Real-time conformational dynamics of SARS-CoV-2 spikes on virus particles

SARS-CoV-2 spike (S) mediates entry into cells and is critical for vaccine development against COVID-19. S is synthesized as a precursor, processed into S1 and S2 by furin proteases, and activated for fusion when human angiotensin-converting enzyme 2 (hACE2) engages the receptor-binding domain (RBD) and when the N-terminus of S2 is proteolytically processed. Structures of soluble ectodomains and native virus particles have revealed distinct conformations of S, including a closed trimer with all RBD oriented downward, trimers with one or two RBDs up, and hACE2-stabilized conformations with up to three RBD oriented up. Real-time information that connects these structures, however, has been lacking. Here we apply single-molecule Forster Resonance Energy Transfer (smFRET) imaging to observe conformational dynamics of S on virus particles. Virus-associated S dynamically samples at least four distinct conformational states. In response to hACE2, S opens into the hACE2-bound S conformation through at least one on-path intermediate, with trypsin partially activating S. Conformational preferences of convalescent patient plasma and monoclonal antibodies suggest mechanisms of neutralization involving either direct competition with hACE2 for binding to RBD or allosteric interference with conformational changes required for entry. Our findings inform on mechanisms of S recognition and on conformations for immunogen design.

Identification of interdependent variables that influence coreceptor switch in R5 SHIV(SF162P3N)-infected macaques

Background

We previously reported that adoption of an “open” envelope glycoprotein (Env) to expose the CD4 binding site for efficient receptor binding and infection of cell targets such as macrophages that express low levels of the receptor represents an early event in the process of coreceptor switch in two rapidly progressing (RP) R5 SHIV_SF162P3N-infected rhesus macaques, releasing or reducing Env structural constraints that have been suggested to limit the pathways available for a change in coreceptor preference. Here we extended these studies to two additional RP monkeys with coreceptor switch and three without to confirm and identify additional factors that facilitated the process of phenotypic conversion.

Results

We found that regardless of coreceptor switching, R5 viruses in SHIV_SF162P3N-infected RP macaques evolved over time to infect macrophages more efficiently; this was accompanied by increased sCD4 sensitivity, with structural changes in the CD4 binding site, the V3 loop and/or the fusion domain of their Envs that are suggestive of better CD4 contact, CCR5 usage and/or virus fusion. However, sCD4-sensitive variants with improved CD4 binding were observed only in RPs with coreceptor switch. Furthermore, cumulative viral load was higher in RPs with than in those without phenotypic switch, with the latter maintaining a longer period of seroconversion.

Conclusions

Our data suggest that the increased virus replication in the RPs with R5-to-X4 conversion increased the rate of virus evolution and reduction in the availability of target cells with optimal CD4 expression heightened the competition for binding to the receptor. In the absence of immunological restrictions, variants that adopt an “open” Env to expose the CD4 binding site for better CD4 use are selected, allowing structural changes that confer CXCR4-use to be manifested. Viral load, change in target cell population during the course of infection and host immune response therefore are interdependent variables that influence R5 virus evolution and coreceptor switch in SHIV_SF162P3N-infected rhesus macaques. Because an "open" Env conformation also renders the virus more susceptible to antibody neutralization, our findings help to explain the infrequent and late appearance of X4 virus in HIV-1 infection when the immune system deteriorates.

An inducible cell-cell fusion system with integrated ability to measure the efficiency and specificity of HIV-1 entry inhibitors

