Effect of transmural versus nontransmural myocardial infarction on inducibility of ventricular arrhythmias during sympathetic stimulation in dogs.

Transmural myocardial infarction interrupts sympathetic nerves and denervates viable muscle distal to myocardial infarction. The effect of sympathetic stimulation on responses to programmed ventricular stimulation was studied in dogs without myocardial infarction (Group I: n = 5), with transmural anterior wall myocardial infarction (Group II: n = 6) and with nontransmural anterior wall myocardial infarction (Group III: n = 9). Ventricular effective refractory period during sympathetic stimulation decreased by 16 +/- 18, 1 +/- 2 and 12 +/- 8 ms (mean +/- SD) in viable muscle of the inferoapical left ventricle in Groups I, II and III, respectively, suggesting efferent sympathetic denervation by transmural myocardial infarction only. Sustained ventricular tachycardia or fibrillation was induced more easily during sympathetic stimulation in six of the six dogs with transmural infarction, but in only two of the nine dogs with nontransmural infarction (p less than 0.01). It is concluded that the partial sympathetic denervation produced by transmural myocardial infarction enhances the ease of induction of ventricular tachycardia and fibrillation during sympathetic stimulation. A similar mechanism may lead to increased risk for lethal arrhythmias during periods of high sympathetic tone in patients with transmural myocardial infarction.

Influence of site of stimulation on measurement of ventricular vulnerability in the normal and ischemic feline heart.

Site of stimulation is an important variable in the inducibility of ventricular tachycardia in both non-human animal infarction models and in humans; that is, proximity of the stimulating electrode to the site of reentry facilitates the induction of sustained arrhythmia. Whether site of stimulation is decisive in measurement of vulnerability to ventricular fibrillation (VF) during acute coronary occlusion has not been fully evaluated. We measured VF thresholds in 9 chloralose-anesthetized cats at 2 right ventricular and 3 left ventricular sites (2 endocardial, 3 intramural) before and after abrupt occlusion of the anterior descending coronary artery. VF thresholds were measured using a single stimulus of increasing intensity delivered during ventricular drive. Although VF thresholds were lower at endocardial sites, there were no significant differences in VF threshold among any of the sites tested at control. After occlusion, VF thresholds fell to a similar extent at all 5 sites tested. The percent reduction in VF threshold at any site was not influenced by the sequence of testing. VF may be precipitated from multiple sites and, unlike ventricular tachycardia, does not represent an isolated focus of arrhythmogenicity.

Sensitivity and specificity of lingular segmental biopsies of the lung.

Open lung biopsy is frequently performed as an emergency procedure in patients with undiagnosed bilateral diffuse pulmonary disease. In many situations, this procedure is undertaken in hemodynamically compromised or septic patients. An expeditious and simple technique to make an accurate diagnosis would be extremely advantageous. Biopsy of the lingular segment addresses most of these issues. Lingular biopsies, however, have been thought to be unreliable. The purpose of the present study was to evaluate the accuracy of lingular open lung biopsies in patients with bilateral diffuse pulmonary disease. Twenty consecutive patients with bilateral diffuse pulmonary disease underwent exploratory left thoracotomy when all noninvasive measures failed to arrive at a definitive etiology. Patients ranged in age from 24 to 79 with a mean of 52.6 years. There were five women and 15 men. Biopsy of the lingula was taken, as well as another area of similar lung involvement. Histopathologic results of the lingular biopsies correlated 100 percent with those from the other segments of the lung. The entire procedure, including rigid bronchoscopic examination, was routinely performed in less than one hour. In conclusion, lingular biopsies, relatively minor surgical procedures, are extremely accurate (100 percent) in making definitive diagnoses.

Evaluation of arrhythmogenicity of surgically induced endocardial versus ischemic myocardial damage.

