Effects of biatrial pacing in prevention of postoperative atrial fibrillation after coronary artery bypass surgery

BACKGROUND

Atrial fibrillation (AF) is common after coronary artery bypass surgery (CABG) and results in prolonged hospitalization. The purpose of this study was to evaluate the efficacy of biatrial pacing in preventing post-CABG AF compared with single-site atrial pacing.

METHODS AND RESULTS

A total of 132 patients who had no history of AF and who underwent CABG were randomized to 1 of the following 4 groups: biatrial pacing (BiA), left atrial pacing (LA), right atrial pacing (RA), or no pacing (control) in postoperative period. Overdrive atrial pacing was performed for 5 days. The incidence of AF was significantly reduced in the BiA group (12.5%) compared with the other 3 groups (LA, 36.4%; RA, 33.3%; control, 41. 9%; P<0.05). The mean length of hospital stay was significantly reduced in the BiA group. At baseline, the mean P-wave duration (P(dur)) and dispersion (P(dis)) were not prolonged. BiA pacing resulted in the most significant percentage of reduction in P(dis) when compared with the LA or RA groups (BiA, 42+/-8%; LA, 13+/-6%; RA, 10+/-9%; P<0.05 for BiA versus LA or RA). No significant differences existed in mean P(dur) and P(dis) between patients who developed AF and those who remained in sinus rhythm at baseline. However, only those patients who remained in sinus rhythm had a significant reduction in mean P(dur) and P(dis) after pacing therapy.

CONCLUSIONS

Biatrial overdrive pacing is more effective in preventing post-CABG AF than single-site atrial pacing; this therapy also results in a shortened hospital stay. The overall reduction in atrial activation time with BiA pacing was reflected in the reduction in P(dis).

Prevention of ventricular fibrillation by pacing in a man with Brugada syndrome

The unique ECG appearance of Brugada syndrome is caused by failure of the dome of the action potential to develop. It occurs when the outward currents (mainly Ito) overwhelm the inward currents (mainly Ica) at the end of phase 1 of the action potential. Because Ito becomes less prominent at a faster rate, increased heart rate is associated with decreased ST segment elevation on ECG and probably decreased incidence of ventricular arrhythmia. We present the first report on prevention of ventricular fibrillation in a man with Brugada syndrome by overdrive pacing from his dual chamber implantable cardioverter defibrillator.

Electrophysiologic testing to identify patients with coronary artery disease who are at risk for sudden death. Multicenter Unsustained Tachycardia Trial Investigators

BACKGROUND

The mortality rate among patients with coronary artery disease, abnormal ventricular function, and unsustained ventricular tachycardia is high. The usefulness of electrophysiologic testing for risk stratification in these patients is unclear.

METHODS

We performed electrophysiologic testing in patients who had coronary artery disease, a left ventricular ejection fraction of 40 percent or less, and asymptomatic, unsustained ventricular tachycardia. Patients in whom sustained ventricular tachyarrhythmias could be induced were randomly assigned to receive either antiarrhythmic therapy guided by electrophysiologic testing or no antiarrhythmic therapy. The primary end point was cardiac arrest or death from arrhythmia. Patients without inducible tachyarrhythmias were followed in a registry. We compared the outcomes of 1397 patients in the registry with those of 353 patients with inducible tachyarrhythmias who were randomly assigned to receive no antiarrhythmic therapy in order to assess the prognostic value of electrophysiologic testing.

RESULTS

Patients were followed for a median of 39 months. In a Kaplan-Meier analysis, two-year and five-year rates of cardiac arrest or death due to arrhythmia were 12 and 24 percent, respectively, among the patients in the registry, as compared with 18 and 32 percent among the patients with inducible tachyarrhythmias who were assigned to no antiarrhythmic therapy (adjusted P<0.001). Overall mortality after five years was 48 percent among the patients with inducible tachyarrhythmias, as compared with 44 percent among the patients in the registry (adjusted P=0.005). Deaths among patients without inducible tachyarrhythmias were less likely to be classified as due to arrhythmia than those among patients with inducible tachyarrhythmias (45 and 54 percent, respectively; P=0.06).

CONCLUSIONS

Patients with coronary artery disease, left ventricular dysfunction, and asymptomatic, unsustained ventricular tachycardia in whom sustained ventricular tachyarrhythmias cannot be induced have a significantly lower risk of sudden death or cardiac arrest and lower overall mortality than similar patients with inducible sustained tachyarrhythmias.

Predictors of outcome in patients with acute coronary syndromes without persistent ST-segment elevation. Results from an international trial of 9461 patients. The PURSUIT Investigators

BACKGROUND

Appropriate treatment policies should include an accurate estimate of a patient's baseline risk. Risk modeling to date has been underutilized in patients with acute coronary syndromes without persistent ST-segment elevation.