HIV-1 envelope glycoproteins (Envs) mediate virus entry by fusing the viral and target cell membranes, a multi-step process that represents an attractive target for inhibition. Entry inhibitors with broad-range activity against diverse isolates of HIV-1 may be extremely useful as lead compounds for the development of therapies or prophylactic microbicides. To facilitate the identification of such inhibitors, we have constructed a cell-cell fusion system capable of simultaneously monitoring inhibition efficiency and specificity. In this system, effector cells stably express a tetracycline-controlled transactivator (tTA) that enables tightly inducible expression of both HIV-1 Env and the Renilla luciferase (R-Luc) reporter protein. Target cells express the HIV-1 receptors, CD4 and CCR5, and carry the firefly luciferase (F-Luc) reporter gene under the control of a tTA-responsive promoter. Thus, Env-mediated fusion of these two cell types allows the tTA to diffuse to the target cell and activate the expression of the F-Luc protein. The efficiency with which an inhibitor blocks cell-cell fusion is measured by a decrease in the F-Luc activity, while the specificity of the inhibitor is evaluated by its effect on the R-Luc activity. The system exhibited a high dynamic range and high Z'-factor values. The assay was validated with a reference panel of inhibitors that target different steps in HIV-1 entry, yielding inhibitory concentrations comparable to published virus inhibition data. Our system is suitable for large-scale screening of chemical libraries and can also be used for detailed characterization of inhibitory and cytotoxic properties of known entry inhibitors.

Adoption of an "open" envelope conformation facilitating CD4 binding and structural remodeling precedes coreceptor switch in R5 SHIV-infected macaques

A change in coreceptor preference from CCR5 to CXCR4 towards the end stage disease in some HIV-1 infected individuals has been well documented, but the reasons and mechanisms for this tropism switch remain elusive. It has been suggested that envelope structural constraints in accommodating amino acid changes required for CXCR4 usage is an obstacle to tropism switch, limiting the rate and pathways available for HIV-1 coreceptor switching. The present study was initiated in two R5 SHIV(SF162P3N)-infected rapid progressor macaques with coreceptor switch to test the hypothesis that an early step in the evolution of tropism switch is the adoption of a less constrained and more "open" envelope conformation for better CD4 usage, allowing greater structural flexibility to accommodate further mutational changes that confer CXCR4 utilization. We show that, prior to the time of coreceptor switch, R5 viruses in both macaques evolved to become increasingly sCD4-sensitive, suggestive of enhanced exposure of the CD4 binding site and an "open" envelope conformation, and this correlated with better gp120 binding to CD4 and with more efficient infection of CD4(low) cells such as primary macrophages. Moreover, significant changes in neutralization sensitivity to agents and antibodies directed against functional domains of gp120 and gp41 were seen for R5 viruses close to the time of X4 emergence, consistent with global changes in envelope configuration and structural plasticity. These observations in a simian model of R5-to-X4 evolution provide a mechanistic basis for the HIV-1 coreceptor switch.

Evolution of and risk factors for psychological distress in patients with psoriasis: the PSYCHAE study

Psychological distress (PD) is common in patients with psoriasis but little is known about its evolution. The aim of this study is to assess the evolution of PD in psoriasis. For this purpose, 1,505 psoriatic patients, who had been previously enrolled in the PSYCHAE study, an observational multicenter Italian study, were re-evaluated after 6 and 12 months. Minor and major PD were assessed using the General Health Questionnaire (GHQ) and Brief Symptoms Inventory (BSI) questionnaires and coping using Brief COPE questionnaire. Minor PD was present in 46 percent of patients but halved during the study. Female gender, surface area, topical steroids, methotrexate, self-distraction, venting and behavioral disengagement were risk factors for minor PD; cyclosporine and humor were protective. Major PD was present in 11 percent of patients and remained stable. Female gender, venting, religion, behavioral disengagement and emotional support were risk factors for major PD; instrumental support was protective. In conclusion, the results obtained suggest that major PD remained stable after 12 months and that coping was a predictor of its evolution.

Psychological distress and coping strategies in patients with psoriasis: the PSYCHAE Study

OBJECTIVE

Our objectives were to determine the prevalence of psychological distress in a large sample of Italian patients with psoriasis; to establish whether disease severity and psychological distress are associated; to identify the strategies employed to cope with psoriasis; to evaluate the coping strategies employed by dermatologists; and to identify potential predictors of psychological distress.

DESIGN

Cross-sectional.