Ventricular tachyarrhythmias are common sequelae of ischemic myocardial damage. To assess the susceptibility to sustained ventricular tachycardia in a canine model in which endocardial excision was performed, 30 adult mongrel dogs were divided into three groups and studied in an open-chest condition, anesthetized under pentobarbital anesthesia, 7 to 14 days after undergoing one of three alternative procedures: (Group A) sham-operated controls, 10 dogs; (Group B) left ventricular endocardial excision, 10 dogs; and (Group C) myocardial infarction produced by a 2-hour occlusion and subsequent reperfusion of the left anterior descending coronary artery, 10 dogs. Using programmed ventricular pacing with two extrastimuli via plunge electrodes at 10 normal sites in the distribution of the left anterior descending coronary artery in each dog, sustained ventricular tachycardia was induced in 0/10 Group A dogs at 0/100 sites and in 0/10 Group B dogs at 0/100 sites; in contrast, in Group C, 7/10 (70%, p less than 0.01) dogs had inducible sustained ventricular tachycardia and at 39/70 (56%, p less than 0.001) sites. Thus, 7 to 14 days following endocardial excision, dogs are no more susceptible to the initiation of sustained ventricular tachycardia than are sham-operated control animals. This is in contrast to dogs with chronic heterogeneous infarctions (Group C) due to coronary occlusion and reperfusion, which are highly susceptible to ventricular tachycardia initiation.

Intracellular myocardial pH measured in vivo with sustained and reperfused coronary occlusion.

Intracellular pH provides an important measure of the adequacy of local tissue perfusion. The purpose of this study was to measure regional intracellular myocardial pH (impH) in the ischemic zone in vivo during experimental canine coronary occlusion, with and without coronary reperfusion. Twenty adult dogs were studied. Ten dogs underwent permanent ligation of the proximal anterior left descending coronary artery (group L), five dogs had coronary reperfusion after 1 hour of total coronary occlusion (group R), and five dogs did not undergo ligation and served as controls (group C). Intracellular myocardial pH was measured by 31phosphorus nuclear magnetic resonance spectroscopy at baseline and then at 15-minute intervals for 6 hours after coronary occlusion (or after sham occlusion in group C). Baseline impH did not differ among groups (group C, 7.22 +/- 0.12 mean +/- standard error of mean; group L, 7.17 +/- 0.07; group R, 7.22 +/- 0.09). During hour 1 of total occlusion, the impH of both groups L (6.58 +/- 0.05) and R (6.55 +/- 0.08) was significantly reduced as compared with the impH of group C (7.3 +/- 0.12; p less than 0.05). At 0 to 1, 1 to 3, and 3 to 5 hours of reperfusion, the impH of group R (7.34 +/- 0.08, 7.27 +/- 0.07, and 7.29 +/- 0.06, respectively for these times) did not differ from group C (7.26 +/- 0.11, 7.21 +/- 0.07, and 7.25 +/- 0.10). At these same times, the impH of group L (6.47 +/- 0.05, 6.57 +/- 0.04, and 6.75 +/- 0.04) was significantly reduced as compared with both groups R and C (p less than 0.05). Thus a severe, persistent regional intracellular myocardial acidosis occurs in the ischemic zone with coronary occlusion but is rapidly corrected by reperfusion within 1 hour.

Initiation of ventricular tachyarrhythmia with programmed stimulation: sensitivity and specificity in an experimental canine model.

Programmed stimulation (PS) is used in the catheterization laboratory and operating room to initiate and study malignant ventricular tachyarrhythmia (VT). The purpose of this study was to evaluate the specificity and sensitivity of PS in short-term studies of 10 normal animals (group A), 10 sham-operated controls (group B), and 10 dogs with chronic myocardial infarction susceptible to inducible VT by an occlusion-reperfusion method (group C). Groups B and C were studied 7 to 14 days after the initial procedure. the pH, PaO2, and PaCO2 were determined and corrected every 30 minutes during the procedure. When bipolar ventricular pacing with three ventricular extrastimuli was used, VT initiation was attempted at 10 normal intramyocardial sites in groups A and B and in close proximity (less than or equal to 1 cm) to areas of infarction in group C. When one ventricular extrastimulus was used during ventricular pacing, VT was induced in dogs with chronic infarctions (3 of 10, 30%, group C). Using two extrastimuli, however, VT was inducible in 4 of 10 (40%) of group A, 6 of 10 60%) of group B, and all 10 (100%) of group C. With three extrastimuli, all 30 dogs had inducible VT. Overall, PS with one extrastimulus was highly specific in 100% but insensitive in 30%. With two extrastimuli the sensitivity increased to 100%, but the specificity fell to 50%. Finally, with three extrastimuli the sensitivity was also 100%, but the specificity decreased to 0%. PS remains an invaluable technique in diagnosing and assessing therapy for patients with VT. The diagnostic implications of this test await more precise pathophysiologic elucidation of arrhythmic mechanisms.

