Cardiovascular mechanisms and consequences of obstructive sleep apnoea.

Obstructive sleep apnoea (OSA) is considered as a risk factor for the development of arterial hypertension, coronary artery disease (CAD), myocardial infarction and stroke. These clinical manifestations are the consequences of elevated sympathetic activity, cardiovascular variability, intrathoracic pressure changes, inflammation, oxidative stress, endothelial dysfunction, insulin resistance and thrombosis provoked by OSA. As a result, OSA is often present in patients with cardiovascular disease (CVD) and the increased prevalence of CVD in OSA population raises both cardiovascular morbidity and mortality and the demand of healthcare resources. Observational cohort studies indicate that untreated patients with OSA have an increased risk of fatal and non-fatal cardiovascular events, an increased risk of sudden cardiac death during the sleeping hours and a higher risk of stroke or death from any cause. Continuous positive airway pressure (CPAP) and oral appliance therapy are the two treatments for OSA whose effects on cardiovascular endpoints have been assessed in randomised trials. There is increasing evidence that adequate CPAP therapy leads to a significant reduction in cardiovascular morbidity.

Myofibrillar Ca2+-stimulated Mg2+-ATPase from chronically ischemic canine heart.

Functional properties of myofibrils from chronically ischemic canine myocardium were evaluated. Ischemia was produced by tight stenosis of left anterior descending artery (LAD), followed by 40 min acute ischemia with prior preconditioning. Animals of the first group were sacrificed after 8 weeks. In the second group, angioplasty of LAD was performed after 8 weeks of ischemia and animals were kept alive for other 4 weeks. Control animals were sham operated. Activity and kinetic parameters of myofibrillar Ca2+-stimulated Mg2+-ATPase were measured in myofibrils isolated from anterior and posterior parts of all hearts. We did not find any differences in maximal velocity (Vmax), half-maximal activation constant for calcium (K(Ca2+)50) and cooperativity coefficient (n(hill)) of myofibrils from different experimental groups as compared to controls, either at pH 7, pH 6.5 (acidosis) or pH 7.5 (alkalosis). K(Ca2+)50 increased in medium simulated acidosis (12.6-33.5 times) and n(hill) decreased significantly in all groups as compared with values obtained at pH 7. These results indicate that activity and Ca2+-sensitivity of myofibrillar Mg2+-ATPase remain unchanged despite deteriorated heart function 8 weeks after LAD obstruction. Experiments have confirmed that Ca2+-stimulated-ATPase from canine heart myofibrils responded to pH decrease by a decreased sensitivity to Ca2+ and a decreased cooperativity. However, sensitivity of the enzyme to the pH changes is unaltered by 8 weeks of chronic ischemia.

Repeated stunning precedes myocardial hibernation in progressive multiple coronary artery obstruction.

OBJECTIVE: The aim of this study was to characterize a regional myocardial flow-function relationship in collateral dependent myocardium produced by multiple coronary artery obstruction. METHODS: Ameroid constrictors were placed around the proximal right (RC) and circumflex (CX) coronary arteries and a silicon tubing cuff around the proximal LAD (left anterior descending artery) (luminal stenosis +/- 77%) in 18 dogs. Weekly two-dimensional echocardiography was performed for regional function (anterior [A], inferoposterior [IP], wall thickening [WT]), and fractional shortening (FS). Colored microspheres injected at baseline and before sacrifice, before and after dipyridamole (0.5 mg/kg) injection, determined resting flow (RF) and coronary reserve (CR), respectively. RESULTS: Coronary angiography performed at four weeks after surgery confirmed occlusion of RC and CX with collateralization and a tight stenosis of LAD. Initially, an episodic reduction in A and IP WT was observed which became persistent later (AWT: 16 +/- 3%; IPWT: 16 +/- 4%, FS: 20 +/- 4%, p < 0.005 vs. baseline [BS]). With dobutamine a biphasic response (improvement in A and IP WT between 5-15 and dysfunction between 20-30 microg/kg/min) was observed. Seven dogs were sacrificed at eight weeks and showed normal RF but reduced transmural CR (A: 75 +/- 18%; IP: 46 +/- 22% of control). Seven dogs underwent PTCA of the LAD at eight weeks and showed gradual improvement in AWT with normalization at 12 weeks (AWT: 30 +/- 5%, p < 0.001 vs. eight weeks). At sacrifice RF and CR in the A wall were normal but there was reduced subendocardial RF in the IP region (64% of BS). Further, biopsy samples showed normal histological findings and high energy phosphate content in all dogs. Radioligand binding assays using 125I-iodocyanopindolol showed downregulation of beta-adrenergic receptor density in the dysfunctional regions compared with control. CONCLUSIONS: In this canine model of viable, collateral dependent and reversibly dysfunctional myocardium, there was early episodic dysfunction followed by persistent dysfunction which was initially associated with normal RF and later with subendocardial hypoperfusion.

