Diagnostic efficiency of troponin T measurements in acute myocardial infarction

BACKGROUND

The present study was designed to evaluate the efficiency of a newly developed troponin T enzyme immunoassay for the detection of acute myocardial infarction.

METHODS AND RESULTS

The study comprised 388 patients admitted with chest pain and suspected myocardial infarction and 101 patients with skeletal muscle damage and additional suspected myocardial cell damage. Troponin T was elevated to more than twice the analytical sensitivity of the assay (0.5 microgram/l) in all patients with non-Q wave (range, 1.2-5 micrograms/l) and Q wave infarction (range, 3-220 micrograms/l). Troponin T appeared in serum as early as 3 hours after onset of pain in 50% of the patients and remained elevated in all patients for more than 130 hours, revealing release kinetics of both free cytosolic and structurally bound molecules. The diagnostic efficiency of troponin T was superior to that of creatine kinase-MB (98% versus 97%) and remained at 98% until 5.5 days after admission, if patients with unstable angina were excluded from analysis. In the 79 patients with unstable angina, troponin T was elevated (range, 0.55-3.1 micrograms/l) in at least one blood sample from each of 37 patients (56%). Circulating troponin T was correlated to the presence of reversible ST segment or T wave changes on the electrocardiogram (p less than 0.005) and to the frequency of in-hospital complications. In the 101 patients with skeletal muscle damage and suspected additional cardiac muscle damage, troponin T was the most useful test; its efficiency was 89% or 94% (depending on the discriminator value used) as compared with 63% for creatine kinase-MB.

CONCLUSIONS

Thus, the data of the study indicate that the newly developed troponin T test improves the efficiency of serodiagnostic tools for the detection of myocardial cell necrosis as compared with conventionally used cardiac enzymes.

Intracellular compartmentation of cardiac troponin T and its release kinetics in patients with reperfused and nonreperfused myocardial infarction

In a previous study on the diagnostic efficiency of troponin T measurements in patients with suspected acute myocardial infarction (AMI), the authors found a high variability of troponin T serum concentration changes on day 1 in patients with AMI who underwent thrombolytic treatment. Therefore, the aims of the present study were to investigate the intracellular compartmentation of troponin T and to analyze the effects of AMI reperfusion on the appearance kinetics of cardiac troponin T in serum. Cardiac troponin T was measured with a newly developed bideterminant sandwich assay using cardiospecific, affinity-purified polyclonal antibodies and peroxidase-labeled monoclonal antibody. An unbound cytosolic troponin T pool was found in ultracentrifuged homogenates of myocardial tissue of different species ranging from 0.013 to 0.036 mg/g wet weight. The soluble troponin T molecule had electrophoretic properties identical to troponin T compartmented in the myofibrils. The clinical study group comprised 57 patients with AMI undergoing thrombolytic treatment. Blood flow to the infarct zone and point of time of reperfusion were tested by immediate and late angiography. The appearance of troponin T in serum on day 1 after the onset of AMI depended strongly on reperfusion and on duration of ischemia before reperfusion. Thus, in patients with early reperfused AMI, a marked peak in troponin T serum concentrations was found at 14 hours after the onset of pain. This early troponin T peak was absent in patients with AMI reperfusion occurring greater than 5.5 hours after the onset of pain and in patients with nonreperfused AMI. By contrast, the kinetics of troponin T release after the first day after AMI were unaffected by reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Noninvasive measurement of regional cerebral blood flow by near-infrared spectroscopy and indocyanine green

Clinicians lack a practical method for measuring CBF rapidly, repeatedly, and noninvasively at the bedside. A new noninvasive technique for estimation of cerebral hemodynamics by use of near-infrared spectroscopy (NIRS) and an intravenously infused tracer dye is proposed. Kinetics of the infrared tracer indocyanine green were monitored on the intact skull in pigs. According to an algorithm derived from fluorescein flowmetry, a relative blood flow index (BFI) was calculated. Data obtained were compared with cerebral and galeal blood flow values assessed by radioactive microspheres under baseline conditions and during hemorrhagic shock and resuscitation. Blood flow index correlated significantly (rs = 0.814, P < 0.001) with cortical blood flow but not with galeal blood flow (rs = 0.258). However, limits of agreement between BFI and CBF are rather wide (+/- 38.2 +/- 6.4 mL 100 g-1 min-1) and require further studies. Data presented demonstrate that detection of tracer kinetics in the cerebrovasculature by NIRS may serve as valuable tool for the noninvasive estimation of regional CBF. Indocyanine green dilution curves monitored noninvasively on the intact skull by NIRS reflect dye passage through the cerebral, not extracerebral, circulation.

