Two-pore K+ channels, NO and metabolic inhibition.

Ischemic preconditioning is a potent endogenous mechanism protecting many organs from the devastating effects of prolonged ischemia. In the heart, NO is one mediator of this myoprotective response thought to involve activation of the K(ATP) channel. Ischemic preconditioning is known to be induced by metabolic inhibition using sodium cyanide (NaCN) in single cardiomyocytes. In the present study, we show for the first time that the end effector channel activated by NaCN has been incorrectly identified. The channel activated is not K(ATP) but instead belongs to the relatively new family of two-pore domain potassium channels (K2P). Further when activated by metabolic ischemia, the amplitude of K2P current is directly modulated by activators and inhibitors of the NO pathway.

High resolution mechanical function in the intact porcine heart: mechanical effects of pacemaker location.

The necessity to quantify the mechanical function with high spatial resolution stemmed from the advancement of myocardial salvaging techniques. Since these therapies are localized interventions, a whole field technique with high spatial resolution was needed to differentiate the normal, diseased, and treated myocardium. We developed a phase correlation algorithm for measuring myocardial displacement at high spatial resolution and to determine the regional mechanical function in the intact heart. Porcine hearts were exposed and high contrast microparticles were placed on the myocardium. A pressure transducer, inserted into the left ventricle, synchronized the pressure (LVP) with image acquisition using a charge-coupled device camera. The deformation of the myocardium was measured with a resolution of 0.58+/-0.04 mm. Within the region of interest (ROI), regional stroke work (RSW), defined as the integral of LVP with respect to regional area, was determined on average at 21 locations with a resolution of 27.1+/-2.7 mm2. To alter regional mechanical function, the heart was paced at three different locations around the ROI. Independent of the pacemaker location, RSW decreased in the ROI. In addition, a gradient of increasing RSW in the outward direction radiating from the pacemaker was observed in all pacing protocols. These data demonstrated the ability to determine regional whole field mechanical function with high spatial resolution, and the significant alterations induced by electrical pacing.

Thrombogenic performance of a st. Jude bileaflet mechanical heart valve in a sheep model.

The sheep model is preferred for chronic evaluation of prosthetic heart valves, surgical techniques, and endocardiographic studies. A bileaflet mechanical heart valve (MHV) was implanted into a sheep model to study its in vivo performance and to evaluate the thrombogenic potential of the valve. Transesophageal echocardiography and transcranial Doppler ultrasonography measurements were conducted before and after the valve implantation. Platelet activity state (PAS) assay measurements were also conducted before and after the implantation surgery. After sheep euthanasia, the MHV was explanted and scanning electron microscopy (SEM) was performed on the explanted valve to examine changes to the MHV surface. Tissue blocks were taken from the sheep brain, left ventricle, aorta, spleen, and lung lobes for histological examination. Our results indicated that after the MHV implantation, more embolic signals were detected in the sheep carotid artery, increasing monotonously as a function of implantation time. Echocardiographic parameters including blood aortic velocity, transvalvular pressure gradient, and velocity time integral increased. PAS increased significantly after valve implantation. SEM pictures demonstrated calcium and phosphate deposition on the valve surfaces. Histological examination demonstrated hemorrhage in the lung tissue, pulmonary thrombosis, and osteogenesis in heart tissue.

Tissue-engineered myocardial patch derived from extracellular matrix provides regional mechanical function.

BACKGROUND: Extracellular matrix (ECM), a tissue-engineered scaffold, recently demonstrated cardiomyocyte population after myocardial implantation. Surgical restoration of myocardium frequently uses Dacron as a myocardial patch. We hypothesized that an ECM-derived myocardial patch would provide a mechanical benefit not seen with Dacron. METHODS AND RESULTS: Using a canine model, a full thickness defect in the right ventricle was repaired with either Dacron or ECM. A third group had no surgery and determined baseline RV function. Eight weeks later, global systolic function was assessed by the preload recruitable stroke work relationship. Regional systolic function was measured by systolic area contraction (SAC), calculated by high density mechanical mapping. Tau was used to assess global diastolic function. Recoil rate and diastolic shear were used as measures of regional diastolic function. After functional data acquisition, tissue was fixed for histological evaluation. Global systolic and diastolic functions were similar at baseline and after ECM and Dacron implantation. Regional systolic function was greater in the ECM group compared with the Dacron group (SAC: 4.1+/-0.9% versus -1.8+/-1.1, P<0.05). Regional diastolic function was also greater in the ECM group (recoil rate (degrees sec(-1)): -44+/-7 versus -17+/-2, ECM versus Dacron; P<0.05). Immunohistochemical analysis revealed cardiomyocytes in the ECM implant region, a finding not seen with Dacron. CONCLUSIONS: At 8 weeks, an ECM-derived tissue-engineered myocardial patch provides regional mechanical function, likely related to cardiomyocyte population. These results are in sharp contrast to Dacron, a commonly used myocardial patch.