Protein kinase C expression and subcellular distribution in chronic myocardial ischemia. Comparison of two different canine models.

We studied protein kinase C (PKC) isozyme expression and activity distribution in two models of chronically ischemic canine myocardium: (1) single vessel obstruction (SVO), produced by tight stenosis of LAD followed by preconditioning and acute ischemia (40 min); (2) three vessel obstruction (3VO), produced by LAD-stenosis and gradual occlusion of right coronary artery and left circumflex. In both models after 8 weeks of chronic ischemia the dogs were either sacrificed or had PTCA of the LAD with a follow up of another 4 weeks. Control dogs were sham operated. PKC activity was measured in subcellular fractions of tissue samples from anterior and posterior regions in the presence of histone and gamma-[32P]-ATP. PKC isozymes were detected by Western blotting. All regions perfused by the obstructed coronaries were dysfunctional at 8 weeks when compared to baseline, with improvement of anterior wall function after PTCA of LAD. PKC activity was elevated in the membrane fraction of SVO, but unchanged in the 3VO model. PKCs alpha, epsilon, and zeta prevailed in cytosol fraction of the controls (cytosol/membrane ratios were +/- 3.34, 1.38 and 4.56 for alpha, epsilon and zeta, respectively), consistent with PKC activity distribution, while delta was not detected. There was no significant difference between the groups concerning the relative membrane amount of the isozymes. PKCs alpha and epsilon were decreased in the cytosol fraction of both models at 8 weeks (for anterior region, by 56 and 57% in SVO and by 49 and 46% in 3VO, respectively) without there being any differences between anterior and posterior regions, and were low also in the PTCA group. PKC zeta distribution however varied between the two models. The amount of PKC zeta isozyme was downregulated by 45% after 8 weeks of chronic ischemia and returned towards the control values after PTCA in the anterior region of SVO, while it did not change in anterior wall after 8 weeks in 3VO but was significantly decreased (by 47%) in posterior region after PTCA. In conclusion, our results suggest modified PKC signalling in chronically ischemic canine myocardium.

Shoshin syndrome: two case reports representing opposite ends of the same disease spectrum.

Thiamine deficiency can have cardiovascular and neurological manifestations. Cardiac beriberi is classically thought to represent a high-output state with oliguria and lactic acidosis. The condition can, however, also present itself with a low cardiac output and fulminant vascular collapse, or as an acute fatal form, causing sudden death, without clear-cut signs of cardiomegaly. In the western society beriberi is mainly encountered in alcoholics. We report on two cases, one with high-output failure and the other with low-output failure and cardiovascular collapse. In both patients the diagnosis of shoshin syndrome was made, and and both showed a spectacular improvement of congestive heart failure symptoms after treatment with thiamine. A therapeutic trial with thiamine is the only way to rapid diagnosis.

Calcium uptake by the sarcoplasmic reticulum, high energy content and histological changes in ischemic cardiomyopathy.

