Early results with the Carbo-seal composite valve conduit for aortic root replacement

BACKGROUND AND AIMS OF THE STUDY

Composite graft replacement of the aortic root is still a complex operation, transgraft hemorrhage being one of the most severe complications. The aim of the study was to evaluate early results with the Carbo-seal composite conduit for aortic root replacement.

METHODS

A retrospective review of 21 patients operated on for ascending aortic aneurysm and/or dissection with the open technique between August 1993 and February 1998 is presented; 12 patients had Marfan syndrome and nine were non-Marfan.

RESULTS

There were two operative deaths (9.5%) due to low cardiac output. Two patients were re-explored for bleeding which was not due to transgraft hemorrhage. Postoperative complications were one hemothorax, one pneumothorax and two pericardial effusions. During the follow up, one patient died of rupture of a descending aortic aneurysm, and one patient in atrial fibrillation had a transient ischemic attack. At the closing of the follow up, the remaining patients were well and free of complications.

CONCLUSIONS

Carbo-seal may be considered a reliable device for use in aortic root replacement, though a longer follow up and a larger patient population are necessary to confirm these positive early results.

beta2-Adrenergic receptor regulation by GIT1, a G protein-coupled receptor kinase-associated ADP ribosylation factor GTPase-activating protein

G protein-coupled receptor activation leads to the membrane recruitment and activation of G protein-coupled receptor kinases, which phosphorylate receptors and lead to their inactivation. We have identified a novel G protein-coupled receptor kinase-interacting protein, GIT1, that is a GTPase-activating protein (GAP) for the ADP ribosylation factor (ARF) family of small GTP-binding proteins. Overexpression of GIT1 leads to reduced beta2-adrenergic receptor signaling and increased receptor phosphorylation, which result from reduced receptor internalization and resensitization. These cellular effects of GIT1 require its intact ARF GAP activity and do not reflect regulation of GRK kinase activity. These results suggest an essential role for ARF proteins in regulating beta2-adrenergic receptor endocytosis. Moreover, they provide a mechanism for integration of receptor activation and endocytosis through regulation of ARF protein activation by GRK-mediated recruitment of the GIT1 ARF GAP to the plasma membrane.

Guanine nucleotide exchange on ADP-ribosylation factors catalyzed by cytohesin-1 and its Sec7 domain

ADP-ribosylation factors (ARFs) are 20-kDa guanine nucleotide-binding proteins that require specific guanine nucleotide-exchange proteins (GEPs) to accelerate the conversion of inactive ARF-GDP to active ARF-GTP. Cytohesin-1, a 46-kDa ARF GEP, contains a central Sec7 domain of 188 amino acids similar in sequence to a region of the yeast Sec7 protein. Cytohesin-1 and its 22-kDa Sec7 domain (C-1 Sec7), synthesized in Escherichia coli, were assayed with recombinant non-myristoylated ARFs and related proteins to compare their GEP activities. Both were effective with native mammalian ARFs 1 and 3. Cytohesin-1 accelerated GTPgammaS (guanosine 5'-3-O-(thio)triphosphate) binding to recombinant human ARF1 (rARF1), yeast ARF3, and ARD1 (a 64-kDa guanine nucleotide-binding protein containing a C-terminal ARF domain). In contrast, C-1 Sec7 enhanced GTPgammaS binding to recombinant human ARFs 1, 5, and 6; yeast ARFs 1, 2, and 3; ARD1; two ARD1 mutants that contain the ARF domain; and Delta13ARF1, which lacks the N-terminal alpha-helix. Neither C-1 Sec7 nor cytohesin-1 increased GTPgammaS binding to human ARF-like ARL proteins 1, 2, and 3. Thus, ARLs, initially differentiated from ARFs because of their inability to activate cholera toxin, differ also in their failure to interact functionally with C-1 Sec7 or cytohesin-1. As C-1 Sec7 was much less substrate-specific than cytohesin-1, it appears that structure outside of the Sec7 domain is important for ARF specificity. Data obtained with mutant ARF constructs are all consistent with the conclusion that the ARF N terminus is an important determinant of cytohesin-1 specificity.

Localization of ADP-ribosylation factor domain protein 1 (ARD1) in lysosomes and Golgi apparatus

ADP-ribosylation factor domain protein 1 (ARD1) is a member of the ADP ribosylation factor (ARF) family of guanine nucleotide-binding proteins that differs from other ARFs by the presence of a 46-kDa amino-terminal extension which acts as a GTPase-activating protein (GAP) for its ARF domain. Similar to ARF GAPs, the GAP domain of ARD1 contains a zinc finger motif and arginine residues that are critical for activity. It differs from other ARF GAPs in its covalent association with the GTP-binding domain and its specificity for the ARF domain of ARD1. ARFs are presumed to play a key role in the formation of intracellular transport vesicles and in their movement from one compartment to another. We report here that ARD1 overexpressed in cells, as a fusion or nonfusion protein, is localized in vesicular structures that are concentrated mainly in the perinuclear region, but are found also throughout the cytosol. Microscopic colocalization and subcellular fractionation studies showed that ARD1 was associated with the Golgi complex and lysosomal structures. ARD1 expressed as a green fluorescent fusion protein was initially associated with the Golgi network and subsequently localized to lysosomes. Lysosomal and Golgi membranes isolated from human liver by immunoaffinity contained native ARD1. Localization to these organelles, therefore, did not appear to be a result of overexpression. These observations suggest that the ARF-related protein ARD1 may play a role in the formation or function of lysosomes and in protein trafficking between Golgi and lysosomes.

Molecular characterization of the GTPase-activating domain of ADP-ribosylation factor domain protein 1 (ARD1)

ADP-ribosylation factors (ARFs) are approximately 20-kDa guanine nucleotide-binding proteins recognized as critical components in intracellular vesicular transport and phospholipase D activation. Both guanine nucleotide-exchange proteins and GTPase-activating proteins (GAPs) for ARFs have been cloned recently. A zinc finger motif near the amino terminus of the ARF1 GAP was required for stimulation of GTP hydrolysis. ARD1 is an ARF family member that differs from other ARFs by the presence of a 46-kDa amino-terminal extension. We had reported that the ARF domain of ARD1 binds specifically GDP and GTP and that the amino-terminal extension acts as a GAP for the ARF domain of ARD1 but not for ARF proteins. The GAP domain of ARD1, synthesized in Escherichia coli, stimulated hydrolysis of GTP bound to the ARF domain of ARD1. Using ARD1 truncations, it appears that amino acids 101-190 are critical for GAP activity, whereas residues 190-333 are involved in physical interaction between the two domains of ARD1 and are required for GTP hydrolysis. The GAP function of the amino-terminal extension of ARD1 required two arginines, an intact zinc finger motif, and a group of residues which resembles a sequence present in Rho/Rac GAPs. Interaction between the two domains of ARD1 required two negatively charged residues (Asp427 and Glu428) located in the effector region of the ARF domain and two basic amino acids (Arg249 and Lys250) found in the amino-terminal extension. The GAP domain of ARD1 thus is similar to ARF GAPs but differs from other GAPs in its covalent association with the GTP-binding domain.