HIV disease and an atherosclerotic ascending aortic aneurysm.

Cardiovascular dysfunction appears to be an important complication of human immunodeficiency virus (HIV) infection and is being reported with greater frequency. There have been recent reports in the literature of HIV patients who suffer from vascular lesions such as large artery vasculopathy secondary to vasculitis, as well as accelerated atherosclerosis of the coronary arteries. The latter has been linked to patients on protease inhibitors that are used as part of a highly active antiretroviral therapy (HAART) regimen and have also been implicated in a lipodystrophy syndrome. We report a rare case of an HIV-infected patient on HAART who presented with a large ascending aortic aneurysm associated with symptomatic severe aortic regurgitation. A noteworthy finding on pathological analysis of the aorta was an etiology of accelerated atherosclerosis rather than the more expected vasculitis.

Effects of ischemia on epicardial deformation in the passive rabbit heart.

BACKGROUND: Surgically induced ischemia in the arrested heart can result in changes in the mechanical properties of the myocardium. Regions of ischemia may be characterized based on the amount of epicardial deformation for a given load. Computer aided speckle interferometry (CASI), which tracks the movement of clusters of particles, is developed as a technique for measuring epicardial deformation, thereby determining the perfusion status of the passive heart. MATERIALS AND METHODS: Silicone carbide particles and retroreflective beads were dispersed randomly onto the epicardial surface of 11 isolated rabbit hearts to form speckle images. The hearts were arrested with hyperkalemic Krebs-Henseleit buffered solution. Each heart was then exposed to a series of intracavitary pressures, and at each pressure speckle images were acquired with a charge-coupled device (CCD) camera. Nine hearts were exposed to global ischemia, and two hearts were exposed to regional ischemia by occluding the second diagonal branch of the left anterior descending artery (LAD). The hearts were again loaded and the speckle images were acquired. CASI was used to determine the distribution of deformation field. RESULTS: CASI was able to determine displacements with a spatial resolution of about 50 microns. Global ischemia resulted in a significant increase in the maximum principle strain and the first invariant of the 2-D strain tensor. In the regionally ischemic heart, a large difference in deformation between the ischemic and perfused regions was clearly observed. CONCLUSION: Based on epicardial deformation, CASI is able to distinguish between perfused and ischemic myocardium, with a spatial resolution of 50 microns.

Damage to pulmonary artery catheter during transmyocardial laser revascularization.

UNLABELLED: This case report describes damage to a pulmonary artery catheter (PAC) during transmyocardial laser revascularization. We observed persistent bleeding and a temperature reading of "too high" from the temperature connection port of PAC during cardiopulmonary bypass while the patient's nasopharyngeal temperature read 34 degrees C. This alerted us to the possibility of PAC damage during creation of laser channels in the right coronary artery territory on the inferior surface of the heart. This is a unique complication related to this coronary revascularization procedure. IMPLICATIONS: We report an unusual case of pulmonary artery catheter (PAC) damage during transmyocardial laser revascularization (TMLR). This observation should alert the anesthesiologist to the fact that the PAC may be damaged when TMLR is performed on the right side of the heart. We recommend that the PAC be withdrawn during this procedure.

Both metabolic inhibition and mitochondrial K(ATP) channel opening are myoprotective and initiate a compensatory sarcolemmal outward membrane current.