Non-invasive assessment of perioperative myocardial cell damage by circulating cardiac troponin T

Troponin T is a unique cardiac antigen which is continuously released from infarcting myocardium. Its cardiospecificity as a marker protein might be particularly useful in assessing myocardial cell damage in patients undergoing cardiac surgery. Therefore, circulating troponin T was measured in serial blood samples from 56 patients undergoing cardiac surgery and in two control groups--22 patients undergoing minor orthopaedic surgery and 12 patients undergoing lung surgery by median sternotomy. In both control groups no troponin T could be detected, whereas activities of creatine kinase were raised in all 12 lung surgery controls and activities of the MB isoenzyme were raised in five of the 12 patients in the lung surgery group and in four of the 22 patients in the orthopaedic surgery group, respectively. All the patients undergoing coronary artery bypass grafting (n = 47) and cardiac surgery for other reasons (n = 9) had detectable concentrations of troponin T. Five patients had perioperative myocardial infarction detected as new Q waves and R wave reductions. In these five patients troponin T release persisted and serum concentrations (5.5-23 micrograms/l) reached a peak on the fourth postoperative day. In the 51 patients without perioperative myocardial infarction serum concentrations and the release kinetics of troponin T depended on the duration of cardiac arrest. In patients in whom aortic cross clamping was short troponin T increased slightly on the first postoperative days; in patients with longer periods of aortic cross clamping troponin T concentrations were higher and remained so beyond the fifth postoperative day. In patients with non-specific changes on the electrocardiogram troponin T concentrations were significantly higher on days 1 and 4 after operation than in patients with normal postoperative electrocardiograms(11.2 (5) and 4.5 (2.6) v 8.2 (3.4) and 2.9 (1.6) 1microg/l). Serum concentrations of troponin T showed some myocardial cell damage in every patient undergoing cardiac surgery. The persistent increases that were more common in patients with longer periods of cardiac arrest must have been caused by damage to the contractile apparatus. These results suggest that perioperative myocardial cell necrosis may be more common than indicated by changes of the QRS complex on the electrocardiogram.

Pressure is proinflammatory in lung venular capillaries

Endothelial responses may contribute importantly to the pathology of high vascular pressure. In lung venular capillaries, we determined endothelial [Ca(2+)](i) by the fura-2 ratioing method and fusion pore formation by quantifying the fluorescence of FM1-43. Pressure elevation increased endothelial [Ca(2+)](i). Concomitantly evoked exocytotic events were evident in a novel spatial-temporal pattern of fusion pore formation. Fusion pores formed predominantly at vascular branch points and colocalized with the expression of P-selectin. Blockade of mechanogated Ca(2+) channels inhibited these responses, identifying entry of external Ca(2+) as the critical triggering mechanism. These endothelial responses point to a proinflammatory effect of high vascular pressure that may be relevant in the pathogenesis of pressure-induced lung disease.

Normal endothelium

In recent decades, it has become evident that the endothelium is by no means a passive inner lining of blood vessels. This 'organ' with a large surface (approximately 350 m2) and a comparatively small total mass (approximately 110 g) is actively involved in vital functions of the cardiovascular system, including regulation of perfusion, fluid and solute exchange, haemostasis and coagulation, inflammatory responses, vasculogenesis and angiogenesis. The present chapter focusses on two central aspects of endothelial structure and function: (1) the heterogeneity in endothelial properties between species, organs, vessel classes and even within individual vessels and (2) the composition and role of the molecular layer on the luminal surface of endothelial cells. The endothelial lining of blood vessels in different organs differs with respect to morphology and permeability and is classified as 'continuous', 'fenestrated' or 'discontinuous'. Furthermore, the mediator release, antigen presentation or stress responses of endothelial cells vary between species, different organs and vessel classes. Finally there are relevant differences even between adjacent endothelial cells, with some cells exhibiting specific functional properties, e.g. as pacemaker cells for intercellular calcium signals. Organ-specific structural and functional properties of the endothelium are marked in the vascular beds of the lung and the brain. Pulmonary endothelium exhibits a high constitutive expression of adhesion molecules which may contribute to the margination of the large intravascular pool of leucocytes in the lung. Furthermore, the pulmonary microcirculation is less permeable to protein and water flux as compared to large pulmonary vessels. Endothelial cells of the blood-brain barrier exhibit a specialised phenotype with no fenestrations, extensive tight junctions and sparse pinocytotic vesicular transport. This barrier allows a strict control of exchange of solutes and circulating cells between the plasma and the interstitial space. It was observed that average haematocrit levels in muscle capillaries are much lower as compared to systemic haematocrit, and that flow resistance of microvascular beds is higher than expected from in vitro studies of blood rheology. This evidence stimulated the concept of a substantial layer on the luminal endothelial surface (endothelial surface layer, ESL) with a thickness in the range of 0.5-1 microm. In comparison, the typical thickness of the glycocalyx directly anchored in the endothelial plasma membrane, as seen in electron micrographs, amounts to only about 50-100 microm. Therefore it is assumed that additional components, e.g. adsorbed plasma proteins or hyaluronan, are essential in constituting the ESL. Functional consequences of the ESL presence are not yet sufficiently understood and acknowledged. However, it is evident that the thick endothelial surface layer significantly impacts haemodynamic conditions, mechanical stresses acting on red cells in microvessels, oxygen transport, vascular control, coagulation, inflammation and atherosclerosis.

