIVES

This study was designed to validate strain measurements obtained using magnetic resonance tagging with spatial modulation of magnetization (SPAMM). We compared circumferential segment shortening measurements (%S) obtained using SPAMM to sonomicrometry %S in a canine model with (n = 28) and without (n = 3) coronary artery ligation.

BACKGROUND

Magnetic resonance tagging enables noninvasive measurement of myocardial strain, but such strain measurements have not yet been validated in vivo.

METHODS

Circumferential sonomicrometry crystal pairs were placed in apical myocardium at ischemic risk in ligation studies and in adjacent and remote myocardium. The %S was obtained from closely juxtaposed sonomicrometry and SPAMM sites.

RESULTS

Paired data were available from 19 of 31 studies. Both methods distinguished remote from ischemic function effectively (p = 0.014 for SPAMM and p = 0.002 for sonomicrometry). SPAMM %S was similar to sonomicrometry %S in ischemic myocardium (2 +/- 3 vs. 0 +/- 3 p = 0.067) but was slightly higher than sonomicrometry %S in remote myocardium (11 +/- 10 vs. 7 +/- 5, p = 0.033). End-systolic (n = 30) and late systolic (n = 34) SPAMM %S correlated well with sonomicrometry %S (r = 0.84, p < 0.0001 and r = 0.88, p < 0.0001).

CONCLUSIONS

Magnetic resonance tagging using SPAMM can quantitate myocardial strain in ischemic and remote myocardium. This study validates its application in scientific investigation and clinical assessment of patients with myocardial ischemia.

Effect on coronary artery flow reserve and resistance in the remote area after acute coronary artery occlusion in the pig model

BACKGROUND

It has been reported that vasodilator function in remote myocardial regions supplied by "angiographically normal" coronary arteries is impaired in patients after acute myocardial infarction (MI). The aim of this study was to determine whether coronary artery flow reserve and coronary artery resistance in remote, nonischemic areas are also altered in experimental MI.

METHODS

Experiments were performed in anesthetized pigs. In group 1 infarction was induced by ligation of the left-anterior descending artery (LAD); group 2 consisted of sham-operated animals. Hemodynamic parameters, coronary artery resistance, and myocardial blood flow (MBF) were measured before and 4 hours after MI under rest and during infusion of adenosine.

RESULTS

Coronary artery dilation by adenosine caused a similar increase in MBF before and 4 hours after coronary artery occlusion. Resting MBF after acute MI was not altered, although a significant reduction (15%; P < .04) in mean aortic pressure was observed compared with baseline. Coronary artery resistance was significantly reduced by adenosine (P < .04) before MI, as well as at 4 hours after MI (P < .03). Coronary artery flow reserve was not adversely affected. The sham-operated animals showed similar results without any significant differences between the two study groups.

CONCLUSION

This study indicates that an acute MI in pigs did not increase coronary artery resistance in the remote area after MI and therefore did not adversely affect coronary artery flow reserve in the nonischemic vascular bed. Further studies are necessary to fully understand the exact mechanism of the alterations in remote flow reserve of patients after MI.

Automated tracking of left ventricular wall thickening with intracardiac echocardiography

OBJECTIVE

We developed and evaluated a new method to automatically measure regional left ventricular wall thickening by analyzing the radiofrequency backscatter signal from an intracardiac echocardiographic catheter.

METHODS

We inserted 10-MHz echocardiographic catheters in 11 dogs. Wall thickness was perturbed by altering loading conditions and inotropic state. The backscatter signal from a single selected radial scan line was digitized. An automated algorithm identified the digitized endocardial and epicardial signals, tracked them throughout the cardiac cycle, and plotted the spatial difference over time. Pressure-thickness loops were generated.

RESULTS

End-systolic and end-diastolic thickness and percent wall thickening from the unedited, unsmoothed signals compared favorably with independent manual analysis of transthoracic echocardiographic images of the same region: r = 0.89 for wall thickness and 0.81 for systolic thickening.

CONCLUSION

The backscatter signal from an intracardiac echocardiographic device can be analyzed automatically to continuously assess regional left ventricular wall thickening and generate pressure-thickness loops.

Effects of critical coronary stenosis on global systolic left ventricular function quantified by pressure-volume relations during dobutamine stress in the canine heart

OBJECTIVES

In this study we quantified the effects of a critical coronary stenosis on global systolic function using pressure-volume relations at baseline and during incremental dobutamine stress.

BACKGROUND

The effects of coronary stenosis have previously been analyzed mainly in terms of regional (dys)function. Global hemodynamics are generally considered normal until coronary flow is substantially reduced. However, pressure-volume analysis might reveal mechanisms not fully exposed by potentially load-dependent single-beat parameters. Moreover, no systematic analysis by pressure-volume relations of the effects of dobutamine over a wide dose range has previously been presented.

METHODS

In 14 dogs left ventricular volume and pressure were measured by conductance and micromanometer catheters, and left circumflex coronary flow by Doppler probes. Measurements in control and with left circumflex stenosis were performed at baseline and at five levels of dobutamine (2.5 to 20 microg/kg/min). The end-systolic pressure-volume relation (ESPVR) dP/dtMAX vs. end-diastolic volume (dP/dtMAX - V(ED)) and the relation between stroke work and end-diastolic volume (preload recruitable stroke work [PRSW]) were derived from data obtained during gradual caval occlusion.