Mediation of cardiac ischemia by thromboxanes released from human platelets.

We evaluated the consequences of platelet activation within the coronary circulation and determined the contribution of released thromboxanes, the most potent vasoconstrictors known, to the ensuing cardiac ischemia. Human platelets were isolated by sepharose column chromatography from blood of normal donors and added to the crystalloid perfusate of a Langendorff rabbit heart (platelet counts greater than or equal to 10,000/microliters). Following thrombin-induced (1 U/ml) platelet activation, the coronary flow decreased by 30 +/- 10% (mean +/- SEM, P less than 0.02), the mean concentration of thromboxane B2 in the coronary sinus effluent rose to 62 +/- 25 pmol/ml, and immediate, often irreversible cardiac ischemia as monitored by nicotinamide adenine dehydrogenase autofluorescence photography, ensued. However, with high concentrations of the platelet inhibitor and vasodilator, prostaglandin E1 (1.0 mM), the coronary flow increased by 50 +/-= 15%, and the epicardial fluorescence remained unchanged despite a small (10 +/- 3 pmol/ml) increase in coronary sinus thromboxanes. Platelets isolated from donors who ingested aspirin were incapable of thromboxane synthesis (less than 5 pmol/ml) but remained normally responsive to thrombin-induced activation. When these platelets were challenged by thrombin during cardiac perfusion, however, coronary flow and epicardial fluorescence remained unchanged. We conclude that platelet activation within the coronary circulation can induce irreversible cardiac ischemia, which, however, can be prevented by appropriate pharmacologic inhibition of platelet function. Furthermore, the fact that cardiac perfusion was preserved during a thrombin challenge of platelets from aspirin-treated donors establishes a fundamental role for the products of cyclooxygenase activity (e.g., thromboxanes) in the genesis of this form of myocardial ischemia.

Histopathologic factors conducive to experimental ventricular tachycardia.

Ventricular tachyarrhythmia is the leading cause of sudden cardiac death. Determination of the substrates conducive to the initiation of this arrhythmia remains an important clinical goal. The purpose of this study was to correlate histopathologic findings, specifically: pattern (heterogeneous versus homogeneous infarct morphology), distribution (viable epicardial and/or endocardial rim), and infarct size, with susceptibility to the initiation of sustained ventricular tachycardia employing programmed electrical stimulation in two canine models of experimental myocardial infarction. Twenty-one adult dogs were randomly divided into two groups: 12 dogs underwent two-stage, 2-hour occlusion of the proximal left anterior descending coronary artery and nine animals underwent permanent, complete occlusion of the left anterior descending coronary artery with latex embolization. With programmed ventricular pacing with two premature ventricular extrastimuli, initiation of ventricular tachycardia was attempted, open chest, two weeks after infarction. Electrophysiologic evaluation of the infarct type correlated significantly with the histologic morphology of the infarction (p less than 0.001). The presence of a viable epicardial rim was an extremely important variable for ability to induce sustained ventricular tachycardia (p = 0.04). The presence of an endocardial rim was not significant (p = 1.0). Infarct size alone was only marginally related to ventricular tachycardia inducibility (p = 0.08). Nonuniform infarcts were more conducive to the initiation of sustained ventricular tachycardia than were homogeneous infarcts (p = 0.025). The presence of a large, nonuniform infarct correlated best with inducibility (p = 0.0002). Thus in these experimental models, specific infarct morphologies correlate significantly with susceptibility to inducible sustained ventricular tachyarrhythmias.

