Skeletal muscle extra-aortic counterpulsation in dogs with dilated cardiomyopathy

Skeletal muscle extra-aortic counterpulsation was performed in seven dogs with dilated cardiomyopathy. A left latissimus dorsi dynamic descending thoracic aortomyoplasty was used as the autologous counterpulsator. Pulse train stimulation in diastole was used to initiate contraction and fibre type transformation. Two of the dogs died within 48 hours of surgery. The device was successfully activated in the five remaining dogs, but in one individual it failed within 48 hours of activation. Serial echocardiographic examinations of dogs in which the device functioned successfully (n = 4) showed trends towards the decrease in the left ventricular systolic internal dimension, left ventricular diastolic internal dimension, E-point to septal separation and left atrial diameter in systole seven to 14 days following the procedure, although these changes failed to persist in the long-term. The results suggest that skeletal muscle for cardiac assistances such as extra-aortic muscle counterpulsation, might be a therapeutic option for dogs with cardiac failure due to dilated cardiomyopathy.

The incidence of significant pericardial effusion and tamponade following major aortic root surgery

OBJECTIVE

To examine the hypothesis that the incidence of significant pericardial effusion following aortic root surgery is higher than anticipated after cardiac surgery.

DESIGN

A retrospective data analysis.

SETTING

A tertiary referral centre for cardiothoracic surgery.

SUBJECTS

All patients undergoing aortic root surgery either with or without aortic valve replacement between January 1991 and July 1993.

RESULTS

Three patients developed late cardiac tamponade (7-10 days post-operatively) and a further three developed clinically significant pericardial effusions as a result of post-pericardiotomy syndrome. The 31.6% (95% confidence limit: 12.5-56%) incidence of significant pericardial effusions following aortic root surgery is therefore significantly higher than anticipated after cardiac surgery (0.8-6).

CONCLUSION

These data support the hypothesis that the incidence of significant pericardial effusion following aortic root surgery is higher than anticipated after cardiac surgery. We recommend that echocardiography is routinely performed during the post-operative period in these patients to exclude significant pericardial effusions.

Aortic root replacement and extraanatomic bypass for interrupted aortic arch in an adult

We describe an unusual case of interrupted aortic arch, aneurysmal ascending aorta, and aortic regurgitation in a 24-year-old man. He presented with general malaise, weakness of his legs, and hypertension. A single-stage operation was performed in which the aortic root was replaced with concomitant extraanatomic bypass of the interrupted segment of the aortic arch. He made a full recovery and has returned to work.

Preconditioning in isolated superfused human muscle

Studies in isolated superfused rabbit papillary muscles indicate that preconditioning (PC) is not confined to arterially perfused myocardium. In the present study PC of isolated human right atrial trabeculae was investigated avoiding the problems of invasive experimentation in patients. Atrial trabeculae were suspended in an organ bath, superfused with Tyrode's solution and field stimulated at 1 Hz. After stabilization, muscles were randomly allocated to five groups (n = 8 per group). Control (C) muscles had no additional treatment. PC was induced by 3 min rapid pacing at 3 Hz with hypoxic substrate-free buffer, followed by reoxygenation with substrate for 12 min. In two additional groups 8-p-sulfophenyltheophylline (SPT) was added to the superfusate either during stabilization in controls (C+SPT) or during preconditioning (PC+SPT). In the final group, R-phenyl-isopropyl adenosine (R-PIA) was added to the superfusate for 5 min to see whether or not this could substitute for preconditioning. All muscles were then exposed to 90 min hypoxia with no substrate and pacing at 3 Hz, followed by 120 min reoxygenation at 1 Hz. Recovery of developed tension was significantly improved by PC 46.5 +/- 2.4% v 24.6 +/- 2.3% in controls) and this protective effect was blocked by the addition of SPT without adversely affecting controls (recovery in PC+SPT, 25.8 +/- 4.1% and C+SPT, 22.7 +/- 2.9%). R-PIA protected the muscles to a similar extent as PC (43.8 +/- 1.9%). These data provide evidence for the involvement of adenosine in preconditioning in human myocardium.

Myoplasty--a surgical option for end-stage heart failure

Congestive heart failure is a growing problem in the Western world, which modern therapeutic options are doing little to ameliorate. Dynamic cardiomyoplasty may be one option which has great potential. This article reviews the use of skeletal muscle for circulatory assist and suggests that, with further work, it should take a significant place in the treatment armamentarium.

