Anticoagulant therapy and central nervous system complications in patients with prosthetic valve endocarditis

Management of anticoagulation in patients with infective endocarditis

Infective endocarditis (IE) carries a high risk of vascular complications (e.g., cerebral embolism, intracerebral hemorrhage, and renal infarction), which are correlated with increased early and late mortality. Although anticoagulation is the cornerstone for management of thromboembolic complications, it remains controversial and challenging in patients with IE. An appropriate anticoagulation strategy is crucial to improving outcomes and requires a good understanding of the indication, timing, and regimen of anticoagulation in the setting of IE. Observational studies have shown that anticoagulant treatment failed to reduce the risk of ischemic stroke in patents with IE, supporting that IE alone is not an indication for anticoagulation. In the absence of randomized controlled trials and high-quality meta-analyses, however, current guidelines on IE were based largely on observational data and expert opinion, providing few specific recommendations on anticoagulation. A multidisciplinary approach and patient engagement are required to determine the timing and regimen of anticoagulation in patients with IE, especially in specific situations (e.g., receiving warfarin anticoagulation at the time of IE diagnosis, cerebral embolism or ischemic stroke, intracerebral hemorrhage, or urgent surgery). Collectively, individualized strategies on anticoagulation management of IE should be based on clinical evaluation, available evidence, and patient engagement, and ultimately be developed by the multidisciplinary team.

Coagulation Disorders in Infective Endocarditis: Role of Pathogens, Biomarkers, Antithrombotic Therapy (Systematic Review)

The issue of antithrombotic therapy in patients with infective endocarditis has been studied for over 75 years. During that time studying of pathogenesis of the disease and its embolic complications, lead to the introduction of the concept of “immunothrombosis”. That mechanism allows infective agents (mostly bacteria) to be cloaked from the immune system and to multiply freely, leading to growth of vegetation, thus resulting in higher chance of fragmentation. Small-scale experimental and clinical studies on the correction of hemostatic disorders in infective endocarditis, that were performed in 20th century, didn’t show any significant results, that could affect clinical practice. However, reinterpretation of available data on coagulative system will allow to have elements of hemostasis as an application point in treating infective endocarditis. The article will discuss latest insights on the role of hemostasis system in pathophysisology of infective endocarditis, its effects on the development of the embolic complications, perspectives for diagnostics and treatment.

Clinical Outcomes Associated With the Use of Anticoagulant and Antiplatelet Agents in Patients Undergoing Treatment for Infective Endocarditis: A Pilot Study

PURPOSE

The use of antithrombotic therapy may increase morbidity and mortality in patients with infective endocarditis (IE). This study evaluated the use of oral anticoagulant and antiplatelet agents on the development of embolic complications and bleeding episodes within 30 days of IE diagnosis.

METHODS

This pilot study was a retrospective medical record review of patients receiving treatment for IE between July 1, 2012, and July 31, 2017. The 2 study arms were patients receiving long-term anticoagulant/antiplatelet therapy versus patients not receiving therapy at the time of IE. Patients were eligible for inclusion if they had definite IE per modified Duke criteria and received at least 48 h of antibiotic therapy. The primary and secondary outcomes evaluated the incidence of embolic phenomenon and bleeding events in each group, respectively.

FINDINGS

Of 129 patients with IE, 34 met the eligibility criteria, with 20 patients on receiving anticoagulant/antiplatelet therapy and 14 patients not receiving anticoagulant/antiplatelet therapy. The median age was 63 years, with 50% male patients. Staphylococcus aureus was the infecting pathogen in 41% of patients. Embolic events occurred in 30% of patients receiving anticoagulant/antiplatelet therapy versus 7.1% of those not receiving therapy. No patients in the anticoagulant/antiplatelet therapy arm experienced a bleeding event, whereas 7.1% of those in the comparator arm did.