BACKGROUND: Blockade of oxidative phosphorylation may activate ATP sensitive mitochondrial potassium (mitoK(ATP)) channels. We examined whether both metabolic inhibition and mitoK(ATP) channel openers protect both the whole organ and isolated cells from ischemia. METHODS AND RESULTS: Using a Langendorff preparation, one group of isolated rabbit hearts were exposed to ischemic preconditioning (IPC) via 2 episodes of flow interruption. The second group of hearts was preconditioned with 2 episodes of either the metabolic inhibitor, sodium cyanide (NaCN), or the mitoK(ATP) channel opener, diazoxide. The third group of hearts was exposed to the mitoK(ATP) channel inhibitor, 5-hydroxydecanoic acid (5-HD) prior to preconditioning with NaCN, diazoxide or IPC. Controls had no drug infused. Then, ischemia was induced in all hearts by left anterior descending coronary artery occlusion and infarct size was determined. Compared with controls (40+/-3%), infarct size was significantly reduced in hearts preconditioned with NaCN, diazoxide or IPC (18+/-3%, 26+/-3%, 21+/-2%, respectively; P<0.05 versus control). These reductions were reversed by 5-HD (36+/-3%, 33+/-2%, 37+/-2%; NaCN, diazoxide, IPC, respectively). Secondly, whole cell patch clamped isolated guinea pig ventricular myocytes were preconditioned with 2 episodes of either NaCN or diazoxide followed by Tyrodes perfusion with membrane potential set to -70 mV. Control cells were exposed to Tyrodes solution. All cells were then clamped to -20 mV and exposed to NaCN, which caused induction of an outward potassium current. Compared with controls, the average time to induction of the outward current was significantly reduced in cells preconditioned with either brief application of NaCN (11.6+/-1.8 versus 5.1+/-1.0 minutes, control versus NaCN, P<0.05) or diazoxide (5.5+/-1.4 versus 2.0+/-0.8 minutes, control versus diazoxide, P<0.05). CONCLUSIONS: Preconditioning protects the heart through mitoK(ATP). This protection also alters a surface membrane current, which may be important in myocardial protection.

Myocardial recovery from ischemia is impaired in CD36-null mice and restored by myocyte CD36 expression or medium-chain fatty acids.

Long-chain fatty acid uptake, which provides a large part of myocardial energy, is impaired in human and murine hearts deficient in the membrane fatty acid translocase, FAT/CD36. We examined myocardial function in CD36-null mice using the working heart. Fatty acid oxidation and stores of glycogen, triglycerides, and ATP were reduced in CD36-deficient hearts and were restored to WT levels by rescue of myocyte CD36. Under normal perfusion conditions, CD36-null hearts had similar cardiac outputs and end-diastolic pressures as WT or transgenic hearts. After 6 min of ischemia, cardiac output decreased by 41% and end diastolic pressure tripled for CD36-null hearts, with no significant changes in WT or transgenic hearts. Null hearts also failed more frequently after ischemia as compared with WT or transgenics. To dissect out contribution of fatty acid uptake, a perfusate-lacking fatty acids was used. This decreased cardiac output after ischemia by 30% in WT hearts as compared with 50% for CD36-deficient hearts. End diastolic pressure, a negative index of myocardial performance, increased after ischemia in all heart types. Addition to the perfusate of a medium-chain fatty acid (caprylic acid) that does not require CD36 for uptake alleviated poor ischemic tolerance of CD36-null hearts. In summary, recovery from ischemia is compromised in CD36-deficient hearts and can be restored by CD36 rescue or by supplying medium-chain fatty acids. It would be important to determine whether the findings apply to the human situation where polymorphisms of the CD36 gene are relatively common.

Modeling stroke risk after coronary artery bypass and combined coronary artery bypass and carotid endarterectomy.