Clearance of gentamicin during cardiac surgery

Treatment with an aminoglycoside plus flucloxacillin is commonly used to prevent wound infection and endocarditis after cardiac surgery. Cardiopulmonary bypass, blood transfusion and the lack of a steady state greatly affect handling of gentamicin. Urinary gentamicin excretion is not predictable in terms of preoperative risk factors possibly because there is no clear relationship between serum levels and gentamicin clearance. A study was performed to determine whether the existing prophylactic regimen gave adequate serum levels during surgery and to compare renal excretion of gentamicin and the trough serum levels. Ten patients received gentamicin (1.5 mg/kg at the start of surgery followed by 80 mg tds for 2 days) and flucloxacillin 500 mg qds for 2 days. Serum and urinary concentrations of gentamicin were assayed during surgery and in the early postoperative period. The median apparent serum half-life during the first 8 h was 2.5 h (95%CI 1.7-3.2 h). The median gentamicin clearance was 37 mL/min(95%CI 23-64 mL/min) and the creatinine clearance 85 mL/min (95%CI 72-210 mL/min). Serum levels remained above 1 mg/L during surgery but urinary concentrations varied between 0.4 and 364 mg/L (median 70 mg/L). At 24 h (but not 8 or 16 h), trough serum levels appeared to be related to the amount of gentamicin excreted but the relationship was not quite statistically significant (P = 0.057). Despite the effects of cardiopulmonary bypass, therapeutic serum gentamicin levels were maintained during surgery and reduced renal excretion in the postoperative period was associated with raised levels.

Antibiotic prophylaxis in cardiac surgery: factors associated with potentially toxic serum concentrations of gentamicin

Aminoglycosides are commonly used with flucloxacillin in the prevention of wound infection and endocarditis after cardiac surgery. Earlier studies suggested that the use of aminoglycosides is associated with a small but significant rise in serum creatinine. A regression analysis was performed to identify the preoperative and postoperative factors of importance in determining serum gentamicin concentrations. Serum assays might then be confined to those at particular risk of elevated serum levels. Patients received gentamicin 1.5 mg/kg at the start of surgery followed by 80 mg tds for two days in addition to flucloxacillin. Trough and peak serum gentamicin concentrations were assayed on the first and second days after surgery and urine concentrations were measured with each full catheter bag. Patient characteristics, drug therapy, operation, fluid balance and routine investigations were recorded. A total of 95 of 104 patients were evaluable. Linear discriminant analysis of factors selected by forward stepwise regression identified ten of the 15 patients with subsequent elevated gentamicin concentrations, by using age, and preoperative serum creatinine, systolic blood pressure and serum aspartate transaminase. After operation, factors such as serum creatinine, the quantity of frusemide administered in 24 h, and the integral of the systolic blood pressure over 24 h identified 12 of the 15 patients. However, no satisfactory model could predict urinary concentrations. The discriminant function using preoperative factors prospectively identified 11 of 12 patients with elevated trough levels from a total of 101 further patients. Postoperative gentamicin concentrations cannot reliably be predicted from patient characteristics. Trough assays should be performed or prophylactic courses limited to 24 h.

Physiology and clinical applications of cardiopulmonary exercise testing

Advances in the technology of gas exchange analysers have made cardiopulmonary exercise testing a relatively simple, cheap and reliable diagnostic tool. Its practice and uses include grading the severity of heart failure, evaluation of the cause of exertional dyspnoea and monitoring a patient's response to therapy. Areas of debate and future development are highlighted.

Management of massive haemoptysis

Massive haemoptysis is rare but associated with a high mortality. Even in a major regional cardiothoracic centre only one or two cases will be seen annually. As a consequence, no consensus about its investigation and management has emerged, with the result that much time may be lost on inappropriate investigation and treatment may be misdirected.

Metabolic analysis of latissimus dorsi coupled to a mock circulation

A mock circulation system has been used to examine the metabolic and hemodynamic responses of untrained and trained latissimus dorsi muscle in a normal animal model. The metabolic response of untrained latissimus dorsi to differing stimulation regimes runs parallel to its mechanical performance. The ratio of power generated to oxidative capacity (a measure of metabolic efficiency) was maintained to a greater extent in muscle trained for 5 months subjected to specific fatigue tests, falling by only 20% (as opposed to 80% observed in untrained control muscle). This approach to studying metabolic and hemodynamic performance may have relevance when skeletal muscle is used for cardiac assistance.

