On-line assessment of regional ventricular wall motion by transesophageal echocardiography with color kinesis during minimally invasive coronary artery bypass grafting

Feasibility of a three-axis epicardial accelerometer in detecting myocardial ischemia in cardiac surgical patients

OBJECTIVE

We investigated the feasibility of continuous detection of myocardial ischemia during cardiac surgery with a 3-axis accelerometer.

METHODS

Ten patients with significant left anterior descending coronary artery stenosis underwent off-pump coronary artery bypass grafting. A 3-axis accelerometer (11 x 14 x 5 mm) was sutured onto the left anterior descending coronary artery-perfused region of left ventricle. Twenty episodes of ischemia were studied, with 3-minute occlusion of left anterior descending coronary artery at start of surgery and 3-minute occlusion of left internal thoracic artery at end of surgery. Longitudinal, circumferential, and radial accelerations were continuously measured, with epicardial velocities calculated from the signals. During occlusion, accelerometer velocities were compared with anterior left ventricular longitudinal, circumferential, and radial strains obtained by echocardiography. Ischemia was defined by change in strain greater than 30%.

RESULTS

Ischemia was observed echocardiographically during 7 of 10 left anterior descending coronary artery occlusions but not during left internal thoracic artery occlusion. During ischemia, there were no significant electrocardiographic or hemodynamic changes, whereas large and significant changes in accelerometer circumferential peak systolic (P < .01) and isovolumic (P < .01) velocities were observed. During 13 occlusions, no ischemia was demonstrated by strain, nor was any change demonstrated by the accelerometer. A strong correlation was found between circumferential strain and accelerometer circumferential peak systolic velocity during occlusion (r = -0.76, P < .001).

CONCLUSIONS

The epicardial accelerometer detects myocardial ischemia with great accuracy. This novel technique has potential to improve monitoring of myocardial ischemia during cardiac surgery.

Color encoding of endocardial motion improves the interpretation of contrast-enhanced echocardiographic stress tests by less-experienced readers

BACKGROUND

We hypothesized that color encoding of endocardial motion could aid less-experienced readers in detection of wall-motion abnormalities at rest and stress in patients with poor acoustic windows.

METHODS

Color-encoded images (color kinesis) were obtained at rest and peak dobutamine stress in 4 standard views during intravenous infusion of contrast agent in 117 patients with poorly visualized endocardium. In 101 of 117 patients (86%), in whom contrast enhancement allowed endocardial tracking, images were reviewed by two expert readers without color overlays. Each reader graded regional wall motion as normal, abnormal, or uninterpretable, and their consensus grades served as a gold standard. The same images were then reviewed and graded with and without color overlays by 3 cardiology fellows. The accuracy of the interpretation was calculated against the gold standard separately for the 3 vascular territories (left anterior descending, left circumflex, and right coronary arteries) and averaged for the 3 fellows.

RESULTS

With the addition of color encoding: (1) the number of uninterpretable segments decreased by 55% at rest and 61% at peak stress; and (2) all 3 fellows reached higher levels of accuracy in all 3 vascular territories both at rest (6%-82% average) and at stress (73%-80%).

CONCLUSION

The addition of color encoding of wall motion to contrast-enhanced images obtained in patients with poor acoustic windows during stress tests improves the interpretation of regional left ventricular function by less-experienced readers.

Evaluation of regional aortic distensibility using color kinesis

Regional aortic stiffness cannot be evaluated by conventional methods. Regional aortic wall velocity during systole in the descending aorta was evaluated by using transesophageal echocardiography with color kinesis. The authors defined regional aortic distensibility (RAD) by considering pulse pressure, with RAD (microm/s/mm Hg) = (regional aortic wall velocity)/(pulse pressure). RAD was evaluated in 38 patients who had coronary artery disease (CAD) and 10 who did not. RAD decreased depending on aging (partial regression coefficient was -5.39 x 10(-1), p<0.001), and RAD was lower in the CAD group than that in the no-CAD group (p<0.05). In the CAD group, 19 patients had a single fixed plaque (4 calcified and 15 noncalcified plaques). RAD in the calcified plaque was lower than that in the noncalcified plaque (p<0.01), and RAD was lower in the noncalcified plaque than that in the no-plaque region (p<0.05). In noncalcified plaques, the relation between RAD and maximum intimal thickness had a significant correlation, r=0.7, p<0.001. The residual of RAD from the regression line was significantly larger in the calcified plaque than that in the noncalcified plaque (p<0.001). In conclusion, RAD can express increasing regional aortic wall stiffness brought about by arteriosclerosis quantitatively. Color kinesis provides information on characteristic difference between calcified and noncalcified plaque.