Measurement of neutrophil content in brain and lung tissue by a modified myeloperoxidase assay

Myeloperoxidase (MPO) activity is assessed for the quantification of neutrophil accumulation in tissues. In particular, it may be used to support in vivo data on leukocyte kinetics obtained by intravital microscopy and to clarify whether phenomena observed on the organ surface reflect the situation of the whole organ microcirculation. Previous measurements of MPO activity were limited by interference with other peroxidases and by inhibition of MPO activity by specific enzymes. To circumvent these limitations, a modified assay was devised that combined a two-step tissue homogenization technique with heat incubation in a continuous photometric measurement. MPO activity was quantified in neutrophils isolated from rat and rabbit whole blood, rat brain and rabbit lung and compared with intravital microscopic data on leukocyte accumulation. The modified assay is characterized by high reproducibility, strong correlation of MPO activity with number of neutrophils and full recovery of neutrophils added to tissue homogenate. MPO activity per neutrophil was 342.9 +/- 11.7 mU/10(6) cells in rats and 40.3 +/- 0.8 mU/10(6) cells in rabbits. MPO activity in tissue was significantly lower in rat brains (18.9 +/- 29.7 mU/g) as compared to rabbit lungs (741 +/- 67 mU/g). Whereas global cerebral ischemia/reperfusion did not increase MPO activity in rat brain (18.1 +/- 26.1 mU/g), intravenous infusion of cobra venom factor (1,447 +/- 407 mU/g) or endotoxin (1,439 +/- 285 mU/g), enhanced MPO activity in rabbit lung. These results parallel microcirculatory data from the organ surface. Therefore they supplement the intravital microscopic observations by demonstrating that these are indeed representative of deeper parenchymal tissue areas.

Prognostic value of Doppler echocardiographic mitral inflow patterns: implications for risk stratification in patients with chronic congestive heart failure

OBJECTIVES

This prospective study tested whether transmitral flow patterns add incremental value to peak oxygen consumption (VO2) in determining the prognosis of patients with chronic congestive heart failure (CHF) and systolic dysfunction.

BACKGROUND

Peak VO2 is an objective marker of functional capacity and is routinely used as a criterion to identify heart transplant candidates. Diastolic dysfunction limits functional capacity, but its prognostic importance relative to that of peak VO2 is unknown.

METHODS

Peak VO2 and mitral inflow velocities were prospectively measured in 311 consecutive patients (mean age 54 years, 84% male) with impaired left ventricular function (ejection fraction <40%; 88 patients with ischemic and 223 with dilated cardiomyopathy) who were evaluated for heart transplant candidacy.

RESULTS

During a mean follow-up period of 512 +/- 314 days, 65 patients died and 43 patients underwent heart transplantation. Diastolic filling patterns, peak VO2 and left ventricular end-diastolic diameters were independent predictors of cardiac mortality. In patients with peak VO2 < or = 14 ml/min per kg body weight, the outcome was markedly poorer in the presence of restrictive filling patterns as compared with their absence (two-year survival rate 52% vs. 80%). Similarly, despite peak VO2 levels >14 ml/min per kg, the outcome was less favorable in the presence of restrictive filling patterns (two-year survival rate 80% vs. 94%). A risk-stratification model based on the identified independent noninvasive predictors separated groups into those with high (93%), intermediate (65%) and low (39%) two-year survival rates.

CONCLUSIONS

Transmitral flow patterns add incremental value to peak VO2 in determining the prognosis of patients with CHF and impaired systolic function.

A novel signaling mechanism between gas and blood compartments of the lung

Propagation of inflammatory signals from the airspace to the vascular space is pivotal in lung inflammation, but mechanisms of intercompartmental signaling are not understood. To define signaling mechanisms, we microinfused single alveoli of blood-perfused rat lung with TNF-alpha, and determined in situ cytosolic Ca(2+) concentration ([Ca(2+)](i)) by the fura-2 ratio method, cytosolic phospholipase A(2) (cPLA(2)) activation and P-selectin expression by indirect immunofluorescence. Alveolar TNF-alpha increased [Ca(2+)](i) and activated cPLA(2) in alveolar epithelial cells, and increased both endothelial [Ca(2+)](i) and P-selectin expression in adjoining perialveolar capillaries. All responses were blocked by pretreating alveoli with a mAb against TNF receptor 1 (TNFR1). Crosslinking alveolar TNFR1 also increased endothelial [Ca(2+)](i). However, the endothelial responses to alveolar TNF-alpha were blocked by alveolar preinjection of the intracellular Ca(2+) chelator BAPTA-AM, or the cPLA(2) blockers AACOCF(3) and MAFP. The gap-junction uncoupler heptanol had no effect. We conclude that TNF-alpha induces signaling between the alveolar and vascular compartments of the lung. The signaling is attributable to ligation of alveolar TNFR1 followed by receptor-mediated [Ca(2+)](i) increases and cPLA(2) activation in alveolar epithelium. These novel mechanisms may be relevant in the alveolar recruitment of leukocytes.