Regulated exocytosis in chromaffin cells. Translocation of ARF6 stimulates a plasma membrane-associated phospholipase D

The ADP-ribosylation factor (ARF) GTP-binding proteins have been implicated in a wide range of vesicle transport and fusion steps along the secretory pathway. In chromaffin cells, ARF6 is specifically associated with the membrane of secretory chromaffin granules. Since ARF6 is an established regulator of phospholipase D (PLD), we have examined the intracellular distribution of ARF6 and PLD activity in resting and stimulated chromaffin cells. We found that stimulation of intact chromaffin cells or direct elevation of cytosolic calcium in permeabilized cells triggered the rapid translocation of ARF6 from secretory granules to the plasma membrane and the concomitant activation of PLD in the plasma membrane. To probe the existence of an ARF6-dependent PLD in chromaffin cells, we measured the PLD activity in purified plasma membranes. PLD could be activated by a nonhydrolyzable analogue of GTP and by recombinant myristoylated ARF6 and inhibited by specific anti-ARF6 antibodies. Furthermore, a synthetic myristoylated peptide corresponding to the N-terminal domain of ARF6 inhibited both PLD activity and catecholamine secretion in calcium-stimulated chromaffin cells. The possibility that ARF6 participates in the exocytotic reaction by controlling a plasma membrane-bound PLD and thereby generating fusogenic lipids at the exocytotic sites is discussed.

Characterization of a GDP dissociation inhibitory region of ADP-ribosylation factor domain protein ARD1

ADP-ribosylation factors (ARFs) are approximately 20-kDa guanine nucleotide-binding proteins initially identified by their ability to stimulate cholera toxin ADP-ribosyltransferase activity and later recognized as critical components in intracellular vesicular transport and phospholipase D activation. ARF domain protein 1 (ARD1) is a member of the ARF family that differs from other ARFs by the presence of a 46-kDa amino-terminal extension. We previously reported that this extension acts as a GTPase-activating protein for the ARF domain of ARD1 (Vitale, N., Moss, J., and Vaughan, M. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 1941-1944). Both GTP binding and GTP hydrolysis are necessary for physiological function of guanine nucleotide-binding proteins, and the rates of GDP/GTP exchange and GTPase activity are critical in the activation/deactivation cycle. Dissociation of GDP from the ARF domain of ARD1 was faster than from ARD1 itself (both proteins synthesized in Escherichia coli). Using deletion mutations, it was demonstrated that the 15 amino acids directly preceding the ARF domain were responsible for decreasing the rate of GDP dissociation but not guanosine 5-[gamma-thio]triphosphate dissociation. By site-specific mutagenesis it was shown that hydrophobic amino acids in this region were particularly important in stabilizing the GDP-bound form of ARD1. It is suggested that, like the amino-terminal segment of ARF, the equivalent region in ARD1, located between the GTPase-activating protein and ARF domains, may act as a GDP dissociation inhibitor.

Impairment of lung and chest wall mechanics in patients with acute respiratory distress syndrome: role of abdominal distension

Recent data have suggested that the elastic properties of the chest wall (CW) may be compromised in patients with ARDS because of abdominal distension (4). We partitioned CW and lung (L) mechanics, assessed the role of abdominal distension, and verified whether the underlying disease responsible for ARDS affects the impairment of respiratory mechanics. Volume-pressure (V-P) curves (interrupter technique) were assessed in nine patients with surgical ARDS and nine patients with medical ARDS. Relative to nine patients undergoing heart surgery, V-P curves of the respiratory system (rs) and L of patients with surgical or medical ARDS showed a rightward displacement. V-P curves of the CW and the L showed an upward concavity in patients with medical ARDS and a downward concavity in patients with surgical ARDS. Although the CW and the abdomen (abd) V-P curves in patients with medical ARDS were similar to those obtained in patients undergoing heart surgery, they showed a rightward shift and a downward flattening in patients with surgical ARDS. In five of these patients, a reduction in static end-inspiratory pressure of the abd (69+/-4%), rs (30+/-3%), CW (41+/-2%), and L (27+/-3%) was observed after abdominal decompression for acute bleeding. Abdominal decompression therefore caused an upward and leftward shift of the V-P curves of the respiratory system, chest wall, lung, and abdomen. In conclusion we showed that impairment of the elastic properties of the respiratory system may vary with the underlying disease responsible for ARDS. The flattening of the V-P curve at high pressures observed in some patients with ARDS may be due to an increase in chest wall elastance related to abdominal distension. These observations have implications for the assessment and ventilatory management of patients with ARDS.

Long-term follow-up of open commissurotomy versus bileaflet valve replacement for rheumatic mitral stenosis

OBJECTIVE

Despite the achievements of third generation mechanical cardiac valve prostheses, conservative procedures are still considered the best surgical option for rheumatic mitral valve stenosis. To compare long-term results of open mitral commissurotomy (Group A) and mitral valve replacement with bileaflet prostheses (Group B) a 15-year follow-up study was carried out.

METHODS

From January 1981 to May 1996, 540 consecutive patients with pure isolated rheumatic mitral stenosis underwent mitral valve surgery: 300 had mitral commissurotomy and 240 valve replacement. The follow-up was 99.05% complete and ranged between 1 and 185 months in Group A and from 1 to 171 months in Group B.

RESULTS

Hospital mortality was 2% in Group A and 2.08% in Group B. Late mortality was 1% in Group A and 3% in Group B. The 10-year survival rates were 98.7% +/- 1% in Group A and 93.7% +/- 3% in Group B. There was a statistically significant difference of freedom from reoperation in Group B (97.7% +/- 1%) versus Group A (88.1% +/- 2%) (P = 0.04). In group A 14 embolic events occurred (93.7% +/- 2%), and 15 (6.52%) in Group B (83.9% +/- 7%). Haemorrhagic events were observed in 2 patients (0.68%) of Group A (99.3% +/- 0.5%) and in 3 patients (1.3%) of Group B (98.4% +/- 1%).

CONCLUSIONS

Long term results of mitral commissurotomy were more satisfactory than those obtained with bileaflet valves. Reoperation rate was higher in mitral commissurotomy.

Obstruction of mechanical mitral prostheses: analysis of pathologic findings

BACKGROUND

The pathologic and echocardiographic findings observed in 87 patients with mitral valve obstruction were reviewed to ascertain the incidence of pannus formation versus that of thrombosis, the relationship between the two, and the time to the occurrence of pannus versus the time to thrombosis.