Technique for implantation of phrenic nerve electrodes.

Permanent ventilatory support is necessary in patients with upper motor neuron respiratory muscle paralysis and central alveolar hypoventilation. Weaning these patients from chronic ventilation is extremely advantageous. Diaphragm pacing accomplishes this goal. In the past implantation of phrenic nerve electrodes has been undesirable either because the procedure is too extensive or because of the high failure rates. This report describes a simple, expeditious, and uniformly successful technique for bilateral phrenic nerve electrode placement.

Assessment of exercise oxygen consumption as preoperative criterion for lung resection.

Determination of preoperative pulmonary function is crucial in avoiding complications from pulmonary resection. Many have employed static pulmonary function testing in an attempt to decrease morbidity and mortality from lung resections. The purpose of the present study was to correlate preoperative static pulmonary function, one-second forced expiratory volume (FEV1), and exercise O2 consumption (MVO2) with postoperative morbidity and mortality. Fifty consecutive patients underwent preoperative FEV1 and MVO2 determinations. A criterion for surgical resection included an FEV1 greater than 1.7 liters for pneumonectomy, greater than 1.2 liters for lobectomy, and greater than 0.9 liters for wedge resection. The surgeon was blinded as to the results of MVO2 studies. Mean age was 63.8 years (range, 47 to 76 years). There were 10 pneumonectomies, 28 lobectomies, and 12 wedge resections. Among the 50 surgical candidates selected solely on the standard FEV1 values, mortality was 4% (2/50) and morbidity, 12% (6/50). Stratification on the basis of exercise performance showed a 29% mortality (2/7) and a 43% morbidity (3/7) in patients with an MVO2 less than 10 ml/kg/min. Patients with an MVO2 less than 20 but greater than 10 ml/kg/min had a 10.7% morbidity (3/28), and there were no deaths. No patients with an MVO2 greater than 20 ml/kg/min sustained any morbidity or died (p less than 0.001). We conclude that exercise is an important criterion in the preoperative evaluation of patients for pulmonary surgery. An MVO2 less than 10 ml/kg/min is associated with significant morbidity and mortality.

Unilateral high-frequency jet ventilation during one-lung ventilation for thoracotomy.

One-lung ventilation is indicated during thoracic operations for bronchopleural fistula, pulmonary abscess, and pulmonary hemorrhage in spite of the possibility of the development of severe hypoxemia. To evaluate methods for improving oxygen transport during one-lung ventilation, we applied high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) to the nondependent lung following deflation to atmospheric pressure in each procedure, and measured the effects on cardiac output and arterial oxygenation. In each case, the dependent lung was ventilated with conventional intermittent positive pressure ventilation (IPPV). Eight patients were studied during posterolateral thoracotomy using double-lumen endobronchial tubes. HFJV or CPAP to the nondependent lung improved arterial oxygenation significantly during both closed and open stages of the surgical procedures (p less than 0.008). When the chest was open, HFJV maintained satisfactory cardiac output, whereas CPAP usually decreased cardiac output (p less than 0.008). There were no significant differences in mean partial pressure of arterial carbon dioxide between HFJV, CPAP, and deflation to atmospheric pressure. In conclusion, HFJV to the nondependent lung provides not only satisfactory oxygenation but also good cardiac output, thereby maintaining better oxygen transport than CPAP or deflation to atmospheric pressure, while the dependent lung is ventilated with IPPV during one-lung ventilation for thoracotomy.

Current status of coronary artery bypass grafting for coronary artery atherosclerosis.

