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Biomedical subjects

G M Lawrie

Publications and source records attributed to G M Lawrie.

At least 19 recordsLinked to original sources
PubMed1999

Can retrograde cardioplegia alone provide adequate protection for cardiac valve surgery?

BACKGROUND: When aortic insufficiency is present, antegrade delivery of cardioplegia requires coronary cannulation. Use of retrograde cardioplegia simplifies administration. The efficacy of the retrograde route alone in ensuring adequate myocardial protection may be assessed by the clinical outcome. METHODS AND RESULTS: We used closed transatrial coronary sinus perfusion as the sole method of cardioplegia delivery in 100 patients who underwent valve operations, either isolated or combined with coronary (n=24), ascending aortic aneurysm (n=8), or other procedures. Eighty-one patients were in New York Heart Association (NYHA) Class III or IV; 23 had undergone previous heart operations; 23 were admitted from the coronary care unit (CCU); and 20 had left ventricular ejection fraction (LVEF) of < or = 40%. Operative mortality was 2%. An intra-aortic balloon pump was required in eight patients. On univariate analysis, perioperative use of inotropes (n=26) was related to age > or = 70 years (p=0.02), COPD (p=0.05), pulmonary hypertension (p=0.005), higher NYHA Class (p=0.0006), preoperative heart failure (p=0.006), lower LVEF (p=0.0003), urgency (p=0.00001), admission from the CCU (p=0.006), repeat operation (p=0.03), coronary artery disease (p=0.02), and longer ischemic (p=0.02) and bypass times (p=0.0003). On multivariate stepwise logistic regression analysis, use of inotropes was related to preoperative lower LVEF (p=0.02) and urgency of operation (p=0.0002). Perioperative complications included ventricular arrhythmia in six, heart block in one, renal dysfunction in nine, and stroke in two patients; no patient had myocardial infarction. CONCLUSION: Good clinical results can be obtained by using retrograde cardioplegia alone without prior doses of antegrade cardioplegia in all valve operations.

Adult↗
PubMed1998

Identification of different lipid phases and calcium phosphate deposits in human carotid artery plaques by MAS NMR spectroscopy.

Accumulation of lipids in atherosclerotic plaques causes progressive narrowing of the arterial lumen, often followed by thrombosis and ischemia. Currently several different methods, most requiring disruption of the plaque, are used to study the physical properties of lipids accumulated in plaques, and lipid composition is typically determined by chemical analysis of completely disrupted plaques. In this study, 13C magic angle spinning NMR spectroscopy (MAS NMR) was used to determine in situ the lipid composition and molecular organization of all lipid phases in human carotid artery plaques (ex vivo). Protocols were developed to observe signals from one lipid phase without interference from other phases. In addition, 31P MAS NMR detected calcification in plaques by the signals from inorganic phosphate complexed to calcium. Together, 13C and 31P MAS NMR comprise a powerful nondisruptive approach for determining the quantity and phase state of components in arterial plaques.

Calcium Phosphates↗
PubMed1998

Mitral valve repair vs replacement. Current recommendations and long-term results.

Techniques now exist to correct abnormalities of all components of the mitral valvular apparatus except extensive loss of pliable leaflet area. Thus, paradoxically, myxomatous valves with redundant leaflets represent the ideal candidates for mitral valve repair. Repair for mitral insufficiency can be performed for some rheumatic valves, but patient selection is critical. Loss of leaflet area, leaflet thickening, and extensive calcification of the leaflets or commissures are contraindications to repair. The abnormalities of the subvalvular apparatus are less important because a complete set of new chordae can be reconstructed using PTFE suture material. Some cases of endocarditis are ideal for repair using localized débridement and pericardial patch repair with or without PTFE chordal replacement. True ischemic mitral regurgitation of the Carpentier type I category is still something of a surgical enigma. Because it is a restrictive leaflet motion problem, annuloplasty alone is not always effective, and the outcome of any given repair attempt is less predictable. Repairs in patients with small annuli and multiple leaflet defects requiring complex series of maneuvers have a low probability of success. Furthermore, such patients with small left ventricular cavities are more prone to experience SAM. Several factors contributing to which therapy is chosen for mitral valve disease are summarized in Table 1. Patient selection, accurate evaluation of the cause or causes of mitral regurgitation, and well-executed application of the appropriate techniques for repair are all critical factors in the early and late success of mitral valve repair.

Adult↗
PubMed1997

Assessment of myocardial viability with 99mTc-sestamibi tomography before coronary bypass graft surgery: correlation with histopathology and postoperative improvement in cardiac function.