BACKGROUND AND PURPOSE: The goals of this study were to compare the ability of statewide and institutional models of stroke risk after coronary artery bypass (CAB) to predict institution-specific results and to examine the potential additive stroke risk of combined CAB and carotid endarterectomy (CEA) with these predictive models. METHODS: An institution-specific model of stroke risk after CAB was developed from 1975 consecutive patients who underwent nonemergent CAB from 1994 to 1999 in whom severe carotid stenosis was excluded by preoperative duplex screening. Variables recorded in the New York State Cardiac Surgery Program database were analyzed. This model (model I) was compared with a published model (model II) derived from analysis of the same variables using New York statewide data from 1995. Predicted and observed stroke risks were compared. These formulas were applied to 154 consecutive combined CAB/CEA patients operated on between 1994 and 1999 to determine the predicted stroke risk from CAB alone and thereby deduce the maximal added risk imputed to CEA. RESULTS: Risk factors common to both models included age, peripheral vascular disease, cardiopulmonary bypass time, and calcified aorta. Additional risk factors in model I also included left ventricular hypertrophy and hypertension. Risk factors exclusive to model II included diabetes, renal failure, smoking, and prior cerebrovascular disease. Our observed stroke rate for isolated CAB was 1.7% compared with a rate predicted with model II (statewide data) of 1.56%. The observed stroke rate for combined CEA/CAB was 3.9%. When the Stony Brook model (model I) based on patients without carotid stenosis was used, the predicted stroke rate was 2.8%. When the statewide model (model II), which included some patients with extracranial vascular disease, was used, the predicted stroke rate was 3.4%. The differences between observed and predicted stroke rates were not statistically significant. CONCLUSIONS: Estimation of stroke risk after CAB was similar whether statewide data or institution-specific data were used. The statewide model was applicable to institution-specific data collected over several years. Common risk factors included age, aortic calcification, and peripheral vascular disease. The observed differences in the predicted stroke rates between models I and II may be due to the fact that carotid stenosis was specifically excluded by duplex ultrasound from the patient population used to develop model I. Modeling stroke risk after CAB is possible. When these models were applied to patients undergoing combined CAB/CEA, no additional stroke risk could be ascribed to the addition of CEA. Such models may be used to identify groups at increased risk for stroke after both CAB and combined CAB/CEA. The ultimate place for CEA in patients undergoing CAB will be defined by prospective randomized trials.

Gap junction uncoupling protects the heart against ischemia.

BACKGROUND: Many stimuli can successfully protect the heart against ischemia. We investigated whether gap junction uncoupling before ischemia was myoprotective. We also studied the function of the adenosine triphosphate-dependent potassium channel, which has been implicated in the mechanism of pharmacologic preconditioning, with respect to gap junction physiology. METHODS: Twenty-eight rabbit hearts were placed on a Langendorff perfusion apparatus. Five were given a 5-minute infusion of 1 mmol/L heptanol (a gap junction uncoupler), 5 were given 10 micromol/L 2,3-butanedione monoxime (an electromechanical uncoupler), and 6 were given no drug. The left anterior descending coronary artery was then occluded for 1 hour and reperfused for 2 hours. Six hearts received 10 micromol/L glybenclamide before heptanol to evaluate the role of the adenosine triphosphate-dependent potassium channel. Six hearts underwent ischemic preconditioning with 2 cycles of 5 minutes of global ischemia and reperfusion. Action-potential duration of the ischemic zone, left ventricular developed pressure, and coronary flow were measured continuously. Infarct size was determined at the end of reperfusion. RESULTS: Heptanol significantly reduced infarct size (from 46% +/- 2% to 22% +/- 5%, P <.01), an effect that was not prevented by glybenclamide. Butanedione monoxime decreased developed pressure but did not significantly reduce infarct size (46% +/- 5% vs 46% +/- 2%, P = not significant). There were no differences among groups with regard to developed pressure or action-potential duration. CONCLUSION: Directly blocking gap junctions preconditions the heart. This protection is not a direct result of a decrease in developed pressure before a prolonged ischemic period nor is it achieved through a mechanism involving the adenosine triphosphate-dependent potassium channel.

Isoform-specific stimulation of cardiac Na/K pumps by nanomolar concentrations of glycosides.