Coronary artery bypass grafting has now undergone 18 years of proven benefit in the treatment of myocardial ischemic disease. The technique of CABG has been further extended to other situations in which myocardial blood supply is threatened, such as cardiac trauma, aneurysms of coronary arteries, and congenital lesions. The emphasis in choosing CABG over medical therapy in 1985 should be preservation of myocardium at jeopardy of infarction as well as relief of angina. Proximal stenoses in vessels subserving viable muscle that is ischemic at rest or with minimal exercise should be treated with reperfusion by angioplasty or CABG to prevent further injury. After infarction occurs and ventricular function is impaired, CABG is also necessary to preserve remaining myocardium at jeopardy. Such an aggressive approach seems warranted with today's excellent surgical results. Long-term results have also improved, as more attention has been paid to saphenous vein graft preparation, use of mammary artery grafts, complete revascularization, use of antiplatelet agents, control of spasm, and identification of hypercoagulable states that may require sodium warfarin (Coumadin). Angioplasty of vein grafts and distal anastomoses also appears promising to help extend the results of initial CABG. Figure 1 is our recommended approach for the treatment of coronary atherosclerosis.

Current status of surgery for ventricular tachyarrhythmias.

This article outlines the accepted histopathologic and electrophysiologic theories underlying the etiology of medically refractory ventricular tachyarrhythmias. It delineates the indications and techniques for the electrophysiologic study of the ventricle. Finally, the surgical procedures available as well as their indications and results are elucidated.

Pacemaker therapy.

This article reviews the indications for pacemaker implantation and the techniques and devices currently in use. The management of patients who require permanent pacemakers and the potential complications involved are discussed. The article concludes with a brief synopsis of temporary pacing.

Cyclosporine in cardiac transplantation.

Cyclosporine is a new immunosuppressive drug that acts early in the exposure of a host to allogeneic stimulation. It is a peptide of fungal origin. It has selective action on T cells, leaving the other cells of the immune system intact. It acts by preventing the function of the early activation signals of T cells, such as the acquisition of receptors for Il 2 and Il 1. It is lipophilic, moderately well absorbed by the gut, and metabolized by the liver. Factors affecting absorption or hepatic metabolism alter the amount of cyclosporine available in the circulation. Circulating levels can be measured by radioimmunoassay or HPLC. Doses should be tailored to trough levels taken approximately 12 hours after an oral or intravenous dose or to individual pharmacokinetic curves. The drug is nephrotoxic, hepatotoxic, and neurotoxic. In addition, cyclosporine has been associated with hypertension, hemolytic-uremic syndrome, increased incidence of intravascular thrombotic events, hypertrichosis, gum hyperplasia, pericardial effusion, and lymphoproliferative disorders. Despite these complications, cyclosporine usage seems to have improved short-term cardiac allograft survival and to have reduced the complications associated with side effects of steroids. As a result, cyclosporine has spawned a resurgence of interest in cardiac transplantation, which will be of great benefit in prolonging the lives of patients with end-stage cardiac disease.

Histopathologic correlates of inducible ventricular tachycardia in two experimental canine models of myocardial infarction.

Ventricular tachyarrhythmias are the leading cause of sudden cardiac death. Determination of the substrates conducive to the initiation of ventricular tachyarrhythmias remains an important clinical goal. The purpose of this study was to correlate electrophysiologic and histopathologic parameters conducive to the initiation of sustained ventricular tachycardia using programmed electrical stimulation in two canine models of myocardial infarction. Histopathologic correlates included: infarct pattern (heterogeneous vs. homogeneous morphology), distribution (viable epicardial or endocardial rim), and size. Twenty-one adult dogs were randomly divided into two groups: (1) 12 dogs underwent two-stage, 2-hour occlusion of the proximal left anterior descending coronary artery (LAD); and (2) nine animals had permanent, complete occlusion of the LAD with latex embolization. Using programmed ventricular pacing with two premature ventricular extrastimuli, initiation of ventricular tachycardia was attempted at both 1 and 2 weeks after infarction with the chest closed and opened each time. Electrophysiologic evaluation of the infarct type correlated significantly with the histologic morphology of the infarction (p less than 0.001), the presence of a viable epicardial rim was an extremely important discriminating variable for ability to induce sustained ventricular tachycardia (p = 0.04). The presence of an endocardial rim was not significant (p = 1.0). Infarct size alone was only marginally related to ventricular tachycardia inducibility (p = 0.08). Non-uniform infarcts were more conducive to the initiation of sustained ventricular tachycardia than homogeneous infarcts (p = 0.025). The presence of a large, non-uniform infarct was the best overall discrimination variable for inducibility (p = 0.0002). Thus, in these experimental models, specific infarct morphologies correlate significantly with susceptibility to inducible sustained ventricular tachyarrhythmias.

