Donor-like surface traps on two-dimensional electron gas and current collapse of AlGaN/GaN HEMTs.

The effect of donor-like surface traps on two-dimensional electron gas (2DEG) and drain current collapse of AlGaN/GaN high electron mobility transistors (HEMTs) has been investigated in detail. The depletion of 2DEG by the donor-like surface states is shown. The drain current collapse is found to be more sensitive to the addition of positive surface charges. Surface trap states with higher energy levels result in weaker current collapse and faster collapse process. By adopting an optimized backside doping scheme, the electron density of 2DEG has been improved greatly and the current collapse has been greatly eliminated. These results give reference to the improvement in device performance of AlGaN/GaN HEMTs.

[A clinical study of preoperative prophylactic application of intra-aortic balloon pump in extreme high-risk patients undergoing coronary artery bypass grafting].

OBJECTIVE: To compare the clinical outcome between the intra-aortic balloon pump (IABP) inserted in the preoperative prophylactic condition and in the emergent condition for the patients with extreme high risks undergoing coronary artery bypass grafting (CABG). METHODS: Totally 92 extreme high risk patients undergoing CABG combined with IABP supporting, whose European System for Cardiac Operative Risk Evaluation were equal or more than 12 points, some also undergoing surgical operations of myocardial infarction mechanical complications from January 2008 to June 2011, were analyzed retrospectively. According to the IABP established time, these patients were divided into two groups: preoperative group (57 cases) and passive group (35 cases). Items of comparison between two groups were the rate of mortality, myocardial infarction rate, severity of postoperative myocardial dysfunction and inotropic drug consumption quantity, IABP support time, respiratory support time, ICU stay time, renal function and IABP related complications. RESULTS: Perioperative mortality and myocardial infarction rate in preoperative group (1.8%, 3.5%) were significant lower than those in passive group (11.4%, 17.1%) (χ(2) = 3.949, P = 0.047; χ(2) = 5.077, P = 0.024). Compared to passive group, the IABP support time, respiratory support time, and ICU stay time (t = 4.113-4.795); severity of postoperative myocardial dysfunction and inotropic drug consumption quantity, and renal dysfunction (χ(2) = 5.077-23.521) were decreased significantly in preoperative group (all P < 0.05). There were no significant difference in IABP related complications (P = 0.431). CONCLUSIONS: For extreme high risk CABG patients, comparing to passive insertion of the IABP, preoperative prophylactic application of IABP shows the advantages in reducing perioperative mortality, myocardial infarction rate, inotropic drug consumption quantity, renal dysfunction, ICU stay time, respiratory support time and IABP support time.

[The outcomes of restrictive mitral annuloplasty and coronary artery bypass grafting for ischemic mitral regurgitation and reverse left ventricular remodeling].

OBJECTIVE: To retrospectively summarize and analyze the short and mid term follow-up outcomes of combined coronary artery bypass grafting (CABG) and restrictive mitral annuloplasty in curing ischemic cardiomyopathy and ischemic mitral regurgitation (IMR), and to study its effect on reverse left ventricular remodeling. METHODS: From January 2000 to June 2008, 111 patients of coronary artery disease with moderate to severe IMR underwent combined CABG and restrictive mitral annuloplasty, downsizing by 1-2 ring sizes. There were 81 male and 30 female patients. The age ranged from 36 to 83 years with a mean of (63 ± 18) years. Preoperative transthoracic echocardiography showed minimal to moderate IMR in 7 cases, moderate to severe in 65 cases and severe in 39 cases. The left arterial diameter (LAD) was (58 ± 6) mm, left ventricular end-diastolic diameter (LVEDD) was (61 ± 8) mm, left ventricular ejection fraction (LVEF) was 46% ± 6%. Serial studies were performed to assess the survival rate, the extent of mitral regurgitation (MR), LVEF, the leaflet coaptation height, LAD, LVEDD, New York Heart Association (NYHA) functional class. RESULTS: Hospital mortality was 2.7% (3 cases). Each case received an undersized ring. Intraoperative transesophageal echocardiography showed that no regurgitation in 69 cases, minimal in 34 cases, minimal to moderate in 5 cases, moderate to severe in 3 cases which received mitral valve replacement. The 3-, 12- and 24-month survival rate was 96.2%, 93.5% and 89.7% respectively. Mitral regurgitation grade decreased after the operative procedure (P < 0.01). LVEF increased from (46 ± 6)% to (53 ± 6)% (24 months follow-up) (P < 0.01). LAD decreased from (58 ± 6) mm to (46 ± 6) mm (24 months follow-up) (P < 0.01). LVEDD decreased from (61 ± 8) mm to (48 ± 10) mm (24 months follow-up) (P < 0.01). There was no significant decline of LVEDD in 18 cases (16.2%) whose preoperative mean LVEDD was (69 ± 9) mm. NYHA functional class improved after operative procedures (P < 0.01). At 24 months follow-up, 2 cases received valvular replacement. CONCLUSIONS: Combined CABG and restrictive mitral annuloplasty is a feasible and effective treatment for IMR, the short and mid term outcomes are satisfactory, and a significant reduction of LVEDD and an increase of LVEF due to reverse ventricular remodeling were observed.

