## 3 Results  
The study investigated 47 male and 2 female patients aged 69 (65-76) years. All patients were in sinus rhythm before surgery. Three patients were excluded after baseline measurements, since the surgical procedure was changed and no unilateral ITA graft was used.  
The mean value of SNR overall measurements was \(-1.80\pm 0.08\) AU (arbitrary units, mean \(\pm\) standard error). The SNR was significantly affected by surgery (Figure 3, Table 1).  
SNR values were highest at baseline and dropped persistently after surgery at both sides of the chest. The lowest SNR occurred at the measurement H2. A partial recovery of SNR was noted at H24 and H144. The SNR remained significantly below the baseline value until the last measurement H144 (Table 1).  
The use of ITA had a small but consistent effect on the perioperative response of SNR; 2.8% of the SNR variance was determined by ITA alone (\(\sigma^{2}\) = 8.33 vs. \(\sigma^{2}\) = 8.57 \(\chi^{2}\)(dft) = 121, \(p<0.001\)).  
Compared to baseline, SNR values decreased at H2 significantly more on the ITA side than on the other side of the chest wall (\(\Delta\)7.85 AU vs. \(\Delta\)6.86 AU, \(p<0.001\)). Conversely, the partial recovery of SNR between H2 and H24 was higher on the ITA side (\(\Delta\)3.52 AU vs. \(\Delta\)2.31 AU, \(p<0.001\)). At H24, SNR values of both sides were comparable (\(-\)2.45 AU vs. \(-\)2.40 AU, \(p=0.427\)). Only a nominal increase of SNR until H144 was observed on the chest wall side without ITA preparation (\(\Delta\)1.20 AU vs. its preceding value at H24). Finally, SNR values remained significantly different at H144 (\(-\)2.53 AU vs. \(-\)1.20 AU for the ITA and the other side, respectively, \(p<0.001\)) (Tables 1 and 2).  
The effects of surgery and ITA preparation were independent from age, sex, weight and height of the patients. Heart rhythm returned to sinus rhythm in most patients at H24 and H144. Therefore, only the effects of atrial or ventricular pacing at H2 were tested, and no significant effect on SNR was found.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & **ITA Side** & **95\% CI** & \(\mathbf{p_{1}}\) & **Other Side** & **95\% CI** & \(\mathbf{p_{2}}\) \\ \hline BL & 1.89 & 0.61–3.17 & & 2.15 & 0.87–3.44 & 0.121 \\ \hline H2 & \(-\)5.96 & (\(-\)7.22)–(\(-\)4.70) & \(<\)0.001 & \(-\)4.71 & (\(-\)5.97)–(\(-\)3.45) & \(<\)0.001 \\ \hline H24 & \(-\)2.45 & (\(-\)4.03)–(\(-\)0.87) & \(<\)0.001 & \(-\)2.40 & (\(-\)3.98)–(\(-\)0.82) & 0.427 \\ \hline H144 & \(-\)2.53 & (\(-\)3.78)–(\(-\)1.28) & \(<\)0.001 & \(-\)1.20 & (\(-\)2.45)–0.05 & \(<\)0.001 \\ \hline \end{tabular}
\end{table}
Table 1: Signal-to-noise ratio (SNR) in arbitrary units. 95% CI: 95% confidence interval. SNR was calculated before (BL) and two hours (H2), one day (H24) and six days (H144) after surgery. ITA side: side of the chest wall with preparation of the internal thoracic artery; other side: side of the chest wall without ITA preparation; \(p_{1}\) for comparison against baseline; \(p_{2}\) for the difference between both sides.  
Figure 3: SNR values before (baseline) and two hours (H2), one day (H24) and six days (H144) after surgery. Means and 95% confidence intervals are shown.