Myocardial ischemic preconditioning during minimally invasive direct coronary artery bypass grafting attenuates ischemia-induced electrophysiological changes in human ventricle

OBJECTIVE

Ischemic preconditioning (IPC) has been found to protect the myocardium in animal studies. However, clinical studies have been limited and the clinical effects of IPC are still uncertain. The purpose of this study was to assess whether IPC has any protective effect on the human myocardium during minimally invasive CABG (MIDCAB), by means of epicardial electrophysiological testing.

METHOD

Forty-five patients with left anterior descending artery disease who underwent a MIDCAB procedure were evaluated. In the present study, the electrical potentials which were not affected by cardio-pulmonary bypass or cardioplegia were measured. The ratio of longitudinal to transverse conduction velocity (phiL /phiT), and QT, JT dispersions were measured using plaque electrodes in the preischemic state, during a 5-minute coronary occlusion, during the subsequent 5-minute reperfusion, during 5- and 10-minute anastomosis periods, and after anastomosis.

RESULT

The phiL/phiT was 2.2 +/- 0.2 at baseline. Anisotropy was exaggerated during the 5-minute coronary occlusion (2.6 +/- 0.3). During anastomosis, conduction velocities were decreased, but showed no further deterioration (2.4 +/- 0.3, and 2.4 +/- 0.3, respectively). QT and JT dispersions were improved by reperfusion.

CONCLUSION

The effectiveness of IPC during the MIDCAB procedure was confirmed electrophysiologically. Anisotropy and dispersions were minimized after IPC, therefore IPC demonstrated antiarrhythmic protective effects on the human myocardium.

Mechanisms of hemodynamic changes during off-pump coronary artery bypass surgery

PURPOSE

To describe the mechanisms of hemodynamic changes during off-pump coronary artery bypass graft surgery (OP-CABG).

SOURCE

Pertinent medical literature in the English and French languages was identified through a Medline computerized literature search and a manual search of selected articles, using off-pump coronary artery surgery, beating heart surgery, hemodynamic, and transesophageal echocardiography as key words. Human and animal studies were included.

PRINCIPAL FINDING

Hemodynamic variations in OP-CABG may be due to mobilization and stabilization of the heart, or myocardial ischemia occurring during coronary occlusion. Suction type and compression type stabilizers produce hemodynamic effects through different mechanisms. Heart dislocation (90 degrees anterior displacement) and compression of the right ventricle to a greater extent than the left ventricle are responsible for hemodynamic alterations when using suction type stabilizers. Compression of the left ventricular outflow tract and abnormal diastolic expansion secondary to direct deformation of the left ventricular geometry are proposed mechanisms for hemodynamic derangements with compression type stabilizer. Coronary occlusion during the anastomosis can have additional effects on left ventricular function, depending on the status of collateral flow. The value and limitations of electrocardiographic (ECG), hemodynamic and echocardiographic monitoring modalities during OP-CABG are reviewed.

CONCLUSIONS

In summary, hemodynamic changes which can either be secondary to the stabilization technique or to transient ischemia represent an important diagnostic challenge during off-bypass procedures. The mechanism can vary according to the stabilization system. Current monitoring such as ECG and hemodynamic monitoring are used but remain limited in establishing the cause of hemodynamic instability. Transesophageal echocardiography is used in selected patients to diagnose the etiology of hemodynamic instability and can direct therapy, particularly in those with severe myocardial systolic and diastolic dysfunction, mild to moderate mitral regurgitation, or for patients who are unstable during the procedure.