BACKGROUND: Assessment of myocardial viability by 99mTc-sestamibi remains controversial. Accordingly, we investigated the use of sestamibi as a marker of myocardial viability, defined by histopathology, and for predicting improvement of myocardial function after coronary artery bypass graft surgery (CABG). METHODS AND RESULTS: 99mTc-sestamibi perfusion tomography and radionuclide angiography were performed within 2 days before CABG in 21 patients with > or = 75% stenosis of the left anterior descending coronary artery and resting anterior wall dyssynergy. During CABG, transmural myocardial biopsies were obtained from the dyssynergic anterior wall and from normal myocardial segments to determine the extent of viable myocardium by histopathology. Improvement of regional left ventricular function was evaluated by radionuclide angiography at 6 to 8 weeks after CABG. There was a good correlation (r=.85, P<.001) between the quantified sestamibi activity and the extent of viable myocardium determined morphometrically. Among 21 biopsied dyssynergic myocardial segments, 11 improved their function after CABG and 10 failed to improve. Biopsied segments with improved postoperative function had significantly higher sestamibi activity (81+/-5% versus 49+/-16%, P<.0001) and significantly lower extent of interstitial fibrosis (7+/-4% versus 31+/-21%, P=.0002) than segments that failed to improve. A 55% threshold of 99mTc-sestamibi activity had positive and negative predictive values of 79% and 100%, respectively, for recovery of function after CABG in the biopsied segments. CONCLUSIONS: Myocardial 99mTc-sestamibi activity correlates well with the extent of viable myocardium and predicts improvement in regional function after CABG. This lends support to the use of sestamibi as a myocardial viability agent.

Adult↗
PubMed1996

Hemodynamic effects of different pacing ratios in chronic dynamic double cardiomyoplasty.

BACKGROUND: Dynamic cardiomyoplasty is being used clinically worldwide, and evaluated by a clinical trial (phase III) in the United States. Some centers stimulate the skeletal muscle wrap with every heart beat (1:1 [muscle:heart]), whereas others use every other heart beat (1:2). Recent concern over the possible deleterious effects of too-frequent stimulation of the muscles motivated the attempt to evaluate, in a canine model of chronic, double cardiomyoplasty, the effects of two different pacing ratios on several hemodynamic parameters of interest. METHODS: Double cardiomyoplasty was performed using both latissimus dorsi muscles in 11 dogs. Fatigue resistance was achieved using the clinical transformation protocol. At a final experiment, acute cardiac failure was induced by administration of propranolol. Hemodynamic measurements of eight physiologic variables were averaged over complete pacing cycles, including the nonpaced beat at a 1:2 pacing ratio. RESULTS: The net effects of latissimus dorsi muscle stimulation at each of two pacing ratios were compared using nonparametric statistics. With the exception of left ventricular pressure (p = 0.0262) and its first derivative, dP/dt (p = 0.0099), there was no significant difference between hemodynamic performance at the two pacing ratios. CONCLUSIONS: In this canine model, pacing every other beat produces hemodynamic results that are statistically similar to pacing every beat. Less frequent stimulation of the latissimus dorsi muscle may preserve its function and improve clinical results without compromising hemodynamic benefit.

Acute Disease↗
PubMed1996

Undersensing of the tiny QRS complexes that emerged after the isolation of the right ventricle in a patient with ventricular tachycardia.

This article describes a patient who underwent right ventricular disconnection for medically refractory ventricular tachycardia associated with arrhythmogenic right ventricular dysplasia. After the operation there was no ventricular tachycardia recurrence. Two years after the operation, he received a permanent VVI pacemaker for the symptomatic second-degree AV block. Sensing function of the pacemaker was normal for the normal QRS complexes, but the tiny QRS complexes that appeared after the arrhythmia surgery were not sensed by the pacemaker and therefore caused no problem.

Adult↗
PubMed1994

Acute impairment of coronary blood flow by dynamic cardiomyoplasty.