SETTING

Thirty-nine Italian dermatology centres.

SUBJECTS

One thousand five hundred and eighty (1580) patients with psoriasis.

METHODS

Minor psychological distress was evaluated using the General Health Questionnaire-12 (GHQ-12) and major psychopathological distress using the Brief Symptom Inventory (BSI); coping strategies were evaluated using the Brief COPE questionnaire; disease severity was evaluated using the body surface area index.

RESULTS

Patients were aged 44 +/- 13 years (mean +/- SD) and were mainly men (57%). Minor psychological distress was present in 46% of patients and major psychopathological distress in 11% of them. Both minor (54% vs. 40%, P < 0.0001) and major (17% vs. 7%, P < 0.0001) distress were more frequent in women than in men. The psychological status of women was worse than that of men independently from the extension of psoriasis. There was no association between the presence of distress and the treatment prescribed by dermatologists. Planning and active coping were the strategies most commonly employed by patients to cope with psoriasis, but there were between-gender differences. Most dermatologists employed a 'problem-orientated' attitude in caring for patients.

CONCLUSIONS

(i) Psychological distress was relatively frequent in our patients with psoriasis; (ii) female gender was the most important predictive factor for psychological distress; (iii) there was no association between psoriasis severity and psychological distress; (iv) planning and active coping were the coping strategies most frequently employed by patients; and (v) most dermatologists employed a problem-orientated attitude in caring for patients.

Do children with developmental dyslexia have an implicit learning deficit?

OBJECTIVE

The purpose of this study was to investigate the effects of specific types of tasks on the efficiency of implicit procedural learning in the presence of developmental dyslexia (DD).

METHODS

Sixteen children with DD (mean (SD) age 11.6 (1.4) years) and 16 matched normal reader controls (mean age 11.4 (1.9) years) were administered two tests (the Serial Reaction Time test and the Mirror Drawing test) in which implicit knowledge was gradually acquired across multiple trials. Although both tests analyse implicit learning abilities, they tap different competencies. The Serial Reaction Time test requires the development of sequential learning and little (if any) procedural learning, whereas the Mirror Drawing test involves fast and repetitive processing of visuospatial stimuli but no acquisition of sequences.

RESULTS

The children with DD were impaired on both implicit learning tasks, suggesting that the learning deficit observed in dyslexia does not depend on the material to be learned (with or without motor sequence of response action) but on the implicit nature of the learning that characterises the tasks.

CONCLUSION

Individuals with DD have impaired implicit procedural learning.

Chronic urticaria: diagnostic recommendations

A group of European recognized dermatologists - the European Working Group on the Diagnosis of Chronic Urticaria - met on 12 March 1999 to discuss best practice for assessing and diagnosing patients with chronic urticaria. These are their recommendations. The recommendations will be valuable for the majority of cases, but are not exhaustive and may not include every possible precipitating factor.

Exercise-induced paroxysmal atrioventricular block during nuclear perfusion stress testing: evidence for transient ischemia of the conduction system

BACKGROUND

Whether tachycardia-dependent paroxysmal AV block, an uncommon complication of exercise stress testing in patients with infranodal conduction disturbances, can result from acute ischemia of the conduction system is still speculative, and is based on post-hoc evidence of right coronary artery disease and abolition of block after coronary angioplasty.

METHODS AND RESULTS

In two patients, from a database of 3000 undergoing nuclear exercise stress testing, transient paroxysmal AV block developed 1-4 minutes after the injection of the radionuclide agent. Nuclear perfusion imaging demonstrated stress-induced ischemia of the posteroseptal segments, which corresponds to the anatomical region of the His bundle, and perfusion recovery in the images obtained at rest. Angiography disclosed critical narrowing of the right coronary artery in both cases.

CONCLUSION

Nuclear myocardial perfusion imaging provides noninvasive evidence that transient ischemia of the posteroseptal segment, anatomically corresponding to the His bundle, can result in paroxysmal AV block in patients with severe right coronary artery and chronic infranodal conduction disturbances. The demonstration of the underlying pathophysiological mechanism is useful for selecting the most effective treatment strategy.