Recent advances in echocardiographic evaluation of left ventricular anatomy, perfusion, and function

This article provides a brief overview of several recently developed, emerging technologies and discusses their potential uses on clinical grounds. These new technologies include three-dimensional imaging, objective automated evaluation of ventricular function with acoustic quantification, assessment of regional ventricular performance using color kinesis and tissue Doppler imaging, harmonic imaging, and power Doppler imaging. Our hope is that readers will gain a better understanding of the principles underlying these technological advances, which will help them to integrate these new techniques efficiently into their clinical practices.

Detection of regional temporal abnormalities in left ventricular function during acute myocardial ischemia

Echocardiographic diagnosis of myocardial ischemia is based on visualizing hypokinesis, which occurs late in the ischemic cascade. We hypothesized that temporal changes in endocardial motion may constitute sensitive early markers of ischemia. Two protocols were performed in 19 anesthetized pigs. Protocol 1 included 54 intracoronary balloon occlusions. Transthoracic images were acquired at baseline and every 15 s during 5 min of occlusion and reperfusion. In protocol 2, ischemia was induced in 12 animals by use of graded dobutamine infusion, after creating significant partial occlusions without a resting wall motion abnormality. Systolic and diastolic endocardial motion was color encoded using color kinesis and analyzed using custom software. All ischemic episodes caused detectable and reversible changes. The earliest sign of ischemia was tardokinesis in 31/54 occlusions, whereas hypokinesis appeared first in 23/54 cases. Dobutamine-induced ischemia caused tardokinesis first in 9/12 and hypokinesis in 3/12 animals. Reversible ischemic changes in regional left ventricular performance can be objectively detected using analysis of echocardiographic images and will likely improve the early noninvasive diagnosis of acute ischemia.

Transesophageal echocardiographic (TEE) evaluation of ventricular function

Transesophageal echocardiography (TEE) provides excellent delineation of ventricular function in the ambulatory and critical settings. Major indications include the acutely ill patient with suboptimal images with other techniques and the intraoperative assessment of patients undergoing cardiac surgery and of cardiac patients undergoing noncardiac surgery. The methodology of quantification of ventricular function is quite accurate, though it has inherent limitations. Newer technologies, such as edge enhancement techniques, three-dimensional acquisition, and contrast agents, all have the potential to improve evaluation of ventricular function with TEE. Stress imaging with TEE is possible with dobutamine and with pacing techniques. This is sage and accurate, and it is indicated in patients, such as the morbidly obese, who are impossible to image by other methods.

Local cardiac wall stabilization influences the reproducibility of regional wall motion during off-pump coronary artery pass surgery

OBJECTIVE

Myocardial ischemia is a risk factor during off-pump coronary artery bypass procedures. The development of new regional wall motion abnormalities assessed by transesophageal echocardiography (TEE) is a very sensitive sign of myocardial ischemia. To facilitate anastomosis, the epicardial area of the anastomosis site is often immobilized by a "stabilizer." This study was designed to investigate whether cardiac wall stabilization with an epicardial stabilizer could affect the interpretation of wall motion during coronary anastomosis without cardiopulmonary bypass.

METHODS

The TEE videotapes of 15 adult patients were investigated. Left ventricular (LV) transgastric short and long axis views were divided according to a modified 16-segment method. LV wall motion was scored using a 5-grade scale by two independent blinded investigators during pre-occlusion, occlusion, and reperfusion of anastomosed coronary arteries. The wall motion scores of a stabilized segment combined with two adjacent segments were compared with those of non-stabilized segments. Interobserver agreement was assessed using the weighted kappa statistic.

RESULTS

A total of 216 segments were analyzed by two investigators. The interobserver kappa coefficient in pre-occlusion and reperfusion periods was 0.87, 0.87 and 0.86, 0.87, respectively, indicating high agreements without stabilizer. During the occlusion period in stabilized and non-stabilized segments, it was 0.59 and 0.76, respectively, showing significantly less reproducibility in the presence of stabilizer.

CONCLUSION

Cardiac wall stabilization affects the reproducibility in the interpretation of regional wall motion during off-pump coronary artery bypass surgery. Caution should be used when monitoring for myocardial ischemia using TEE during coronary artery bypass surgery with epicardial stabilizer.