Flow dynamics of a novel counterpulsation device characterized by CFD and PIV modeling.

BACKGROUND: Historically, single port valveless pneumatic blood pumps have had a high incidence of thrombus formation due to areas of blood stagnation and hemolysis due to areas of high shear stress. METHODS: To ensure minimal hemolysis and favorable blood washing characteristics, particle image velocimetry (PIV) and computational fluid dynamics (CFD) were used to evaluate the design of a new single port, valveless counterpulsation device (Symphony). The Symphony design was tested in 6-h acute (n=8), 5-day (n=8) and 30-day (n=2) chronic experiments in a calf model (Jersey, 76 kg). Venous blood samples were collected during acute (hourly) and chronic (weekly) time courses to analyze for temporal changes in biochemical markers and quantify plasma free hemoglobin. At the end of the study, animals were euthanized and the Symphony and end-organs (brain, liver, kidney, lungs, heart, and spleen) were examined for thrombus formations. RESULTS: Both the PIV and the CFD showed the development of a strong moving vortex during filling phase and that blood exited the Symphony uniformly from all areas during ejection phase. The laminar shear stresses estimated by CFD remained well below the hemolysis threshold of 400 Pa inside the Symphony throughout filling and ejection phases. No areas of persistent blood stagnation or flow separation were observed. The maximum plasma free hemoglobin (<10mg/dl), average platelet count (pre-implant = 473 ± 56 K/µl and post-implant = 331 ± 62 K/µl), and average hematocrit (pre-implant = 31 ± 2% and post-implant = 29 ± 2%) were normal at all measured time-points for each test animal in acute and chronic experiments. There were no changes in measures of hepatic function (ALP, ALT) or renal function (creatinine) from pre-Symphony implantation values. The necropsy examination showed no signs of thrombus formation in the Symphony or end organs. CONCLUSIONS: These data suggest that the designed Symphony has good washing characteristics without persistent areas of blood stagnation sites during the entire pump cycle, and has a low risk of hemolysis and thrombus formations.

Hemodynamic and left ventricular pressure-volume responses to counterpulsation in mock circulation and acute large animal models.

Alternative therapies for treating heart failure patients are being explored to provide effective options for patients with progressive heart failure. Cardiac assist devices that promote myocardial recovery may be a potential solution. Ventricular assist devices (VAD) have demonstrated long-term efficacy and intraaortic balloon pumps (IABP) have shown short-term successes. In this paper, testing of a hybrid counterpulsation device (CPD) that couples the attributes of device longevity (VAD) with less invasive surgery (IABP) is presented. Hemodynamic and ventricular pressure-volume responses to a 40 ml CPD and 40 ml IABP were evaluated in vitro in an adult mock circulation and in vivo in a large animal heart failure model. The CPD is a flexing diaphragm ventricle with a controlled stroke volume up to 85 cc through a single, valveless cannula. In this study, the CPD was cannulated to the brachiocephalic artery to provide 40 ml of counterpulsation support. The CPD effectively provided diastolic augmentation increasing coronary flow and afterload reduction. These results were comparable to IABP. These preliminary studies suggest that CPD may be an effective therapy for treating patients with early stage heart failure.

Successful VATS ligation of a large anomalous branch producing IMA steal syndrome after MIDCAB.

The occurrence of a flow "steal phenomenon" from a large branch of the internal mammary artery (IMA) is rare and its pathogenesis is still controversial. We describe a case of a patent large anomalous left IMA branch which produced recurrent angina 3 years post MIDCAB. Transcatheter coil obliteration of the vessel produced symptomatic relief. However, six months later, chest pains recurred in association with unwinding of the coil and recannulization of the collateral vessel. Successful ligation of the culprit branch using a VATS approach is presented.

A new technique to create an artificial stenosis in the native LAD using a hemoclip.

