Effects of atrial fibrillation on coronary artery bypass graft flow.

OBJECTIVES: No detailed studies exist of coronary artery bypass graft flow during atrial fibrillation. We examined the effects on bypass graft flow of atrial fibrillation following coronary artery bypass grafting. METHODS: Immediately after surgical revisualization, atrial fibrillation was induced in 18 patients by high frequency atrial pacing. Hemodynamic variables were measured in sinus rhythm and atrial fibrillation. The graft flow in pedicled left internal thoracic artery grafts and in saphenous vein grafts was also measured using transit-time flowmetry. RESULTS: Left internal thoracic artery graft flow had a greater diastolic component than saphenous vein graft flow, as shown by the percent diastolic time-flow integral (86 +/- 10% in the left thoracic artery and 62 +/- 12% in the saphenous vein, P < 0.0001). The induced atrial fibrillation caused significant deterioration in hemodynamics: heart rate and central venous pressure increased, and mean arterial pressure and cardiac index decreased (all P < 0.0025). In left internal thoracic artery grafts (n = 18) and also in saphenous vein grafts (n = 20), graft flow decreased significantly with atrial fibrillation (44.3 +/- 26.2 to 26.2 +/- 20.7 ml/min in the left internal thoracic artery, P = 0.0003; 39.7 +/- 15.6 to 33.3 +/- 14.3 ml/min in the saphenous vein, P = 0.001). The reduction in graft flow due to atrial fibrillation was much larger in left internal thoracic artery grafts than in saphenous vein grafts (P = 0.0008). CONCLUSIONS: Direct measurement of coronary artery bypass graft flow shows that atrial fibrillation after surgery significantly reduces graft flow. The effect is much larger in left internal thoracic artery grafts with their strong diastolic component than in saphenous vein grafts.     

Effect of aortocoronary bypass surgery on left ventricular function and coronary sinus blood flow in patients with severe left ventricular dysfunction

Left ventricular function and coronary sinus blood flow were evaluated in 7 patients with severe left ventricular dysfunction at rest before and after aortocoronary bypass surgery, and during exercise after surgery. Same evaluations were performed in 8 normal subject (G-C). Cardiac index (CI) at rest (2.09 +/- 0.55 l/min/m2) significantly increased after operation (2.94 +/- 0.59 l/min/m2) (p less than 0.02). There was no difference between CI during exercise after operation (5.94 +/- 1.51 l/min/m2) and that in G-C. Left ventricular end-diastolic pressure (LVEDP) at rest before operation (16 +/- 8 mmHg) was significantly higher than that in G-C (p less than 0.05). This difference disappeared after operation. LVEDP during exercise after operation (25 +/- 10 mmHg) was significantly higher than that in G-C (p less than 0.01). Coronary sinus blood flow (CSF) at rest (73 +/- 15 ml/min) significantly increased after operation (123 +/- 44 ml/min) (p less than 0.02). There was no difference between CSF during exercise after operation (282 +/- 99 ml/min) and that in G-C. These data indicated that the aortocoronary bypass surgery was effective on left ventricular function and coronary sinus blood flow in patients with severe left ventricular dysfunction.     

A critical look at temporary ventricular pacing following cardiac surgery.

The effect of atrial, ventricular, and atrioventricular (A-V) sequential pacing on cardiac output (CO) was evaluated in patients within 24 hours after cardiac surgery. In patients with normal sinus rhythm, ventricular pacing reduced CO by as much as 42% (average, 14%), whereas atrial and A-V sequential pacing at the same rate increased CO by averages of 13% and 19%, respectively. In patients with junctional rhythm, increase of the heart rate by ventricular pacing produced an increase in CO, however, and an additional 25% increase in CO could be obtained by atrial or A-V sequential pacing at the same rate. Atrial or A-V sequential pacing was superior to ventricular pacing at the same rate and they are the preferred methods for temporary carciac pacing in the postoperative period. In suitable cases elective A-V sequential pacing is an effective method for increasing CO after cardiac surgery.     

Impact of biventricular and left ventricular pacing on hemodynamics and left ventricular dyssynchrony compared with right ventricular pacing in the early postoperative period following cardiac surgery

Objectives

The aims of this study were to test the hypotheses that in the postoperative period following corrective surgery for congenital heart defects: (i) atrio-right ventricular (RA-RV) pacing decreases cardiac output (CO) compared with right atrial (RA) pacing, (ii) atrio-biventricular (RA-BiV) and left ventricular (RA-LV) pacing improves CO compared with RA-RV pacing.

Study design

Prospective observational study.

Patients

Children 0-2 years of age referred for surgery of congenital heart defects were studied during intrinsic rhythm and atrial, atrio-right ventricular, atrio-left ventricular and atrio-biventricular pacing. CO, extrapolated from mean systolic aortic velocity (MSAV), and left ventricular dyssynchrony were assessed using transthoracic echocardiography.

Results

RA-RV pacing induced a significant decrease in CO (MSAV 0.52 ± 0.19 m/s to 0.46 ± 0.16 m/s, p = 0.01) and a significant increase in LV dyssynchrony (8.7 ± 7.9 ms to 33 ± 21 ms, p = 0.001). RA-BiV pacing induced a significant increase in CO (MSAV 0.46 ± 0.16 m/s to 0.52 ± 0.18 m/s, p = 0.01) and a significant decrease in LV dyssynchrony (33 ± 21 ms to 7 ± 4 ms, p = 0.0003) compared with RA-RV pacing. RA-LV pacing induced a significant decrease in LV dyssynchrony (33 ± 21 ms to 9 ± 7 ms, p = 0.0007) without a significant improvement of CO compared with RA-RV pacing.

Conclusions

RA-BiV pacing improves CO compared with RA-RV pacing in the early postoperative period following pediatric cardiac surgery. This improvement is related to a reduction in left ventricular dyssynchrony.     

Noninvasive assessment of patients following aortocoronary bypass surgery.

A simple, accurate, noninvasive method is required for the objective evaluation of aortocoronary bypass surgery. Stress myocardial imaging with intravenous injection of potassium-43 or thallium-201 was used an average of 4.4 months after direct myocardial revascularization in 77 patients to assess the accuracy of stress myocardial imaging in predicting completeness of revascularization. The results were correlated with maximal treadmill exercise tests, extent of revascularization and status of bypass grafts (occlusion, stenosis and distal disease). We found stress myocardial imaging to be a more sensitive method than the stress electrocardiogram for the detection of incomplete revascularization. The method appears to be a sensitive noninvasive means of evaluating the results of aortocoronary bypass surgery.