[The application of Atricure bipolar radiofrequency system in ablation of different parts and different times of pig heart atrium and the analysis of transmural lesions].

OBJECTIVE: To analyze the transmural lesions of different parts of the pig heart atrium received different times of ablation applied with Atricure bipolar radiofrequency system. METHODS: Six fresh (ex vivo time<20 min) pig hearts with atrium preserved intact were used as the experimental objects and experimental groups were divided according to the ablation position. The Atricure bipolar radiofrequency system was applied in the ablation of the parts of the atrium, such as posterior wall of left atrium, anterior wall of left atrium, anterior wall of right atrium and posterior wall of left atrium close to mitral posterior ring. Ablate the position of the atrium lengthened about 2.0 cm with the same thickness with an interval of 0.5 cm for 4 times respectively, also recording the time of every ablation. For each part and each time of ablation, the ablated atrial tissue was preserved with 4% formaldehyde and 5% glutaraldehyde, and was sent for observation under light microscope and transmission electron microscope. The ablation time and lesion were analyzed statistically. RESULTS: In the same position of the atrium, ablation time decreased with the times of the ablation, in different position of the atrium with same time of ablation, time showed a positive proportion with the thickness of the atrium. CONCLUSIONS: Atricure bipolar radiofrequency system is very safe and efficient, also convenient for manipulation. With regard to the relatively thinner part of the atrium, such as posterior wall and anterior wall of left atrium, at least two times of ablation can ensure transmural lesion of the atrial tissue, but to the position of the atrium such as anterior wall of right atrium and posterior wall of left atrium close to mitral posterior ring, 3 to 4 times of ablation can ensure transmural lesion of the atrial tissue.

[Surgical treatment of post-infarction left ventricular aneurysm: clinical analysis].

OBJECTIVE: To explore the clinical experiences, efficacies and postoperative left ventricular remodeling changes of surgical ventricular reconstruction in the treatment of post-infarction left ventricular aneurysm. METHODS: The investigators reviewed retrospectively the clinical data, operative approaches and follow-up outcomes of consecutive 194 patients with post-infarction left ventricular aneurysm, who underwent surgical ventricular reconstruction between January 1997 and December 2009. There were 54 cases in the linear group and 137 cases in the endoventricular patch plasty group. The changes of ventricular remodeling were measured by peri-operative and follow-up echocardiography. RESULTS: All patients underwent surgery with a mean cardiopulmonary bypass duration of (103 ± 35) min and aortic cross clamp duration of (62 ± 26) min. There were 8 per-operative deaths with a mortality rate of 2.2%. Angina pectoris of other cases disappeared and heart function greatly improved. After operation, the ventricular remodeling results showed that in the linear group, there was not significant difference in the changes of ventricular remodeling of post-op 2 weeks, 6 months, 1 year and 5 years versus pre-operation. However, in the endoventricular patch group, the changes of ventricular remodeling of post-op 2 weeks and follow-up 6 months versus pre-operation were significantly reduced (P < 0.05). End-systolic volume (LVESV) reduced from (129 ± 27) ml to (65 ± 8) ml and end-systolic volume index (LVESVI) decreased from (104 ± 14) ml/m(2) to (44 ± 6) ml/m(2) and the subgroup of LVEF < 35% was the most significant in the changes of LVESV and LVESVI. But LVEF improved significantly at post-operation and follow-up (from preoperation 42% ± 11% to 52% ± 7% during follow-up). CONCLUSIONS: For patients with infarction left ventricular aneurysm, left ventricular reconstruction is quite effective. The choice of operative approaches is determined by the size and range of ventricular aneurysm. Both string suture and endoventricular patch plasty technique can yield similarly satisfactory surgical outcomes. After operation, ventricular volume significantly decreases and cardiac function greatly improves.