RESULTS

In control, dobutamine gradually increased heart rate up to 20 microg/kg/min, the inotropic effect blunted at 15 microg/kg/min. With stenosis, the chronotropic effect was similar, however, contractile state was optimal at approximately 10 microg/kg/min and tended to go down at higher levels. At baseline, the positions of ESPVR and PRSW, but not of dP/dtMAX - V(ED), showed a significant decrease in function with stenosis. No differences between control and stenosis were present at 2.5 microg/kg/min; the differences were largest at 15 microg/kg/min.

CONCLUSIONS

Pressure-volume relations and incremental dobutamine may be used to quantify the effects of critical coronary stenosis. The positions of these relations are more consistent and more useful indices than the slopes. The positions of the ESPVR and PRSW show a reduced systolic function at baseline, normalization at 2.5 microg/kg/min and a consistent significant difference between control and stenosis at dobutamine levels of 5 microg/kg/min and higher.

Effects of preload, afterload and inotropy on dynamics of ischemic segmental wall motion

OBJECTIVES

This study sought to explore the separate and combined effects of changes in preload, afterload and contractility on the dynamics of systolic bulging.

BACKGROUND

The extent of ischemic systolic bulging has been shown to be mechanically disadvantageous to left ventricular pump performance. The factors that determine ischemic segmental wall motion have not been systematically studied.

METHODS

Fourteen beagles were instrumented with sonomicrometers, micromanometer pressure gauges and a balloon in the inferior vena cava. Regional function was evaluated before and after 90 s of proximal left circumflex coronary artery occlusion. Occlusions were repeated after increasing systolic pressure by 5 to 10 (afterload I) and 15 to 20 mm Hg (afterload II) with graded aortic occlusion during inotropic stimulation with dobutamine (2.5 and 5 micrograms/kg body weight per min intravenously), with simultaneous 5 micrograms/kg per min dobutamine infusion and afterload II and during 2.5% halothane (negative inotrope) concentration. A 20-min recovery period was allowed between each stage of the experiment so that regional function returned to its preocclusion level. Ischemic wall motion was characterized by percent systolic bulging and its peak positive systolic lengthening rate (+dL/dt).

RESULTS

Because bulging is markedly influenced by regional preload, systolic bulging was characterized over a wide range of end-diastolic lengths of the ischemic segment during caval balloon occlusion. During each intervention, a decrease in regional preload increased the extent of percent systolic bulging. This preload dependency was more pronounced with dobutamine infusions. An increase in afterload was not associated with increased percent systolic bulging at any given preload. At a predetermined preload, bulging was not appreciably altered when an increase in left ventricular systolic pressure was not associated with a change in peak positive first derivative of left ventricular pressure (+dP/dt) but was significantly worse when peak +dP/dt increased. Dobutamine caused a dose-dependent increase in percent systolic bulging and peak +dL/dt that was positively correlated with peak +dP/dt.

CONCLUSIONS

By using different loading and inotropic interventions and analyzing the regional wall motion behavior over a range of regional preloads, we can conclude that preload and rate of pressure (tension) development are the principal determinants of systolic bulging. Increases in left ventricular pressure alone had a minimal effect on systolic bulging.

Remote noninfarcted region dysfunction soon after first anterior myocardial infarction. A magnetic resonance tagging study

BACKGROUND

Previous studies have demonstrated hyperkinetic endocardial motion of noninfarcted myocardium early after myocardial infarction (MI). We wished to substantiate the findings of increased function of remote noninfarcted regions using magnetic resonance (MR) myocardial tagging in patients soon after anterior MI.

METHODS AND RESULTS

Twenty-eight patients (25 male; mean age, 52 years) were studied on day 5 +/- 2 after first anterior MI. All had single-vessel left anterior descending coronary artery (LAD) disease and had received reperfusion therapy but had evidence of regional left ventricular (LV) dysfunction and an ejection fraction (EF) < or = 50%. Breath-hold, segmented k-space, gradient-echo MR tagging was performed with short-axis imaging spanning the LV. Percent circumferential shortening (%S) on a topographic basis, LV mass, and EF were measured. Regional %S was compared with that in 10 normal subjects (7 male; mean age, 43 years). We found reduced intramyocardial %S throughout the LV in the patient group. Percent shortening was lower in patients compared with control subjects at all sites along the long axis of the ventricle (9 +/- 5% versus 23 +/- 3% at the apex, P < .0001; 11 +/- 5% versus 21 +/- 3% at the midventricle, P < .0001; 14 +/- 3% versus 17 +/- 5% at the base, P < .02). The basal lateral and midinferior regions, remote from LAD territory, demonstrated reduced %S and a strong trend toward reduced %S, respectively.

CONCLUSIONS

Patients on day 5 after first anterior MI with single-vessel disease demonstrate reduced intramyocardial circumferential shortening throughout the LV, including remote noninfarcted regions. Potential mechanisms include altered coronary vasodilatory properties, changes in regional mechanical load, or mechanical tethering to infarcted regions.