Leukocyte kinetics in pulmonary microcirculation: intravital fluorescence microscopic study

To determine the site of sequestration of leukocytes in the lung, we investigated the kinetics of fluorescently labeled erythrocytes and leukocytes in pulmonary arterioles, venules, and alveolar capillaries in vivo by using fluorescence videomicroscopy. The subpleural pulmonary microcirculation of the ventilated rabbit lung was visualized via a transparent window implanted into the right thoracic wall. Fluorescein isothiocyanate-labeled erythrocytes were administered intravenously, whereas leukocytes were labeled in vivo by intravenous injection of rhodamine 6G. Rolling and adherence of leukocytes on the surface of the vessel walls were observed in arterioles as well as in venules. The median velocity of nonadherent leukocytes was significantly higher in arterioles than in venules (84 +/- 12 vs. 15 +/- 3% of erythrocyte velocity, respectively). In alveolar capillaries the majority of leukocytes were retained at distinct sites for periods of 0.1 to > 5 s (median 0.61 s). The relative velocity of leukocytes moving in capillaries was comparable to that determined in arterioles (80 +/- 9% of erythrocyte velocity). These measurements indicate that leukocyte sequestration in the lung is governed by the retention of leukocytes in capillaries and by the interaction of leukocytes with microvascular endothelium of arterioles and venules. We propose that the kinetics of these phenomena determine the equilibrium between circulating and sequestered leukocytes.

Role of L-selectin in leukocyte sequestration in lung capillaries in a rabbit model of endotoxemia

After a variety of pathophysiologic stimuli, neutrophils accumulate in lung capillaries and contribute to the pathogenesis of acute lung injury. Lung neutrophil sequestration has previously been attributed to mechanical retention of stiffened neutrophils, but L-selectin-mediated leukocyte/endothelial interaction may be an essential step. We investigated the effect of the anti-L-selectin antibody HuDreg 200 on leukocyte sequestration and microhemodynamics in alveolar capillaries in a model of acute endotoxemia. We used in vivo fluorescence microscopy to analyze kinetics of fluorescently labeled red and white blood cells in alveolar capillary networks of the rabbit lung. Investigations were performed over 2 h after an intravenous infusion of 0.2 ml/kg body weight (bw) NaCl, 2 mg/kg bw HuDreg 200, 20 microg/kg bw lipopolysaccharide (LPS) of Escherichia coli 0111:B4, or the combination of HuDreg 200 and LPS, respectively. Infusion of LPS induced leukocyte sequestration in alveolar capillaries, which was accompanied by a reduction of alveolar capillary perfusion and functional capillary density. These effects could be completely blocked by pretreatment of animals with HuDreg 200. We conclude that L-selectin-mediated leukocyte/endothelial interaction is a necessary prerequisite for leukocyte sequestration in alveolar capillaries in this model. Impaired alveolar capillary perfusion appeared to result directly from capillary leukocyte sequestration.

Determination of left ventricular filling parameters by pulsed Doppler echocardiography: a noninvasive method to predict high filling pressures in patients with coronary artery disease

This study investigated the influence of left ventricular end-diastolic filling pressure (LVEDP) on instantaneous transmitral inflow velocities as assessed by pulsed Doppler echocardiography. The study was performed in 87 consecutive patients with coronary artery disease (12 women, 65 men, mean age 58 +/- 8 years, range 37 to 78 years) in whom Doppler tracings of mitral inflow velocities were recorded 24 hours before diagnostic cardiac catheterization. The ratio of early-to-late diastolic velocity integrals was significantly correlated with LVEDP (r = 0.35, SD = 0.77, p less than 0.001). In addition, in a comparison patients with LVEDP greater than or equal to 20 mm Hg to those with LVEDP less than 20 mm Hg, peak early filling velocity (R) was significantly higher, peak late filling velocity (A) was lower, and hence R/A and area under the early filling curve/area under the late diastolic filling curve (E/L) ratios were significantly higher in patients with markedly elevated filling pressures (LVEDP 20 mm Hg: R = 41 +/- 12, A = 56 +/- 16, R/A = 0.75 +/- 0.23, E/L = 1.0 +/- 0.4, n = 54, and LVEDP greater than or equal to 20 mm Hg: R = 49 +/- 18, A = 46 +/- 12, R/A = 1.23 +/- 0.9, E/L = 1.94 +/- 1.2, n = 34. An E/L ratio greater than or equal to 1.4 showed a sensitivity of 59%, a specificity of 83%, a positive predictive accuracy of 69%, and a negative predicting accuracy of 76% in detecting patients with markedly elevated LVEDP.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of blood flow on the leukocyte-endothelium interaction in pulmonary microvessels