Net primary production of a forest ecosystem with experimental CO2 enrichment

The concentration of atmospheric carbon dioxide was increased by 200 microliters per liter in a forest plantation, where competition between organisms, resource limitations, and environmental stresses may modulate biotic responses. After 2 years the growth rate of the dominant pine trees increased by about 26 percent relative to trees under ambient conditions. Carbon dioxide enrichment also increased litterfall and fine-root increment. These changes increased the total net primary production by 25 percent. Such an increase in forest net primary production globally would fix about 50 percent of the anthropogenic carbon dioxide projected to be released into the atmosphere in the year 2050. The response of this young, rapidly growing forest to carbon dioxide may represent the upper limit for forest carbon sequestration.

A short-term trial of tacrolimus ointment for atopic dermatitis. European Tacrolimus Multicenter Atopic Dermatitis Study Group

BACKGROUND

Tacrolimus (FK 506) is an effective immunosuppressant drug for the prevention of rejection after organ transplantation, and preliminary studies suggest that topical application of tacrolimus is effective in the treatment of atopic dermatitis.

METHODS

We conducted a randomized, doubleblind, multicenter study that compared 0.03 percent, 0.1 percent, and 0.3 percent tacrolimus ointment with vehicle alone in patients with moderate to severe atopic dermatitis. The ointment was applied twice daily to a defined, symptomatic area of 200 to 1000 cm2 of skin for three weeks. The primary end point was the change in the summary score for erythema, edema, and pruritus between the first and last days of treatment.

RESULTS

After three weeks of treatment, the median percentage decrease in the summary score for dermatitis on the trunk and extremities was 66.7 percent for the 54 patients receiving 0.03 percent tacrolimus, 83.3 percent for the 54 patients receiving 0.1 percent tacrolimus, 75.0 percent for the 51 patients receiving 0.3 percent tacrolimus, and 22.5 percent for the 54 patients receiving vehicle alone (P<0.001). The results for the face and neck were similar. The differences among the three tacrolimus groups were not statistically significant. A sensation of burning at the site of application was the only adverse event that was significantly more frequent with tacrolimus than with vehicle alone (P<0.001). Throughout the study, most patients in all three tacrolimus groups had blood concentrations of tacrolimus below 0.25 ng per milliliter. The highest concentration was 4.9 ng per milliliter, which was reported in the group receiving 0.3 percent tacrolimus.

CONCLUSIONS

The short-term application of tacrolimus ointment is effective in the treatment of atopic dermatitis, with the sensation of burning being the main side effect.

[Combination of transesophageal atrial pacing and echo-dipyridamole test in the diagnosis of coronary disease in patients with suspected angina pectoris and negative exercise test]

BACKGROUND

Echo-dipyridamole test is an useful tool for non-invasive demonstration of inducible myocardial ischemia in patients with coronary artery disease, its sensitivity being consistently higher as compared with classic exercise stress testing. However, in patients with single vessel who often perform a normal or borderline stress test, even the sensibility of echo-dipyridamole test is comparatively reduced.

METHODS

In 19 patients with clinically suspected angina (effort-related in 4, at rest in 8, mixed in 7) and normal exercise stress test, standard echo-dipyridamole test was performed. Thereafter, rapid atrial pacing, a procedure associated with a sharp increase of myocardial oxygen consumption, was performed by means of a transoesophageal catheter during the proceeding 5 min and during 4 min of repeated dipyridamole 0.56 mg/kg infusion.