[Aortic arch operation under deep hypothermic circulatory arrest].

OBJECTIVE: To summarize the surgical experience of aortic arch operation under deep hypothermic circulatory arrest. METHODS: 22 patients suffering from aortic dissection or descending aorta aneurysm with the involvement of aortic arch received operation under deep hypothermic circulatory arrest. Eight patients underwent ascending aorta and partial aortic arch replacement, one patient received aortic root, ascending aorta, and partial aortic arch replacement, 2 patients received ascending aorta and total arch replacement, 2 patients received aortic valve replacement plus ascending aorta and partial aortic arch replacement, 8 patients underwent ascending aorta and total arch replacement plus elephant trunk technique (stunted elephant trunk used in 6 cases), and 1 patient received left partial aortic arch and descending aorta replacement. Coronary artery bypass grafting was performed concomitantly in 4 cases. RESULTS: Three patients died peri-operatively with a mortality rate of 13.6%. One patient had aortic dissection rupture before operation leading to cardiac tamponade, acute inferior myocardial infarction, and cardiac arrest. This patient received operation while resuscitation. After operation, the patient had severe right heart failure and died 16 hours later. One patient had bleeding and multi-organ failure, and died 3 days later. The third patient, with acute aortic dissection did not awake after operation, had pulmonary infection and multi-organ failure, and died 39 days later. Re-thoracotomy for bleeding was required in 3 cases; delayed awareness occurred in 3 cases; and 2 cases had renal failure after operation. CONCLUSIONS: Aortic arch operation includes partial aortic arch replacement, total arch replacement, and total arch replacement with elephant trunk technique. The operation procedure is selected according to the primary lesion and how aortic arch has been affected. Deep hypothermic circulatory arrest with selective cerebral perfusion facilitates complicated aortic arch operation, resulting in a reduction of mortality and morbidity for arch aneurysms or dissection.

[Surgical treatment of obstructive hypertrophic cardiomyopathy with ventricular septal myectomy concomitant mitral valve replacement].

OBJECTIVE: To summarize the experiences and results of ventricular septal myectomy concomitant mitral valve replacement (MVR) for obstructive hypertrophic cardiomyopathy (OHCM). METHODS: From January 2000 to June 2007, 22 patients of OHCM with moderate or severe mitral regurgitation underwent concomitant ventricular septal myectomy concomitant MVR. There were 20 male and 2 female patients. The age ranged from 28 to 51 years old with a mean of (36 + or - 5) years old. The left ventricular out tract gradient pressure (LVOTGP) was 55 to 120 mm Hg (1 mm Hg = 0.133 kPa), with a mean of (88.0 + or - 15.8) mm Hg. The manifestation of pre-operative UCG, intra-operative transesophageal echocardiography (TEE) and post-operative UCG in 10 d, 6 months and 1 year were compared and analyzed. RESULTS: One patient died in hospital due to serious ventricular arrhythmias. The intra-operative TEE showed that the phenomenon of systolic anterior motion (SAM) of mitral valve disappeared in all patients. Twenty-one cases were followed-up. The intra-operative TEE and post-operative UCG in every period of all 21 cases survived indicated that the mean LVOTGP and interventricular septal thickness (IVST) decreased obviously (P < 0.01). CONCLUSION: Concomitant ventricular septal myectomy concomitant MVR is an effective and safe treatment for OHCM with moderate or severe mitral regurgitation, the short and mid-term outcome is excellent.