METHODS

Pannus morphology (concentric or eccentric), its location on the valve (atrial, ventricular, atrioventricular), and the presence and relationship of associated thrombi (atrial, ventricular, atrioventricular) were analyzed. The times between valve replacement and the occurrence of obstruction were also compared.

RESULTS

There were 10 caged-ball valves, 65 tilting-disc valves, and 12 bileaflet valves. Seventy-two patients underwent prosthetic replacement, and 15 underwent thrombolysis. Pannus alone was found in 27, pannus and thrombus in 39, and thrombus alone in 21. Primary thrombosis occurred earlier than pannus formation (p = 0.04); this was true for patients with bileaflet valves (p = 0.006) and those with tilting-disc valves (p = 0.04). Pannus was atrial in 19.7% (13/66), ventricular in 21.2% (14/66), and atrioventricular in 59.1% (39/66). Pannus morphology was concentric in 22.7% (15/66) and eccentric in 77.3% (51/66). Atrial secondary thrombi occur more often in patients with atrioventricular pannus (p = 0.04). Eight patients had reobstruction; this was caused by pannus formation in 5 and by thrombosis in 3. Five underwent reoperation, and 3 underwent thrombolysis. Reobstruction occurred earlier than the first event.

CONCLUSIONS

The frequency of pannus formation is much higher than that of thrombus formation, but thrombosis is of earlier onset than pannus formation. Thrombosis is due to the deposition of clots on the prosthesis, and a pannus occurs as the result of an inflammatory reaction developing on both valve surfaces.

Thrombolysis for prosthetic valve thrombosis: indications and results

BACKGROUND AND AIMS OF THE STUDY

Prosthetic valve obstruction is caused by thrombi or fibrous tissue overgrowth, or both; thrombolysis avoids reoperation-related risks, but is effective only on clots. Hence, the study aims were to: (i) further assess our indication criteria for thrombolysis in prosthetic valve thrombosis; and (ii) evaluate treatment and follow up in a large patient population.

METHODS

Between January 1991 and January 1994, 20 cases of prosthetic thrombosis were treated with thrombolysis using recombinant tissue type plasminogen activator (rt-PA). Indication criteria for thrombolysis were: (i) recent onset of symptoms; (ii) transesophageal echocardiographic (TEE) evidence of clots on the valve or cardiac chambers; and (iii) a partially preserved disc excursion. All patients were fitted with mechanical valves (four caged balls, 10 tilting discs, six bileaflets), with 17 valves located in the mitral and three in the aortic position. Symptoms of obstruction comprised cardiac failure in 11 cases and/or embolism in 10.

RESULTS

After rt-PA infusion, normal prosthetic function was restored in all patients, though one underwent successful reoperation five days later. During infusion, five patients had a transient ischemic attack and one a minor transient peripheral embolism. Recurrence of thrombosis occurred in three patients during follow up; subsequent thrombolysis was successful in two, without complication.

CONCLUSIONS

As treatment proved satisfactory, the reliability of our indicational criteria was confirmed. Only transient complications arose during treatment with recurrent thrombosis most common in those patients who had more thrombogenic valve prostheses.

Interaction of the GTP-binding and GTPase-activating domains of ARD1 involves the effector region of the ADP-ribosylation factor domain

ADP-ribosylation factors (ARFs) are a family of approximately 20-kDa guanine nucleotide-binding proteins and members of the Ras superfamily, originally identified and purified by their ability to enhance the ADP-ribosyltransferase activity of cholera toxin and more recently recognized as critical participants in vesicular trafficking pathways and phospholipase D activation. ARD1 is a 64-kDa protein with an 18-kDa carboxyl-terminal ARF domain (p3) and a 46-kDa amino-terminal extension (p5) that is widely expressed in mammalian tissues. Using recombinant proteins, we showed that p5, the amino-terminal domain of ARD1, stimulates the GTPase activity of p3, the ARF domain, and appears to be the GTPase-activating protein (GAP) component of this bifunctional protein, whereas in other members of the Ras superfamily a separate GAP molecule interacts with the effector region of the GTP-binding protein. p5 stimulated the GTPase activity of p3 but not of ARF1, which differs from p3 in several amino acids in the effector domain. After substitution of 7 amino acids from p3 in the appropriate position in ARF1, the chimeric protein ARF1(39-45p3) bound to p5, which increased its GTPase activity. Specifically, after Gly40 and Thr45 in the putative effector domain of ARF1 were replaced with the equivalent Asp and Pro, respectively, from p3, functional interaction of the chimeric ARF1 with p5 was increased. Thus, Asp25 and Pro30 of the ARF domain (p3) of ARD1 are involved in its functional and physical interaction with the GTPase-activating (p5) domain of ARD1. After deletion of the amino-terminal 15 amino acids from ARF1(39-45p3), its interaction with p5 was essentially equivalent to that of p3, suggesting that the amino terminus of ARF1(39-45p3) may interfere with binding to p5. These results are consistent with the conclusion that the GAP domain of ARD1 interacts with the effector region of the ARF domain and thereby stimulates GTP hydrolysis.

Exocytosis in single chromaffin cells: regulation by a secretory granule-associated Go protein

1. Besides having a role in signal transduction, trimeric G proteins may also be involved in membrane trafficking events. In chromaffin cells, G alpha o has been found associated with the membrane of secretory granules. Here we examined the role of Go in regulated exocytosis using pressure microinjection combined with amperometric measurement of catecholamine secretion from individual chromaffin cells. 2. Microinjection of GTP gamma S and mastoparan strongly inhibits the amperometric response to either nicotine or high K+. 3. The presence of mastoparan in the cell incubation medium had no effect on K(+)-evoked secretion, suggesting that mastoparan blocks the exocytotic machinery through an intracellular target protein not located just beneath the plasma membrane. 4. Microinjection of anti-G alpha o antibodies potentiates by more than 50% the K(+)-evoked secretion, whereas anti-G alpha i1/2 antibodies have no effect. 5. Thus an inhibitory Go protein, probably associated with secretory granules, controls exocytosis in chromaffin cells. The intracellular proteins controlling organelle-associated G proteins are currently unknown. The neuronal cytosolic protein GAP-43 stimulates G alpha o in purified chromaffin granule membranes and inhibits exocytosis in permeabilized cells. We show here that microinjection of a synthetic peptide corresponding to the domain of GAP-43 that interacts with Go inhibits secretion. We suggest that GAP-43 or a related cytosolic protein controls the exocytotic priming step in chromaffin, cells by stimulating a granule-associated Go protein.