IMPLICATIONS

This retrospective pilot study indicates that patients with IE receiving anticoagulant/antiplatelet agents may be at an increased risk for embolic episodes versus those who are not. Larger, prospective studies are necessary to find a definitive correlation.

Follow-up and management of valvular heart disease patients with prosthetic valve: a clinical practice guideline for Indian scenario

PURPOSE

Valvular heart disease (VHD) patients after prosthetic valve implantation are at risk of thromboembolic events. Follow-up care of patients with prosthetic valve has a paramount role in reducing the morbidity and mortality. Currently, in India, there is quintessential need to stream line the follow-up care of prosthetic valve patients. This mandates the development of a consensus guideline for the antithrombotic therapy in VHD patients post prosthetic valve implantation.

METHODS

A national level panel was constituted comprising 13 leading cardio care experts in India who thoroughly reviewed the up to date literature, formulated the recommendations, and developed the consensus document. Later on, extensive discussions were held on this draft and the recommendations in 8 regional meetings involving 79 additional experts from the cardio care in India, to arrive at a consensus. The final consensus document is developed relying on the available evidence and/or majority consensus from all the meetings.

RESULTS

The panel recommended vitamin K antagonist (VKA) therapy with individualized target international normalized ratio (INR) in VHD patients after prosthetic valve implantation. The panel opined that management of prosthetic valve complications should be personalized on the basis of type of complications. In addition, the panel recommends to distinguish individuals with various co-morbidities and attend them appropriately.

CONCLUSIONS

Anticoagulant therapy with VKA seems to be an effective option post prosthetic valve implantation in VHD patients. However, the role for non-VKA oral therapy in prosthetic valve patients and the safety and efficacy of novel oral anticoagulants in patients with bioprosthetic valve need to be studied extensively.

Resuming anticoagulant therapy after intracerebral bleeding

The clinical benefit of resuming anticoagulant treatment after an anticoagulants-associated intracranial hemorrhage (ICH) is debated. No randomized trial has been conducted on this particular clinical issue. The risk of ICH recurrence from resuming anticoagulant therapy is expected to be higher after index lobar than deep ICH and in patients with not amendable risk factors for ICH. Retrospective studies have recently shown improved survival with resumption of treatment after index anticoagulants-associated ICH. Based on these evidences and on the risk for thromboembolic events without anticoagulant treatment, resumption of anticoagulation should be considered in all patients with mechanical heart valve prosthesis and in those with amendable risk factors for anticoagulants-associated ICH. Resumption with direct oral anticoagulants appears a reasonable option for non-valvular atrial fibrillation (NVAF) patients at moderate to high thromboembolic risk after deep ICH and for selected NVAF patients at high thromboembolic risk after lobar ICH. For VTE patients at high risk for recurrence, resumption of anticoagulation or insertion of vena cava filter should be tailored on the estimated risk for ICH recurrence.

Neurologic complications in infective endocarditis: identification, management, and impact on cardiac surgery

Neurologic complications of infective endocarditis (IE) are common and frequently life threatening. Neurologic events are not always obvious. The prediction and management of neurologic complications of IE are not easily approached algorithmically, and the impact they have on timing and ability to surgically repair or replace the affected valve often requires a painstaking evaluation and joint effort across multiple medical disciplines in order to achieve the best possible outcome. Although specific recommendations are always tailored to the individual patient, there are some guiding principles that can be used to help direct the decision-making process. Herein, we review the pathophysiology, epidemiology, manifestations, and diagnosis of neurological complications of IE and further consider the impact they have on clinical decision making.