RESULTS

Standard echo-dipyridamole test induced ventricular wall motion abnormalities in 3 patients (one with borderline exercise stress test), whereas repeated pacing-sensitized procedure obtained wall motion abnormalities (apical, septal and lateral) in the same and in 4 additional patients. Coronary angiography demonstrated > 70% stenosis in 8/19 patients (single vessel disease in 5), 7 of whom had been correctly recognized by pacing-dipyridamole test; therefore, sensitivity of the latter as compared with standard dipyridamole test was 87% and 37% respectively. The anatomic correlation of induced wall motion abnormalities with coronary arterial stenosis was demonstrated in all cases. Specificity was 100% with both methods.

CONCLUSIONS

Although limited by its restricted patient population, this study suggests that atrial pacing, performed via transoesophageal catheter, can significantly improve the positive predictive value of echo-dipyridamole test in coronary artery disease. By means of this simple procedure, the possibility of non invasively diagnosing even single vessel stenosis in patients with inconclusive exercise stress testing can be significantly improved.

Family history, smoking habits, alcohol consumption and risk of psoriasis

We have conducted a multicentre case-control study to assess the epidemiological importance of previously suggested risk factors for psoriasis, including family history of the disease, smoking and alcohol consumption. Newly diagnosed psoriatics, with a history of skin manifestations no longer than 2 years were eligible as cases; as controls we selected subjects with newly diagnosed dermatological conditions other than psoriasis. Interviews were performed by trained medical investigators using a structured questionnaire. Two-hundred and fifteen cases, aged 16-65 years (median age 38), and 267 controls, aged 15-65 years (median age 36), were interviewed and included in the analysis. Family history was a risk factor for psoriasis; the multiple logistic regression (MLR) adjusted-odds ratio was 18.8 (95% confidence interval 6.4-54.8) for a history in parents, and 3.2 (95% confidence interval 1.5-6.6) for a history in siblings. The risk of psoriasis was higher for current smokers than for those who had never smoked. The MLR adjusted odds ratio was 2.1 (95% confidence interval 1.1-4.0) for people smoking 15 cigarettes or more per day. The risk of psoriasis was higher for alcohol drinkers: compared with teetotallers the MLR adjusted-odds ratios were 1.3 (95% confidence interval 0.8-2.3) for subjects drinking one or two drinks/day and 1.6 (95% confidence interval 0.9 to 3.0) for those drinking three or more. However, the trend in risk was not statistically significant. Our study confirms the role of family history in psoriasis and provides some evidence of a dose-response relationship for an association between smoking habits and psoriasis.

[Therapy and prevention of atrial fibrillation]

In the last decade, broader insights into the mechanisms and clinico-prognostic significance of atrial fibrillation have prompted a dramatic shift in the clinician's decision making process in terms of treatment and prevention of this common rhythm disturbance. In fact, evidence of short- or long-term untoward effects on cardiac function and the risk of cerebrovascular accidents, together with a much wider therapeutic armamentarium, form the rationale for the present far more aggressive attitude, aiming at restoring sinus rhythm in all patients in whom an even weak chance exists. The newer class IC (flecainide, propafenone) and class III (amiodarone, sotalol) antiarrhythmic agents are widely and successfully utilized to restore and to maintain sinus rhythm, with significant advantages in comparison with classic quinidine derivatives in terms of efficacy and patient compliance, as demonstrated in clinical controlled trials. Moreover, calcium channels blocking agents as verapamil and diltiazem have been demonstrated more effective than digitalis in the limitation of ventricular rate in patients with chronic atrial fibrillation. Although the advantages of long-term anticoagulation and/or antiaggregation in patients with atrial fibrillation are still being widely investigated at the present time, data obtained in the last years favoured a wider use of this treatment. Many non-pharmacologic interventions have been shown as dramatically effective in particular aspects of atrial fibrillation. Permanent atrial or atrioventricular pacing, alone or in association with antiarrhythmic drugs, has come out as first choice option in patients with bradycardia-tachycardia syndrome. Transcatheter ablation and antiarrhythmic surgical techniques are more and more widely utilized with increasing success in cases refractory to conventional approaches.