Circulating leukocytes are retained in the microcirculation of the lung. The site of leukocyte retention, however, is still a subject of controversy, and the effects of microvascular blood flow on the leukocyte-endothelium interaction in pulmonary microvessels are unknown. We used in vivo fluorescence microscopy to analyze microhemodynamics and the flow behavior of in vivo-labeled leukocytes in pulmonary arterioles, venules, and alveolar capillaries. Microvascular blood flow was altered by variation of cardiac output. Leukocytes were found to roll and to stick on arteriolar and more pronouncedly on venular endothelium. During their passage through alveolar capillaries, a fraction of passing leukocytes became static for 0.1 to > 5 s. Under control conditions, leukocytes were concentrated approximately 8-fold more in arterioles and 24-fold more in venules than in the blood passing through these vessels. The concentration in capillaries was 1.5 times greater than in venules. The velocity of rolling leukocytes in arterioles and venules correlated significantly with the shear rate in these vessels, whereas the density of sticking cells was negatively correlated with the shear rate. The differences between leukocyte rolling and sticking in arterioles and in venules cannot be explained by respective hemodynamic conditions. In alveolar capillaries, the percentage of temporarily static leukocytes and the time of their stasis were inversely correlated with red-blood-cell (RBC) velocity. We conclude that leukocytes are retained in pulmonary arterioles, venules, and alveolar capillaries according to microvascular blood flow and endothelial factors.

Contribution of selectins to leucocyte sequestration in pulmonary microvessels by intravital microscopy in rabbits

1. Sequestration of leucocytes in the lung is the net result of leucocyte rolling and sticking in pulmonary arterioles and venules and their retention in alveolar capillaries. 2. In order to investigate whether adhesion molecules of the selectin family contribute to these phenomena the effects of fucoidin (an inhibitor of L- and P-selectin) on microhaemodynamics and leucocyte kinetic were studied in pulmonary arterioles, capillaries and venules by means of intravital fluorescence microscopy in a rabbit model. 3. Fucoidin reduced leucocyte rolling in pulmonary arterioles and venules by 75 and 83%, respectively, without affecting leucocyte sticking. In alveolar capillaries, fucoidin reduced leucocyte retention and accelerated leucocyte passage, thus reducing the alveolar transit time of leucocytes by 62%. 4. It is concluded that rolling of leucocytes in pulmonary microvessels is mediated by selectins, whereas sticking relies on selectin-independent mechanisms. 5. Leucocyte retention in alveolar capillaries is not due solely to mechanical hindrance of leucocyte passage through narrow vessel segments, as previously hypothesized, but also depends on interaction of leucocytes with the capillary endothelium.

Efficacy of intravenous prourokinase and a combination of prourokinase and urokinase in acute myocardial infarction

Fifty-four patients with Q-wave acute myocardial infarction (AMI) were treated with heparin combined with intravenous single-chain urokinase-type plasminogen activator (prourokinase). To determine the optimal treatment regimen, prourokinase was applied in 3 different ways: group I received a bolus of 7.5 mg and a subsequent infusion of 40.5 mg over 60 minutes. Patency of the infarct artery was observed in 7 patients (50%) at the end of the infusion time. One hour after the end of the infusion the fibrinogen level had decreased to 87 +/- 12% of the preinfusion level; the plasminogen and alpha-2 antiplasmin levels to 61 +/- 13% and 59 +/- 34%, respectively. In group II prourokinase was administered as a 7.5 mg bolus followed by 66.5 mg over 60 minutes. Eleven patients (55%) had patent infarct-related coronary arteries and fibrinogen, plasminogen and alpha-2 antiplasmin levels had decreased to 58 +/- 29%, 38 +/- 18% and 21 +/- 14%, respectively. Group III was treated with a bolus of 3.7 mg prourokinase and 250,000 IU urokinase followed by 44.3 mg prourokinase, resulting in a patency rate of 65% (13 patients). Fibrinogen, plasminogen and alpha-2 antiplasmin levels decreased to 76 +/- 15%, 67 +/- 15% and 47 +/- 29%, respectively. Fibrin-specific thrombolysis can be achieved with glycosylated prourokinase. At higher dosages considerable systemic activation of the fibrinolytic system with little enhancement of the observed therapeutic effect occurred. The combination of prourokinase and urokinase yielded a higher patency rate than either dosage of prourokinase alone, although the difference was not statistically significant in this pilot trial.