Usefulness of anticoagulant therapy in the prevention of embolic complications in patients with acute infective endocarditis

Background. The use of anticoagulant therapy (ACT) in patients with acute infective endocarditis (IE) remains a controversial issue. Our study attempts to estimate the impact of ACT on the occurrence of embolic complications and the usefulness of ACT in the prevention of embolism in IE patients. Methods. The present authors analyzed 150 patients with left-sided IE. Embolisms including cerebrovascular events (CVE) and the use of ACT were checked at the time of admission and during hospitalization. Results. 57 patients (38.0%) experienced an embolic event. There was no significant difference in the incidence of CVE and in-hospital mortality between patients with and without warfarin use at admission, although warfarin-naïve patients were significantly more likely to have large (>1 cm) and mobile vegetation. In addition, there was no significant difference in the incidence of postadmission embolism and in-hospital death between patients with and without in-hospital ACT. On multivariate logistic regression analysis, ACT at admission was not significantly associated with a lower risk of embolism in patients with IE. Conclusions. The role of ACT in the prevention of embolism was limited in IE patients undergoing antibiotic therapy, although it seems to reduce the embolic potential of septic vegetation before treatment.

Prosthetic valve endocarditis: what is the evidence for anticoagulant therapy?

The use of anticoagulant therapy in prosthetic valve endocarditis is a controversial management issue. Some authorities believe that anticoagulation increases the potential risk of cerebral haemorrhage after a thromboembolism whereas others, however, affirm that cessation of anticoagulation itself increases the risk of thromboembolism and subsequent morbidity and mortality. We reviewed the association of anticoagulant therapy and cerebral complications in patients with prosthetic valve endocarditis. Our results suggest that anticoagulant therapy reduces the risk of thromboembolism and is not associated with increased risk of intracranial haemorrhage.

Antithrombotic and thrombolytic therapy for valvular disease: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Antithrombotic therapy in valvular disease is important to mitigate thromboembolism, but the hemorrhagic risk imposed must be considered.

METHODS

The methods of this guideline follow those described in Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines. Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

In rheumatic mitral disease, we recommend vitamin K antagonist (VKA) therapy when the left atrial diameter is > 55 mm (Grade 2C) or when complicated by left atrial thrombus (Grade 1A). In candidates for percutaneous mitral valvotomy with left atrial thrombus, we recommend VKA therapy until thrombus resolution, and we recommend abandoning valvotomy if the thrombus fails to resolve (Grade 1A). In patients with patent foramen ovale (PFO) and stroke or transient ischemic attack, we recommend initial aspirin therapy (Grade 1B) and suggest substitution of VKA if recurrence (Grade 2C). In patients with cryptogenic stroke and DVT and a PFO, we recommend VKA therapy for 3 months (Grade 1B) and consideration of PFO closure (Grade 2C). We recommend against the use of anticoagulant (Grade 1C) and antiplatelet therapy (Grade 1B) for native valve endocarditis. We suggest holding VKA therapy until the patient is stabilized without neurologic complications for infective endocarditis of a prosthetic valve (Grade 2C). In the first 3 months after bioprosthetic valve implantation, we recommend aspirin for aortic valves (Grade 2C), the addition of clopidogrel to aspirin if the aortic valve is transcatheter (Grade 2C), and VKA therapy with a target international normalized ratio (INR) of 2.5 for mitral valves (Grade 2C). After 3 months, we suggest aspirin therapy (Grade 2C). We recommend early bridging of mechanical valve patients to VKA therapy with unfractionated heparin (DVT dosing) or low-molecular-weight heparin (Grade 2C). We recommend long-term VKA therapy for all mechanical valves (Grade 1B): target INR 2.5 for aortic (Grade 1B) and 3.0 for mitral or double valve (Grade 2C). In patients with mechanical valves at low bleeding risk, we suggest the addition of low-dose aspirin (50-100 mg/d) (Grade 1B). In valve repair patients, we suggest aspirin therapy (Grade 2C). In patients with thrombosed prosthetic valve, we recommend fibrinolysis for right-sided valves and left-sided valves with thrombus area < 0.8 cm(2) (Grade 2C). For patients with left-sided prosthetic valve thrombosis and thrombus area ≥ 0.8 cm(2), we recommend early surgery (Grade 2C).