[His bundle block 2:1 during paroxysmal supraventricular tachycardia involving an occult accessory atrio-His pathway]

A high degree AV block during paroxysmal supraventricular tachycardia is an uncommon and short-lasting finding in patients with intranodal re-entry circuits. The AV block is the result of temporary inadequacy of the infranodal conduction system--which is not part of the circuit--to cope with the sudden increase in heart rate in terms of refractory periods and conduction velocity. In a patient with paroxysmal reciprocating tachycardia at a very high rate (230-250 bpm), 2:1 intra-hisian AV block was constantly observed after arrhythmia initiation by atrial extrastimuli. This persisted for 1-4 minutes and then progressively subsided passing through a period of 3:2 intra- infra-hisian AV block until it reached 1:1 conduction with transient left bundle branch block. The latter occasionally disappeared as result of retrograde activation of the area of functional anterograde block and of subsequent noncompensatory pause, following a premature ventricular depolarization. Tachycardia-dependent AV block was abolished by verapamil and flecainide, because of lengthening of the tachycardia cycle length. Functional and electropharmacological features of retrograde conduction were consistent with an extranodal concealed atrio-hisian accessory pathway acting as the retrograde limb of the re-entry circuit. Moreover, His bundle electrogram was prolonged and polyphasic even in sinus rhythm. Therefore, tachycardia-dependent advanced AV block can occur not only in truly intranodal re-entry but also in very fast atrio-hisian re-entry tachycardias with evidence of transient impairment of intra-hisian conduction, distal to the insertion of the accessory pathway. Localized morphofunctional pathological changes in the His bundle are probably involved in the mechanism of this uncommon pattern.

[Clinical framework of psoriatic arthropathy. Proposal of an evaluation protocol]

Psoriatic arthropathy is an inflammatory seronegative arthritis characterized by an involvement of peripheral or axial joints in association with psoriasis. In this study the clinical features of both skin and joints have been observed simultaneously by a rheumatologist and a dermatologist. We have finally proposed a clinical protocol based on PASI to evaluate psoriasis and on a simple subset classification to estimate joint involvement.

Evaluation of skin irritation and contact sensitizing potential of fenticonazole

A double blind, randomized clinical trial was performed on twelve healthy volunteers to evaluate the irritation potential of fenticonazole 2% cream (Lomexin) and spray versus micomazole 2% cream and econazole 1% spray. The contact-sensitizing potential of the two fenticonazole preparations was also investigated. There was no evidence of irritation after the treatments with fenticonazole cream, its excipients, miconazole cream and fenticonazole spray excipients, whereas signs of irritation were observed in four cases after treatment with the spray formulations (two after fenticonazole, two after econazole). The contact-sensitizing test was performed only with fenticonazole 2% cream and spray. Neither spray nor cream formulation of fenticonazole showed evidence of sensitization in any of the twelve subjects.

Permanent form of junctional reciprocating tachycardia involving an atrio-hisian accessory pathway: electrophysiologic and histologic correlations

We present clinical, electrophysiologic and morphologic correlations of a patient with a permanent form of junctional reciprocating tachycardia, who died from a lung tumor. At electrophysiologic study, the tachycardia circuit was suspected to involve an atrio-Hisian accessory pathway antegradely and the AV node retrogradely; a ventriculo-atrial accessory pathway was excluded. Pathologic examination revealed a right-sided atrio-Hisian accessory pathway and an area of abnormal dispersion in the distal His bundle fibers. This case is consistently different from another previously reported case in which a concealed, serpiginous, septal atrioventricular accessory pathway was demonstrated by anatomic examination. Thus, different substrates seem to be responsible for the permanent form of junctional reciprocating tachycardia.