Acute torsion of the gallbladder: review of the literature and report of a case.

A case report is presented, and the literature reviewed, of acute torsion of the gallbladder. Originally described as a rare pathological entity, it is being witnessed more frequently as a probable concomitant of increasing life expectancy. Because it is a benign condition if diagnosed rapidly and treated surgically, it should be considered in differential diagnostic possibilities. When encountered intraoperatively, prompt recognition of the process should lead to detorsion of the organ and cholecystectomy as the procedure of choice.

Colo-pericardial fistula: complication of colonic interposition.

This report discusses a unique and previously unreported complication of a colonic interposition following esophageal replacement. A 7-year-old boy under-went a right colonic interposition following extensive esophageal lye burn. Fifteen years post-colonic interposition, the 22-year-old man was admitted to an adult medical ward with chest pain, cardiomegaly, and fever. Barium swallow revealed a colo-pericardial fistula with massive pericarditis. The patient survived an immediate thoracotomy with the removal of the colon and a pericardiectomy. Several months later the patient underwent a successful left colonic interposition. This case illustrates that immediate and aggressive surgical therapy may prevent an otherwise fatal outcome.

Management of unresectable malignant esophageal obstruction.

Malignant esophageal obstruction (MEO), especially with esophago-respiratory fistula (ERF), requires efforts to achieve a meaningful degree of palliation. Laser vaporization (LV) of the esophageal tumor and placement of an endoesophageal prosthesis (EEP) represents a new combination for palliation of MEO. The purpose of the present study was to evaluate the neodymium-yttrium-aluminum-garnet (Nd:Yag) laser in reopening the esophageal channel to permit both swallowing and insertion of an EEP. Twenty-three consecutive patients with MEO were evaluated, and ERF was documented by preoperative contrast study in eight patients. All 23 patients underwent laser vaporization, dilation, and surgical placement of EEP. Adequate swallowing was attained in 21 patients; one patient with an ERF experienced recurrent aspiration from failure of the EEP to occlude the fistulous tract. Operative morbidity was 17% (4/23), which included: wound infection, 2; persistence of ERF, 1; esophageal perforation, 1; and food impaction, 1. Thirty-day operative mortality was 9% (2/23). Palliation was excellent in 87% (20/23), with discharge from the hospital by the seventh postoperative day. Mean survival was 3.3 months. We conclude that laser vaporization followed by placement of an EEP represents a major advance in the palliation of MEO.

Cardiac surgical techniques for treating intractable ventricular tachyarrhythmias.

Recurrent, sustained ventricular tachyarrhythmias unresponsive to medical therapy are associated with a one-year mortality of 70 to 85%. Patients who are susceptible to these reentrant arrhythmias usually have a history of previous myocardial infarction or chronic myocardial ischemic disease. More specifically, these patients demonstrate both anatomic and electrophysiologic derangements. Experimental work suggests that regions of non-uniform damage render the ventricle more susceptible to ventricular tachyarrhythmias; even relatively large areas of homogeneous myocardial ischemic damage may not display the same susceptibility to these arrhythmias. Surgical techniques are being devised to treat patients with ventricular tachyarrhythmias refractory to medical management. These have provided control of arrhythmias in patients whose disease was previously resistant to all medical treatment. The evolving surgical therapies presently employed share either of two pathophysiologic consequences which render them successful: the homogeneous ablation of previous heterogeneous myocardial ischemic damage or the delimiting of an arrhythmogenic focus by excluding conduction to surrounding myocardium. Finally, antitachycardia and defibrillating devices have also been developed to facilitate the management of patients not controlled satisfactorily with either conventional or investigative drugs. All physicians will need to be familiar with these devices.