METHODS AND RESULTS

We analyzed the relation between baseline characteristics and the 30-day incidence of death and the composite of death or myocardial (re)infarction in 9461 patients with acute coronary syndromes without persistent ST-segment elevation enrolled in the PURSUIT trial [Platelet glycoprotein IIb/IIIa in Unstable angina: Receptor Suppression Using Integrilin (eptifibatide) Therapy]. Variables examined included demographics, history, hemodynamic condition, and symptom duration. Risk models were created with multivariable logistic regression and validated by bootstrapping techniques. There was a 3.6% mortality rate and 11.4% infarction rate by 30 days. More than 20 significant predictors for mortality and for the composite end point were identified. The most important baseline determinants of death were age (adjusted chi(2)=95), heart rate (chi(2)=32), systolic blood pressure (chi(2)=20), ST-segment depression (chi(2)=20), signs of heart failure (chi(2)=18), and cardiac enzymes (chi(2)=15). Determinants of mortality were generally also predictive of death or myocardial (re)infarction. Differences were observed, however, in the relative prognostic importance of predictive variables for mortality alone or the composite end point; for example, sex was a more important determinant of the composite end point (chi(2)=21) than of death alone (chi(2)=10). The accuracy of the prediction of the composite end point was less than that of mortality (C-index 0.67 versus 0.81).

CONCLUSIONS

The occurrence of adverse events after presentation with acute coronary syndromes is affected by multiple factors. These factors should be considered in the clinical decision-making process.

[A study on the size, location and medical function of the Jaedong Jejoongwon]

This is the study of Jaedong Jejoongwon, the first westernized hospital in Korea founded in 1885. To build the groundwork for study of Jejoongwon, its size, location, building structure, and medical functions were studied. At the same time, the history of Jejoongwon, particularly that of the time when there arose a need for its moving and expansion, was studied. Jaedong Jejoongwon was founded in a renovated building. The building was formerly owned by Hong Young-sik, who was killed while leading the Gapsinjungbyun. According to the existing block plan of Jaedong Jejoongwon, when it was opened in 1885, it was located in the place which later became a park. Nowadays this park is to northwest of the Constitutional Court. At that time, its size was about 600 p'yung. As the medical school was built, from end of 1885 to early 1886, Jejoongwon was expanded to north, and its size was enlarged to 862.16 p'yung. Jaedong Jejoongwon reflected the characteristics of western medical system. When it was opened in 1885, Jejoongwon consisted of a servants' room, an assistants' room, the outpatient clinic, the operation room (which was also used as the pharmacy), surgical wards, women's wards, and general wards. In 1886, as the number of patients was increased and medical school was opened, the function and the structure of hospital changed. The most significant change was that a new medical school building was built, as the nearby buildings were brought. The medical school consisted of the students' dormitory, a chemistry laboratory, and classrooms. Moreover, new functions were added to already-existed hospital building : a contagious ward, a waiting room for outpatients, an eye ward, a darkroom, a room for special diagnosis and treatment, and a vaccination room. Also, from the time when it was first opened, Jejoongwon needed the expansion, as too many patients came in and the medical education was started. Therefore, in the summer of 1886, Allen positively explored ways toward the hospital's moving. At last, in early 1887, Jaedong Jejoongwon moved to Kurigae on along with the development of medical education and medical treatment, shows how the modern medical system was formed and developed in Korea.

Detection of microcalcifications using spatial filtering

This paper studied the feasibility of applying a spatial filter, called the iris filter, in microcalcification detection. While a majority of techniques manipulate data in the transform space, this spatial filter was chosen in an attempt to reduce computation. The iris filter has the ability to differentiate between circular and line-like objects. It computes the convergence of nearby gradient vectors relative to the centre of the filter. However, as the results of this paper show, the decrease in the constraint factor, which is an inner limit of the support region of the filter, also leads to a decrease in the detection ability of the filter. Hence, this filter is not ideal for detection of microcalcifications.

A new bacterial white spot syndrome (BWSS) in cultured tiger shrimp Penaeus monodon and its comparison with white spot syndrome (WSS) caused by virus

This paper describes a new bacterial white spot syndrome (BWSS) in cultured tiger shrimp Penaeus monodon. The affected shrimp showed white spots similar to those caused by white spot syndrome virus (WSSV), but the shrimp remained active and grew normally without significant mortalities. The study revealed no evidence of WSSV infection using electron microscopy, histopathology and nested polymerase chain reaction. Electron microscopy indicated bacteria associated with white spot formation, and with degeneration and discoloration of the cuticle as a result of erosion of the epicuticle and underlying cuticular layers. Grossly the white spots in BWSS and WSS look similar but showed different profiles under wet mount microscopy. The bacterial white spots were lichen-like, having perforated centers unlike the melanized dots in WSSV-induced white spots. Bacteriological examination showed that the dominant isolate in the lesions was Bacillus subtilis. The occurrence of BWSS may be associated with the regular use of probiotics containing B. subtilis in shrimp ponds. The externally induced white spot lesions were localized at the integumental tissues, i.e., cuticle and epidermis, and connective tissues. Damage to the deeper tissues was limited. The BWS lesions are non-fatal in the absence of other complications and are usually shed through molting.