CONCLUSIONS

These antithrombotic guidelines provide recommendations based on the optimal balance of thrombotic and hemorrhagic risk.

Anti-thrombotic therapy in infective endocarditis

Despite advances in medical and surgical treatment, infective endocarditis (IE) still carries a high risk of morbidity and mortality. One of the determinants of an adverse outcome is the presence of systemic embolization and in particular, of CNS embolization. IE vegetations consist of bacteria, platelets and inflammatory cells in a fibrin mesh. The interactions between pathogens, platelets and the coagulation system are critical to vegetation initiation and growth. This understanding has led to the study of the effect of anti-thrombotic treatment on IE vegetation formation and embolization. Although it has been demonstrated that antiplatelet and anticoagulant strategies have an impact on in vitro and animal models of IE, results from the available clinical studies are conflicting. In this article, we provide an overview of the available experimental and clinical data on anti-thrombotic treatment in IE and summarize the current guidelines. An early diagnosis, prompt empiric antibiotic treatment and a careful selection of patients who benefit from early surgical intervention remain essential in the prevention of embolic complications. In patients who have other indications for antiplatelet or anticoagulant treatment, the continuation of this treatment is deemed safe in the absence of hemorrhagic complications.

Warfarin therapy and incidence of cerebrovascular complications in left-sided native valve endocarditis

Anticoagulant therapy has been anticipated to increase the risk of cerebrovascular complications (CVC) in native valve endocarditis (NVE). This study investigates the relationship between ongoing oral anticoagulant therapy and the incidence of symptomatic CVC in left-sided NVE. In a prospective cohort study, the CVC incidence was compared between NVE patients with and without ongoing warfarin. Among 587 NVE episodes, 48 (8%) occurred in patients on warfarin. A symptomatic CVC was seen in 144 (25%) patients, with only three on warfarin. CVC were significantly less frequent in patients on warfarin (6% vs. 26%, odds ratio [OR] 0.20, 95% confidence interval [CI] 0.06-0.6, p = 0.006). No increase in haemorrhagic lesions was detected in patients on warfarin. Staphylococcus aureus aetiology (adjusted OR [aOR] 6.3, 95% CI 3.8-10.4) and vegetation length (aOR 1.04, 96% CI 1.01-1.07) were risk factors for CVC, while warfarin on admission (aOR 0.26, 95% CI 0.07-0.94), history of congestive heart failure (adjusted OR 0.22, 95% CI 0.1-0.52) and previous endocarditis (aOR 0.1, 95% CI 0.01-0.79) correlated with lower CVC frequency.

The outcome of patients with transient ischemic attacks and stroke treated with anticoagulants

Long-term anticoagulant treatment was given to 25 patients with transient ischemic attacks (TIA) and 49 stroke patients with reversible ischemic neurological deficit or cerebral embolism. Another 16 TIA patients were observed without anticoagulant treatment. Life table analyses, comparing the observed with the expected frequency, revealed increased mortality in the TIA patients irrespective of whether or not they had received anticoagulants. The stroke patients treated with anticoagulants also had a higher mortality than expected. On the other hand, the incidence of subsequent stroke was not higher than expected in the TIA and stroke patients treated with anticoagulants, while it was significantly increased in the TIA patients not treated with anticoagulants. Thus, the risk of stroke, but not the risk of death, was normalized by the anticoagulant treatment. Unacceptably serious bleeding complications were seen in the group of stroke patients with anticoagulant treatment. Bleeding complications, in both TIA and stroke patients, seemed to be related to lengthy treatment, high blood pressure on admission or insufficient patient compliance.