It is well-known that micromolar to millimolar concentrations of cardiac glycosides inhibit Na/K pump activity, however, some early reports suggested nanomolar concentrations of these glycosides stimulate activity. These early reports were based on indirect measurements in multicellular preparations, hence, there was some uncertainty whether ion accumulation/depletion rather than pump stimulation caused the observations. Here, we utilize the whole-cell patch-clamp technique on isolated cardiac myocytes to directly measure Na/K pump current (I(P)) in conditions that minimize the possibility of ion accumulation/depletion causing the observed effects. In guinea pig ventricular myocytes, nanomolar concentrations of dihydro-ouabain (DHO) caused an outward current that appeared to be due to stimulation of I(P) because of the following: (1) it was absent in 0 mM [K(+)](o), as was I(P); (2) it was absent in 0 mM [Na(+)](i), as was I(P); (3) at reduced [Na(+)](i), the outward current was reduced in proportion to the reduction in I(P); (4) it was eliminated by intracellular vanadate, as was I(P). Our previous work suggested guinea pig ventricular myocytes coexpress the alpha(1)- and alpha(2)-isoforms of the Na/K pumps. The stimulation of I(P) appears to be through stimulation of the high glycoside affinity alpha(2)-isoform and not the alpha(1)-isoform because of the following: (1) regulatory signals that specifically increased activity of the alpha(2)-isoform increased the amplitude of the stimulation; (2) regulatory signals that specifically altered the activity of the alpha(1)-isoform did not affect the stimulation; (3) changes in [K(+)](o) that affected activity of the alpha(1)-isoform, but not the alpha(2)-isoform, did not affect the stimulation; (4) myocytes from one group of guinea pigs expressed the alpha(1)-isoform but not the alpha(2)-isoform, and these myocytes did not show the stimulation. At 10 nM DHO, total I(P) increased by 35 +/- 10% (mean +/- SD, n = 18). If one accepts the hypothesis that this increase is due to stimulation of just the alpha(2)-isoform, then activity of the alpha(2)-isoform increased by 107 +/- 30%. In the guinea pig myocytes, nanomolar ouabain as well as DHO stimulated the alpha(2)-isoform, but both the stimulatory and inhibitory concentrations of ouabain were approximately 10-fold lower than those for DHO. Stimulation of I(P) by nanomolar DHO was observed in canine atrial and ventricular myocytes, which express the alpha(1)- and alpha(3)-isoforms of the Na/K pumps, suggesting the other high glycoside affinity isoform (the alpha(3)-isoform) also was stimulated by nanomolar concentrations of DHO. Human atrial and ventricular myocytes express all three isoforms, but isoform affinity for glycosides is too similar to separate their activity. Nevertheless, nanomolar DHO caused a stimulation of I(P) that was very similar to that seen in other species. Thus, in all species studied, nanomolar DHO caused stimulation of I(P), and where the contributions of the high glycoside affinity alpha(2)- and alpha(3)-isoforms could be separated from that of the alpha(1)-isoform, it was only the high glycoside affinity isoform that was stimulated. These observations support early reports that nanomolar concentrations of glycosides stimulate Na/K pump activity, and suggest a novel mechanism of isoform-specific regulation of I(P) in heart by nanomolar concentrations of endogenous ouabain-like molecules.

Combined coronary artery bypass and carotid endarterectomy: long-term results.

PURPOSE: We determined late survival, freedom from late stroke, and freedom from late cardiac events in patients treated by combined coronary artery bypass and carotid endarterectomy (CAB/CEA). METHODS: All patients who underwent CAB/CEA in our institution between January 1994 and December 1999 were identified. Follow-up data were obtained from office records and telephone interviews. Endpoints included death from any cause, stroke, and non-fatal cardiac events (MI, CHF, percutaneous transluminal angioplasty with stenting, redo CAB). Data were expressed in life table format. RESULTS: Over a 6-yr period 154 patients had combined CAB/CEA with a 3.9% postoperative stroke rate. Six patients (3.9%) died, leaving 148 patients for follow-up. Average follow-up was 38 +/- 23 months (range: 1-82 months). During the follow-up period two patients (1.4%) had late strokes and 17 patients (11%) had late non-fatal cardiac events. The late mortality rate was 13% (19 patients). Of the late mortalities, four were related to cardiac disease and one to stroke. Using Kaplan-Meier analysis, the 5-yr survival probability was 80 +/- 4.3%. The freedom from late ipsilateral neurologic events was 98 +/- 1.3% at 5 yr. The freedom from late cardiac events was 82 +/- 4.6% at 5 yr. CONCLUSIONS: The large majority of patients with combined coronary and carotid artery disease can be expected to live for greater than 5 yr. Therefore, these patients should be considered candidates for prophylactic CEA for stroke prevention, even when their carotid lesions are asymptomatic. Successful CAB/CEA provides good long-term survival and freedom from late cardiac events, as well as excellent freedom from late stroke. Further reduction in perioperative events will make this operative approach even more attractive in patients with combined disease.