Development of an opiate-based anaesthetic technique for use in dogs with cardiomyopathy

An opiate-based anaesthetic technique has been developed for use in dogs with end-stage heart failure due to dilated cardiomyopathy. It has been used in dogs undergoing translocation of the left latissimus dorsi around the descending thoracic aorta to create an autologous counterpulsation system. Anaesthesia was induced with barbiturate (10 mg/kg thiopentone) and fentanyl (500 micrograms) and maintained by an infusion of fentanyl (0.5 micrograms/kg/minute) [corrected] in addition to halothane (0.1 to 0.5 per cent) and nitrous oxide (20 to 60 per cent). This technique provided safe anaesthesia for major intrathoracic surgery.

Development of mock circulation models for the assessment of counterpulsation systems

STUDY OBJECTIVE

This study entailed the development of mock circulation models to assess and compare the haemodynamic efficacy of extra-aortic counterpulsation (using trained skeletal muscle wrapped around the proximal descending aorta) and conventional intra-aortic balloon counterpulsation. DESIGN AND EXPERIMENTAL MATERIALS: Hydraulic Windkessel type lumped parameter models were used either in conjunction with native skeletal muscle or as a dynamic simulation of counterpulsation. The haemodynamic performance of the wrapped latissimus dorsi muscle of the normal sheep was assessed using an artificial load to simulate the pressurised proximal descending aorta. Mock circulation models of counterpulsation comprised Windkessel compliance chambers, laminar flow resistors, a blood analogue, a prosthetic blood pump, and a purpose made hydraulic counterpulsator.

MEASUREMENTS AND MAIN RESULTS

An electrically stimulated muscle wrap, 5 cm in length, previously trained for 2 weeks at 3 V and 35 Hz, was assessed for haemodynamic performance in a mock circulation: volume of fluid displaced = 14.1(SD 1.8) ml; pressure increase from 100 mm Hg = 14.9(2.1) mm Hg; external work per contraction cycle = 180(70)mJ; external mean power = 800(100) mW. In a simulation of intra-aortic balloon counterpulsation, haemodynamic benefit (ie, an increase in proximal flow rate and endocardial viability ratio and a reduction in left ventricular stroke power) was assessed with respect to defined parameters.

CONCLUSIONS

This paper demonstrates the potential of the mock circulation models both for the investigation of muscle wrap performance and for the comparison of extra-aortic muscle with intra-aortic balloon counterpulsation.

Aortic counterpulsation for up to 28 days with autologous latissimus dorsi in sheep

This article reports the development and assessment of an entirely autologous extraaortic counterpulsation system using skeletal muscle (latissimus dorsi). The technique has been performed and assessed in 16 sheep to quantify the effectiveness of counterpulsation over periods up to 28 days and to optimize the stimulation regimens for muscle contraction and fiber-type transformation. Hemodynamic changes have been quantified by calculation of the endocardial viability ratio. This has shown an increase of between 12% and 89% for 28 days. The wide variety of increase observed has been related to the development of an optimum flap configuration. The technique of surface impedance monitoring of flap blood flow has allowed the start of electrical stimulation after 48 hours with the introduction of hemodynamic benefit (1:4 mode) during the process of fiber-type transformation (in situ training). Extraaortic counterpulsation with autologous latissimus dorsi has been shown to be effective and safe for as long as 28 days. It has not been associated with any thromboembolic or infective complications, which we attribute to the exclusion of any foreign material in the design.

Electrophoretic and computer analysis of skeletal muscle used for cardiac assistance