Antithrombotic Therapy in Valvular Heart Disease—Native and Prosthetic

This chapter about antithrombotic therapy in native and prosthetic valvular heart disease is part of the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this chapter are the following: For patients with rheumatic mitral valve disease and atrial fibrillation (AF), or a history of previous systemic embolism, we recommend long-term oral anticoagulant (OAC) therapy (target international normalized ratio [INR], 2.5; range, 2.0 to 3.0) [Grade 1C+]. For patients with rheumatic mitral valve disease with AF or a history of systemic embolism who suffer systemic embolism while receiving OACs at a therapeutic INR, we recommend adding aspirin, 75 to 100 mg/d (Grade 1C). For those patients unable to take aspirin, we recommend adding dipyridamole, 400 mg/d, or clopidogrel (Grade 1C). In people with mitral valve prolapse (MVP) without history of systemic embolism, unexplained transient ischemic attacks (TIAs), or AF, we recommended against any antithrombotic therapy (Grade 1C). In patients with MVP and documented but unexplained TIAs, we recommend long-term aspirin therapy, 50 to 162 mg/d (Grade 1A). For all patients with mechanical prosthetic heart valves, we recommend vitamin K antagonists (Grade 1C+). For patients with a St. Jude Medical (St. Paul, MN) bileaflet valve in the aortic position, we recommend a target INR of 2.5 (range, 2.0 to 3.0) [Grade 1A]. For patients with tilting disk valves and bileaflet mechanical valves in the mitral position, we recommend a target INR of 3.0 (range, 2.5 to 3.5) [Grade 1C+]. For patients with caged ball or caged disk valves, we suggest a target INR of 3.0 (range, 2.5 to 3.5) in combination with aspirin, 75 to 100 mg/d (Grade 2A). For patients with bioprosthetic valves, we recommend vitamin K antagonists with a target INR of 2.5 (range, 2.0 to 3.0) for the first 3 months after valve insertion in the mitral position (Grade 1C+) and in the aortic position (Grade 2C). For patients with bioprosthetic valves who are in sinus rhythm and do not have AF, we recommend long-term (> 3 months) therapy with aspirin, 75 to 100 mg/d (Grade 1C+).

A randomized trial of aspirin on the risk of embolic events in patients with infective endocarditis

OBJECTIVES

This study examined the effect of aspirin on the risk of embolic events in infective endocarditis (IE).

BACKGROUND

Embolism is a major complication of IE, and studies in animal models have shown that platelet inhibition with aspirin can lead to more rapid vegetation resolution and a lower rate of embolic events.

METHODS

We conducted a randomized, double-blinded, placebo-controlled trial of aspirin treatment (325 mg/day) for four weeks in patients with IE to test the hypothesis that the addition of aspirin would reduce the incidence of clinical systemic embolic events. Patients with perivalvular abscess were excluded. Serial cerebral computed tomograms and transesophageal echocardiograms were obtained in a subset of patients.

RESULTS

During the four-year study period, 115 patients were enrolled: 60 assigned to aspirin and 55 assigned to placebo. Embolic events occurred in 17 patients (28.3%) on aspirin and 11 patients (20.0%) on placebo, with an odds ratio (OR) of 1.62 (95% confidence interval [CI] 0.68 to 3.86, p = 0.29). There was a trend toward a higher incidence of bleeding in the patients taking aspirin versus placebo (OR 1.92, 95% CI 0.76 to 4.86, p = 0.075). Development of new intracranial lesions was similar in both groups. Aspirin had no effect on vegetation resolution and valvular dysfunction.

CONCLUSIONS

In endocarditis patients already receiving antibiotic treatment, the addition of aspirin does not appear to reduce the risk of embolic events and is likely associated with an increased risk of bleeding. Aspirin is not indicated in the early management of patients with IE.

Infections of intracardiac devices

Intracardiac devices are increasingly used to correct hemodynamically dysfunctional valves and electrophysiologic abnormalities. These devices become infected at relatively low rates. Nevertheless, when these low rates are applied to widely used devices, significant numbers of infections result. Additionally, these infections have been associated with high degrees of morbidity and high mortality rates. This article reviews the epidemiology, microbiology, clinical presentation, and medical as well as surgical therapy of intracardiac device infections.