Regulated exocytosis in chromaffin cells. A potential role for a secretory granule-associated ARF6 protein

The ADP-ribosylation factor (ARF) GTP-binding proteins are believed to function as regulators of vesicular budding and fusion along the secretory pathway. To investigate the role of ARF in regulated exocytosis, we have examined its intracellular distribution in cultured chromaffin cells by subcellular fractionation and immunoreplica analysis. We found that ARF6 is specifically associated with the membrane of purified secretory chromaffin granules. Chemical cross-linking and immunoprecipitation experiments suggested that ARF6 may be part of a complex with betagamma subunits of trimeric G proteins. Stimulation of intact chromaffin cells or direct elevation of cytosolic calcium in permeabilized cells triggered the rapid dissociation of ARF6 from secretory granules. This effect could be inhibited by AlF4- which selectively activates trimeric G proteins. Furthermore, a synthetic myristoylated peptide corresponding to the N-terminal domain of ARF6 strongly inhibited calcium-evoked secretion in streptolysin-O-permeabilized chromaffin cells. The possibility that ARF6 plays a role in the effector pathway by which trimeric G proteins control exocytosis in chromaffin cells is discussed.

Characterization of a GTPase-activating protein that stimulates GTP hydrolysis by both ADP-ribosylation factor (ARF) and ARF-like proteins. Comparison to the ARD1 gap domain

ADP-ribosylation factors (ARFs) are approximately20-kDa guanine nucleotide-binding proteins that participate in vesicular transport in the Golgi and other intracellular compartments and stimulate cholera toxin ADP-ribosyltransferase activity. Both GTP binding and hydrolysis are necessary for its physiological functions, although purified mammalian ARF lacks detectable GTPase activity. An ARF GTPase-activating protein (GAP) was purified >15,000-fold from rat spleen cytosol using (NH4)2SO4 precipitation and chromatography on Ultrogel AcA 34, DEAE-Sephacel, heparin-Sepharose, hydroxylapatite, and Ultrogel AcA 44. In fractions ( approximately100-kDa proteins) from Ultrogel AcA 44, a major protein band of approximately50 kDa on SDS-polyacrylamide gel electrophoresis correlated with GAP activity, consistent with it being a homodimer, thus differing from an ARF GAP purified from rat liver (Makler, V., Cukierman, E., Rotman, M., Admon, A., and Cassel, D. (1995) J. Biol. Chem. 270, 5232-5237). Purified spleen GAP accelerated hydrolysis of GTP bound to recombinant ARF1, ARF3, ARF5, and ARF6; no effect of NH2-terminal myristoylation was observed. ARF GAP also activated GTP hydrolysis by ARL1, which is 56% identical in amino acid sequence to ARF1, but lacks ARF activity. ARD1 is a 64-kDa guanine nucleotide-binding protein that contains an 18-kDa ARF domain at its carboxyl terminus; the ARF domain lacks the amino-terminal alpha-helix found in native ARF and hence is similar to the amino-terminal truncated mutant Delta13ARF1. Both the ARF domain of ARD1 and Delta13ARF1 were poor substrates for ARF GAP. The non-ARF1 domain of ARD1 enhanced the GTPase activity of the ARF domain, but not that of the ARF proteins and Delta13ARF1, i.e. it lacks the relatively broad substrate specificity exhibited by ARF GAP.

Annexin II in exocytosis: catecholamine secretion requires the translocation of p36 to the subplasmalemmal region in chromaffin cells

Annexin II is a Ca(2+)-dependent membrane-binding protein present in a wide variety of cells and tissues. Within cells, annexin II is found either as a 36-kD monomer (p36) or as a heterotetrameric complex (p90) coupled with the S-100-related protein, p11. Annexin II has been suggested to be involved in exocytosis as it can restore the secretory responsiveness of permeabilized chromaffin cells. By quantitative confocal immunofluorescence, immunoreplica analysis and immunoprecipitation, we show here the translocation of p36 from the cytosol to a subplasmalemmal Triton X-100 insoluble fraction in chromaffin cells following nicotinic stimulation. A synthetic peptide corresponding to the NH2-terminal domain of p36 which contains the phosphorylation sites was microinjected into individual chromaffin cells and catecholamine secretion was monitored by amperometry. This peptide blocked completely the nicotine-induced recruitment of p36 to the cell periphery and strongly inhibited exocytosis evoked by either nicotine or high K+. The light chain of annexin II, p11, was selectively expressed by adrenergic chromaffin cells, and was only present in the subplasmalemmal Triton X-100 insoluble protein fraction of both resting and stimulated cells. p11 can modify the Ca(2+)- and/or the phospholipid-binding properties of p36. We found that loss Ca2+ was required to stimulate the translocation of p36 and to trigger exocytosis in adrenergic chromaffin cells. Our findings suggest that the translocation of p36 to the subplasmalemmal region is an essential event in regulated exocytosis and support the idea that the presence of p11 in adrenergic cells may confer a higher Ca2+ affinity to the exocytotic pathway in these cells.

Trimeric G proteins control regulated exocytosis in bovine chromaffin cells: sequential involvement of Go associated with secretory granules and Gi3 bound to the plasma membrane

Regulated secretion requires both calcium and MgATP. Studies in diverse secretory systems indicate that ATP is required to prime the exocytotic apparatus whereas Ca2+ triggers the final ATP-independent fusion event. In this paper, we examine the possible role of trimeric G proteins in these two steps of exocytosis in chromaffin cells. We show that in the presence of low concentrations of Mg2+, mastoparan selectively stimulates G proteins associated with purified chromaffin granule membranes. Under similar conditions in permeabilized chromaffin cells, mastoparan inhibits ATP-dependent secretion but is unable to trigger ATP-independent release. This inhibitory effect of mastoparan on secretion was specifically reversed by anti-Galphao antibodies and a synthetic peptide corresponding to the carboxyl terminus of Galphao. In contrast, mastoparan required millimolar Mg2+ for the activation of plasma membrane-bound G proteins and stimulation of ATP-independent secretion in permeabilized chromaffin cells. The latter effect was completely inhibited by anti-Galphai3. By confocal immunofluorescence and immunoreplica analysis, we provide evidence that in chromaffin cells Go is preferentially associated with secretory granules, while Gi3 is essentially present on the plasma membrane. Our findings suggest that these two trimeric G proteins act in series in the exocytotic pathway in chromaffin cells: a secretory granule-associated Go protein controls the ATP-dependent priming reaction, whereas a plasma membrane-bound Gi3 protein is involved in the late calcium-dependent fusion step, which does not require ATP.