Multisite pacing for prevention of atrial tachyarrhythmias: potential mechanisms

OBJECTIVES

To determine the effects of single-, dual-, triple- and quadruple-site atrial pacing on atrial activation and refractoriness in normal canine hearts.

BACKGROUND

Multisite pacing has been suggested to be superior to single-site pacing for prevention of atrial tachyarrhythmias. However, the underlying electrophysiological mechanisms are undetermined at the moment, as is the rationale for the selection of pacing locations and the number of pacing sites.

METHODS

In 13 normal beagle dogs, an epicardial multielectrode (128 bipoles) and a multiplexer mapping system were used to reconstruct epicardial atrial activation patterns obtained during simultaneous stimulation from up to four electrodes located in the high and low right and left atrium, respectively. For all pacing modes (single-, dual-, triple- and quadruple-site pacing), total activation times and local effective refractory periods at eight randomly selected sites as well as local recovery intervals were determined. In a subgroup of five dogs, total epicardial activation times were also obtained during single-site septal stimulation (septal group).

RESULTS

Activation times and local recovery intervals were minimized by triple-site stimulation, whereas a fourth site did not produce further shortening. Septal stimulation produced epicardial activation times comparable to quadruple-site stimulation. Local refractory periods and their dispersion always remained unaffected. Functional conduction blocks apparent during single-site were found to resolve during multisite stimulation.

CONCLUSIONS

Multisite pacing can prevent functional conduction blocks by multidirectional excitation and a reduction in total activation time. Triple-site and, possibly, septal pacing modes are expected to be most efficient because both minimize total activation times and maximize the multidirectionality of excitation. In spite of unaffected local refractory periods, the shortening of local recovery intervals might homogenize atrial repolarization and, thus, contribute to the preventive effects of multisite pacing.

A unified functional/anatomic substrate for circus movement atrial flutter: activation and refractory patterns in the canine right atrial enlargement model

OBJECTIVES

This study was designed to test the concept of a functional/anatomic interaction in a canine model of reentry based on right atrial enlargement and to elucidate the electrophysiologic basis for functional conduction block.

BACKGROUND

The monotonic feature of atrial flutter suggests a uniform substrate for the arrhythmia. Atrial flutter in the sterile pericarditis model is due to single-loop circus movement around a functional or a functional/anatomic obstacle near the atrioventricular (AV) ring. Sustained circus movement requires a critical interaction of a functional arc of block, a natural obstacle, the AV ring and a zone of slow conduction. The location of the inferior vena cava predisposes the lower right atrium to single-loop reentry.

METHODS

In 11 dogs with right atrial enlargement, 127 bipolar epicardial electrograms were obtained during atrial flutter. For correlation of activation and refractory maps, the effective refractory period under each electrode was determined using the extrastimulus technique.

RESULTS

Atrial flutter was due to single-loop reentry around functional arcs of block near the AV ring (n = 2) or around functional/anatomic obstacles (n = 8) involving the inferior vena cava. A slow zone was located between the arc and the AV ring and between the inferior vena cava and AV ring, respectively. During initiation, the arc joined the AV ring, forcing activation to proceed around the free end of the arc before breaking through the arc near the AV ring. Arrhythmia termination required the arc of block to rejoin the AV ring. Inducibility of sustained atrial flutter was associated with a marked spatial dispersion of refractoriness. The configuration of the functional arc of block was critically dependent on the spatial pattern of refractoriness.

CONCLUSIONS

Atrial flutter requires a similar functional or functional/anatomic substrate independent of the underlying etiology. The spatial distribution of refractoriness in enlarged canine atria provides an adequate substrate for the development of functional conduction block.

Holter monitoring before, during and after percutaneous transluminal coronary angioplasty for evaluation of high-resolution trend recordings of leads CM5 and CC5 for ST-segment analysis

Frequency-modulated Holter monitoring of leads CM5 and CC5 was performed before, during and after percutaneous transluminal coronary angioplasty (PTCA) in 16 patients with stenosis of the left anterior descending coronary artery, in 5 patients with stenosis of the left circumflex coronary artery, and in 5 patients with stenosis of the right coronary artery. All patients presented with 1-vessel coronary artery disease and stable or unstable angina pectoris. ST-segment analysis was based on high-resolution trend recordings. During balloon inflations all patients had significant (at least 0.1 mV) ST-segment changes in lead CM5. In lead CC5, associated ST-segment deviations were found in 22 of 26 patients. During 29.2 +/- 13.6 hours before PTCA, 90 spontaneous episodes with significant ST-segment deviations were detected in 10 patients. Of these episodes, 17% were characterized by ST-segment deviations in lead CC5 only, 57% by ST-segment deviations in lead CM5 only, and 27% by simultaneous ST-segment deviations in both leads. Asymptomatic episodes occurred twice as frequently as symptomatic episodes (66 vs 34%). Symptomatic episodes were more often characterized by ST-segment deviations of at least 0.15 mV (48 vs 9%, p less than 0.001) and by ST-segment deviations observed in both leads simultaneously (48 vs 15%, p less than 0.001). During 34.8 +/- 10.6 hours after successful PTCA, 5 spontaneous asymptomatic episodes with significant ST-segment deviations were detected in 2 patients.