OBJECTIVES: Sarcoplasmic reticulum (SR) Ca2+ uptake, myocardial high energy content and histology were examined in different zones of hearts from patients with ischemic cardiomyopathy. METHODS AND RESULTS: Unfractionated homogenates were prepared from left ventricular samples obtained in three zones of each heart: an infarct-remote zone, an outer peri-infarct zone, and an inner peri-infarct zone. Oxalate-supported 45Ca2+ uptake was measured at 37 degrees C using a filtration method. Maximum rate (Vmax) of uptake in absence or in presence of ryanodine was lower in inner peri-infarct (7.4 +/- 0.7 and 9.5 +/- 0.8 nmol min-1 mg-1 of protein, respectively; mean +/- SEM) and outer peri-infarct tissues (8.8 +/- 0.8 and 12.0 +/- 0.8 nmol min-1 mg-1) than in infarct-remote myocardium (12.7 +/- 2.1 and 15.8 +/- 2.2 nmol min-1 mg-1). The apparent affinity constants for Ca2+ (KCa) as well as the Hill coefficients were not different. Homogenate DNA (1.6 +/- 0.1, 1.6 +/- 0.1 and 1.7 +/- 0.1 mg/g of remote, inner peri-infarct and outer peri-infarct myocardium, respectively) and adenine nucleotides contents (ATP: 15 +/- 1.3, 14 +/- 0.8 and 15 +/- 1.0 mumol/g dry weight, respectively) were similar in all tissues. Fibrosis was increased in inner peri-infarct tissue (37 +/- 6%; vs. 13 +/- 2% and 12 +/- 2% in both remote and outer peri-infarct tissues, respectively), but the number of abnormal cells was not significantly different. CONCLUSION: The decrease of Ca2+ uptake in ischemic cardiomyopathy is not homogeneous in the ventricular wall, and reflects a decreased number/activity of SR Ca(2+)-ATPase, without altered Ca(2+)-affinity or increased Ca2+ leakage through ryanodine receptors.

LDL hypercholesterolemia is associated with accumulation of oxidized LDL, atherosclerotic plaque growth, and compensatory vessel enlargement in coronary arteries of miniature pigs.

The association between accumulation of oxidized low density lipoprotein (LDL) and (1) progression of atherosclerotic plaques and (2) compensatory enlargement was assessed in the coronary arteries of LDL-hypercholesterolemic miniature pigs. In miniature pigs fed a 4% cholesterol diet, LDL cholesterol levels increased from 27+/-3.5 mg/dL (mean+/-SEM, n=36) to 250+/-28 mg/dL (n=10), 260+/-15 mg/dL (n=6), and 260+/-17 mg/dL (n=10) at 6, 14, and 24 weeks, respectively. Mean intimal areas of lesions in the left anterior descending coronary artery of hypercholesterolemic pigs were 0.16+/-0.046 mm2 at 6 weeks (n=10) and increased 5.4-fold (n=6, P<.05) and 10.6-fold (n=10, P<.001) at 14 and 24 weeks, respectively. Plaque growth was associated with an increase in mean internal elastic lamina area, from 1.44+/-0.17 to 4.38+/-0.52 mm2 (P=.007) and in mean luminal area from 1.42+/-0.15 mm2 in control pigs to 4.38+/-0.52 mm2 in pigs fed a cholesterol diet for 24 weeks (P=.007 vs control). Levels of total LDL in the intima, measured immunocytochemically, were 0.031+/-0.0098, 0.11+/-0.057 (P< or =.05), and 0.43+/-0.082 U (P<.001) at 6, 14, and 24 weeks, respectively. Corresponding levels of oxidized LDL were 0.034+/-0.023, 0.11+/-0.050 (P<.05), and 0.44+/-0.065 U (P<.001), respectively, suggesting that virtually all LDL in the intima is oxidized. Levels of oxidized LDL in the lesions were correlated with the intimal areas (r=.85, P<.0001) but were independent of plasma levels of LDL cholesterol and of oxidized LDL. Plaque levels of oxidized LDL were also correlated with internal elastic lamina areas (r=.72, P<.0001) and with luminal areas (r=.50, P=.0098). Plaque growth in the coronary arteries of LDL-hypercholesterolemic miniature pigs is associated with (1) an increase in plaque levels of oxidized LDL at constant plasma levels of LDL cholesterol and of oxidized LDL and (2) compensatory vessel enlargement proportional to plaque levels of oxidized LDL.