The study of hemodynamics associated with coronary atherosclerotic stenosis has been limited due to the lack of a safe, accurate, and reliable technique to create an artificial stenosis in an animal model. Existing techniques have often resulted in myocardial infarction (MI) or severe injury to the vessel and have been difficult to accurately quantify and reproduce. We developed a new technique to create an artificial stenosis in the native left anterior descending (LAD) coronary artery using a hemoclip in an experimental off-pump coronary artery bypass graft (CABG) animal model that overcomes these limitations. The native LAD was dissected at its proximal end and a hemoclip was applied to create varying degrees of artificial stenosis in 30 mongrel dogs during experimental off-pump CABG procedures. The precise application of the hemoclip was predetermined using a mathematical formula to calculate the reduced circumference required to create a specific stenosis. Using these calculations, artificial stenoses of 25%, 50%, 75%, and 90% were created in the LAD. Postoperative angiography demonstrated only 5-10% error between the true (angiography) and estimated (hemoclip technique) stenosis values. In all cases, the vessel remained intact without any apparent external trauma, and no indications of MI were present during electrocardiograph (ECG) monitoring. The creation of an artificial coronary stenosis using the hemoclip technique was safe, reliable, easy, and accurate.

Spectral analysis of graft flow for anastomotic error detection in off-pump CABG.

OBJECTIVE: Flow probes have been introduced as a non-invasive means of anastomotic quality assessment in off-pump coronary artery bypass graft (CABG). Flow waveform morphology cannot reliably be assessed visually unless severe anastomotic stenosis is present ( > 90%). We applied spectral analysis techniques to determine whether the frequency content of graft flow can improve the surgeon's ability to detect anastomotic errors. METHODS: Forty-six mammary to left anterior descending artery (LAD) anastomoses were created in mongrel dogs during off-pump CABG surgery. Graft flow was measured using transit-time flow probes with the LAD closed, and the mammary graft patent and with varying degrees of stenosis. The degree of anastomotic stenosis was created by an artificial stitch and verified by random postoperative angiography. Spectral analysis of the graft flow waveforms was performed. Differences in the magnitude and phase components of the graft flow for the first five harmonics were determined for the varying anastomosis test conditions. Differences were determined using analysis of variance and least square means techniques. RESULTS: The magnitude of the fundamental (zeroth) harmonic was statistically different in the internal mammary artery (IMA) with 0-25% stenosis compared to IMA with 50-75% stenosis (P < 0.01 ). Further, the magnitude of the first, second, and fourth harmonics were statistically different in IMA with 0-25% compared to IMA with 75% (P < 0.01). The phase of the first harmonic was statistically different in IMA with 25% stenosis than IMA with 50% stenosis (P < 0.01 ). No differences in interaction between the LAD and IMA for all ranges of stenosis were detected (P > 0.50). CONCLUSION: Spectral analysis of graft flow waveforms may be beneficial in detecting lesser degrees of anastomotic stenosis (i.e. < 90%) compared to traditional visual assessment of mean graft flow and/or graft flow waveform morphology.

Neural network pattern recognition analysis of graft flow characteristics improves intra-operative anastomotic error detection in minimally invasive CABG.

OBJECTIVE: The intra-operative assessment of the quality of anastomosis in minimally invasive coronary artery bypass surgery (CABG) is critical. Recent investigations demonstrated that flow probes used intra-operatively to assess anastomotic errors may give the surgeon a false sense of confidence as only severely stenotic anastomoses (>90%) could be reliably detected. We developed a neural network system using graft flow data and assessed its potential to improve anastomotic error detection. METHODS: Mammary to LAD grafts (n = 46) were constructed in mongrel dogs off-pump. Continuous beat-to-beat graft flow was recorded using transit-time flow probes. Various degrees of anastomotic stenoses (0-100%) were created by an additional suture. The degree of anastomotic stenosis was confirmed by postoperative angiography. A learning vector quantization neural network was created using heart rate, mean aortic pressure, mean systolic, maximum systolic, minimum systolic, mean diastolic, maximum diastolic, minimum diastolic, and mean graft flows. In addition, a spectral analysis of the flow waveforms was performed and the magnitude and phase of the first five harmonics were used to further develop the neural network. RESULTS: The neural network pattern recognition system was 94% accurate in detecting any stenosis >50%. To validate the model, a testing set was used with 20% of the data values, and the accuracy remained at 100% above chance alone. CONCLUSION: Pattern recognition of transit-time flow probe tracings using neural network systems can detect anastomotic errors significantly better than the surgeon's visual assessment, thereby improving the clinical outcome of minimally invasive CABG.

A review of transit-time flow measurement for assessing graft patency.