Functional transient receptor potential vanilloid 1 and transient receptor potential vanilloid 4 channels along different segments of the renal vasculature

AIM

Transient receptor potential vanilloid 1 (TRPV1) and vanilloid 4 (TRPV4) cation channels have been recently identified to promote endothelium-dependent relaxation of mouse mesenteric arteries. However, the role of TRPV1 and TRPV4 in the renal vasculature is largely unknown. We hypothesized that TRPV1/4 plays a role in endothelium-dependent vasodilation of renal blood vessels.

METHODS

We studied the distribution of functional TRPV1/4 along different segments of the renal vasculature. Mesenteric arteries were studied as control vessels.

RESULTS

The TRPV1 agonist capsaicin relaxed mouse mesenteric arteries with an EC50 of 25 nm, but large mouse renal arteries or rat descending vasa recta only at >100-fold higher concentrations. The vasodilatory effect of capsaicin in the low-nanomolar concentration range was endothelium-dependent and absent in vessels of Trpv1 -/- mice. The TRPV4 agonist GSK1016790A relaxed large conducting renal arteries, mesenteric arteries and vasa recta with EC50 of 18, 63 nm and ~10 nm respectively. These effects were endothelium-dependent and inhibited by a TRPV4 antagonist, AB159908 (10 μm). Capsaicin and GSK1016790A produced vascular dilation in isolated mouse perfused kidneys with EC50 of 23 and 3 nm respectively. The capsaicin effects were largely reduced in Trpv1 -/- kidneys, and the effects of GSK1016790A were inhibited in Trpv4 -/- kidneys.

CONCLUSION

Our results demonstrate that two TRPV channels have unique sites of vasoregulatory function in the kidney with functional TRPV1 having a narrow, discrete distribution in the resistance vasculature and TRPV4 having more universal, widespread distribution along different vascular segments. We suggest that TRPV1/4 channels are potent therapeutic targets for site-specific vasodilation in the kidney.

Doppler echocardiographic assessment of left ventricular filling dynamics in patients with coronary heart disease and normal systolic function

The purpose of this study was to assess altered left ventricular diastolic filling by noninvasive means in patients with coronary artery disease and normal systolic pump function. Mitral inflow velocity was measured by pulsed Doppler, and left ventricular volumes were obtained from cross-sectional echocardiography at rest and during upright bicycle exercise. Peak and integrated early and late diastolic filling velocities were calculated from Doppler-derived time-velocity curves. Studies were performed in normal subjects (group I, n = 8) and in patients with angiographically proven coronary artery disease (Group II, n = 18). The ejection fraction was not significantly different in group II as compared to group I (group I, 60 +/- 7%; group II, 55 +/- 11%). During exercise, ejection fraction increased significantly in group I by 7.6%, but did not increase in group II. In all cases, diastolic filling showed a biphasic pattern. At rest, the major part of diastolic filling occurred during early diastole: the ratio of early filling velocity integral (E) to the late filling velocity integral (L) was significantly greater in group I than in group II (group I, 1.74 +/- 37; group II, 1.19 +/- 3, P less than 0.001). During exercise, early diastolic filling was unchanged in normal subjects but decreased in patients, with a significant decrease in E/L index of 34% (P less than 0.001). Thus, pulsed Doppler echocardiography provides a useful method for assessing noninvasively exercise-induced changes in left ventricular diastolic filling dynamics in patients with coronary artery disease.

Intercaval block in normal canine hearts : role of the terminal crest

BACKGROUND

The intriguing monotony in the occurrence of intercaval conduction block during typical atrial flutter suggests an anatomic or electrophysiological predisposition for conduction abnormalities.

METHODS AND RESULTS

To determine the location of and potential electrophysiological basis for conduction block in the terminal crest region, a high-density patch electrode (10x10 bipoles) was placed on the terminal crest and on the adjacent pectinate muscle region in 10 healthy foxhounds. With a multiplexer mapping system, local activation patterns were reconstructed during constant pacing (S(1)S(1)=200 ms) and introduction of up to 2 extrastimuli (S(2), S(3)). Furthermore, effective refractory periods were determined across the patch. If evident through online analysis, the epicardial location of conduction block was marked for postmortem verification of its endocardial projection. Marked directional differences in activation were found in the terminal crest region, with fast conduction parallel to and slow conduction perpendicular to the intercaval axis (1.1+/-0.4 versus 0.5+/-0.2 m/s, P<0.01). In the pectinate muscle region, however, conduction velocities were similar in both directions (0.5+/-0.3 versus 0.6+/-0.2 m/s, P=NS). Refractory patterns were relatively homogeneous in both regions, with local refractory gradients not >30 ms. During S(3) stimulation, conduction block parallel to the terminal crest was inducible in 40% of the dogs compared with 0% in the pectinate muscle region.