ARD1, a 64-kDa bifunctional protein containing an 18-kDa GTP-binding ADP-ribosylation factor domain and a 46-kDa GTPase-activating domain

The alpha subunits of the heterotrimeric guanine nucleotide-binding proteins (G proteins) hydrolyze GTP at a rate significantly higher than do most members of the Ras family of approximatelly 20-kDa GTP-binding proteins, which depend on a GTPase-activating protein (GAP) for acceleration of GTP hydrolysis. It has been demonstrated that an inserted domain in the G-protein alpha subunit, not present in the much smaller Ras-like proteins, is responsible for this difference [Markby, D. W., Onrust, R. & Bourne, H. R. (1993) Science 262, 1895-1900]. We report here that ARD1, a 64-kDa protein with an 18-kDa carboxyl-terminal ADP-ribosylation factor (ARF) domain, exhibited significant GTPase activity, whereas the ARF domain, expressed as a recombinant protein in Escherichia coli, did not. Addition of the 46-kDa amino-terminal extension (similarly synthesized in E. coli) to the GTP-binding ARF-domain of ARD1 enhanced GTPase activity and inhibited GDP dissociation. The kinetic properties of mixtures of the ARF and non-ARF domains were similar to those of an intact recombinant ARD1. Physical association of the two proteins was demonstrated directly by gel filtration and by using the immobilized non-ARF domain. Thus, like the alpha subunits of heterotrimeric G proteins, ARD1 appears to consist of two domains that interact to regulate the biological activity of the protein.

Survival despite almost complete fibrous obstruction of a Sorin tilting disc mitral prosthesis

We report the case of a 40-year-old woman whose Sorin tilting disc mitral prosthesis was obstructed by fibrous overgrowth to the point of near occlusion. The unusual features of this case are that the patient survived reoperation and that her preoperative symptoms were mild despite an immobile disc and near occlusion of the valve. In most similar cases in the literature, preoperative symptoms have been acute and mortality has been high.

Long-term follow-up of different models of mechanical and biological mitral prostheses

Three hundred eighty-five valve prostheses were implanted between 1974 and 1981 in patients with isolated mitral disease: 157 caged-ball valves (156 Starr-Edwards; 1 Smeloff-Cutter) (group A), 107 tilting-disc valves (44 Bjork-Shiley, 49 Sorin, 14 Lillehei-Kaster) (group B), 121 porcine bioprostheses (45 Carpentier-Edwards, 66 Liotta, 10 Hancock) (group C). Perioperative mortality was 9.5% in group A, 11.2% in group B and 6.6% in group C. The follow-up was 86% complete. Actuarial freedom from complications was calculated as follows (linearised rates in brackets) in groups A, B and C, respectively: survival: 47.01% +/- 0.11 (3% patient/yr), 53.37% +/- 0.08 (1.8% patient/yr), 61.24% +/- 0.05 (2.2% patient/yr); thromboembolism: 67.94% +/- 0.09 (1.18% patient/yr); 73.07% +/- 0.06 (1% patient/yr); 97.43% +/- 0.02 (0.02% patient/yr); anticoagulation-related hemorrhage: 84.10% +/- 0.13 (0.18% patient/yr), 97.21% +/- 0.01 (0.12% patient/yr), 100%; prosthetic valve endocarditis: 100% in groups A and B, 95.76% +/- 0.02 (0.18% patient/yr) in group C; valve-related mortality: 87.52% +/- 0.03 (0.75% patient/yr), 87.96% +/- 0.03 (0.56% patient/yr), 82.53% +/- 0.04 (0.93% patient/yr); valve failure: 81.22% +/- 0.07 (0.56% patient/yr), 63.36% +/- 0.1 (1.06% patient/yr), 14.31% +/- 0.05 (4% patient/yr); treatment failure: 78.81% +/- 0.05 (1.12% patient/yr), 76.44% +/- 0.09 (0.62% patient/yr), 80.97% +/- 0.04 (1% patient/yr); all valve-related morbidity and mortality: 40.43% +/- 0.13 (1.93% patient/yr), 57.76% +/- 0.08 (1.43% patient/yr), 14.96% +/- 0.05 (4.18% patient/yr); all valve-related morbidity and mortality at 5 years: 91.97% +/- 0.02 (7.8% patient/yr), 87.06% +/- 0.03 (3.6% patient/yr), 90.27% +/- 0.03 (2.6% patient/yr); at 10 years: 80.4% +/- 0.03 (4.6% patient/yr), 75.91% +/- 0.03 (2.6% patient/yr), 37.44% +/- 0.05 (4.18% patient/yr).(ABSTRACT TRUNCATED AT 250 WORDS)

GAP-43 controls the availability of secretory chromaffin granules for regulated exocytosis by stimulating a granule-associated G0

Besides having a role in signal transduction, heterotrimeric G proteins may also be involved in membrane trafficking events as suggested by their presence in specific intracellular compartments. In chromaffin cells, G alpha 0 is associated with secretory organelles, and its activation inhibits exocytosis. Although plasma membrane-bound G proteins are activated by cell-surface receptors, the intracellular proteins controlling organelle-associated G proteins are currently unknown. GAP-43, a neuronal protein enriched in axonal growth cones and presynaptic terminals, is one possible candidate since it can directly stimulate purified G0. We have investigated the interaction of adrenal medullary GAP-43 with chromaffin granule-associated G0 and its effect on catecholamine secretion. Cytosolic and depalmitoylated membrane-extracted GAP-43 were found to stimulate guanine nucleotide binding and exchange activity in chromaffin granule membranes. In permeabilized chromaffin cells, both forms of GAP-43 blocked calcium-dependent exocytosis, and this effect was inhibited by specific antibodies against G alpha 0. A synthetic peptide corresponding to the GAP-43 domain that interacts with G0 inhibited catecholamine secretion. This effect could be selectively reversed by the COOH-terminal peptide of G alpha 0. These results indicate that GAP-43 may be an endogenous pseudoreceptor for the secretory granule-bound form of G0 and can thereby control calcium-regulated exocytosis in chromaffin cells.

Early experience with the Jyros bileaflet valve in the mitral position: high incidence of valve thrombosis

The Jyros valve is a new bileaflet valve with the unusual feature that the hinge is expected to rotate continuously inside the housing. Nine isolated Jyros mitral prostheses were implanted from July to October 1993. All patients survived the surgical procedure and during the follow up underwent transthoracic (TTE) and transesophageal echocardiograms (TEE) for the evaluation of hinge rotation. Neither TTE nor TEE were able to show hinge rotation in any patient at any time. Five patients had prosthetic thrombosis. In the successfully treated with thrombolysis. In the remaining patient thrombolysis was contraindicated. Eight patients are alive; one died of gastro-intestinal bleeding a few months after discharge. The absence of hinge rotation may be the triggering mechanism of valve thrombosis although no explanted prostheses were available for examination. Further studies are necessary to understand the mechanism of valve thrombosis with the Jyros bileaflet prosthesis.

