Real time assessment of myocardial revascularization during coronary artery bypass surgery by means of ultrasonic integrated backscatter

Reduction of systolic and diastolic dysfunction by retrograde coronary sinus perfusion during off-pump coronary surgery

OBJECTIVES

We evaluated the protective effects of retrograde coronary sinus perfusion to offset potential systolic and diastolic dysfunction (myocardial stunning) after temporary regional ischemia needed for off-pump coronary artery bypass grafting.

METHODS

Twenty Yorkshire-Duroc pigs (31.8 +/- 3.9 kg) underwent 15 minutes of mid-left anterior descending coronary artery ischemia in the beating heart. In 8 pigs, no protective measures were used. In 12 pigs, an aorta-coronary sinus shunt (with conventional cannulas) allowed retrograde perfusion during temporary ischemia; in 6 of these pigs, no leakage to the right atrium was ensured. Regional endocardial contraction was measured with sonomicrometer crystals. Systolic dysfunction (impaired regional shortening), diastolic dysfunction (contraction extending into early diastole), and coronary sinus nitric oxide and endothelin-1 levels were recorded.

RESULTS

Before ischemia, contraction did not extend into the diastolic interval. During ischemia, paradoxic bulging occurred in all hearts except in the occlusive coronary sinus shunt group (16% +/- 6% of baseline, P <.01). Sixty minutes after ischemia, systolic segment shortening recovered 36% +/- 24% without retrograde perfusion versus 56% +/- 20% and 61% +/- 14% with coronary sinus shunting (P <.05). Diastolic dysfunction (as percentage of diastolic time in contraction) was 38% +/- 16% in the nontreated group versus 22% +/- 22% and 9% +/- 9% (P <.05) after shunting and occlusive shunting, respectively. This correlated with a left ventricular end-diastolic pressure increase of 4 mm Hg in the ischemic group versus no change in the retrograde perfusion groups. Nitric oxide decreased 15% without shunting and increased 8% after occlusive coronary sinus shunting (P <.05).

CONCLUSIONS

Retrograde coronary sinus perfusion during simulated off-pump coronary revascularization diminishes systolic and diastolic dysfunction. An aortic-coronary sinus shunt is a rapid, recognized approach that can improve myocardial muscle and endothelial safety during off-pump coronary artery bypass grafting.

Integrated backscatter during harmonic and fundamental frequency imaging--effect of depth, mechanical index, and tissue anisotropy: implications for myocardial tissue characterization

OBJECTIVE

To explore the potential advantages of tissue harmonic imaging (THI) versus fundamental frequency imaging (FFI) when applied to tissue characterization.

METHODS

A Philips Medical Systems Sonos 5500 echocardiograph equipped with a broadband transducer (S4) and an on-line quantitative analysis software package (Acoustic Densitometry) was used for imaging. The effect of mechanical index (MI), imaging depth, and anisotropy on relative backscatter amplitude was evaluated.

RESULTS

This study demonstrated that imaging with tissue harmonics generated relatively greater backscatter values at clinically relevant imaging depths and instrument settings referenced to FFI. This effect was dependent on MI setting. A direct relationship between backscatter amplitude and MI was demonstrated. Additionally, tissue anisotropy had similar effects on integrated backscatter amplitude during both THI and FFI. However, relative backscatter values at each fiber orientation are greater during THI at similar instrument settings when referenced to FFI.

CONCLUSION

Tissue harmonic imaging may offer advantages over FFI for myocardial tissue characterization.

Prediction of functional recovery of the left ventricle after coronary revascularization in patients with prior anterior myocardial infarction: a myocardial integrated backscatter study

Cyclic variation (CV) of myocardial integrated backscatter (IBS), which reflects intrinsic contractile performance, can predict myocardial viability in patients with a reperfused acute myocardial infarction (MI), but the use of this method has not been validated for chronic left ventricular (LV) dysfunction. The aim of this study was to examine whether myocardial IBS was useful for predicting LV functional recovery after coronary revascularization in 17 patients with prior anterior MI and LV dysfunction (ejection fraction <50%). Within 24 h of the revascularization procedure (percutaneous transluminal coronary angioplasty or coronary stenting), IBS curves were obtained by placing the region of interest on the anterior wall on the short-axis IBS image. The patients had repeat left heart catheterization at 3 or 6 months after the revascularization procedure, and were grouped according to the patterns of the IBS curve within the anterior wall. In 8 patients (group A), the IBS curve had a synchronized pattern with the magnitude of CV > or = 3.5, and in the remaining 9 patients (group B), the curve had either an asynchronized pattern or the magnitude of CV was less than 3.5 dB even in the case of synchronized pattern, or both. At baseline, there were no significant differences in LV functional indices between the 2 groups. After the follow-up period, the LV end-systolic volume decreased (75 +/- 21 ml to 56 +/- 20ml, p = 0.05), LV ejection fraction increased (35 +/- 12% to 50 +/- 14%, p = 0.014), and LV end-diastolic pressure decreased (19 +/- 10 mmHg to 13 +/- 6 mmHg, p = 0.02) in group A, whereas only the LV ejection fraction increased (34 +/- 9% to 40 +/- 11%, p = 0.03) in group B; LV end-systolic volume (72 +/- 19 ml to 66 +/- 16 ml, p = 0.126) and LV end-diastolic pressure (18 +/- 12 mmHg to 14 +/- 8 mmHg, p = 0.184) showed no significant changes. In conclusion, IBS is valuable for predicting LV functional recovery after coronary revascularization in patients with LV dysfunction caused by a remote anterior MI. A large-scale study is be needed to establish these data.

Alterations of myocardial ultrasonic tissue characterization by coronary angioplasty in patients with chronic stable coronary artery disease

We conducted a study to delineate the alterations in the cyclic changes of myocardial ultrasonic integrated backscatter (IBS) in patients receiving angioplasty for chronic coronary artery disease. Ultrasonic tissue characterization (UTC) and dobutamine stress echocardiography were performed in 43 patients before and 24 h after angioplasty, as well as before the follow-up angiography 3 months later. For segments being normokinetic with ischemic burden, the blunted amplitude and increased nadir deviation of IBS cyclic modulation recovered soon after angioplasty. For dyssynergic segments with contractile reserve, the angioplasty rebuilt the amplitude before the wall motion recovered, but corrected the nadir deviation tardily. In both circumstances, the coronary restenosis abolished the initial restoration. Those nonviable segments persistently revealed large deviations and small weighted amplitudes irrelevant to coronary lesions. The progress of myocardial ischemia, the development of wall motion dyssynergy and, then, the loss of viability, show different patterns of alterations in UTC after alleviating coronary obstructions.