James M. Levett

Thermodilution cardiac output: A critical analysis and review of the literature

Abstract A critical analysis of the thermodilution method of cardiac output determination has been presented. The factors determining cardiac output calculations have been discussed and specific sources of error have been analyzed. This method offers advantages of internal electrical calibration, use of physiologic fluid as indicator, minimal recirculation, lack of requirement for a withdrawal system, and a short interval between successive determinations. The method has compared favorably to other methods of cardiac output determination and is easily used in the modern clinical setting because of its technical simplicity and the availability of flow-directed balloon-tipped catheters with thermistors. Specific sources of error include factors influencing the temperature of the injectate bolus, the determination of initial baseline blood temperature, the integration of the time-temperature curve, the technique of injection, and the method of sampling. These errors depend both upon experimental technique and upon the internal calibrations and methods of curve integration as determined by the manufacturer. In general, the method can be used to accurately determine cardiac output when it is applied systematically and the sources of error are understood.

Sympathectomy in the Treatment of Angina and Arrhythmias

Sympathectomy has been used as treatment for several different cardiac conditions. These include classic angina pectoris, Prinzmetals angina, paroxysmal atrial tachycardia, ventricular tachycardia, and long QT syndrome. To understand the rationale of such treatment, the innervation of the human heart is reviewed with discussion of the cardiac plexus and coronary innervation. Results in published studies are summarized and discussed.

Measuring for improvement: from Toyota to thoracic surgery.

BACKGROUND Measuring quality has become a high priority in the era of managed care. Nevertheless, it can be counterproductive to use the same methods for measuring improvement in surgical procedures and processes as we use for measurement in basic research. Techniques of statistical process control have been used for many years to measure process improvement in industry and are now being applied to health care. METHODS Examples of using statistical process control charts to monitor coronary artery bypass grafting mortality, intensive care unit admission time, and length of stay are reviewed. RESULTS The major advantage of using control chart methodology is that it allows one to determine whether the process being evaluated is in fact stable and to detect when significant or special cause variation occurs. CONCLUSIONS Summary statistics currently provided to purchasers of care and regulatory agencies do not ensure that the processes being evaluated are stable. We need to look at data over time with statistically validated methods such as control charts to better monitor our processes of care and thereby provide accurate statistics.

Myocardial Rupture: III. Chamber Pressure, Rate of Distention, and Ventricular Disruption in Isolated Hearts

We have developed an in vitro technique for producing myocardial rupture in lamb hearts, which relates tensile strength to a variety of conditions which can prevail in normal and infarcted human hearts. Retrograde perfusion of saline solution and inflation of the left ventricle was used to apply progressive stress to the left ventricular wall. Three separate sites of myocardial rupture were observed and occurred with the frequency of 54% at the papillary muscle, 30% at the interventricular septum, and 16% at the free wall of the left ventricle. The distribution and configuration of the experimental ruptures were similar to those usually noted as complications of human myocardial infarction. The mean rupturing pressure was 526 mm Hg in normal lamb hearts. Application of these techniques should ultimately provide data relevant to the diagnosis, prevention, and treatment of myocardial rupture.

Comparison of prosthetic graft materials as intracardiac right atrial patches

An experimental animal model was developed to study the fate of prosthetic graft materials within the heart. Autologous pericardium, bovine pericardium, polytetrafluoroethylene, woven Dacron, and autologous right atrium (control) patches were implanted into the wall at three sites on the right atrium in each of 10 dogs (six patches for each graft material). The atria were harvested 90-100 days later and histologic examination and quantitation of calcium were performed. Chronic inflammation and fibrosis were found in 29 of 30 grafts. Cartilage formed in 26 of 30 sites and was found both in the center and around the edges of the grafts. In addition to cartilage, bone including marrow elements formed in the two autologous materials at 4 of the 12 sites and in 1 of the Dacron graft sites. Calcium content was greater in the control and the bovine pericardial grafts than in the other graft materials (P = NS). The incidence and degree of inflammation, fibrosis, calcification and cartilage, and bone formation were similar in all materials. We conclude that the healing process of these intracardiac graft materials is a generalized phenomenon independent of the inherent properties of a specific graft material.

Effects of dimethyl sulfoxide on systemic and cerebral hemodynamic variables in the ischemic canine myocardium

The effects of dimethyl sulfoxide (DMSO) infusion on cerebral blood flow (CBF) and systemic hemodynamics were studied in a canine model of myocardial ischemia. Immediately after ligation, cardiac output dropped from 2.09 ± 0.11 (SEM) in the control group and 1.79 ± 0.13 in the DMSO group to 1.07 ± 0.21 and 1.0 ± 0.08 L/min, respectively; there were no significant differences for 2 h. By the third hour and thereafter, the DMSO group had a significantly (p < .05) higher cardiac output (1.65 ± 0.08 L/min) than the control group (1.15 ± 0.10 L/min). The cardiac output increase at 3 h was accompanied by significantly (p <.05) lower systemic vascular resistance (SVR) in the DMSO group (5315 ± 248 dyne · sec/cm5) as compared to the control group (7892 ± 442 dyne · sec/cm5). There were no significant differences in heart rate, mean arterial pressure, pulmonary artery wedge pressure, or cerebral or pulmonary resistances in the control as compared to the DMSO group. Higher CBF values were noted at one hour and thereafter in the DMSO as compared to the control group (p < .05). Low-dose DMSO given as an iv bolus improved cardiac output and CBF and lowered SVR in this canine model of experimental myocardial ischemia.