Antibodies to cardiac Purkinje cells: further characterization in autoimmune diseases and atrioventricular heart block

We confirmed the occurrence of IgG antibodies reacting with ox cardiac conducting tissue in the serum of some human subjects. These antibodies failed to react with all ox cardiac conducting tissue cells; they reacted only with the cells defined as Purkinje cells. Having checked 352 sera, we found that the prevalence of antibodies to Purkinje cells was 11% in normal subjects (no correlation with sex and age), 14% in systemic lupus erythematosus, 21% in rheumatoid arthritis, 18% in progressive systemic sclerosis, and 23% in Sjögren syndrome. In 50 patients with permanent pacemakers for chronic non-postinfarction atrioventricular (AV) block the prevalence was 30% (P = 0.008). In a selected set of 29 patients with clinically idiopathic AV block located at or below the level of the His bundle the prevalence was 34.5% (P = 0.006). The possible role of anti-Purkinje cell antibodies in autoimmune damage of cardiac conduction tissue is discussed.

Long-term prognostic significance and electrophysiological evolution of intraventricular conduction disturbances complicating acute myocardial infarction

Fifty-nine patients with post-infarctional, isolated intraventricular conduction disturbances (IVCD) who survived the acute stage of myocardial infarction were followed up after hospital discharge for a mean period of 11.4 +/- 4.8 months. Fourteen patients (24%) had HV interval prolongation (greater than 55 ms) during AMI (group A), and 45 patients had normal HV intervals (76%, group B). His bundle recordings were repeated during follow-up in 48 survivors after a mean period of 7.2 +/- 0.7 months. Infranodal conduction delay in the acute stage of infarction was correlated with a higher incidence of heart failure during AMI (78% of patients in group A vs 22% in group B, p less than 0.001), and with higher rate of cardiac mortality during follow-up (50% in group A vs 13% in group B, p less than 0.01). Survivors of group A showed a higher functional NYHA class, a higher incidence of CHF, and a higher prevalence of complex ventricular arrhythmias at Holter monitoring. No statistically significant difference in late sudden death was evident between the two groups of patients, and the global incidence of late AV block was 2%. At repeat His bundle recording no significant change (greater than 5 ms) in HV interval could be demonstrated in comparison to the acute phase recording, neither in patients with prolonged nor in patients with normal HV time. We conclude that HV prolongation in patients with isolated, post-infarctional IVCD is correlated with a worse prognosis, both during acute infarction and during the follow-up period, which presumably reflects wider anatomic damage in comparison to patients with normal HV time. The low incidence of late AV block and the electrophysiological demonstration of the stability of infranodal conduction several months after AMI indicate that these patients do not require permanent prophylactic pacing after acute myocardial infarction.

Role of the polymorphonuclear neutrophils in the phototoxic reaction in porphyria cutanea tarda

We have compared the superoxide production of polymorphonuclear cells (PMNLs) from healthy donors, when incubated with either control or porphyria cutanea tarda (PCT) sera at 4, 24 and 48 hours after exposure in vivo to UVA light. Serum from UVA-irradiated (1-5 J/cm2) PCT patients generated significantly greater amounts of superoxides from PMNLs than serum from UVA-irradiated (8-12 J/cm2) normal controls. This indicates that serum factors activated by porphyrin plus UVA stimulate neutrophilic granulocytes to liberate superoxides, triggering a series of events that cause tissue damage. The vascular lesions in patients with PCT could be, at least in part, due to this cytotoxic effect.

Hemodynamic effects of antiarrhythmic drugs in acute myocardial infarction

The hemodynamic effects induced by an i.v. administration of Amiodarone (5 mg/Kg in 10 min + continuous infusion of 0.6 mg/min for 4-40 hrs), Propafenone (1-2 mg/Kg in 5 min + continuous infusion of 10-15 mcg/Kg/min for 24 hrs) and Mexiletine (250 mg in 15 min + 250 mg in 1 hr) have been evaluated in patients with acute myocardial infarction complicated by sinus tachycardia and hyperdynamic pattern, ventricular or supraventricular arrhythmias. The hemodynamic serial determinations have been comprehensive of: heart rate; systolic, diastolic and mean pressure; central venous pressure; arterial and wedge pulmonary pressure; cardiac output and cardiac index; vascular systemic resistences; left ventricular stroke work index; left ventricular mean ejection rate; double and triple product. In all of the three groups we observed: a reduction of cardiac index associated with an increase of left and right ventricular filling pressure and a reduction either of left ventricular stroke work index and left ventricular mean ejection rate; these hemodynamic changes were less significant after Mexiletine than after Amiodarone or Propafenone. These data confirm the negative inotropic effect of the three drugs; anyhow, these changes are usually well tolerated by patients affected by AMI with a sufficiently preserved ventricular function. The authors, however, reccommend an accurate hemodynamic monitoring of the effects of the drugs also to identify patients with a not overt ventricular failure which may become manifest after drug administration.