Skeletal muscle has an inherent plasticity which allows it to undergo fibre type transformation when induced by a specific stimulus. Electrical stimulation has been used here to induce transformation of a predominantly fast type skeletal muscle towards a slow, more fatigue-resistant phenotype, which is more suitable for use in long-term cardiac assistance. Muscle samples from animals electrically stimulated for periods up to 6 months have been analysed by electrophoresis for myosin heavy chain (MHC) and myosin light chain (MLC) fast and slow isoforms. Densitometry and computer analysis have been used to determine the pattern of transformation of the different myosin subunits over this time period. MHC and MLC 2 fast to slow isoform switching preceded that of the alkali light chains (MLC1 and MLC3). After 3 months of stimulation the MHC slow isoform was found to have doubled in concentration relative to the unstimulated control muscle and by 4 months accounted for almost 50% of the total MHC content. The slow isoform accounted for 75% of the MLC2 after 4 months of stimulation. The protein products of mRNA isolated from stimulated muscle samples, translated in vitro and separated by electrophoresis, showed that transformation at the mRNA level preceded that at the protein level. By 2-4 weeks of stimulation MLC2 slow isoform mRNA represented over 60% of the total MLC2 mRNA population. An understanding of the molecular structure of muscle during transformation provides insight into its haemodynamic performance in cardiac assistance.

Biochemical and structural adaptation of autologous skeletal muscle used for counterpulsation

We have studied in a normal animal model (sheep), the biochemical and morphological adaptation of electrically stimulated skeletal muscle used for extra aortic counterpulsation. Immunocytochemical analysis of latissimus dorsi, using monoclonal antibodies to slow and fast myosin heavy chains, indicated an increase in the population of mixed fibres after stimulation for one week. By one month, up to 70% of fibres expressed both slow and fast myosin heavy chains in addition to the 15% of fibres expressing only slow myosin heavy chains. After 4 months, the population of mixed fibres was further transformed towards purely slow fibres to give values of 40 and 67% of fibres expressing only slow myosin heavy chain at 4 and 6 months, respectively. Increased staining, both in intensity and area, for NADH tetrazolium reductase activity (an enzyme of the oxidative metabolic pathway) was detected by 28 days. An increase in mitochondrial number was observed also by 28 days, further indicating a shift towards an oxidative metabolism. The molecular adaptation of latissimus dorsi was achieved by stimulation every fourth cardiac cycle at 35 Hz, 3 V, initiated 48 hours after the operation; this being a marked reduction in the delay from operation prior to stimulation. Evaluation of other regimes indicated that more frequent modes, or an increase in voltage or frequency, caused damage to the muscle during the early phase of molecular adaptation. A thorough understanding of the time sequence of the different adaptive processes is required to determine the ideal regime of stimulation initiated promptly after mobilisation of the muscle; aimed at harvesting the maximum amount of energy from the autologous muscle.

Persistent conduction disturbances following coronary artery bypass surgery: cold cardioplegic vs. intermittent ischaemic arrest (32 degrees C)

Two-hundred patients undergoing coronary artery bypass grafting were analysed to assess the incidence of new and persistent conduction disturbances in the postoperative period. Two groups, each of 100 patients, were studied. One group underwent surgery during cold crystalloid cardioplegic arrest with moderate whole-body hypothermia (28 degrees C). The second group was subjected to intermittent ischaemic arrest with mild whole-body hypothermia (32 degrees C). The incidence of postoperative conduction defects was significantly higher in the cardioplegic group.

Palliative intubation of malignant oesophageal strictures

A 6-year experience (1981-1987) of palliative intubation of irresectable malignant oesophageal strictures is reported in 110 patients with a mean age of 70.3 (range 41-90) years. Pulsion intubation was performed on 71 patients, 11 (15.5%) of whom died, and traction intubation on 39 with 6 (15.4%) deaths. Seven deaths resulted from instrumental perforation, but six other patients survived perforation and left the hospital in satisfactory condition. Mean in-patient stay was 8 (range 1-26) days. Non-fatal tube-related complications were more common in pulsion intubation, but was found to be highly effective in relieving dysphagia, with shortened hospital stay (mean 6 days) and acceptable morbidity and mortality rates. These results indicate the trend towards, and the increased safety of, pulsion intubation.

Early experience using a purpose-built pulse train stimulator for cardiac assistance with skeletal muscle

We have developed and evaluated a prototype external pulse train stimulator for use with a new technique of circulatory assistance. This involves the use of skeletal muscle (latissimus dorsi) wrapped around the thoracic aorta as an entirely autologous extra-aortic counterpulsation system. The stimulator has been successful in initiating both muscle contraction at the desired part of the cardiac cycle (diastole) and the necessary fibre-type transformation required for long-term work (fatigue resistance). The background to the development of the stimulator and the early haemodynamic results are described in this paper. The evaluation of the prototype design and the areas for future development are discussed.