PET scan predicts recovery of left ventricular function after coronary artery bypass operation.

BACKGROUND: Viable but hypocontractile myocardium can show functional improvement after revascularization (hibernation). It is sometimes difficult, however, to predict viability and recovery in patients with severe left ventricular function. This study sought to identify possible predictive factors of recovery of cardiac function after revascularization in patients with three-vessel disease. METHODS: Positron emission tomography (fluoro-18-deoxyglucose uptake for metabolism; nitrogen 13-labeled ammonia for flow) and equilibrium-gated nuclear angiography (for the global ejection fraction) were performed in 59 patients with three-vessel disease before and after undergoing coronary artery bypass grafting. The positron emission tomographic data were expressed as match normal (flow and metabolism normal), mismatch (low flow, high metabolism), match viable (moderate decrease in flow and metabolism), and match necrosis (low flow and metabolism). RESULTS: Stepwise logistic regression analysis showed that only mismatch regions played a significant role in predicting postoperative improvement in function (p = 0.019). There were 1.7 +/- 1.5 mismatch regions in 31 patients who showed an improvement in their ejection fraction (0.47 +/- 0.14 versus 0.58 +/- 0.11; mean +/- standard deviation) versus 0.8 +/- 1.0 mismatch regions (p = 0.017) in patients who did not show recovery. There was more pronounced functional improvement with increasing numbers of mismatch regions, and patients with at least one mismatch region had a high likelihood of recovery (p < 0.001). In patients with a very low preoperative ejection fraction and two or more mismatch regions, there was early significant recovery (0.27 +/- 0.08 versus 0.46 +/- 0.06; p = 0.009). CONCLUSIONS: At least one mismatch region must be present for there to be a postoperative functional benefit. When a low left ventricular ejection fraction is associated with mismatch, early recovery is substantial.

Only hibernating myocardium invariably shows early recovery after coronary revascularization.

BACKGROUND: The aims of this study were to identify hibernating myocardium (hypocontractile, hypoperfused viable myocardium that regains contractility after revascularization) in the clinical setting and to predict functional outcome in patients with coronary artery disease after coronary revascularization. METHODS AND RESULTS: Preoperative data related to the anterior free wall of the left ventricle were collected in 50 coronary bypass surgery candidates (positron emission tomography [PET], [13N]NH3 for flow, and [18F]FDG for metabolism [MET]; equilibrium-gated nuclear angiography [EGNA] for regional ejection fraction [REF]; and histological data from myocardial biopsies for percentage fibrosis and viable myocytes). Three months after surgery, the patients had follow-up PET and EGNA investigations. A principal-components analysis identified four patient clusters. Cluster 1 (n = 9) had normal viable myocardium. Cluster 2 (n = 18) had viable hypocontractile myocardium (REF, 39 +/- 12%) showing a PET mismatch pattern. Cluster 3 (n = 16) had viable hypocontractile myocardium associated with morphological myocyte injury showing a matched moderate decrease in flow (66 +/- 11%) and MET (70 +/- 11%). Cluster 4 (n = 7) had hypocontractile myocardium with mainly scar tissue (fibrosis, 74 +/- 12%). After surgery, only cluster 2, with hibernating myocardium, showed significant improvement in REF (from 39 +/- 12% to 50 +/- 13%, P < .05). Cluster 3, with sites of morphological myocyte injury, showed no recovery. The stepwise logistic regression showed a combination of low preoperative REF and high MET to be the best predictor of functional recovery (P < .008). CONCLUSIONS: Multivariate analysis identifies hibernating myocardium showing early postrevascularization recovery, as opposed to viable but myolytic myocardium with no early recovery. Postrevascularization recovery can be predicted (combination of low REF and high MET) by noninvasive techniques.

Molecular changes of titin in left ventricular dysfunction as a result of chronic hibernation.