[Hemodynamic effects of propafenone in acute myocardial infarct]

The hemodynamic effects of Propafenon were evaluated in 11 patients with acute myocardial infarction complicated by atrial and/or ventricular arrhythmias (atrial fibrillation in 4 cases, atrial premature beats in 3 cases, ventricular premature beats Class II-IVa in 4 and rapid sustained ventricular tachycardia in one case). Drug was administered as a bolus of 1-2 mg/kg in 5 min, followed by a 10-15 gamma/kg/min infusion for 24 hours in 7 patients. Serial measurements were taken of heart rate, systemic blood pressure, right atrial, pulmonary and capillary wedge pressure, cardiac output, cardiac index, total systemic resistances, left ventricular stroke work index, left ventricular ejection time and left ventricular mean ejection rate (LVMER) (8 cases) and PEP/LVET ratio (5 cases). After the intravenous bolus, a significant reduction of cardiac index (p less than 0.01) and LVMER (p less than 0.05) parallel to an increase of total systemic resistances and PEP/LVET ratio (p less than 0.01 and p less than 0.05 respectively); was observed no other parameter varied significantly. The peak hemodynamic effect was observed after 10 minutes and return to normal required from 30 minutes to 3-6 hours in the more severely affected patients. No late negative inotropic action was evident in 6 out of 7 patients who received long term infusion. Suppression or greater than 80% reduction of premature beats was evident in 9/12 cases. Sinus node function, atrioventricular and intraventricular conduction, and the QTc interval did not vary significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

[Electrophysiological mechanisms of tachyarrhythmias associated with the sick sinus syndrome (author's transl)]

Atrail programmed stimulation (APS) and His bundle recordings were performed in 24 patients with assessed sick sinus syndrome, 14 of whom had previously suffered from bouts of spontaneous paroxysmal tachycardias (Group I) and 10 with no history of previous similar complication (Group II). APS reproduced re-entry arrhythmias in 13 cases of Group I (92%). In 6 cases, junctional reciprocating tachycardia was elicited and the atrioventricular node function curve showed a typical steplike profile, consistent with longitudinal dissociation of the node itself as a cause of reciprocation. In 7 cases with previous paroxysmal atrial tachycardias, APS elicited intra-atrial re-entry arrhythmias. Absolutely no arrhythmia was elicited by APS in the 10 cases of Group II. High incidence of basal prolongation of conduction intervals was observed in both Groups (11 cases in Group I, 6 cases in Group II). Intra-atrial and/or atrio-nodel conduction delays were recognized in all the cases with intra-atrial re-entry arrhythmias. These results suggest that so called bradycardia-tachycardia syndrome should be regarded as an independent clinical form from the sick sinus syndrome, sharing with the latter the sinusal disfunction only. Re-entry mechanisms seems to be mainly responsible for the inititation of paroxysmal tachyarrhythmias: re-entry in the atrium, based on stable conduction delays, is probably correlated with scattered lesions of the same degenerative process affecting the sinus node. On the contrary, the frequent association of sick sinus syndrome with junctional paroxysmal tachycardia and its comples dissociation mechanism of the a-v node, raises the suspicion that, in such cases, two completely different processes are merely coexisting: a degenerative lesion of the sinus node and an anatomical or functional anomaly of a separate portion of the conduction system.