Prediction of 1-year survival after thrombolysis for acute myocardial infarction in the global utilization of streptokinase and TPA for occluded coronary arteries trial

BACKGROUND

When a patient survives thrombolysis for acute myocardial infarction, little information from large studies exists from which to estimate prognosis during follow-up visits.

METHODS AND RESULTS

Baseline, in-hospital, and later survival data were collected from 41 021 patients enrolled in Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries, a randomized trial of 4 thrombolytic-heparin regimens with standard aspirin and beta-blockade. Cox proportional hazards models were developed to predict 1-year survival in 30-day survivors (n=37 869) from baseline clinical and ECG factors and in-hospital factors; a combined model then was developed (C-index 0.800). The model was simplified into a nomogram to predict individual outcomes (C-index 0.754). Factors reflecting demographics (advanced age, lighter weight), larger infarctions (higher Killip class, lower blood pressure, faster heart rate, longer QRS duration), cardiac risk (smoking, hypertension, prior cerebrovascular disease), and arrhythmia were important predictors of death between 30 days and 1 year. Black race was associated with a substantial increase in risk after considering other factors. Revascularization was associated with reduced risk between 30 days and 1 year.

CONCLUSIONS

When evaluating a patient who has survived acute infarction treated with thrombolysis, clinicians can estimate the likelihood of survival from factors easily measured during admission. Although many risk factors clearly relate to age, left ventricular dysfunction, or clinical instability, black race is an unexplained risk factor requiring further examination.

Clinical trials in acute myocardial infarction: should we adjust for baseline characteristics?

BACKGROUND

Clinical trials concerning acute myocardial infarction often evaluate short-term death. Several baseline characteristics are predictors of death, most notably age. Adjustment for one or more predictors in a multivariable analysis may be considered to correct the estimate of the treatment effect for any imbalance that by chance may have occurred between the randomized groups. Moreover, adjustment results in a stratified estimate of the effect of treatment.

METHODS AND RESULTS

The effects of adjustment (correction for imbalance and stratification) were studied with logistic regression analysis in the Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO)-I trial. The primary end point was 30-day death, which occurred in 6.3% of 10,348 patients randomly assigned to tissue plasminogen activator and 7.3% of 20,162 patients randomly assigned to streptokinase thrombolytic therapy. This is equivalent to an unadjusted odds ratio of 0.853. No significant imbalance had occurred for any of 17 baseline characteristics considered, including well-known demographic, presenting, and history characteristics. Adjusted for age, the odds ratio was 0.829, which is an 18% increase in estimated effect on the logistic scale. When adjusted for 17 characteristics, the odds ratio was 0.820, an increase of 25%. The increase in effect estimate was largely explained by the stratification effect and only partly by imbalance of predictors.

CONCLUSIONS

Adjustment for predictive baseline characteristics, even when largely balanced, may lead to clearly different estimates of the treatment effect on mortality rates. Adjustment for important predictors such as age is recommended in clinical trials studying patients with acute myocardial infarction.

Stability of methylene chloride spiked passive samplers: an international shipping and transportation study

A stability study was carried out by dynamically spiking Assay Technology Model 541 passive samplers with known amounts of methylene chloride (MeCl2) and shipping them to facilities around the world. Once arrived, these samples remained on site briefly and then were returned to the laboratory in North Chicago, III. A total of 22 sets of samples was prepared. Each sample set contained four passive samplers: blank, low (2.5 ppm), medium (25 ppm), and high (125 ppm) concentrations. Twelve of the 22 sets were separated into 4 groups of 3 sets, with each group defined as a cluster. One cluster was shipped to a pharmaceutical production facility in each country--South Africa, Pakistan, and Indonesia--and then shipped back to the lab, under normal shipping conditions. The fourth cluster was carried by one of the authors, who traveled through all three countries. The remaining 10 sets of samples were kept in the lab as controls. Each returning cluster was analyzed with two lab sets on arrival in the lab. Results obtained were evaluated using a t-test at a 95% confidence level. No significant differences were found in MeCl2 spiked passive samplers between traveled and lab controls, samples stored at room temperature and in the freezer, or analyzed right after being spiked and stored up to 7 weeks. It was concluded that MeCl2 spiked passive samplers were stable for at least 4 weeks at room temperature. There was no impact observed from international shipping and transportation on MeCl2 spiked passive samplers without temperature control.

