The study group comprised of 47 consecutive patients (mean age 61.1±5.1 years, 95.7% male) with ICMP, who underwent CABG with LIMA to LAD graft and left ventricle (LV) reconstruction according to standard indications . Within a week of surgery, stress and rest myocardial perfusion SPECT with 99mTc-MIBI and interoperation TTFM of LIMA grafts were performed on all patients.
Inclusion criteria were: 1) at least 3 months after acute myocardial infarction; 2) ≥75% stenosis of left main or proximal left anterior descending artery (LAD) or ≥75% stenosis of two or more major epicardial vessels; 3) left ventricular ejection fraction (EF) ≤40%; 4) left ventricular end-systolic index ≥60 ml/m2 (by transthoracic echocardiography) .
Exclusion criteria were: 1) rheumatic or inflammatory heart disorders; 2) acute coronary syndrome; 3) recent (< 6 months) cerebral ischemic attack; 4) acute or chronic right ventricle failure (by transthoracic echocardiography); 5) severe pulmonary hypertension; 6) contraindications for cardiopulmonary bypass; 7) contraindication to adenosine administration.
The study was approved by the Local Ethical Committee and conformed to the Declaration of Helsinki on Human Research. Written informed consent was obtained from each patient after explanation of the protocol, its aims, and potential risks.
All operations were performed under conditions of norm-thermal cardiopulmonary bypass standard procedure. A great saphenous vein and a LIMA were harvested according to the routine procedure, the last one was wrapped with papaverine solution in surgical drape to prevent spasms .
In all cases, the LIMA was grafted to the left anterior descending artery and the great saphenous vein was sewn for other target vessels. No sequential anastomoses were included in this series. The LV reconstruction using the D. Cooley or V. Dor method with L. Menicanti modification was made in the case of an LV aneurysm based on preoperative examination and intraoperative evaluation [19, 20].
Quantitative coronary angiography was performed after catheterization of the femoral artery by the Seldinger’s technique on the Axiom Artis coronary angiography system (Siemens; Erlangen, Germany) in a single scheme: a multi-projection right then left coronary angiography according to the method of M. Judkins . All coronary angiographies were done during the preoperative period.
TTFM and evaluation criteria for anastomosis satisfactory
Transit-time flow measurement was performed with VeriQ System (Medi-StimAS, Oslo, Norway) after all anastomoses, ventricle and valves reconstructions were completed, the heart-lung machine was disconnected and hemodynamic parameters became stable (mean arterial pressure fixed of 75-85 mmHg) [3, 22]. Flow parameters recorded in this study included mean graft flow (Q, ml/min), higher pulsatility index (PI), and diastolic filling (DF, %).
A Q value greater than 11.5 ml/min, a normal waveform of blood flow, and diastolic-dominant blood filling was considered as a surrogate marker for satisfactory anastomotic patency .
Myocardial perfusion imaging
Patients were instructed to refrain from caffeine, substances containing methylxanthine, and to avoid nitrates, calcium channel blockers, and beta-blockers for at least 24 h before the scan. All scans were performed after overnight fasting.
All patients underwent a 2-day stress/rest protocol. A pharmacological stress-test (adenosine, 140 mg/kg/min for 6 minutes) combined with low-level exercise was performed in all patients . The heart rate, systemic blood pressure, and 12-lead electrocardiogram were monitored before, during, and after the stress test. A dose of 370 MBq of 99mTc-sestamibi was injected after 3 minutes of stress testing and the same dose on the next day for rest study like described in ASNC guidelines for SPECT nuclear cardiology procedures . Pharmacologic stress testing did not lead to atria-ventricle (AV) conduction delay and/or to ST-segment depression in any patient. The total effective radiation dose was 6-7.3 mSv.
The SPECT data were acquired one hour after injection for both the rest and the stress studies with a solid-state detector CZT cardiac SPECT/CT system (GE Discovery NM/CT 570c). The acquisition time was 7 minutes. The myocardial perfusion imaging (MPI) scans were acquired using low energy multi-pinhole collimator and 19 stationary detectors which simultaneously imaged 19 different views without detector rotation. The acquisition matrix was 32×32 pixels (pixels sizes 4×4×4 mm). Each detector contains 32×32 pixelated (2.46×2.46 mm) CZT elements. A 20% energy window at 140 keV was used. Patients were imaged in the supine position with arms placed over their heads.
CZT images were reconstructed on the dedicated workstation (Xeleris 4.0; GE Healthcare, Haifa, Israel) using maximum-penalized-likelihood iterative reconstruction (60 iterations; Green OSL Alpha 0.7; Green OSL Beta 0.3) to acquire perfusion images in standard cardiac axes (short axis, vertical long axis, and horizontal long axis). The software Myovation for Alcyone (GE Healthcare, Haifa, Israel) was used for image reconstruction, and Butterworth post-processing filter (frequency 0.37; order 7) was applied to the reconstructed slices. The reconstruction was performed in a 70×70 pixels matrix with 50 slices.
Raw MPI-CZT data at stress and rest were visually assessed for motion and attenuation artifacts. Stress/rest images were analyzed with a commercially available software package Cedars QGS/QPS (Cedars-Sinai Medical Center, Los Angeles, CA, USA).
Left ventricle myocardium was presented in a 17-segment polar map format and was computed separately for each vascular territory by the AHA guidelines . Each of the 17 segments was scored based on a semi-quantitative 5-point scoring system: 0 – normal uptake; 1 – mild uptake reduction; 2 – moderate uptake reduction; 3 – severe uptake reduction; and 4 – an absence of radiotracer.
Myocardium perfusion was assessed globally (Global) and from left anterior descending artery (LAD) territory by following parameters: summed stress score (SSS), summed rest scores (SRS), summed difference score (SDS, was calculated as the difference between SSS and SRS), stress TPD (STPD), rest TPD (RTPD), TPD difference (DTPD, was calculated as the difference between STPD and RTPD) [24, 25, 26].
The distribution of continuous variables was checked by using the Shapiro-Wilk’s W-test. Normally distributed continuous variables were presented as the mean ± standard deviation and not normally distributed parameters were shown as the median and interquartile range (Q25, Q75). Categorical variables were presented as numbers and percentages. Group comparisons were analyzed with Student t-test or the Mann—Whitney U-test for continuous variables, and the χ2 or Fisher’s exact test for categorical variables. The Spearman test was used to estimate the correlation coefficient between quantitative variables. The receiver-operating-characteristic (ROC) curve analysis was performed to evaluate the sensitivity and specificity of tests. Areas under the ROC curves were compared using the DeLong method. A value of p<0.05 was considered statistically significant. All analyses were performed using SPSS statistical software 19.0 (SPSS Inc., Chicago, IL, USA) and MedCalc version 17.4 (MedCalc Software, Mariakerke, Belgium).