Comparison of low-dose dobutamine ventriculography with low-dose dobutamine echocardiography for predicting regional improvement in left ventricular function after coronary artery bypass grafting

Myocardial viability: what we knew and what is new

Some patients with chronic ischemic left ventricular dysfunction have shown significant improvements of contractility with favorable long-term prognosis after revascularization. Several imaging techniques are available for the assessment of viable myocardium, based on the detection of preserved perfusion, preserved glucose metabolism, intact cell membrane and mitochondria, and presence of contractile reserve. Nuclear cardiology techniques, dobutamine echocardiography and positron emission tomography are used to assess myocardial viability. In recent years, new advances have improved methods of detecting myocardial viability. This paper summarizes the pathophysiology, methods, and impact of detection of myocardial viability, concentrating on recent advances in such methods. We reviewed the literature using search engines MIDLINE, SCOUPS, and EMBASE from 1988 to February 2012. We used key words: myocardial viability, hibernation, stunning, and ischemic cardiomyopathy. Recent studies showed that the presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and LV dysfunction, but the assessment of myocardial viability did not identify patients with survival benefit from revascularization, as compared with medical therapy alone. This topic is still debatable and needs more evidence.

Hemodynamic and vascular effects of ventricular sourcing by stent-based ventricle to coronary artery bypass in patients with multivessel disease undergoing coronary artery bypass surgery

BACKGROUND

The hemodynamic and vascular effects of ventricular sourcing by a stent-based (VSTENT, Percardia) left ventricle-to-coronary artery bypass were studied in a patient subgroup of the European multicenter ADVANTAGE study (ADjunctive treatment with the VCAB/VSTENT myocardial implANT system in coronary Artery bypass Graft patiEnts).

METHODS AND RESULTS

Twelve patients who underwent VSTENT implantation in addition to coronary artery bypass surgery were studied up to 12 months after the procedure. The VSTENT was implanted distal to a hemodynamically relevant coronary artery stenosis. Coronary flow velocity was assessed at rest and during dobutamine stress. Intraoperative VSTENT implantation was successful in 11 of 12 patients. Early postoperative angiograms showed patent VSTENT in 8 of 11 patients, with predominantly systolic flow distal to the VSTENT. Coronary flow velocity reserve induced by dobutamine stress was 1.7+/-0.1 (P=0.006). VSTENT patency at 2- to 6-month follow-up was present in 5 of 11 patients, with concomitant VSTENT stenosis in 4 of those 5. In all patients, coronary flow velocity increased 3- to 4-fold proximal to the VSTENT, which was associated with a moderate degree of arterial remodeling. Except for target vessel reintervention (n=5), no other major adverse events were observed in 11 of 12 patients. One patient died on the second postoperative day, though the cause was probably not related to the VSTENT implantation.

CONCLUSIONS

VSTENT implantation seems to be safe in the mid-term follow-up and leads to a predominantly systolic coronary flow pattern in the vessel supplied by the VSTENT, with a flow reserve similar or close to that seen with conventional bypass. VSTENT patency rate, however, was unacceptably low at 3- to 6-month follow-up and needs to be improved.

Beneficial effect of coronary artery bypass grafting as assessed by quantitative gated single-photon emission computed tomography

The development of quantitative gated single-photon emission computed tomography (SPECT) has enabled the assessment of left ventricular perfusion, function and wall thickness in a single examination. Accordingly, the present study used gated SPECT to assess the benefit of coronary artery bypass grafting (CABG) in patients with coronary artery disease; 47 of those patients were evaluated before and 5 months after CABG. As a result of coronary revascularization, a significant improvement was observed in global ejection fraction (50+/-12 --> 53+/-11%; p<0.05). In 107 revascularized territories, the average regional reversible defect score (0.8+/-0.5 --> 0.2 +/-0.3; p<0.0001), average regional perfusion score at rest (0.6+/-0.6 --> 0.3+/-0.4; p<0.0001), average regional wall motion score (0.9+/-0.7 --> 0.7+/-0.5; p<0.05), and end-diastolic wall thickness (8.1+/-1.3 --> 8.6+/-1.5 mm; p<0.0005) all improved significantly. Even in 34 non-revascularized territories, the average regional reversible defect score (0.5+/-0.7 --> 0.2+/-0.5; p<0.03), average regional wall motion score (0.8+/-1.1 --> 0.5 +/-1.0; p<0.03) and end-diastolic wall thickness (8.0+/-1.4 --> 9.1+/-2.0 mm; p<0.03) all improved significantly. These results indicate that improvement in myocardial ischemia, hibernation and left ventricular function with CABG can be assessed in detail with gated SPECT.