Distinct heterotrimeric GTP-binding-proteins act in series to control the exocytotic machinery in chromaffin cells

Regulated exocytosis requires both calcium and MgATP. Although the biochemical events responsible for ATP-dependent calcium-activated secretion have not been elucidated yet, some progress has been made in determining the relative order of the ATP- and calcium-dependent steps. Studies on permeabilized secretory cells have shown that MgATP acts before calcium and maintains the secretory apparatus in a "primed" state. In this paper, we examine the possible role of heterotrimeric G-proteins in these two steps of exocytosis in permeabilized chromaffin cells. We show that mastoparan and other activators of heterotrimeric G-proteins inhibit the MgATP-dependent reaction, but stimulate the late calcium-dependent step of exocytosis. Non-hydrolyzable GTP analogues (GTP-gamma-S and GMP-PNP) mimic the dual effects of mastoparan on secretion, but with different potencies, suggesting the involvement of two distinct heterotrimeric G-proteins in regulated exocytosis. GPAnt-2, a substance P related peptide known to inhibit the stimulation of Gi and Go by mastoparan, reverses, in a dose-dependent manner, both the inhibitory and stimulatory effects of mastoparan on secretion. These results indicate that two distinct heterotrimeric G-proteins from the Gi/o family may act in series in the exocytotic pathway in chromaffin cells: one controls the ATP-dependent priming step, whereas the second is involved in the late calcium-dependent fusion step which does not require ATP.

Acute postoperative block of mechanical prostheses: incidence and treatment

Acute intermittent postoperative block of mechanical prostheses is a rare and life-threatening complication; its incidence and treatment are not well defined. Between January 1975 and June 1991, 2839 mechanical prostheses were implanted using the same technique: mattress suture for mitral valve replacement and simple suture for aortic valve replacement. Prosthetic block occurred in eight patients: four following mitral valve replacement and four after aortic valve replacement. The blocked prosthesis was always a tilting disc valve (five Sorin, two Björk-Shiley and one Medtronic). The event occurred over a time interval of 6-48 h (mean(s.d.) 17.3 (15.6)h). All patients having mitral valve replacement needed emergency prosthetic replacement. In aortic valve replacement, reoperation was necessary in two patients; the disc block disappeared in the others. All patients are alive with a follow-up ranging between 3 and 168 (mean 32.5) months. No structural failure was found in explanted prostheses leading to a diagnosis of extrinsic block. The overall incidence of this complication was 0.28% (eight of 2839); 0.24% (four of 1645) for mitral valve replacement and 0.33% (four of 1194) for aortic valve replacement respectively (n.s.). It was exclusively related to tilting disc valves (0.44%; eight of 1830) versus ball and bileaflets valve (0 of 1009). In mitral valve replacement reoperation on patients is mandatory; in aortic valve replacement patients the left ventricular pressure itself can overcome the prosthetic block. Attention should be paid to valve excision and suture techniques as tilting disc prostheses are more vulnerable to extrinsic block. Furthermore, their use is contraindicated in redo operations and mitral valve replacement with total or partial preservation of mitral apparatus.

[Surgical treatment of incessant atrial tachycardia: description of a case]

A 50 year old woman with no evidence of structural heart disease was referred for ectopic incessant repetitive atrial tachycardia uncontrolled by medical therapy. Intracavitary and transesophageal simultaneous recordings revealed the earliest atrial electrical activity to be located in the left atrium. Intraoperative electrophysiologic mapping demonstrated that the site of earliest atrial activation was in a small diverticulum of the left atrial appendage. Excision of the appendage and isolation of left atrium was carried out with restoration of sinus rhythm. The patient was arrhythmia-free till 24 months later. Surgical treatment appears to be an effective therapeutic option for drug-resistant ectopic atrial tachycardia.

Exocytosis in chromaffin cells: evidence for a MgATP-independent step that requires a pertussis toxin-sensitive GTP-binding protein

We have previously described that mastoparan, an amphiphilic tetradecapeptide that activates heterotrimeric G-proteins, inhibits Ca(2+)-induced MgATP-dependent secretion from streptolysin-O-permeabilized chromaffin cells [Vitale, Mukai, Rouot, Thiersé, Aunis and Bader (1993) J. Biol. Chem. 268, 14715-14723]. Our observations suggest the involvement of an inhibitory G(o)-protein, possibly located on the membrane of secretory granules, in the final stages of the exocytotic pathway in chromaffin cells. Here, we demonstrate that mastoparan is also able to stimulate the Ca(2+)-dependent secretion of catecholamines in the absence of MgATP in the medium. This MgATP-independent secretion is totally blocked by tetanus toxin, a potent inhibitor of exocytosis in all neurosecretory cells so far investigated, suggesting that the mastoparan target is a component of the exocytotic machinery. Mas17, a mastoparan analogue inactive on G-proteins, had no effect on catecholamine secretion whereas both Mas7, a highly active analogue of mastoparan, and AlF4-, which selectively activates trimeric G-proteins, triggered MgATP-independent secretion. Non-hydrolysable GTP analogues (GTP[S] and p[NH]ppG) mimicked the dual effects of mastoparan on secretion: they inhibited exocytosis in the presence of MgATP and stimulated MgATP-independent secretion. The different potencies displayed by these two analogues suggest the involvement of two distinct G-proteins. Accordingly, the mastoparan-induced MgATP-independent secretion is highly sensitive to pertussis toxin (PTX) whereas the inhibition by mastoparan of secretion in the presence of MgATP is resistant to PTX treatment. When permeabilized cells were incubated with mastoparan, the release of arachidonic acid increased in a PTX-sensitive manner. 7,7-Dimethyl-5,8-eicosadienoic acid, a potent inhibitor of intracellular phospholipase A2, inhibited both the arachidonate release and the MgATP-independent catecholamine secretion evoked by mastoparan. In contrast, neomycin, an inhibitor of phospholipase C, had no significant effect on either the release of arachidonic acid or the secretion of catecholamines provoked by mastoparan. We conclude that two distinct heterotrimeric G-proteins act in series in the exocytotic pathway in chromaffin cells: one controls an ATP-dependent priming step through an effector pathway that remains to be determined, and the second is involved in a late Ca(2+)-dependent step which does not require MgATP but possibly involves the generation of arachidonic acid.