Anastomotic quality is a critical issue in minimally invasive coronary artery bypass surgery, particularly "off-pump". It is important to detect a "poor" anastomosis during the procedure so future re-operation can be avoided. Methods such as intraoperative angiography, thermal angiography, probing of the anastomosis, and graft flow measurement have been used intraoperatively to help identify anastomotic errors. With the evolution of stabilizers, graft patency rates for off-pump cases have improved, but many believe they are still not as high as those of the conventional procedure. For off-pump surgery to be accepted and practiced universally, patency rates must be equivalent to those of "on-pump" cases. Transit-time flow measurement has become an increasingly popular non-invasive method for assessing anastomotic quality. However, it is difficult to establish whether an anastomosis is patent based on mean graft flow alone. Spectral analysis of graft flow waveforms reveal characteristic patterns that identify intermediate ranges of stenosis between fully patent and totally occluded. Together, these two components of graft flow have been used in the construction of a neural network to help identify "faulty" anastomoses. Transit-time flow measurement is a non-invasive tool that can be beneficial in identifying fully patent or nearly occluded grafts, and may also help in distinguishing intermediate stenoses.

Can visual assessment of flow waveform morphology detect anastomotic error in off-pump coronary artery bypass grafting?

OBJECTIVE: Flow probes are being used for intraoperative assessment of anastomotic quality during off-pump coronary artery bypass grafting (CABG). We conducted a survey with the cooperation of 19 international surgeons to assess the ability of surgeons to detect anastomotic errors by evaluating mean flow and flow waveform morphology. MATERIAL AND METHODS: Mongrel dogs underwent mammary to left anterior descending (LAD) grafting. Mean graft flow and flow wave morphology for varying degrees of anastomotic stenoses were recorded using transit-time flow probes. A questionnaire consisting of ten different recorded flow tracings and the corresponding mean flows were given to 20 surgeons from around the world. The surgeons were asked to determine the degree of stenosis and whether they would re-do the anastomosis based upon the mean flow and the flow tracings. RESULTS: All of the 19 surgeons that responded were able to clearly identify a highly stenotic graft (>90% stenosis). However, 24% would re-do a fully patent anastomosis, 58% accepted an anastomosis with moderate stenosis, and 72% accepted anastomoses with severe stenosis. CONCLUSIONS: Evaluation of flow tracing morphology and/or mean flows can be used to reliably detect nearly occluded anastomoses (>90% stenosis). However, surgeons should be cautious in assessing anastomoses with lesser degrees of stenosis, as they may be more difficult to reliably interpret.

Role of graft flow measurement technique in anastomotic quality assessment in minimally invasive CABG.

BACKGROUND: Anastomotic quality is currently the critical issue in minimally invasive coronary surgery. Although little is known about its effectiveness, surgeons routinely assess grafts intraoperatively using flow probes. This study was designed to determine whether mean flow and the pattern of flow tracing in internal mammary artery grafts obtained with a transit-time flow probe are reliable indicators of anastomotic quality. METHODS: Mongrel dogs (n = 14, 30 to 35 kg) underwent off-pump left, right, or left and right internal mammary artery to left anterior descending artery anastomosis (23 grafts). Moderate to severe degrees of stenosis were created at the anastomosis by an additional suture. Internal mammary artery graft flow was measured before and after the stenosis was created with the left anterior descending artery occluded. Angiography was performed at random postoperatively to validate the degree of stenosis. Mean flow and flow tracing morphology were compared under various degrees of stenosis. RESULTS: There were no significant differences in mean graft flow or the morphology of the flow tracing between patent (<15%), mild (<25%), moderate (<50%), and moderately severe (<75%) stenosis. However, mean graft flow decreased (p < 0.05) with severe stenosis (>75%). CONCLUSIONS: Although differences in mean graft flow and graft flow morphology were detectable in anastomoses with severe stenosis (>75%), they were indistinguishable in anastomoses with mild (<25%) to moderately severe (<75%) stenosis. Flow measurement techniques are valuable tools intraoperatively, but surgeons should exercise caution in their interpretation.

Serious wound infections after minimally invasive coronary bypass procedures.