CONCLUSIONS

Even in normal hearts, inducible intercaval block is a relatively common finding. Anisotropic conduction properties would not explain conduction block parallel to the intercaval axis in the terminal crest region, and obviously, refractory gradients do not seem to play a role either. Thus, the change in fiber direction associated with the terminal crest/pectinate muscle junction might form the anatomic/electrophysiological basis for intercaval conduction block.

alpha(v)beta(3) integrin induces tyrosine phosphorylation-dependent Ca(2+) influx in pulmonary endothelial cells

The endothelial alpha(v)beta(3) integrin occurs luminally, where its ligation by soluble agents may induce inflammatory signaling. We tested this hypothesis in bovine pulmonary artery endothelial cell monolayers with the use of vitronectin and cross-linking antibodies to ligate and aggregate the integrin. We quantified the endothelial cytosolic Ca(2+) concentration ([Ca(2+)](i)) according to the Fura 2 ratio imaging method in single cells of confluent monolayers. At baseline, endothelial [Ca(2+)](i) levels remained steady at 86 nmol/L for >20 minutes. Cross-linking of the alpha(v)beta(3) integrin through the sequential exposure of monolayers to anti-alpha(v)beta(3) monoclonal antibody LM609 and secondary IgG resulted in a [Ca(2+)](i) increase of 100% above baseline. This increase commenced in <0.5 minute, peaked in <2 minutes, and decayed to baseline in approximately 5 minutes. Similar responses occurred after the addition of vitronectin (400 microg/mL). In contrast, external Ca(2+) depletion blunted the cross-linking-induced [Ca(2+)](i) increase by 60%, a response that was completely inhibited when the monolayers were also pretreated with thapsigargin. Thus, the [Ca(2+)](i) increase was attributable in part to the release of Ca(2+) from endosomal stores but mostly to Ca(2+) influx across the plasma membrane. Induced aggregation of the alpha(v)beta(3) integrin enhanced tyrosine phosphorylation of phospholipase C-gamma1 and increased the accumulation of inositol-1, 4,5-trisphosphate. Genistein, a broad-spectrum tyrosine kinase inhibitor, abrogated both of these effects, as well as the alpha(v)beta(3)-induced [Ca(2+)](i) increases. We conclude that aggregation of the endothelial alpha(v)beta(3) integrin induces a rapid tyrosine phosphorylation-dependent increase in [Ca(2+)](i). This response may subserve the inflammatory role of alpha(v)beta(3) integrin in blood vessels.

Circus movement atrial flutter in the canine sterile pericarditis model. Relation of characteristics of the surface electrocardiogram and conduction properties of the reentrant pathway

OBJECTIVES

This study was designed to elucidate the basis for the electrocardiographic (ECG) appearance of atrial flutter in the canine sterile pericarditis model.

BACKGROUND

During atrial flutter, the surface ECG may show typical F waves or isolated P waves of any polarity.

METHODS

Electrocardiographic leads II, III and aVF and epicardial atrial activation maps constructed from 127 simultaneously recorded bipolar electrograms were compared in 20 dogs with sterile pericarditis and inducible atrial flutter.

RESULTS

In 10 dogs with F wave atrial flutter, single loop reentry occurred around combined functional/anatomic obstacles that included one or both caval veins and a vertically oriented arc of functional conduction block. In 10 dogs with P wave atrial flutter, a merely functional (n = 4) or combined (n = 6) obstacle involving any atrial vessel and more vertically (n = 5) or more horizontally (n = 5) oriented arcs of block was present. The isoelectric interval between P waves corresponded to the conduction time within the slow zone of the reentrant circuit (96 +/- 27 vs. 100 +/- 24 ms, mean +/- SD). Slow conduction accounted for 65 +/- 8% of the cycle length in P wave atrial flutter, but for only 29 +/- 7% in F wave atrial flutter (p < 0.05). Slow conduction was usually associated with activation of fewer than five epicardial electrodes per 10-ms isochronal interval, reflecting only a small amount of atrial tissue. The polarity of P or F waves was determined by the direction of the major wave front activating the most electrodes per 10-ms isochronal interval, irrespective of whether the right or the left atrium was activated.

CONCLUSIONS

The F waves result from reentrant activation at a relatively constant speed around a vertically oriented functional/anatomic obstacle involving one or both caval veins. The P waves occur when the circuit contains a marked area of slow conduction.