Comparative studies of prosthetic materials in the left atrium of the dog

To assess the healing process of various intracardiac prosthetic graft materials, we inserted autologous left atrium (control), autologous pericardium (AP), bovine pericardium (BP), polytetrafluoroethylene (PTEE) and woven Dacron (WD) patches into excised defects in the left atrial wall of 15 dogs. Two patches were implanted into each heart utilizing six patches for each material. Three months after graft placement, histological examination revealed chronic inflammation and fibrosis for all materials. Dense connective tissue surrounded the grafts in which fibrosis was most prominent. Cartilage formation occurred in 11 grafts 5 BP, 4 PTFE, 1 control and 1 AP site. This change was not evident with WD. The extent of cartilage formation was greatest in BP. Bone formation occurred in 3 BP sites, 2 PTFE and 1 control site. Quantitative calcium concentrations were similar for all of the grafts without bone formation. Calcium concentrations at sites with bone formation averaged 15.13 mg/g±6.39 mg/g compared to 0.939±0.419 for sites without bone formation (p<0.0001). We conclude that while inflammation, fibrosis and connective tissue thickening occur with healing of all graft materials, cartilage and bone formation differ with respect to the material employed.

Cardiovascular Responses to PEEP and CPAP Following Repair of Complicated Congenital Heart Defects

Fourteen infants and children ranging in age from 7 months to 8 years were studied in a hemodynamically stable condition following repair of various heart defects. Changes in cardiac index, stroke index, heart rate, systemic vascular resistance, mean arterial pressure, and central venous pressure were evaluated at levels of 0, 5, and 10 cm H2O using positive end-expiratory pressure (PEEP) in 14 patients and continuous positive airway pressure (CPAP) in 3 patients. No significant changes were found in any of the measurements taken at the different levels.

Preservation of Myocardial High-Energy Phosphates with Vagal Stimulation and Hypothermic Cardioplegia

We examined three methods of inducing hypothermic cardioplegic arrest and related each to preservation of high-energy phosphates. Levels of adenosine triphosphate (ATP) and creatine phosphate (CP) in baseline rat hearts were compared with levels found after vagal stimulation combined with cardioplegia containing 15 mEq of potassium chloride (KCl) per liter, cardioplegia with 15 mEq of KCl per liter alone, and cardioplegia with 30 mEq of KCl per liter alone. Vagal stimulation produced complete electromechanical arrest in a shorter time than either 15 or 30 mEq of KCl alone (p less than 0.001 for both cardioplegic solutions compared with vagal stimulation), with fewer ventricular beats after ischemia than cardioplegic solution containing 15 or 30 mEq of KCl (p less than 0.001 and less than 0.01, respectively). Levels of ATP and CP, although less than baseline levels (p less than 0.01 and less than 0.001, respectively), were greater with vagal stimulation than with either 15 or 30 mEq of KCl (p less than 0.001 and less than 0.05, respectively, for ATP and p less than 0.001 for both CP levels). Furthermore, when all groups were combined, ATP and CP levels were found to correlate negatively with arrest time (r = -0.851 and -0.788, respectively; both r values significant at p less than 0.01) and with the number of ventricular beats after ischemia (r = -0.927 and -0.851, respectively; both r values significant at p less than 0.01). We conclude that electromechanical work quantified as time to arrest after aortic cross-clamping and as number of ventricular beats after ischemia correlates negatively with ATP and CP levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Preservation of myocardial high energy phosphates during cardioplegic arrest with nifedipine.

Nifedipine used both as an additive to cardioplegia solution (CPS) and as pretreatment prior to arrest was studied in a rat model to determine its effect upon ischemic ventricular electromechanical work during arrest and upon high energy phosphate levels. Fifty-one normothermic rats were studied in vivo with infusion of hypothermic (4 degrees C) CPS into the cross-clamped aortic root according to one of the following eight protocols: Group 1, baseline beating hearts; Group 2, CPS containing 15 mEq potassium chloride/liter (KCl/liter); Group 3, CPS containing 30 mEq KCl/liter; Group 4, CPS containing 15 mEq KCl/liter combined with stimulation of the vagus nerve; Groups 5 and 6, CPS with 15 mEq KCl/liter and containing 250 or 500 micrograms of nifedipine per liter; Groups 7 and 8, pretreatment with 100 or 200 micrograms nifedipine/kg given as an intravenous bolus 15 min prior to infusion of CPS with 15 mEq KCl/liter. Time to arrest, number of ischemic ventricular contractions after aortic cross clamping, and ATP and creatine phosphate (CP) levels were recorded. All nifedipine groups arrested more quickly and with fewer ventricular contractions and had ATP and CP levels higher than those of Group 2 (P less than 0.05). There were no differences between the nifedipine groups and Group 3 except that Group 8 (200 micrograms/kg pretreatment) resulted in higher levels of CP than Groups 3, 5, and 6 (P less than 0.05 for all groups). When all groups were combined, time to arrest correlated negatively with ATP (r = -0.863, P less than 0.01) and CP (r = -0.824, P less than 0.01) levels.(ABSTRACT TRUNCATED AT 250 WORDS)