Long term results of surgery for prosthetic valve endocarditis

Operative mortality, recurrence and late survival were analyzed in 64 patients operated for prosthetic valve endocarditis (PVE) between 1980-1992: age, sex, drug addiction, early vs. late PVE, micro-organism, sepsis at the time of surgery, indication for surgery, prosthesis type and site were assessed as potential risk factors. PVE developed after replacement for native valve endocarditis in 23 cases (Group A) and after replacement for other valvular disease in 41 patients (Group B). The overall operative mortality was 28.1% (18/64); 16 operative survivors underwent a second reoperation with eight operative deaths (50%), four of them a third procedure with two operative deaths (50%), and one patient had a successful fourth intervention. Female sex (p = 0.015) and sepsis at the time of surgery (p = 0.013), were found statistically significant independent predictors of operative mortality. Age (p:0.002), mechanical valves (p:0.05) and mitral position (p:0.03) were significant predictors of PVE recurrence. None of the risk factors considered were significant for late survival. Twelve-year actuarial survival for all patients was 52.11 +/- 10%; it was 33.3 +/- 13% for Group A and 73.4 +/- 14% for Group B (p:0.04). Patients with mechanical valves and bioprostheses had an actuarial survival of 39.5 +/- 15% and 48.5 +/- 14% respectively with no significant difference. PVE is still a challenging complication of heart valve replacement; patients with PVE after native valve endocarditis have a very poor outcome. Prompt prosthetic replacement is recommended whenever the antibiotic treatment is unsuccessful and/or the hemodynamic status deteriorates.

Prosthetic valve obstruction: thrombolysis versus operation

An acute obstruction is a life-threatening complication of mechanical valve prostheses, and is caused by the formation of fresh clot or fibrous tissue overgrowth, or both. Accurate selection of the most appropriate treatment for a particular patient is mandatory. From January 1991 to July 1992, 28 cases of prosthetic thrombosis were managed. Twenty patients underwent surgical treatment, with one operative death, and 8 patients were treated with thrombolysis using recombinant tissue-type plasminogen activator (rt-PA). The criteria for using thrombolysis were (1) the recent onset of symptoms, (2) transesophageal echocardiographic evidence of clots on the valve or cardiac chambers, and (3) preserved disc excursions. All patients who underwent thrombolysis had mechanical valves (two bileaflets, four tilting discs, and two ball valves); seven valves were in the mitral position and one was in the aortic. Symptoms of obstruction consisted of cardiac failure in 6 cases or thromboembolism in 5, or both. The mean interval between the onset of symptoms and the initiation of thrombolysis was 81 +/- 65 hours. After infusion of the rt-PA, normal valve function was restored in all patients, as documented by transesophageal echocardiography. No deaths or neurologic complications occurred; there was one episode of minor peripheral embolism. Thrombolysis using rt-PA may be the appropriate treatment in patients with primary thrombosis of mechanical valves, thereby avoiding the operation-related risks.

Short-term results of bovine internal mammary artery use in cardiovascular surgery

Over a 14-month period, 28 bovine internal mammary arteries (Bioflow, Bio-Vascular, Inc.; St. Paul, Minnesota, USA) were implanted in 20 patients at our institutions. In 8 patients, the bovine internal mammary artery was used to bypass coronary vessels: in 4 of these patients, coronary artery bypass grafting was performed because of coronary disease (1 type-I aortic dissection); in the other 4 (all with aortic dissection), the modified Bentall technique was used for coronary artery reimplantation. In the remaining 12 patients, the bovine artery was used in vascular surgery: as a graft for lower-extremity occlusive disease (4 patients), arteriovenous fistula (2 patients), and aorticorenal bypass (1 patient); and as a patch to the carotid bifurcation or the common femoral artery in association with endarterectomy (5 patients). The 21 bovine grafts were all 5 mm in diameter; the 7 bovine patches were 4 mm. Of the 8 coronary bypass patients, 2 who underwent coronary artery bypass grafting had acute postoperative myocardial infarctions, and 2 who underwent the modified Bentall technique died in surgery. Follow-up angiography showed complete bovine internal mammary artery graft occlusion in 2 patients; 2 symptom-free patients refused examination. Of the vascular surgery patients, 1 with mild left leg claudication had graft occlusion, shown by angiography, 4 months after surgery. Renal scintigraphy performed in the patient with aorticorenal bypass 4 months after operation showed no blood flow to the kidney. Two patients died for reasons unrelated to bovine mammary artery grafting. The remaining patients are well and free of complications. In view of the high incidence of early occlusion, we do not recommend use of the bovine internal mammary artery graft in coronary surgery. In vascular surgery, the results are more encouraging; however, studies comprising a larger number of patients and longer follow-up are needed to determine whether the use of the bovine internal mammary artery graft can be recommended.

Mid-term follow-up after heart valve replacement with CarboMedics bileaflet prostheses

The CarboMedics cardiac prosthesis (CarboMedics, Inc., Austin, Tex.) is a relatively new, low-profile bileaflet prosthesis. We report the results of a prospective mid-term evaluation of 426 CarboMedics prostheses implanted at our institution. Three hundred fifty patients had CarboMedics prostheses implanted in the mitral (n = 125), aortic (n = 149), or aortic and mitral positions (n = 76). Hospital mortality was 5.2%. Follow-up was 98% complete, with 478 patient/years and a mean follow-up of 19 months (range 1 to 42 months). Actuarial freedom from complications were calculated as follows (linearized rates in parentheses): late mortality 97% +/- 0.77% (2.7%), thromboembolism 98% +/- 0.4% (0.5%), anticoagulation-related hemorrhage 98.6% +/- 0.4% (0.4%), nonstructural dysfunction 98.5% +/- 0.6 (0.2%), valve-related mortality 91.5% +/- 0.7 (0.5%), valve failure 90.9% +/- 1% (0.7%), treatment failure 92.8% +/- 0.8% (0.7%), and all valve-related morbidity and mortality 90% +/- 2% (2.6%). According to our results, the CarboMedics valve has a low rate of complications that further improves the quality of life in patients with heart valve prostheses.

Exocytosis in chromaffin cells. Possible involvement of the heterotrimeric GTP-binding protein G(o)

The use of non-hydrolyzable analogues of GTP in permeabilized secretory cells suggests that guanine nucleotide-binding regulatory proteins (G proteins) may be involved in regulated exocytosis. Because GTP analogues are known to modulate both monomeric low molecular mass G proteins and heterotrimeric G proteins, we have examined the effect of mastoparan, an activator of heterotrimeric G proteins, on secretion from intact and permeabilized chromaffin cells. In intact cells, mastoparan inhibited catecholamine secretion evoked by nicotine but had no effect on release induced by other secretagogues. In permeabilized cells, mastoparan inhibited calcium-dependent secretion providing that the pores created in the plasma membrane allow the penetration of the peptide into the cytoplasm. These results indicate that mastoparan blocks the exocytotic machinery through an intracellular target protein that may not be located just beneath the plasma membrane. Accordingly, mastoparan was able to stimulate G proteins associated with purified chromaffin granule membranes, in a range of concentration and Mg2+ requirement that was similar to its inhibitory effect on secretion. Mas 17, a mastoparan analogue inactive on purified G proteins, neither modified catecholamine secretion nor stimulated chromaffin granule G proteins. The substance P-related peptide, GPAnt-2, known to antagonize the effects of mastoparan on G(o), blocked both the inhibitory effect of mastoparan on secretion and the mastoparan-stimulated GTPase activity in chromaffin granule membranes. Moreover, specific antibodies raised against the carboxyl terminus of G(o) alpha reversed in a dose-dependent manner the inhibition by mastoparan on catecholamine release and the stimulation by mastoparan of chromaffin granule-associated G proteins. These results suggest that the secretory machinery in chromaffin cells can be blocked by activating a G(o) protein. Consistent with this finding, two other known activators of heterotrimeric G proteins, aluminum fluoride and benzalkonium chloride, inhibited calcium-evoked catecholamine secretion in streptolysin O-permeabilized chromaffin cells. We conclude that an inhibitory G(o) protein, possibly located on the membrane of secretory granules, is involved in the final stages of exocytosis in chromaffin cells.