Variable adaptation of molecular mechanisms in relation to the use of autologous striated muscle to augment myocardial function

Significant recent advances in molecular biology and protein biochemistry have allowed the examination of muscle function at gene and protein level. This article reviews the variable adaptation of molecular mechanisms in striated muscle. The adaptation and transformation of fast skeletal muscle in response to chronic electrical stimulation may have considerable importance in relation to the use of autologous skeletal muscle to augment myocardial function.

Mediastinoscopy in the investigation of primary mediastinal lymphadenopathy

Mediastinoscopy was introduced by Carlens (1) in 1959 to obtain lymph node biopsies from the superior mediastinum in patients with bronchogenic carcinoma. The technique has been widely accepted for clinical staging as a guide to operability and prognosis. We report on a consecutive retrospective series of 110 patients undergoing mediastinoscopy between 1982-1986 for primary mediastinal lymphadenopathy in order to assess the diagnostic value and safety of the procedure. Mediastinoscopy gave a positive histological diagnosis in 74.5% of cases with no false negative results. There were no deaths and one complication only (pneumothorax). This study shows mediastinoscopy to be a safe, accurate and cost effective procedure minimising hospital stay and allowing appropriate treatment to be immediately commenced upon diagnosis. Mediastinoscopy obviates the need for expensive computed tomography or nuclear magnetic resonance scans and we conclude that it is the investigation of choice for primary mediastinal lymphadenopathy after confirmation by plain chest radiography.

Dysrhythmias following coronary artery surgery. A comparison between cold cardioplegic and intermittent ischaemic arrest (32 degrees C) with the effect of right coronary endarterectomy

Dysrhythmias, particularly of supraventricular origin, are an important cause of morbidity following coronary artery bypass grafting (CABG). This study compared the incidence of dysrhythmias in patients undergoing CABG using either cold crystalloid cardioplegia or intermittent ischaemic arrest (32 C). We conclude that the incidence correlated well with right coronary endarterectomy irrespective of the technique of myocardial preservation employed and to the exclusion of other variables.

Hidden foreign body as a cause of recurrent hemoptysis in a teenage girl

Hemoptysis in a teenage girl caused by a foreign body located in the posterior segment of the left lower lobe is described. The patient was seen four years after the initial inhalation. The importance of taking a meticulous history and the use of computed tomography in the localization of the lesion are emphasized, and the use of the fiberoptic bronchoscope in peripheral lesions and in the investigation of hemoptysis is discussed.

Splenic herniation. Case report

A case of splenic herniation complicated by spurious hypertension is described. A misleading provisional diagnosis was made despite computerised tomography (CT Scan). Diaphragmatic herniation is discussed and the use of computerised tomography in the diagnosis of masses arising from the posterior aspect of the diaphragm is emphasized.

Squamous carcinoma in situ of the oesophagus in a patient with achalasia

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Oesteoarticular tuberculosis--an unusual presentation

A patient presented with pain in the wrist and neck and X-rays showed destructive lesions of several carpal bones and cervical vertebrae. The carpal lesion was explored surgically and found to be tuberculous. Chemotherapy resulted in healing at both sites of disease.

Surgical treatment of hydrothorax complicating continuous ambulatory peritoneal dialysis

Acute hydrothorax is a well recognized complication of continuous ambulatory peritoneal dialysis (CAPD) and is usually regarded as a contra-indication to the further use of this form of dialysis. We report the first case of treatment by surgical closure of a communication between the peritoneal and the right pleural cavity enabling CAPD to continue successfully. The development of an acute hydrothorax on CAPD is therefore not a reason to abandon this form of dialysis and can be treated by a simple thoracic surgical procedure.

Oesophageal obstruction due to saccular aneurysm of the distal thoracic aorta

The second reported case and first successful treatment of oesophageal obstruction due to a saccular aneurysm of the distal thoracic aorta is described. The patient, a 69-year-old male, presented with severe dysphagia which was thought to be due either to achalasia or a tumour. Operation, however, revealed a large aneurysm at the level of the diaphragmatic hiatus which was compressing the oesophagus against the right crus. As the anatomy of the aneurysm was unknown and there was a significant risk of damage to the spinal arteries the oesophageal obstruction was treated by transposition of the oesophagus combined with an anti-reflux repair. This has given an excellent clinical result and the aneurysm has remained unchanged over a period of eighteen months.