Use of pharmaceuticals in noninvasive cardiovascular diagnosis

A number of pharmaceuticals are employed as diagnostic agents for cardiovascular diseases. Four groups of agents are reviewed here: 1) vasoactive substances employed as adjuncts to physical maneuvers in diagnosis of structural heart disease; 2) vasodilators used to produce heterogeneity of coronary flow; 3) sympathomimetic agents simulating the effects of exercise on the heart for the purpose of detection of coronary artery stenosis; and 4) ultrasonic contrast agents used to enhance myocardial imaging for the assessment of segmental wall motion. In the first group are amyl nitrate, a vasodilator, and methoxamine and phenylephrine, both vasopressors. The vasodilators of the second group are dipyridamole and adenosine. When combined with scintigraphic perfusion imaging or with echocardiographic assessment of segmental wall motion, these agents can detect single- or multiple-vessel coronary artery disease with sensitivity and specificity comparable to submaximal exercise. They are especially useful for preoperative risk assessment before noncardiac surgery. The sympathomimetic agents of the third group, dobutamine and arbutamine, increase myocardial contractility and heart rate, and dilate the peripheral vasculature. As with the vasodilators, when combined with nuclear or echocardiographic techniques they are equivalent to exercise in detection of coronary disease. They are especially useful in patients with bronchospastic disease and for assessment of myocardial viability. Agents from groups 2 and 3 have acceptable side-effect and safety profiles. The last group reviewed includes echocardiographic contrast agents that, in this investigative setting, are employed to enhance detection of segmental wall motion when used with agents from groups 2 and 3.

Improved identification of viable myocardium using second harmonic imaging during dobutamine stress echocardiography

OBJECTIVE

To determine whether, compared with fundamental imaging, second harmonic imaging can improve the accuracy of dobutamine stress echocardiography for identifying viable myocardium, using nuclear imaging as a reference.

PATIENTS

30 patients with chronic left ventricular dysfunction (mean (SD) age, 60 (8) years; 22 men).

METHODS

Dobutamine stress echocardiography was carried out in all patients using both fundamental and second harmonic imaging. All patients underwent dual isotope simultaneous acquisition single photon emission computed tomography (DISA-SPECT) with (99m)technetium-tetrofosmin/(18)F-fluorodeoxyglucose on a separate day. Myocardial viability was considered present by dobutamine stress echocardiography when segments with severe dysfunction showed a biphasic sustained improvement or an ischaemic response. Viability criteria on DISA-SPECT were normal or mildly reduced perfusion and metabolism, or perfusion/metabolism mismatch.

RESULTS

Using fundamental imaging, 330 segments showed severe dysfunction at baseline; 144 (44%) were considered viable. The agreement between dobutamine stress echocardiography by fundamental imaging and DISA-SPECT was 78%, kappa = 0.56. Using second harmonic imaging, 288 segments showed severe dysfunction; 138 (48%) were viable. The agreement between dobutamine stress echocardiography and DISA-SPECT was significantly better when second harmonic imaging was used (89%, kappa = 0.77, p = 0.001 v fundamental imaging).

CONCLUSIONS

Second harmonic imaging applied during dobutamine stress echocardiography increases the agreement with DISA-SPECT for detecting myocardial viability.

Myocardial viability: recent developments in detection and clinical significance

The long-term prognosis of patients with ischemic cardiomyopathy is highly variable, depending on the extent of myocardial viability and the success and completeness of the revascularization techniques used. Other important factors include left ventricular function, extent of coronary artery disease (CAD), and patient age. Chronic left ventricular dysfunction in ischemic cardiomyopathy is the result of a mixture of scarred as well as hibernating myocardium. In fact, most patients have both scarring and hibernation in different regions. Transmural biopsies of dysfunctional segments reveals that recovery of function is inversely proportional to the extent of fibrosis and that endocardial fibrosis extending over 30% of the myocardial thickness precludes recovery of function.Nagueh et al. [1] evaluated the relation of contractile reserve and thallium uptake in hibernating myocardium to myocardial structure in humans. The authors found that segments with postoperative functional recovery had more wall thickening at low-dose dobutamine echocardiography (DE), higher thallium uptake, and less fibrosis (2.0 vs 28%) than those segments without recovery. Also, segments with viability on DE had less fibrosis, less vimentin and fibronectin, more glycogen, and higher thallium uptake, than those segments without viability. Importantly, segments viable by single-photon emission computed tomography (SPECT) and DE had significantly less fibrosis (1%) than those viable by only one of the two techniques. In this review, we discuss recent developments in the detection of myocardial viability, including echocardiography, nuclear cardiac imaging, magnetic resonance imaging (MRI), and other techniques.