Background —Although dobutamine echocardiography (DE) is widely used to assess myocardial viability in humans, little is known about the relation between contractile reserve and myocardial structure. Methods and Results —We evaluated 20 patients with coronary disease (64±13 years old, ejection fraction 28±7.5%) with DE (up to 40 μg · kg −1 · min −1 ), rest-redistribution 201 Tl single photon emission CT, and quantitative angiography before bypass surgery. During surgery, patients underwent transmural myocardial biopsies (n=37) guided by transesophageal echocardiography to determine the extent of interstitial fibrosis and intracellular and interstitial proteins by histopathology and immunohistochemistry. Among the 37 segments biopsied, 16 recovered function as assessed 2 to 3 months later. Segments with postoperative functional recovery had more wall thickening at low-dose DE (28% versus 3%, P <0.001), higher thallium uptake (69% versus 48%, P =0.03), and less interstitial fibrosis (2% versus 28%, P <0.001). Quantitative angiographic parameters did not predict recovery of function. Segments with DE viability (contractile reserve and/or ischemia) had less fibrosis (2.7% versus 28%, P <0.001), less vimentin and fibronectin (both P <0.01), more glycogen ( P =0.016), and higher thallium uptake (64% versus 35.5%, P <0.05) than those without viability. Viable segments by both DE and thallium had less fibrosis (1%) than those viable by 1 of the 2 techniques (9%) or not viable by both (28%, P =0.005). Thickening at low-dose DE correlated well with the extent of interstitial fibrosis ( r =−0.83, P <0.01). Conclusions —Contractile reserve during DE correlates inversely with the extent of interstitial fibrosis and the amount of fibronectin and vimentin and directly with rest-redistribution thallium uptake.
There is a slowly increasing amount of information on surgical revascularization of high-risk patients with lower ejection fractions. Many of these patients, formerly thought to be best treated by transplantation, can undergo safe and effective revascularization with excellent medium-term results. Factors that are important in predicting the success of surgical revascularization include left ventricular dilitation, elevated left ventricular end-diastolic pressure, redo coronary surgery, depressed white ventricular function, the presence of mitral regurgitation, and the presence of associated systemic diseases, among others. The management of patients with low ejection fraction around the time of coronary surgery is of critical importance; a period of pre-operative “tune-up” in the hospital on intravenous pressures, intra-aortic balloon, counter pulsation, and the use of transesophageal echocardiography, and improved intra-operative myocardial protection techniques have all contributed to improved results. The improvement in mechanical cardiac systems has also contributed toward improved surgical outcomes in this high-risk patient group.
Left ventricular rupture following mitral valve replacement is an unusual and often lethal complication. Despite being well described since the initial description in 1967 by Roberts, this catastrophic complication still occurs. A recent case of a delayed Type III rupture is presented. The pathology and repair of the three recognized types of rupture are reviewed and the preventive measures discussed.
To determine whether the contractile work history of cardiac muscle influences its responsiveness to insulin, we examined the effect of insulin infusion on glycogen metabolism in the rat heart 1 wk after transplantation into a nonworking heterotopic infrarenal position. Nonworking heterografts had higher basal glycogen concentrations than did in situ working hearts of the same animals (29.9 +/- 2.7 vs. 23.3 +/- 0.8 mumol/g; P < 0.05), and a smaller fraction of their glycogen synthase enzyme activity was in the physiologically active glycogen synthase I form (8 +/- 2 vs. 22 +/- 3%; P < 0.02). During a 25-min infusion of insulin (1 U/min) and glucose (30 mg.kg-1.min-1), the fractional glycogen synthase I activity of heterografts remained lower than that of in situ hearts (29 +/- 5 vs. 56 +/- 7%; P < 0.02) and heterografts synthesized glycogen more slowly (0.126 +/- 0.07 vs. 0.352 +/- 0.06 mumol.g-1.min-1; P < 0.02). These effects could be duplicated by a 24-h fast, which similarly increased myocardial glycogen concentration (to 32.9 +/- 5.6 mumol/g). These observations suggest that the performance of repetitive contractile work is necessary to maintain the myocardium maximally responsive to insulin. Mechanical unloading increases myocardial glycogen concentration, thereby reducing the magnitude of insulin's stimulation of glycogen synthase and consequently the rate of incorporation of circulating glucose into glycogen.
While vascular endothelial cells are repeatedly stretched by the pulsatile nature of cardiac output, in vitro models traditionally used to study vascular biology involve static culture techniques. We have recently shown that pulsatile stretching of endothelial cells in culture will increase their rates of proliferation and regulate their secretion of macromolecules. The aim of this study was to determine whether membrane adenylate cyclase is involved in intracellular signalling during pulsatile stress. Bovine aortic endothelial cells were seeded on flexible-bottomed culture wells (3 x 10(5) cells/25 mm well) and allowed to attach for 48 hours. The culture wells were placed in a vacuum-operated stress providing instrument and subjected to 0.5 s of 24% strain, 0.5 s relaxation (60 cycles/min) for 0, 1, 3, 5, 7, 10 and 15 minutes (N = 24 wells/time point). Cells were homogenized and a crude membrane preparation (27,000 x g) was assayed for adenylate cyclase under basal and forskolin (100 microM) stimulated conditions. The results indicate that there is a time-dependent increase in both basal and stimulated adenylate cyclase with cyclic deformation and suggest that there may be a "stretch receptor" coupled to adenylate cyclase which can modulate endothelial cell function with hemodynamic changes.
• Various techniques have been advocated for resuscitation from hypothermic arrest caused by ice-cold freshwater drowning or exposure. We have resuscitated five such patients after emergency hospital admission using cardiopulmonary bypass initiated via median sternotomy. All patients presented to our facility with core temperatures less than 26°C. Three patients had been in full cardiopulmonary arrest for more than 30 minutes prior to arrival. The fourth patient presented in ventricular fibrillation; the fifth was admitted to the hospital in sinus bradycardia that quickly deteriorated to asystole. All had cardiopulmonary bypass emergently initiated via median sternotomy. All were rewarmed on bypass to 37°C and all survived at least 24 hours. Three of the five patients are currently alive and well with normal neurologic function. Cardiopulmonary bypass is an effective technique for resuscitation after hypothermic arrest due to near drowning and/or exposure. (Arch Surg. 1992;127:525-528)
Pulmonary artery balloon counterpulsation is a promising experimental technique for treatment of right ventricular failure. However, clinical application has been limited in that the only device presently available (the large-volume intraaortic balloon) must be placed within a synthetic graft. Because a balloon with a smaller volume (which could be placed through a peripheral vein and be contained entirely within the pulmonary artery) would make the technique feasible on a wider scale, we tested an 8-mL pulmonary artery balloon placed through the femoral vein in 12 dogs. Two groups of animals were compared. One group had the pulmonary artery balloon in place but not counterpulsating; the other had the pulmonary artery balloon in place and counterpulsating. Each group was studied for 12 hours. A variety of hemodynamic parameters were measured. Effective diastolic augmentation and systolic unloading were noted in all 6 dogs that underwent counterpulsation (5.0 +/- 1.1 mm Hg of diastolic augmentation and 9.5 +/- 1.6 mm Hg of systolic unloading). Pulmonary function, as measured by arterial blood gas sampling and pulmonary vascular resistance, was not impaired. Examination of the heart and lungs showed no detrimental pathologic effects of pulmonary artery balloon counterpulsation. Placement of the balloon through a peripheral vein with a guidewire was easy and uncomplicated. We conclude that pulmonary artery balloon counterpulsation is safe over an extended period of 12 hours in the canine model and that diastolic augmentation and systolic unloading can be produced.
