James D. Fonger

Enhanced preservation of acutely ischemic myocardium with transseptal left ventricular assist

Mechanical support for acute regional ischemia without hemodynamic collapse may be achieved percutaneously with an intraaortic balloon pump (IABP) or with transseptal left ventricular assist (TLVA) while awaiting revascularization. The relative benefits of these two percutaneous transfemoral techniques for the treatment of ischemia were compared in a representative animal model. During 90 minutes of regional coronary occlusion, four groups of 8 pigs were treated with either no support (control), IABP, TLVA, or both IABP and TLVA. Cardioplegic arrest for 30 minutes to simulate coronary grafting was followed by 180 minutes of global reperfusion on bypass. In all groups regional wall motion and interstitial pH in the area at risk were significantly depressed with ischemia, but wall motion fully recovered after reperfusion. However, histochemical staining of the area of necrosis/area at risk was significantly reduced with IABP versus control (20.2% versus 34.1%; p < 0.05) and further significantly reduced with TLVA and IABP + TLVA (10.7% and 6.7% versus IABP alone; p < 0.05). We conclude that in supporting even a modest-sized myocardial region at risk (12% of the left ventricle) the area that went on to infarction was significantly reduced with the use of TLVA over IABP. Regional wall motion and myocardial pH measurements did not reflect this difference in the early reperfusion period. The benefit of TLVA over IABP during more extensive or prolonged ischemia may have real clinical significance.

Inhomogeneous and complementary antegrade and retrograde delivery of cardioplegic solution in the absence of coronary artery obstruction

Inhomogeneous delivery of cardioplegic solution may result in postischemic myocardial injury. This study compares the distribution of warm blood antegrade and retrograde cardioplegia to multiple discrete left ventricular myocardial regions in pigs with unobstructed coronary arteries. Cardioplegic solution was delivered antegradely and retrogradely at 150 ml/min, and flows to 1152 individual myocardial regions were determined twice for each route with four different radiolabeled microspheres. The antegrade system delivered greater flow to each gram of myocardium than did the retrograde system (1.37 +/- 0.31 versus 0.39 +/- 0.09 ml/gm per minute, p < 0.001). Flow to individual myocardial regions was significantly inhomogeneous for both antegrade and retrograde cardioplegia, but much more so for retrograde cardioplegia (coefficient of variation was 48% +/- 17% for antegrade cardioplegia and 106% +/- 16% for retrograde cardioplegia; p < 0.001). The pattern of flow to individual myocardial regions was highly reproducible for a given route of delivery as confirmed by repeated measurements with different radioactive microsphere isotopes (correlation coefficients 0.88 +/- 0.12 for AC1-AC2 and 0.84 +/- 0.10 RC1-RC2), but antegrade cardioplegia and retrograde cardioplegia patterns were significantly different and therefore complementary (correlation coefficients 0.03 +/- 0.04, p < 0.001). These findings support the routine combined use of antegrade cardioplegia and retrograde cardioplegia to enhance delivery of cardioplegic solution to all regions of the heart and minimize the potential risk of postischemic myocardial dysfunction.

Human mammary artery endothelial sparing with fibrous jaw clamping

BACKGROUND Temporary clamping of the internal mammary artery pedicle is required for visualization during coronary artery bypass grafting. A nylon fibril jaw surface has been developed for these clamps that exerts pressure only at discrete sites on the pedicle surface. The effect of this new jaw surface on endothelial cell function and integrity after compression is investigated in this study. METHODS Internal mammary artery specimens from 10 patients each were divided into three separate rings, and two of these rings were clamped for 30 minutes with either a smooth or fibrous jaw clamp. Isometric tensions were measured in organ chambers after contraction by relaxing the rings with the endothelium-dependent agent acetylcholine followed by the endothelium-independent agent sodium nitroprusside. The intimal surfaces of similar rings were silver stained to assess the percentage of intact endothelium. RESULTS Endothelium-dependent relaxation was spared after fibrous jaw clamping (75% versus 89%) but significantly impaired after smooth jaw clamping (25% versus 89%; p < 0.001). Endothelium-independent relaxation was unaffected by either intervention. The percentage of remaining intact endothelium upon silver staining was significantly less after smooth than after fibrous jaw clamping (24% versus 48%; p < 0.01). CONCLUSIONS Foam silicone with nylon fibrils on the jaw surface of internal mammary artery clamps preserves endothelial cell function and integrity. The remaining undamaged cells also may facilitate the subsequent regeneration of a confluent endothelial cell layer.