Cardiomyocytes of chronic hibernating myocardium are affected by partial to complete loss of sarcomeres, accumulation of glycogen, adaptations in size and shape of mitochondria, reorganisation of nuclear chromatin and depletion of sarcoplasmic reticulum. The nature of these changes, which from a purely morphologic viewpoint are akin to dedifferentiation, needed further clarification at the molecular level. For this purpose we have studied the expression and reorganization of titin, one of the earliest markers of cardiomyocytes differentiation. By use of monoclonal antibodies, recognizing different epitopes distributed over the whole length of the titin molecule, we were able to detect changes in its molecular organization as a result of chronic hibernation. The epitopes of the titin molecule attached to the Z-disc and those present close to the M-line remained detectable at all stages of hibernation, while epitopes at the A-I junction and parts of the myosin anchoring region of the molecule became masked or were lost. A fragmented or punctuated appearance of the titin staining pattern with antibodies to A-I junction related epitopes is found in cells which we consider to represent a more advanced stage of dedifferentiation. Changes in the distribution of the titin molecule or its molecular environment in hibernating myocardium resemble at least in part changes occurring during muscle cell differentiation, although in reversed order.

Chronic ischemic viable myocardium in man: Aspects of dedifferentiation.

Histologic analysis of biopsies derived from patients with chronic dysfunctional but viable (hibernating) myocardium showed characteristic cell alterations. These changes consisted of a partial to complete loss of sarcomeres, accumulation of glycogen, and disorganization and loss of sarcoplasmic reticulum. Most of the adaptive changes that these affected cells undergo are suggestive of dedifferentiation. In the present study the expression and organizational pattern of contractile and cytoskeletal proteins such as titin, cardiotin, and α-smooth muscle actin were assessed in hibernating and normal myocardium because the expression and organization of these constituents have been related to certain stages of cardiomyocyte differentiation. In normal cells titin shows a cross-striated staining pattern, whereas cardiotin displays a fibrillar array, parallel to the sarcomeres. α-Smooth muscle actin is not expressed in adult cardiomyocytes. The expression of titin in a punctated pattern and the marked decrease to virtual absence of cardiotin in hibernating cardiomyocytes speak in favor of an embryonic phenotype of these cells. The re-expression of α-smooth muscle actin in hibernating cells strongly supports this hypothesis. The observations on three different structural proteins of heart muscle suggest that hibernating myocardium acquired aspects of muscle cell dedifferentiation.

Histological alterations in chronically hypoperfused myocardium. Correlation with PET findings.

BACKGROUND: In patients with chronic coronary artery disease (CAD) and left ventricular dysfunction, flow/metabolic studies of the myocardium with positron emission tomography (PET) are able to distinguish viable but dysfunctional myocardium from irreversible ischemic injury and scar tissue. In this study, PET findings of blood flow and metabolism in chronically hypoperfused myocardium were correlated with histology. METHODS AND RESULTS: We studied 33 patients suffering from CAD. In each patient, myocardial blood flow and metabolism were measured with PET 1 or 2 days before revascularization. During surgery, transmural biopsies were taken from the left ventricular anterior wall and planimetrically scored for the degree of myolysis (sarcomere loss). The amount of connective tissue was calculated using morphometric techniques. Contrast ventriculography demonstrated abnormal wall motion in 23 patients. Fourteen patients with a mismatch pattern (decreased flow with preserved metabolism) in the biopsy region after quantitative analysis of the PET data showed 11 +/- 6 vol% fibrosis and 25 +/- 13% cells with sarcomere loss. The space formerly occupied by sarcomeres was mainly replaced by glycogen and mitochondria. A significant wall motion improvement was noted 3 months after surgery. Nine patients showed a match pattern (concordant flow/metabolism defects). The biopsies revealed 35 +/- 25% fibrosis and 24 +/- 15% glycogen-storing cells. The biopsies of the 10 patients with normal anterior wall motion showed 8 +/- 4% fibrosis and 12 +/- 8% glycogen-accumulating cells. CONCLUSIONS: It can be concluded that areas with impaired wall motion and a PET match pattern show extensive fibrosis. Regions with reduced flow and preserved FDG metabolism, however, contain predominantly viable cells. In these regions, significant recovery of wall motion is found after revascularization. Regions with normal wall motion contain predominantly viable cells. Cells with reduced contractile material and increased glycogen content are mainly found in areas with wall motion impairment but are also present in areas with normal wall motion and a severe stenosis of the coronary vessel.