BACKGROUND: Minimally invasive coronary artery bypass grafting has become an increasingly accepted therapy for selected patients with single-vessel coronary artery disease. Reported morbidity has focused on anastomotic problems, but the occurrence of serious wound complications after these procedures has not been well documented. METHODS: We reviewed our institutional experience with 35 patients to look for the incidence of serious wound complications. RESULTS: Three patients had serious wound problems after minithoracotomy for coronary artery bypass graft procedures. This represents an overall 9% wound morbidity rate and a 100% rate in the obese women. CONCLUSIONS: Wound complications at the incision site after minithoracotomy coronary artery bypass graft procedures seem to occur distinctly in obese women with redundant breasts.

Atrial fibrillation: a delayed presentation of traumatic tricuspid valve incompetence.

Isolated tricuspid valve incompetence resulting from blunt thoracic injury is rare. The diagnosis may be challenging. Subsequent clinical course may be variable. Early surgical intervention rather than medical therapy has been suggested in selected cases. We report a case of blunt chest trauma causing delayed chronic tricuspid regurgitation manifesting primarily as atrial fibrillation many years after the initial blunt chest trauma. Replacement of tricuspid valve restored normal sinus rhythm.

Double grafting of the left anterior descending artery: is the distance between the internal mammary artery and supplemental vein graft anastomoses relevant in graft survival?

INTRODUCTION: Under certain conditions (small internal mammary artery (IMA) or large runoff), double grafting of the left anterior descending (LAD) artery system is necessary to avoid the ominous consequences of myocardial hypoperfusion. Previous studies have shown that a saphenous vein (SVG) adjacent to an IMA graft leads to failure of the IMA. This study compares IMA flow patterns when adjacent ( < 1 cm) and separated (3-4 cm) from a SVG placed on a proximally occluded LAD. METHODS: A SVG and right IMA (PIMA) to proximal LAD (2.5-3 mm) coronary bypass were performed in 12 mongrel dogs. The left IMA (DIMA) was anastomosed to the distal LAD (1.5 mm). All anastomoses were carried out without cardiopulmonary bypass. The native LAD was occluded proximally to the PIMA anastomosis, and all graft flows were measured in competitive and non-competitive flow conditions. RESULTS: Isolated graft to LAD flows were similar for the three conduits. There was a drop in flow in both the PIMA and DIMA when placed in competition with the SVG (10.1+/-3.0 vs. 19.1+/-4.6 ml/min; P < 0.05). The total drop in flow was significantly greater in the PIMA (67.6 vs. 39.9%; P < 0.05). Diastolic flow was better preserved in the distal IMA graft (19.6 + 5.6 vs. 10.2+/-3.0 ml/min; P < 0.05). The patterns of flow were much different during competition and there was significant retrograde systolic flow in all PIMA grafts while there was no (n = 5) or minimal retrograde flow (n = 7) in the DIMA grafts. CONCLUSION: An IMA graft, when adjacent to a SVG, sustains a significant decrease in both total and diastolic flows and develops an oscillating pattern of flow in early systole (retrograde then antegrade). Placing the IMA more distally on the LAD improves flow and decreases retrograde flow. In clinical situations requiring double grafting on the LAD, distance between grafts may be an important factor in maintaining IMA patency.

Clinical experience with the video-assisted saphenectomy procedure for coronary bypass operations.

BACKGROUND: Leg wound complications after saphenectomy are frequent after coronary bypass operations and have a detrimental effect on postoperative quality of life and treatment cost. To reduce morbidity, we evaluated a new technique of video-assisted vein harvest. METHODS: Between March 1996 and October 1996, 50 patients had video-assisted saphenectomy (VAS) and 40 patients had the standard open technique (control group). An additional 13 patients had both procedures (hybrid group). Level of pain, edema, and wound complications were evaluated at discharge and at 2, 4, and 6 weeks postoperatively. RESULTS: The mean operating time for VAS patients was slightly higher than for control (60.6+/-24.7 minutes versus 53.2+/-21.1 minutes; p > 0.05). The average incision length in VAS patients was 13.8+/-8.8 cm for an average of 3.3 grafts per patient. Three VAS procedures were aborted, two because of time constraints, and one because of bleeding, and a segment of vein was lost to injury. The VAS group had considerably less early postoperative pain than the control group (1.7+/-1.2 versus 4.1+/-1.4 [1 = mild, 10 = severe]; p < 0.005) and edema was similar for both groups. Patients in the hybrid group reported less pain in the VAS-operated leg. Serious wound infection occurred in 4 patients, with 2 patients in the control group requiring reoperation for drainage and flap reconstruction. CONCLUSIONS: Based on this initial experience, VAS harvesting, although initially more time consuming, is a rapidly mastered technique, results in shorter overall incision length, and is associated with considerably less postoperative pain than the standard open technique.