Initial experience with MIDCAB grafting using the gastroepiploic artery

BACKGROUND Minimally invasive direct coronary artery bypass grafting with the gastroepiploic artery can be used in primary operations and reoperations to revascularize the inferior or anterior surface of the heart. METHODS Patients who had symptomatic coronary artery disease limited to a single coronary distribution were selected. Coronary targets were grafted with the pedicled gastroepiploic artery through a small midline epigastric incision. Patients were followed with scheduled outpatient clinic visits, Doppler examination, and selective recatheterization. RESULTS Between May 1995 and November 1997, 74 patients underwent gastroepiploic artery minimally invasive direct coronary artery bypass grafting; 33 (45%) had a primary operation and 41 (55%), a reoperation. Grafting was performed to the distal right coronary artery (n = 38), the posterior descending artery (n = 28), or the distal left anterior descending coronary artery (n = 8). There were six deaths (8%) within 30 days after operation. Twenty patients (28%) underwent recatheterization; there were two graft occlusions, two graft stenoses, and five anastomotic stenoses. Of 60 patients seen 2 or more weeks after operation, 53 (88%) had resolution of anginal symptoms at a mean follow-up of 10.9 months (range, 0 to 30 months). CONCLUSIONS Inferior minimally invasive direct coronary artery bypass grafting with the gastroepiploic artery avoids the risks of repeat sternotomy, aortic manipulation, and cardiopulmonary bypass. Patency rates, however, were lower than expected, and there is significant morbidity and mortality associated with high-risk patients undergoing the procedure. Continued follow-up is essential to evaluate long-term graft patency and patient survival.

Directed atraumatic coronary sinus cannulation for retrograde cardioplegia administration

A simple method of coronary sinus cannulation for retrograde cardioplegia administration is described that reduces cardiac manipulation. Intraoperative transesophageal echocardiography is used to direct atraumatic coronary sinus cannulation, confirm the depth of insertion of the cannula tip in relation to the ostium, and reduce overall cannulation time.

Arterial Balloon Catheter: A New Atraumatic Device for Dilating Arterial Grafts

BACKGROUND Harvesting of the internal mammary artery (IMA) for use in myocardial revascularization may result in spasm, which can impair early graft flow. Hydrostatic and mechanical dilatation can exert an intraluminal shear force, causing denudation of the IMA endothelium. A new long balloon dilatation technique (LB) has been developed to mechanically increase IMA diameter and flow without exerting any shear force on the endothelium. METHODS Vascular rings of porcine IMA were divided into four groups: no manipulation (control), metal dilators (MD), short balloon (SB), or LB intraluminal dilation. In situ flows after dilation and percentage of intact endothelium after silver nitrate staining were determined. Endothelium-dependent contractions with arachidonic acid, relaxations with acetylcholine, endothelium-independent contractions with norepinephrine, and relaxation with sodium nitroprusside were recorded in organ chamber experiments. RESULTS Increases in IMA flows were similar in all dilated groups. Endothelium-independent contractions and relaxations of IMA smooth muscle were unaffected by any type of mechanical dilation. However, endothelium-dependent contractions and relaxations were significantly impaired after MD and SB but preserved after LB dilation compared with control. Silver nitrate staining showed a greater preservation of the endothelial coverage after LB dilation. CONCLUSIONS IMA dilatation with the novel arterial LB catheter increases IMA flow and preserves endothelial cell integrity, making it an effective and atraumatic method to relieve IMA spasm before use for coronary artery bypass grafting.

Reoperative Off-Pump CABG

Coronary reoperations continue to play an increasing role in the practice of coronary bypass surgery (1,2). At present, approx 10% of isolated coronary revascularization operations in the United States are reoperations (3). Operative mortality and morbidity are increased for patients undergoing reoperative or redo coronary artery bypass grafting (CABG), with an operative mortality in most series of reoperations three to five times that of primary CABG (1,2,4–6).