[Impact of preoperative clopidogrel in coronary artery bypass grafting].

OBJECTIVE: To analyze and assess the impact of clopidogrel given preoperatively in coronary artery bypass grafting (CABG) surgery. METHODS: From January 2005 to January 2007, 440 consecutive patients undergoing CABG surgery were divided into two groups: the clopidogrel group (with clopidogrel exposure in 5 days prior to surgery, n = 90) and the control group (without clopidogrel exposure > 5 days prior to surgery, n = 350). Patients undergoing emergency surgery because of failed percutaneous transluminal coronary angioplasty and cardiogenic shock, associated valvular surgery, redo-CABG were excluded. Patients who received aspirin and/or heparin treatment before surgery were included. RESULTS: There was no significant difference in two groups regarding age, gender,diabetes mellitus and hypertension. Compared to the control group, patients in clopidogrel group had a higher prevalence of angina class III or IV (66.7% vs. 40.0%, P < 0.01), received more often revascularization within 48 h (41.1% vs. 14.3%, P = 0.02), and had received more frequently stenting (56.7% vs. 13.4%, P < 0.01). Chest tube drainage was significantly increased during the first 24 h following CABG in the clopidogrel group (800 ml vs. 350 ml, P < 0.01). Patients of the clopidogrel group also required more transfusion of packed red blood cells and fresh frozen plasma. Overall re-exploration rate because of bleeding was remarkably higher in the clopidogrel group (4.4% vs. 1.1%, P < 0.01). CONCLUSIONS: Clopidogrel exposure in 5 days or less prior to CABG surgery significantly increases the risk of postoperative bleeding, the need for perioperative transfusion and the incidence of re-exploration. For the elective CABG patient, we suggest that the surgery should to be performed 5 days or more after clopidogrel exposure.

[Coronary endarterectomy and bypass grafting without cardiopulmonary bypass for patients with diffused coronary artery disease].

OBJECTIVE: To review and summarize the early outcomes and clinical experience of coronary endarterectomy (CE) and bypass grafting without cardiopulmonary bypass for patients with diffused coronary artery disease. METHODS: From May 2003 to May 2005, 53 patients with diffused coronary artery disease underwent CE and bypass grafting without cardiopulmonary bypass. There were 41 males and 12 females aged from 55 to 79 (mean 64 +/- 7) years old. 72% patients (38/53) were in Canadian Cardiac Society (CCS) angina class III and IV. 49% (26/53) had history of myocardial infarction. Coronary angiogram revealed that 3 cases had double vessels disease and, other 50 cases had triple vessels disease with 9 left main stem disease. The left ventricular ejection fraction (LVEF) ranged from 0.26 to 0.65 (0.52 +/- 0.17). Seventy endarterectomies were performed in 53 patients totally which included 38 in left anterior descending artery (LAD), 8 in circumflex artery and 24 in right coronary artery. Five cases received on-lay venous patch after CE in LAD and then grafted by internal mammary artery (IMA) on the patch. There were 53 left IMAs, 2 radial arteries, others were great saphenous veins, the mean number of grafts was 3.8 +/- 1.1 with index of completeness of revascularization (ICR) 1.03 +/- 0.07. RESULTS: Intra-operative graft flow-meter was used to check the flow in the grafts before chest closure. There is no death in the group. Sixty-three (90%) out of 70 grafts after CE showed a satisfactory grafts flow intra-operatively. Two patients had peri-operative myocardial infarctions but neither had hemodynamic changes. All patients discharged uneventfully with mean hospital stay 9 days postoperatively. Forty-four patients had 6 to 29 months follow-up with no angina re-occurrence. Six patients had coronary angiogram 3 to 27 months postoperatively with all patent grafts to the CE coronaries. CONCLUSION: CE and bypass grafting without cardiopulmonary bypass is technically feasible and can be performed safely in patients with diffused coronary artery disease with increased completeness of myocardial revascularization.