The aim of this study was to quantify the effects of three different configurations of cardiomyoplasty on coronary blood flow in an acute dog model. Thirteen dogs had both latissimus dorsi muscles harvested and transposed to the chest. Coronary blood flow was measured using Doppler cuff probes on the left anterior descending and circumflex coronary arteries during each of three cardiomyoplasty configurations: left posterior, right anterior, and double. Multiple beat measures were made of systolic and diastolic flow during a control protocol and a subsequent protocol with the muscle(s) paced. Significant flow reductions during pacing were observed in the left anterior descending coronary artery during left posterior (17%, p = 0.003), right anterior (29%, p < 0.0001), and double (35%, p = 0.0001) myoplasty. Similar reductions occurred in the circumflex artery (14%, p = 0.0009; 20%, p = 0.001; 27%, p = 0.0053). The net flow over an entire pacing cycle also was reduced significantly: left anterior descending artery (11%, p = 0.0035; 23%, p = 0.0001; 23%, p = 0.0047) and circumflex artery (10%, p = 0.0025; 17%, p = 0.0018; 21%, p = 0.0091). Thus, in the acute setting cardiomyoplasty depresses coronary blood flow. A chronic setting will be needed to determine the ultimate significance of these results.

Animals↗
PubMed1994

Evolution of surgical techniques for aneurysms of the descending thoracic aorta: twenty-nine years experience with 659 patients.

Between 1953 and 1993, 659 patients underwent descending thoracic aneurysm resection. The most common etiology was atherosclerosis. Pain was the main presenting symptom. Perioperative mortality fell from 24.2% between 1953 and 1964 to 14.3% between 1970 and 1993. Paraplegia occurred in 4.1% (27/659) patients overall and was little affected by time of operation or use of atriofemoral bypass. Paraparesis occurred in 5.9% (39/659) patients and was reduced by use of atriofemoral bypass. The low rate of paraparesis in the earlier experience was offset by the higher perioperative mortality from hemorrhage, attributable to the use of systemic heparin. The use of heparin-free circuits with centrifugal pumps should be considered in patients likely to have a clamp time greater than 30 minutes. The major source of perioperative morbidity and mortality was cardiac causes (48%) followed by perioperative hemorrhage (14.4%), pulmonary complications (14.4%), and rupture of another aneurysmal segment (12.0%). Late mortality occurred most commonly from cardiac causes (30.6% of deaths) and rupture of another aneurysm (16.3% of deaths). Improvement in results was due to general refinements of management in all areas rather than any single factor. These results indicate that complete preoperative assessment of the patient and the entire aorta is essential and that regular life-long follow-up is critical in order to avoid unnecessary morbidity and mortality from cardiac, cerebrovascular, or subsequent aneurysmal complications.

Aortic Aneurysm, Thoracic↗
PubMed1993

Long-term fate of the aortic root and aortic valve after ascending aneurysm surgery.

OBJECTIVE: The authors determined in which patients tube graft replacement could be used. SUMMARY BACKGROUND DATA: Tube graft replacement of ascending aortic aneurysms requires no coronary anastomoses and preserves the native aortic valve, but aortic insufficiency or aortic root aneurysms may develop requiring reoperation. Use of Bentall or Cabrol composite valve graft procedures obviates these problems but requires prosthetic valve replacement and coronary reattachment, both of which are associated with complications. These two procedures have been applied increasingly but because of renewed interest in aortic valve preservation and reconstruction, the authors determined in which patients tube replacement could be used. METHODS: The authors analyzed the fate of 277 patients, mean age 49 +/- 14 years, operated on between 1953 and 1992 by techniques that preserved the aortic root. The most common pathology was atherosclerosis in 104 patients. Perioperative mortality since 1975 was 14%. RESULTS: Fifteen patients required reoperation on the ascending aorta or aortic root; ascending aneurysm reoperation (6 patients); aortic valve replacement (8 patients), and a combined procedure (1 patient). Of these 15 patients, 8 had Marfan's syndrome, 10 had dissections, and 5 had medial degeneration/necrosis. CONCLUSIONS: Simple tube graft replacement of the ascending aorta was a durable technique in patients without Marfan's syndrome or medial degeneration/necrosis and allowed preservation of the native aortic valve in many patients.

Adolescent↗
PubMed1993

New configuration of double cardiomyoplasty based on studies of the length-tension properties of the latissimus dorsi muscle.

A new configuration of double cardiomyoplasty was designed according to studies of the length-tension properties of the linear latissimus dorsi muscle. Four dogs had both their right and left latissimus dorsi muscles dissected from the chest wall and attached to a tensiometer to measure force of contraction. The maximum active tension obtained with stimulation of the linear latissimus dorsi muscle was observed when the muscle was at its resting anatomic length and up to 5% above this length. Eight dogs had a double cardiomyoplasty in which the resting anatomic length of both muscles was maintained. Control hemodynamic parameters obtained with the muscles at rest were compared with stimulated muscle protocols. In a normal heart state, stimulation of the double cardiomyoplasty increased the cardiac output 32% (p < 0.05), the stroke volume 39% (p < 0.05), and the left ventricular pressure 42% (p < 0.05). When acute heart failure was induced with high-dose intravenous propranolol (5 mg/kg), stimulation of the double cardiomyoplasty increased the cardiac output 32% (p = 0.01), the stroke volume 32% (p < 0.05), rate of pressure rise 39% (p < 0.01), and myocardial thickening 39% (p < 0.01). The study demonstrated that this configuration of double cardiomyoplasty provides significant hemodynamic assistance in the normal and acutely failing canine heart.