Management of intracranial infectious aneurysms: a series of 16 cases

OBJECTIVE

The purpose of this study was to better define the management of intracranial infectious aneurysms.

METHODS

We present a retrospective review of the management of 16 patients with intracranial infectious aneurysms. The mean follow-up period was 86 months.

RESULTS

None of the patients had a rehemorrhage during antibiotic treatment. The mortality and long-term outcome from ruptured intracranial infectious aneurysms may be better than previously thought. There was no significant difference in long-term outcome between patients with single or multiple infectious aneurysms or between patients who underwent surgical resection and those who were treated only with antibiotics.

CONCLUSION

Operative treatment should be pursued for patients with ruptured infectious aneurysms. Patients with unruptured intracranial infectious aneurysms should be observed during antibiotic therapy and followed up with cerebral angiography. Surgical resection should be considered if the aneurysm enlarges and the patient's general medical condition allows general anesthesia to be tolerated.

Subarachnoid haemorrhage associated with infectious endocarditis: case report and literature review

Cases of subarachnoid haemorrhage (SAH) as a presenting feature or soon after initiation of antibiotics in infectious endocarditis (IE) have been reported. However, most had documented mycotic aneurysms as the source of haemorrhage. Reports of IE associated with SAH of unclear source are rare. A case of SAH associated with IE is reported. We also reviewed our data set on neurological complications of IE at Mayo Clinic Rochester from 1980 to 1996 for additional cases. In addition to the index case, we identified seven cases of SAH amongst 489 patients (1%) with IE for a total of eight cases. In six patients, initial cerebral angiography, magnetic resonance angiography or autopsy did not show aneurysm or other aetiology for the SAH. A mycotic aneurysm was noted in one case and the other patient had an unruptured mycotic aneurysm of the tip of basilar artery. SAH was located in the basal cistern in two patients, sylvian fissure in three, and hemispheric sulci in three. SAH is an uncommon complication of IE, and in the setting of IE a specific cause, such as mycotic aneurysm, may not be identified.

Infections of intracardiac devices

Intracardiac devices are increasingly used to correct hemodynamically dysfunctional valves and electrophysiologic abnormalities. These devices become infected at relatively low rates. Nevertheless, when these low rates are applied to widely used devices, significant numbers of infections result. Additionally, these infections have been associated with high degrees of morbidity and high mortality rates. This article reviews the epidemiology, microbiology, clinical presentation, and medical as well as surgical therapy of intracardiac device infections.

Neurologic manifestations in Staphylococcus aureus endocarditis: a review of 260 bacteremic cases in nondrug addicts

PURPOSE

To investigate the neurologic manifestations of infective endocarditis caused by Staphylococcus aureus in a population of nondrug addicts with special emphasis on the clinical presentation, epidemiology, and mortality.

PATIENTS AND METHODS

During the period from 1982 to 1991 a total of 8,514 cases of bacteremia with S aureus were reported to the Staphylococcus Laboratory, Copenhagen, Denmark. The medical records of cases of suspected infective endocarditis were retrospectively reviewed and classified according to the new diagnostic criteria for endocarditis proposed by Durack.

RESULTS

A total of 260 cases from 63 hospitals fulfilled the diagnostic criteria. Overall, 91 patients (35%) experienced neurologic manifestations. Sixty-one presented with neurologic symptoms, whereas 30 patients developed neurologic complications at various intervals (median: 10 days) after the debut of the disease. The most frequent neurologic manifestation was unilateral hemiparesis, which occurred in 41 patients (45%). Forty-two percent of the females had neurologic manifestations compared to only 30% of the males (P = 0.06). Cases with native mitral valve infection had a significantly higher frequency of neurologic manifestations compared with all other valvular involvement (44% versus 29%, P = 0.02) but the frequency of neurologic complications was only nonsignificantly higher in those patients with native mitral valve infection than in those patients with native aortic valve infection (44% versus 31%, P = 0.10). Only two of the patients with tricuspid valve infection and none of those with congenital heart disorder experienced neurologic manifestations. A neurologic manifestation occurred in 22 (35%) of the 63 episodes in which vegetations were detected on the echocardiograms, compared with 17 (26%) of the 65 episodes without vegetations (P = 0.38). The mortality was 74% in patients with major neurologic manifestations and 56% in patients without neurologic manifestations (P = 0.008). In patients with neurologic complications the mortality was significantly higher among those treated with antibiotics alone as compared with those treated surgically (65 of 81, 80% versus 2 of 10, 20%; P = 0.0003).