[Slow and fast AV nodal pathways in tachycardia complicating Wolff-Parkinson-White syndrome: report of a case]

Electrophysiologic studies in a patient with intermittent ventricular pre-excitation revealed several types of paroxysmal narrow-QRS tachycardia (PSVT). One type of PSVT was characterized by normal retrograde atrial sequences with P waves occurring simultaneously with QRS. This type of PSVT reflected AV nodal reentry with anterograde slow pathway and retrograde fast pathway conduction. A second PSVT reflected alternation of anterograde fast and slow AV nodal pathway conduction and retrograde anomalous pathway conduction. A third PSVT reflected anterograde slow AV nodal pathway and retrograde anomalous pathway conduction. Moreover, discontinuous AV nodal conduction curves (A1A2/H1H2), characteristic of dual AV nodal pathway conduction, were obtained with programmed atrial extra stimulation. These observations suggest that dual AV nodal pathway conduction can coexist with abnormal bypass tract and can be the cause of PSVT in patients with Wolff-Parkinson-White syndrome.

[Phase 3 and phase 4 bundle of branch block]

Intermittent left bundle branch blocks are present in the ECGs of 1 patient with mitral valve disease. By occurring either after short or long cycles they represent respectively phase 3 and phase 4 blocks. Such mechanisms emphasize the relationship between automatism and conduction. The occurrence of block and of normal conduction during cycles of the same length, its correlation with the conduction of the previous cycle, demonstrate the presence of a functional linking between successive impulses. This linking may occur every time a potential or active macroreentry circuit exist. In our case the circuit is formed by the 2 bundle branches which join distally in the ventricular septum.

[Ergometric test in the diagnostic and prognostic evaluation of arrhythmia]

One thousand three hundred patient's stress tests were analyzed to value arrhythmia outline and its relationship with anamnesis and clinical data. The patients were divided into two groups: group A, with no arrhythmias at rest, and group B with arrhythmias at rest. All classic nosographic arrhythmias were considered. In some teenager patients with arrhythmias at rest and no organic cardiopathy, anomalies disappeared during stress, showing the benignity of the phenomenon. Supraventricular stress induced arrhythmias has 1.2% of incidence in normal subjects, but 81% in heart disease patients. Supraventricular tachycardia was induced in 6 patients. Ventricular stress induced arrhythmias are found in 4.9%. Two cases of sudden death occurred in our groups.

[Permanent atrial standstill and atrial disease]

A case of permanent atrial standstill suspected upon electrocardiogram is reported, and confirmed by electrophysiological investigation. The originality of this case resides in the fact that the atrial standstill marks the developmental outcome of a bradycardia-tachycardia syndrome. This developmental sequence is the subject on discussion. It is concluded that a combination of auricular muscle lesion and sinus node tissue remains the most plausible anatomical and pathophysiological substratum of the bradycardia-tachycardia syndrome which developed into atrial standstill.

[EGG and arrhythmia in subjects with implanted dual-chamber VDD and DDD pacemakers]

The ECGs of four patients with implanted dual chamber VDD and DDD PMKs are shown to demonstrate the difficulty of their interpretation and show some arrhythmias related to dual chamber pacing. In the first patient the DDD PMK caused a high ventricular frequency synchronizing on the atrial fibrillation "f" waves which occurred suddenly some time after PMK implantation; this problem was solved by programming the PMK in VVI. The second and third case, with implanted DDD and VDD PMK respectively, exemplify atrial sensing dysfunction due to atrial catheter displacement. In the fourth patient, with implanted VDD PMK, VDD stimulation periods and VVI ones alternated due to non-adjusted programming. Therefore, the paper re-emphasizes the need for accurate and periodic controls of patients with implanted PMK to correct dysfunction or undesirable patterns of stimulation.

[Myocardial dysfunction subsequent to supraventricular tachycardia]

In a patient without a demonstrable heart disease a congestive heart failure developed during an atrioventricular tachycardia which persisted for 20 days at the rate of 180/b/m'. After conversion to sinus rhythm, by means of transesophageal pacing, a quick regression of the failure symptoms followed. The heart rate increase and the persistence of tachycardia may have determined the depletion of myocardial stores and therefore, the myocardial dysfunction responsible for the cardiac failure. In order to prevent myocardial dysfunctions, it is necessary to interrupt supraventricular tachycardias as early as possible, even when they are observed in patients without any heart disease.

[Effectiveness of diltiazem in controlling ventricular response and improving exercise capacity in chronic atrial fibrillation. Double-blind, cross-over study]

Although digoxin is often the drug of choice to control the ventricular response in chronic atrial fibrillation, it fails to control exercise-induced increase in heart rate. The efficacy of diltiazem to control ventricular response and to improve cardiovascular performance during maximal exercise was investigated in 13 digitalized patients with chronic atrial fibrillation. A placebo controlled prospective randomized double-blind study, was preceded by open titration phase. During the diltiazem treatment phase, mean ventricular response diminished at rest (85 +/- 12 versus 107 +/- 19 during digoxin therapy and versus 101 +/- 18 during digoxin and placebo therapy; p less than 0.001), as well as during maximal exercise (142 +/- 13 versus 159 +/- 17 during digoxin treatment and versus 160 +/- 14 during digoxin plus placebo treatment; p less than 0.001). During exercise (50 W), in a subgroup of 7 patients, mean ventricular rate dropped: 109 +/- 19 versus 142 +/- 21 during digoxin treatment and versus 143 +/- 17 during digoxin plus placebo treatment; p less than 0.001). In all patients, the mean rate at rest decreased about 19.3 +/- 6.9% and at maximal exercise about 10.3 +/- 4.9%. In the subgroup of the 7 patients ventricular mean rate at a load of 50 W decreased about 23.6 +/- 7.9%. In all the patients, maximal exercise capacity improved: the MET mean value increased from 3.59 +/- 1.3 to 4.52 +/- 1.18 (p less than 0.001); the mean value of the maximum exercise (MEC), according to the Redfords formula, increased from 65 +/- 48 to 132 +/- 70 (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)