Acute Disease↗
PubMed1992

Automatic implantable cardioverter defibrillator: surgical approaches for implantation.

Surgical approaches for implantation of the automatic cardioverter defibrillator are sternotomy, left thoracotomy, subxiphoid, and subcostal. Although any one of these may be combined with insertion of one or more of the electrodes transvenously, surgical entry into the chest is required for every noninvestigational defibrillator implantation operation. The approaches differ in exposure provided for selecting electrode sites and for handling untoward events, in amount and location of tissue that must be divided or dissected, and in average time required. The operation is an electrical one. Its purpose is to obtain reliable rhythm sensing so that defibrillation or cardioversion shocks will occur only when necessary, and to obtain low enough defibrillation thresholds for shocks of 30 joules or less to have a 10-joule defibrillation safety margin. Many of the patients have had previous cardiac operations. They usually have low or very low ejection fractions. Intraoperative electrophysiological testing with often multiple defibrillation episodes is required. The choice of approach varies with the state of the patient, the institutional experience, and the surgeon. This article describes technique, and the advantages and disadvantages of the four approaches as used by four surgeons in four different institutions.

Defibrillators, Implantable↗
PubMed1991

The automatic implantable cardioverter-defibrillator: effect of patch polarity on defibrillation threshold.

An automatic implantable cardioverter-defibrillator (AICD) was implanted in 40 patients with sudden cardiac arrest (n = 29), sustained monomorphic ventricular tachycardia (n = 10) or recurrent syncope (n = 1) who were unsuitable for direct ablative surgery or had had unsuccessful medical therapy. The effect of patch electrode polarity on the defibrillation threshold was prospectively evaluated. Two large epicardial patches were used. Initial polarity was selected at random. Ventricular fibrillation was induced by direct current and a preestablished defibrillation protocol employed to assess the minimal energy that would reproducibly defibrillate the heart. Nineteen patients had a lower defibrillation threshold with the inferior left ventricular patch as an anode and nine patients had a lower defibrillation threshold with this patch as a cathode. In general, the defibrillation threshold was lower when this patch was used as an anode than when it was used as a cathode (18 +/- 10 versus 22.6 +/- 12.2 J; p less than 0.01). No preoperative variable predicted optimal polarity. Therefore, the effect of patch polarity on defibrillation threshold should be assessed in each patient at the time of AICD implantation so that the safety margin for satisfactory device function can be maximized.

Aged↗
PubMed1991

Late results of the left subcostal approach for automatic implantable cardioverter defibrillator implantation.

A left subcostal surgical approach was used to implant an automatic implantable cardioverter defibrillator (AICD) in 48 patients with a history of nonfatal cardiac arrest or documented ventricular tachycardia/fibrillation. Electrophysiologic studies before surgery yielded induction of monomorphic or polymorphic ventricular tachycardia in 40 patients, whereas 8 were noninducible. Mean (+/- standard deviation) age was 58 +/- 12 years. Mean ejection fraction was 33 +/- 16%. Thirty patients (63%) had documented coronary artery disease; 14 patients (29%) had previous coronary bypass surgery. The mean intraoperative defibrillation threshold was 13.8 +/- 6.6 J. In 6 patients, an adjunctive right minithoracotomy was used to position 1 patch over the right atrium and thus optimize the defibrillation threshold. Patients with prior exposure to amiodarone and previous coronary bypass surgery had higher defibrillation thresholds at implantation. Two perioperative deaths occurred. There were no infections. Long-term follow-up yielded a 1- and 5-year survival of 0.88 and 0.58, respectively, and a freedom from sudden cardiac death of 1.0 and 0.97, respectively. The nonthoracotomy, left subcostal surgical approach is safe and effective, provides adequate defibrillation thresholds in most patients, and yields long-term survival comparable to other implantation techniques.

Cardiac Pacing, Artificial↗
PubMed1991

Long-term results of coronary bypass surgery. Analysis of 1698 patients followed 15 to 20 years.