CONCLUSIONS

In a population of nondrug addicts with infective endocarditis caused by S aureus the following main conclusions can be drawn: neurologic manifestations occur with a higher frequency in patients with native mitral valve infection. The presence of vegetations on echocardiograms is not a risk factor for developing neurologic complications but this conclusion is based on the results of transthoracic echocardiograms performed in only one half of the patients. The majority of the neurologic manifestations occur on presentation or shortly thereafter and the risk of recurrent embolism is low. Mortality is increased in patients with neurologic manifestations. A neurologic event per se may constitute an indication for surgical treatment.

Cardioembolic stroke

Cardioembolic stroke accounts for 1 out of every 5 to 6 ischemic strokes. A potential cardiac source should be considered in all patients presenting with ischemic neurologic deficits. a clear understanding of the various types of cardiac conditions associated with cardioembolic stroke is important. This article reviews potential cardiac sources of emboli and discusses the role of anticoagulation in both primary and secondary prevention of cardioembolic stroke. The role of echocardiography in evaluating patients with possible cardioembolic stroke is also addressed, and an algorithm is proposed for the use of echocardiography in evaluating patients with ischemic neurologic deficits.

Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres

Intracellular action potentials (IAPs) produced by short fibres in response to their electrical stimulation were analysed. IAPs were calculated on the basis of the Hodgkin-Huxley (1952) model by the method described by Joyner et al. (1978). Principal differences were found in processes of activation of short (semilength L less than 5 lambda) and long fibres under near-threshold stimulation. The shorter the fibre, the lower was the threshold value (Ithr). Dependence of the latency on the stimulus strength (Ist) was substantially non-linear and was affected by the fibre length. Both fibre length and stimulus strength influenced the IAP amplitude, the instantaneous propagation velocity (IPV) and the site of the first origin of the IAP (and, consequently, excitability of the short fibre membrane). With L less than or equal to 2 lambda and Ithr less than or equal to Ist less than or equal to 1.1Ithr, IPV could reach either very high values (so that all the fibre membrane fired practically simultaneously) or even negative values. The latter corresponded to the first origin of the propagated IAP, not at the site of stimulation but at the fibre termination or at a midpoint. The characters of all the above dependencies were unchanged irrespective of the manner of approaching threshold (variation of stimulus duration or its strength). Reasons for differences in processes of activation of short and long fibres are discussed in terms of electrical load and latency. Applications of the results to explain an increased jitter, velocity recovery function and velocity-diameter relationship are also discussed.

Long-term oral ciprofloxacin: experience in the treatment of incurable infective endocarditis

Acute septic infective endocarditis caused by Pseudomonas aeruginosa, in two patients with conditions that made it incurable, was treated with long-term orally administered ciprofloxacin. Bacteremia and symptoms cleared, resulting in subjective well-being without cure for three and one half and 22 months, respectively. Large amounts of ciprofloxacin, 150 and 1,440 g, respectively, were given continuously without apparent adverse reactions. Blood isolates of P. aeruginosa after treatment had limited progression of resistance to ciprofloxacin. Use of orally administered ciprofloxacin provides new opportunities for the long-term treatment of serious infections with restricted risk of bacterial drug resistance and no appreciable side effects.