Evidence for improved cerebral function after minimally invasive bypass surgery.

BACKGROUND: Neurological impairment is a major cause of morbidity after cardiac surgery and may be associated with occurrence of cerebral microemboli generated during cardiopulmonary bypass (CPB). This study evaluates cerebral dysfunction following coronary artery surgery on-pump and off-pump. METHODS: Neurological outcome was evaluated in 322 patients with a coronary artery bypass graft (CABG). Conventional CPB was used (on-pump) in 305 patients and in 17 patients no CPB was used (off-pump). Intraoperatively, a pulsed-wave transcranial Doppler with a 2-MHZ probe measured high-intensity transient signals (HITS) by ultrasonic insonnation of the middle cerebral artery indicating the presence of emboli within the vessel lumen. Transcranial near-infrared spectroscopy measured cerebral venous oxygen saturation for adequate perfusion. Postoperatively, all patients were subjected to the antisaccadic eye movement (ASEM) test, a sensitive indicator of neurocognitive deficits secondary to frontal lobe dysfunction. RESULTS: While there was no significant difference in O2 saturation, the number of microemboli HITS generated was significantly higher in the on-pump group than the off-pump group. In the off-pump group, 16 (94%) of 17 patients had perfect scores on the ASEM test, while only 108 (35.4%) of 305 patients achieved a perfect score in the on-pump group (p < 0.01). Furthermore, while all patients in the off-pump group achieved at least 90%, 28% (86/305) in the on-pump group scored "zero" on the ASEM test. CONCLUSION: Cerebral dysfunction as evidenced by ASEM errors is common following coronary bypass on-pump, but rare with off-pump bypass surgery. Cerebral microemboli generated during CPB may account for this difference.

What in-vitro method should surgeons use to evaluate the clinical behavior of arterial bypass conduits.

UNLABELLED: Surgeons have traditionally relied on ring preparations to predict how arterial bypass conduits will behave in the postoperative circulation. OBJECTIVE: This study compared pharmacologic [norepinephrine (NE) challenge] and physiologic [arterial preload] responses of gastroepiploic (GEA) and internal thoracic (ITA) arteries in a standard static ring preparation and a dynamic perfusion system. METHODS: Six GEAs (1.0-1.5 mm dia.) and six ITAs (1.5-2.0 mm dia.) 11 cm long were harvested from adult pigs and mounted on a computer controlled perfusion system. Inflow pressure was set at 80 mmHg and outflow resistance was adjusted to simulate high (80-90 ml/min) and low (15-20 ml/min) flow demands. NE response (10(-9)-10(-5) M) was measured under low flow conditions and at high flow conditions when distal arterial pressure (load) was reduced. NE response (10(-9)-10(-5) M) was also evaluated in arterial rings (ITA N = 6, GEA N = 6) with tensions adjusted to simulate the loads occurring at low flow (80 mmHg) and high flow (60 mmHg) situations. RESULTS: In the static ring preparation, NE response [ED50] was similar for both GEA and ITA and was not affected by load. The dynamic preparation demonstrated that the GEAs were significantly more responsive to NE than the ITAs [ED50 high flow ITA 6.1 +/- 0.3**, GEA 7.2 +/- 0.3***; *P < 0.05 versus baseline, **P < 0.05 versus low flow values, ***P < 0.05 versus ITA]. Furthermore, in the dynamic preparation, NE response was profoundly affected by reduced load which occurs under high flow conditions [7.18 +/- 0.3 versus 6.1 +/- 0.3 under high flow and 5.8 +/- 0.1 versus no response under low flow conditions]. CONCLUSION: Static ring preparations do not discern differences between ITA and GEA susceptibility to spasm and fail to detect the effect of load. The dynamic preparation demonstrated significant differences between the GEA and ITA potential to spasm which is consistent with widespread clinical experience. Furthermore a dynamic preparation is highly sensitive to reduced load which occurs under high flow conditions. Although it is more demanding, the dynamic preparation provides superior information to the surgeon in predicting the behavior of arterial bypass grafts.