Between 1968 and 1975, 1698 patients underwent coronary artery bypass with autogenous saphenous vein and were followed for up to 20 years. Age at operation was 53.9 +/- 8.4 years, and 1485 were men (88%). Angina was present in 1637 patients (96%). There was single-vessel disease in 306 patients (18%), double-vessel in 642 (38%), triple-vessel in 550 patients (32%) and left main stenosis in 200 (12%). Preoperative left ventricular quality was good in 1185 (70%), poor in 508 (30%), and unknown in five patients. Survival at 20 years was as follows: for single-vessel disease, 40%; double-vessel, 26%; triple-vessel, 20%; and left main, 25%. At 20 years of follow-up, 67% of surviving patients were asymptomatic and 26% were improved. Antianginal drug therapy consisted of nitrates in 49% of patients and beta-blockers in 26%. Graft patency at 0 to 5 years was 633 of 780 grafts (81%); at 6 to 10 years, 415 of 606 grafts (68%); at 11 to 15 years, 271 of 449 grafts (60%); and at 16 to 20 years, 65 of 140 grafts (46%). Coronary bypass reoperation was performed in 324 patients (19%) and survival of these patients was 62% compared to 37% for nonreoperation patients (p less than 0.05). Cox analysis demonstrated that the major determinants of survival related to age at operation, extent of coronary disease, quality of ventricle, history of stroke, and preoperative congestive heart failure. At 20 years of follow-up of this early experience with coronary bypass, 76% of surviving patients had one or more patent grafts and the probability of freedom from reoperation was 0.62.

Coronary Artery Bypass↗
PubMed1991

Design and implementation of a new computerized system for intraoperative cardiac mapping.

A rapid, portable, yet inexpensive and expandable computer-based system utilizing current technology has been developed from experience in the operating room. An efficient operating system well suited for surgery is defined. New technology recording arrays fabricated from multielectrode flexible Kapton strips were developed and found to be easy to use and highly reliable. Novel arrays are created easily for research or special clinical applications. The system displays all incoming data in real time and transfers 16-s epochs to disk on command. After the user defines a beat for analysis, the computer determines the activation time for each channel, rejects unsatisfactory channels, and displays the results for review and modification before plotting the isochronal map on the monitor. The average time to recall data and produce a map is 16 s; if manual review of 120 channels is included, mapping time is less than 4 min. Clinical data recorded during surgery are discussed. The speed and operational ease demonstrated in the operating room make this computer/electrode system valuable both for surgery and for elucidating basic mechanisms of arrhythmias.

Algorithms↗
PubMed1991

Factors predictive of results of direct ablative operations for drug-refractory ventricular tachycardia. Analysis of 80 patients.

During a 9-year period 80 patients with drug-resistant sustained ventricular tachycardia underwent direct surgical ablation of arrhythmogenic myocardium. Sixty-nine were male (86%) and 11 female (14%), with 1.9 +/- 1.1 (standard deviation) ventricular tachycardia morphologies per patient. The mean number of drugs failed was 3.7 +/- 1.6 per patient. The preoperative left ventricular ejection fraction was 36.4% +/- 14.4%. Complete preoperative endocardial mapping data (greater than 4 endocardial sites in each ventricular tachycardia) were available for 60 of the 80 patients (75%) and intraoperative endocardial data in the clinical ventricular tachycardia was obtained in 37 (46.3%) of the patients. In 17 patients mapped intraoperatively by computer-assisted techniques, complete epicardial and endocardial data in the clinical ventricular tachycardia were obtained in 14 patients (82.4%). Overall, 73 of 80 (91.3%) had some mapping data available. Hospital mortality occurred in 10 patients (12.5%) at a mean interval of 13.5 days, range 0 to 62 days. Postoperatively the clinical ventricular tachycardia has not recurred in 65 of 70 surviving patients (92.9%). Nonclinical ventricular tachycardia occurred in another four patients. All nine patients with postoperative ventricular tachycardia responded to drugs. The major factors predictive of hospital mortality were prolonged cardiopulmonary bypass (greater than 150 minutes), preoperative ejection fraction less than 31%, and incomplete preoperative mapping. Hospital mortality in patients with an ejection fraction below 31% was significantly associated with a history of amiodarone usage. At 3 years of follow-up, freedom from sudden cardiac death was 95.7%, and 86.7% of patients were free of ventricular tachycardia on no antiarrhythmic drugs. These results suggest that direct ventricular tachycardia operations are an effective form of therapy for patients with sustained monomorphic ventricular tachycardia.

Adult↗