Stunned left ventricular myocardium after exercise treadmill testing in coronary artery disease

Impact of regional ventricular function, geometry, and dobutamine stress on quantitative 99mTc-sestamibi defect size

BACKGROUND

Serial myocardial perfusion imaging with 99mTc-sestamibi (MIBI) was used to evaluate infarct risk area and salvage after thrombolysis. The purpose of this investigation was to determine whether changes in MIBI defect size observed after reperfusion may result in part from distortion of regional and global left ventricular geometry.

METHODS AND RESULTS

Twenty-five open-chest dogs were subjected to either 15 minutes (groups 1A and 1B) or 3 hours (group 2) of left anterior descending coronary artery occlusion followed by 3 hours of reperfusion. MIBI was injected before occlusion (group 1A) or during occlusion (groups 1B and 2), and serial ECG-gated planar imaging was performed. Dobutamine was infused after 3 hours of reperfusion (groups 1B and 2) to transiently alter left ventricular size and function. Perfusion defect magnitude (DM) and extent (DE) were serially quantified with circumferential profile analysis of end-systolic (ES), end-diastolic (ED), and summed images. Flow was assessed with radiolabeled microspheres and correlated with myocardial MIBI activity. Myocardial thickening was assessed in the risk area with sonomicrometers. In group 1A dogs, ischemic dyskinesis produced large artifactual quantitative MIBI defects on ES images (DM, 9.3 +/- 1.3; DE, 27.8 +/- 6.0) that were significantly smaller on ED images (DM, 4.5 +/- 0.9, P < .05; DE, 4.4 +/- 2.3, P < .05). In addition, DM and DE correlated inversely with myocardial thickening on ES images (DM, r = -.84; DE, r = -.78) and summed images (DM, r = -.72; DE, r = -.61) but not ED images (DM, r = -.12; DE, r = -.15). An index of defect reduction derived from summed images correlated well with thickening fraction in stunned dogs (group 1B, r = .89) but poorly in infarcted dogs (group 2, r = .41) subjected to dobutamine stress.

CONCLUSIONS

99mTc-MIBI defect size may be affected by alteration of left ventricular geometry. Changes in regional function may confound analysis of risk area and myocardial salvage with serial 99mTc-MIBI imaging and may also affect defect size during pharmacological stress with dobutamine. Dobutamine 99mTc-MIBI imaging may be useful for distinguishing viable and nonviable myocardium.

Increased response of diastolic blood pressure to exercise in patients with coronary artery disease: an index of latent ventricular dysfunction?

OBJECTIVE

To determine whether an abnormal response of diastolic blood pressure during treadmill exercise stress testing correlated with the number of obstructed vessels and with left ventricular systolic function in patients with coronary artery disease.

DESIGN

Diastolic blood pressure was measured invasively during exercise stress testing and coronary angiograms and left ventriculograms were obtained at rest in patients with coronary artery disease. The abnormal (> or = 15 mm Hg) diastolic blood pressure response was compared with the number of obstructed coronary arteries and with left ventricular systolic function.

SETTING

Two tertiary referral centres.

PATIENTS

50 consecutive patients (mean age 57 years) with coronary artery disease.

MAIN OUTCOME MEASURES

The increase in diastolic blood pressure during exercise and its correlation with the appearance and disappearance of ST segment deviation, resting left ventricular systolic function, and the number of obstructed coronary arteries.

RESULTS

Group 1: 10 (20%) patients (three with one, four with two, and three with three vessel coronary artery disease) (mean (SD) age 54.7 (12) years) had an abnormal diastolic blood pressure response that appeared 1.2 (0.3) min before ST segment deviation and became normal 0.9 (0.3) min after the ST segment returned to normal. Group 2: 40 (80%) patients (12 with one, 16 with two, and 12 with three vessel coronary arteries disease) (aged 56.8 (8.2) years) had a normal diastolic blood pressure response to stress testing. The ejection fraction (46.3 (5)%) and cardiac index (2.6 (0.1) 1/min/m2) in group 1 were less than in group 2 (61.6 (4.2)% and 3.8 (0.3) 1/min/m2 respectively, p < or = 0.001). The end systolic volume was greater in group 1 than in group 2: 38.7 (0.7 ml/m2 v 28.2 (2.1) ml/m2, p < or = 0.001.

CONCLUSION

In patients with coronary artery disease an abnormal increase in diastolic blood pressure during exercise stress testing correlated well with left ventricular systolic function at rest but not with the number of obstructed coronary arteries. The abnormal response of diastolic blood pressure probably reflects deterioration of myocardial function.

Does the myocardium become "stunned" after episodes of angina at rest, angina on effort, and coronary angioplasty?

To assess whether myocardial stunning occurs after brief periods of ischemia, global and regional ventricular function assessed by radionuclide angiography was studied in 52 patients. Patients were divided into 3 groups according to the type of ischemic episodes. Group 1 consisted of 15 patients studied before, during and after episodes of angina at rest. Seventeen patients studied immediately before and after coronary angioplasty constituted group 2. Group 3 consisted of 20 patients with stable angina studied before, during and after exercise-induced ischemia. Medical therapy was discontinued 48 hours before the study in all patients except those undergoing coronary angioplasty who were receiving diltiazem 180 mg/day. No difference in baseline ejection fraction was found between groups, whereas peak filling rate was statistically lower in group 3 patients. Evidence of left ventricular dysfunction during ischemia was seen in patients in groups 1 and 3, whereas transient ischemia was documented by ST-segment displacement and/or typical chest pain during balloon inflation in group 2. Persistence of systolic or diastolic dysfunction was not observed in any of the 3 groups in the recovery phase after ischemia. In conclusion, transient ischemia caused either by a primary reduction in oxygen supply (angina at rest, coronary angioplasty) or by an increase in oxygen demand (angina on effort) did not reproduce the phenomenon of systolic and diastolic stunning observed in animal experiments, although in all patients the ischemia was of sufficient duration and severity to induce marked ventricular dysfunction. The search for stunned myocardium should be extended to other different clinical models characterized by prolonged ischemia such as unstable angina or myocardial infarction.

Does reperfusion injury exist in humans?

Timely coronary reperfusion as treatment for acute myocardial infarction reduces myocardial infarct size, improves left ventricular function and survival. There is still concern that at the time of reperfusion, a further injury occurs to the myocardium. Theoretically, if this "reperfusion injury" could be treated and eliminated, the outcome for patients with myocardial infarction might further improve. The concept of reperfusion injury is closely tied to the concept that oxygen radicals generated at the time of reperfusion cause tissue damage. There are four basic forms of reperfusion injury. Lethal reperfusion injury is described as myocyte cell death due to reperfusion itself rather than to the preceding ischemia. This concept continues to be controversial in both experimental animal and clinical studies. Vascular reperfusion injury refers to progressive damage to the vasculature over time during the phase of reperfusion. Manifestations of vascular reperfusion injury include an expanding zone of no reflow and a deterioration of coronary flow reserve. This form of reperfusion injury has been documented in animal models and probably occurs in humans. Stunned myocardium refers to postischemic ventricular dysfunction of viable myocytes and probably represents a form of "functional reperfusion injury." This phenomenon is well documented in both animal models and humans. Reperfusion arrhythmias represent the fourth form of reperfusion injury. They include ventricular tachycardia and fibrillation that occur within seconds to minutes of restoration of coronary flow after brief (5 to 15 min) episodes of myocardial ischemia. True reperfusion arrhythmias occur in only a small percentage of patients receiving thrombolytic therapy for acute myocardial infarction and are not a sensitive indicator for successful reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)