Factors affecting internal mammary artery graft survival: how is competitive flow from a patent native coronary vessel a risk factor?

Recent studies have suggested that competitive flow is an important factor in early internal mammary artery (IMA) graft failure. Flow competition from minimally diseased native coronary vessels has been implicated in the failure of IMA grafts, but does not seem to affect saphenous vein grafts (SVG). The objective of this study was to determine the effects of competitive flow on SVG and IMA grafts and to compare the patterns of flow dynamics and pressure on proximal and distal grafts to the left anterior descending (LAD) artery; factors that may be involved in graft failure. Twelve mongrel dogs underwent coronary artery bypass grafting using IMAs and a SVG to an open LAD artery. The right IMA (PIMA) and the SVG were anastomosed in the proximal LAD and the left IMA (DIMA) was anastomosed at a more distal location. The procedure was performed through a left thoracotomy, using an "off pump" technique. Graft flows were measured isolated and in competition. The IMAs and SVG provided flow levels similar to the native LAD when each one was the sole inflow to the LAD. During competitive flow conditions, total and diastolic SVG flows were reduced 54.4 and 50.5%, respectively (P < 0.05). Total and diastolic PIMA and DIMA flows were reduced more drastically (68.6-73.3 and 69.5-68.1%, respectively; P < 0.05). The DIMA had better preservation of diastolic flow compared to PIMA. A delay in the pressure wave was noted in the isolated IMAs, but not in the SVG. This pattern of flow disappeared during competition due to the large, systolic retrograde flow up the IMA grafts. In conclusion, IMAs compared to the SVG are longer and narrower conduits with lower levels of flow during competition. Low levels of flow and oscillating flow (retrograde/ antegrade) may be poorly tolerated by the IMA endothelium and may be factorial to graft failure. These data suggest that a more distal placement of the IMA graft may be protective to the arterial graft under competitive flow conditions.

Preventing gastroepiploic artery spasm: papaverine vs calcium channel blockade.

UNLABELLED: The gastroepiploic artery (GEA) is a highly vasoactive artery gaining wider acceptance as a conduit for coronary artery bypass surgery. A variety of agents are used to dilate the GEA prior to grafting; however, little is known about the duration of their effect in the immediate postoperative period. This study evaluated three calcium channel blockers and papaverine in preventing graft spasm. METHODS: Porcine GEA segments (10-12 cm in length) were connected to a computer-controlled perfusion system with a constant in-flow pressure and distal resistance to simulate bypass flow (80-100 ml/min). Norepinephrine (NE; 10(-9) to 10(-5) M) was given in incremental doses at baseline before the vasodilator, immediately after (0 hr), and again at 2 hr after the vasodilator. Changes in flow and ED50 were recorded. Group INT (N = 25) received papaverine (PAP), diltiazem, nifedipine (NFP), or verapamil (VPL) intraluminally, while group EXT (N = 25) received the same dilators externally. RESULTS: All arteries showed dose-dependent vasoconstriction to NE prior to treatment. Immediately after receiving the vasodilator, arteries in both groups (INT and EXT) showed initial protection against NE-induced spasm with the exception of arteries receiving NFD externally. However, at 2 hr, for group INT, only VPL and NFD prevented NE-induced graft spasm (VPL: 40.4 +/- 6.8 ml/min vs 17.9 +/- 3.3 ml/min and NFD: 27.0 +/- 6.5 ml/min vs 13.1 +/- 0.9 ml/min, P < 0.02). In group EXT, after 2 hr, only VPL- and PAP-treated grafts showed resistance to NE-induced vasospasm (VPL: 35.6 +/- 7.3 ml/min vs 15.0 +/- 6.9 ml/min and PAP: 47.4 +/- 15.1 ml/min vs 8.0 +/- 2.0 ml/min, P < 0.001). CONCLUSIONS: Papaverine, a lipophilic vasodilator, when given externally on the perivascular fat of the GEA, prevented graft spasm for up to 2 hr. In contrast, intraluminally applied papaverine did not show graft protection against NE-induced spasm. Nifedipine prevented NE-induced spasm only when given intraluminally. Verapamil proved to be the most potent and versatile vasodilator with effective graft protection of up to 2 hr whether applied externally or internally and was the preferred agent for protecting against GEA spasm.