ALCAPA syndrome: an example of chronic myocardial hypoperfusion?

OBJECTIVES: The purpose of this study was to evaluate functional variables and morphologic correlates of chronically hypoperfused myocardium before and after revascularization. BACKGROUND: Neonates with congenital anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA syndrome) develop some myocardial necrosis shortly after birth. The survivors of this event are left with a localized infarction and an almost entirely collateral circulation-dependent perfusion of the left ventricle that results in poor global left ventricular function. Survival beyond infancy is uncommon because of severe left heart failure. Revascularization, however, brings about functional recovery with good clinical outcome. The ALCAPA syndrome is thus characterized by chronic collateral circulation-dependent low perfusion, low contraction matching and potential revivability. METHODS: Five patients with ALCAPA syndrome are presented, with preoperative and postoperative clinical findings and histologic data obtained from intraoperative transmural biopsy specimens. RESULTS: The angiographically assessed preoperative ejection fraction was 33 +/- 19% (mean +/- SD). Postoperative echocardiographic follow-up revealed normal left ventricular function in all patients. Histologic study of the biopsy specimens taken from the region perfused by the anomalous artery showed a variable degree of fibrosis (51 +/- 32%). The ultrastructure of the remaining myocytes revealed viable characteristics, but a substantial percent (46 +/- 26%) showed a markedly reduced fraction of contractile material. CONCLUSIONS: These ultrastructural studies suggest delayed subcellular adaptive responses in the chronically hypoperfused myocardium of patients with ALCAPA syndrome.

Catecholamine response to a gradual increase of intracranial pressure.

To determine the catecholamine response to progressive intracranial hypertension, intracranial pressure (ICP) was raised gradually by continuous expansion of an epidural balloon in seven dogs. Hemodynamic parameters, ICP, and cerebral perfusion pressure (CPP) were monitored continuously and serum catecholamine levels began to rise when CPP was in the low-positive range (20 to 30 mm Hg), reaching a peak just after brain death (CPP < or = o mm Hg). There was no correlation between ICP and the catecholamine peak. Compared to control values, the mean increase was 286-fold for epinephrine and 78-fold for norepinephrine. Temporally, the catecholamine peak corresponded well with the observed hemodynamic changes. These results suggest that ischemia in certain parts of the brain stem is responsible for the hemodynamic changes observed in intracranial hypertension (such as the Cushing response), and they show that catecholamines play an important role in these hemodynamic changes.

Variable effects of explosive or gradual increase of intracranial pressure on myocardial structure and function.

BACKGROUND: Studies done in potential donors for heart transplantation and in experimental animals have suggested that brain death can have major histopathological and functional effects on the myocardium. METHODS AND RESULTS: We developed experimental models of brain death using dogs to study the hemodynamic and catecholamine changes, the extent of myocardial structural damage, and the recovery potential of donor hearts obtained from brain-dead donors. Brain death was caused by increasing the intracranial pressure (ICP) suddenly or gradually by injecting saline in an epidural Foley catheter. In a first series of experiments, dogs given a sudden rise in ICP (n = 5) showed a hyperdynamic response and a 1,000-fold increase in the level of epinephrine after brain death. Histology revealed 93 +/- 2% of the myocardium to be severely ischemic. Dogs given a gradual rise in ICP (n = 6) showed a lesser hyperdynamic response, almost 200-fold increase in the level of epinephrine after brain death, and mild ischemic damage to the myocardium (23 +/- 1%). In a second series, hearts obtained from brain-dead and non-brain-dead donors were transplanted in recipients, and the weaning and recovery potential were studied. All four recipients with hearts from non-brain-dead donors were weaned with good functional recovery. Also, all four recipients with hearts from brain-dead dogs given a gradual rise in ICP were weaned with only moderate functional recovery. However, only two of four recipients with hearts from donors given a sudden rise in ICP were weaned and showed poor functional recovery. CONCLUSIONS: Our results indicate that a sudden rise in ICP can cause irreversible myocardial damage.