ITA versus SVG: a comparison of instantaneous pressure and flow dynamics during competitive flow.

OBJECTIVE: Competitive flow from patent native coronary vessels is implicated in the failure of internal thoracic artery (ITA) grafts, but it is not thought to affect saphenous vein graft (SVG) patency. This study examines instantaneous pressure and flow dynamics in left ITA and SVG grafts in competition with a patent left anterior descending (LAD) artery. METHODS: SVG (3.0-4.0 mm) and ITA (1.5-2.0 mm) to proximal LAD (2.5-3.0 mm) coronary bypass was performed in 10 mongrel dogs. Flow and pressure were measured in the occluded (No Competition) and opened (Competition) ITA, SVG and LAD. RESULTS: The ITA and SVG, when each was the sole inflow to the LAD, provided similar flow as the native LAD. During competitive flow, total LAD flow was preserved and flow in the ITA and SVG were reduced (8.20 +/- 1.25 and 10.00 +/- 1.73 ml/min; P < 0.005). SVG diastolic flow was reduced to 11.52 +/- 2.17 ml min (55.5%); P < 0.003. Flow in the SVG remained predominantly antegrade. In contrast, ITA diastolic flow was reduced more drastically, to 5.37 +/- 1.25 ml/min (80.7%); P < 0.0001. When the ITA was the only inflow to the LAD, there was delay in the LAD pressure wave. This delay disappears during competition due to the large, systolic retrograde flow up the ITA. CONCLUSION: The ITA, compared to the SVG, is a longer and narrower conduit with lower levels of flow during competition. Due to a delay in the pressure wave, the ITA flow is retrograde during early systole. Low levels of flow, with a markedly decreased diastolic phase, and the oscillating pattern in systole (retrograde/antegrade) may be poorly tolerated by the ITA endothelium and lead to graft deterioration.

Anastomotic complications in minimally invasive coronary bypass grafting.

BACKGROUND: Anterior wall myocardial revascularization through a left anterior minithoracotomy is an increasingly accepted procedure. Technical failure at the anastomotic site, promoting persistent or recurrent angina, is known to occur and may be underrecognized. This report summarizes the incidence of technical failure in an initial clinical experience and describes potential causes of early postoperative complications. METHODS: Between December 1995 and May 1996, 15 patients underwent left internal mammary artery-to-left anterior descending artery revascularization without extracorporeal circulation. The surgical indication was single-vessel coronary disease in all patients. We exposed the left anterior descending artery target site through a 10-cm left anterior fourth space thoracotomy. The fourth costal cartilage was resected and the left internal mammary artery was harvested under direct visualization. Two 4-0 polypropylene sutures snared in tourniquets proximal and distal to the anastomotic site were used to obtain a bloodless field and stabilization of the left anterior descending artery. RESULTS: All patients had procedures initially deemed successful based on disappearance of angina or postoperative transthoracic Doppler examination of the internal mammary artery 3 to 5 days postoperatively. However, 3 patients presented with recurrent angina at 2, 6, and 8 weeks. Angiography or direct visualization at operation demonstrated the technical complication (stenosis at the anastomotic site in 2 and snare injury in the native vessel in 1). Two patients required reoperation. CONCLUSIONS: Initial results with minimally invasive coronary bypass grafting have generated great enthusiasm worldwide, but there is no consensus on how the procedure should be performed. These results suggest that a nonstabilized anastomosis results in an unacceptable failure rate. Furthermore, sutures encircling the left anterior descending artery should not be used for vessel stabilization as injury of the artery may occur.

Instrumentation for minimally invasive internal thoracic artery harvest.

The anterior fourth interspace minithoracotomy is our current choice for exposure of the anterior myocardial wall for minimally invasive coronary bypass grafting procedures. This approach provides direct access to the left anterior descending coronary artery for anastomosis, and good exposure of the midsegment of the internal thoracic artery. We describe the use of instrumentation that facilitates the harvest of the left internal thoracic artery under direct vision. The use of this retractor system, which elevates the third and fourth and depresses the second and first ribs, permits better visualization of the internal thoracic artery and allows for proximal internal thoracic artery harvest without rib resection.