Pharmacotherapy for erectile dysfunction

OBJECTIVE

To review current pharmacologic treatment options for erectile dysfunction.

METHODS

Relevant literatures from the past two decades regarding the following treatments were reviewed: intracavemous injection, topical therapy, transurethral therapy and oral drugs.

STUDY SELECTION

More than 125 originally identified articles were reviewed, and 45 were selected that especially addressed the stated purpose.

RESULTS

Among the pharmacologic treatment options available, intracavemous injection therapy remains the most effective although the drop-out rate is high. Topical creams and gels have not been very successful. Transurethral alprostadil can be more effective if a constriction device is applied at the base of the penis. Oral sildenafil has the highest patient acceptance rate although systemic side effects can be a major drawback.

CONCLUSIONS

Effective pharmacotherapies for ED of various etiologies are now available. However, proper evaluation of every patient should be performed before giving treatment so that a number of potentially life-threatening causes of erectile dysfunction would not be missed.

Prenyltransferase inhibitors block superoxide production by pulmonary vascular smooth muscle

We recently showed that the farnesyltransferase inhibitor FTI-277 blocks interleukin 1beta (IL-1beta)-induced nitric oxide production in pulmonary vascular smooth muscle cells (SMC), whereas the geranylgeranyltransferase inhibitor GGTI-298 enhances this effect. Here we show that IL-1beta and platelet-derived growth factor (PDGF) stimulate superoxide production by pulmonary vascular SMC and that this effect is blocked by both FTI-277 and GGTI-298, suggesting that farnesylated and geranylgeranylated proteins are required for superoxide production. We also show that FTI-277 and GGTI-298 block superoxide production stimulated by constitutively active mutant H-Ras. Furthermore, superoxide production by IL-1beta, PDGF factor, and constitutively activated Ras is blocked by diphenyleneiodonium, implicating NAD(P)H oxidase as the generating enzyme. Given the role of oxidant radicals in vascular reactivity and injury, the action of both FTI-277 and GGTI-298 in suppressing superoxide generation by an inflammatory cytokine as well as by a potent smooth muscle mitogen may be therapeutically useful.

Prognostic models based on literature and individual patient data in logistic regression analysis

Prognostic models can be developed with multiple regression analysis of a data set containing individual patient data. Often this data set is relatively small, while previously published studies present results for larger numbers of patients. We describe a method to combine univariable regression results from the medical literature with univariable and multivariable results from the data set containing individual patient data. This 'adaptation method' exploits the generally strong correlation between univariable and multivariable regression coefficients. The method is illustrated with several logistic regression models to predict 30-day mortality in patients with acute myocardial infarction. The regression coefficients showed considerably less variability when estimated with the adaptation method, compared to standard maximum likelihood estimates. Also, model performance, as distinguished in calibration and discrimination, improved clearly when compared to models including shrunk or penalized estimates. We conclude that prognostic models may benefit substantially from explicit incorporation of literature data.

Immunoglobulin M and G immunoblots in the diagnosis of parvovirus B19 infection

BACKGROUND AND PURPOSE

To identify parvovirus B19 infection by means of immunoglobulin (Ig) G and IgM immunoblots among immunocompetent patients who tested negative or had low-titer B19 IgM antibodies in enzyme-linked immunosorbent assays (ELISA).

METHODS

Serum samples were obtained from 20 patients with parvovirus B19 infection. Another 130 study subjects presumed to be without B19 infection (40 medical personnel and 90 prisoners) were also included. All sera from the patient and study groups tested positive for IgG or IgM with ELISA and were further evaluated using the immunoblot method. Detection of B19 DNA by nested polymerase chain reaction (PCR) was also performed on IgG and IgM positive sera.

RESULTS

IgM immunoblots disclosed one false positive IgM ELISA result in the patient group and three false positive results in the study group. In the patient group, four patients were in the latter stage of antibody response to B19 infection as suggested by the low titer of anti-B19 IgM, incomplete IgM immunoblots, with only a weak viral capsid protein VP-N reaction band, and fading but still strong reaction bands on IgG immunoblots. Strong reaction bands on IgG immunoblots comparable to these four patients were found in three of the 130 study group sera. Furthermore, B19 DNA was detected in three of the four patients and one of the three study subjects by means of nested-PCR. A serum sample from one study subject showed strong IgG but no IgM reactivity to viral capsid protein VP2; nested PCR identified B19 DNA in this serum sample.

CONCLUSIONS

Immunoblots and nested PCR should be applied in the diagnosis of B19 infection for patients with low-titer anti-B19 IgM tested by means of ELISA. For diagnosis of B19 infections in certain clinical entities such as chronic arthritis of recent onset and hydrops fetalis, B19 IgM antibodies may have disappeared but B19 infection can still be recognized by the intensity of the reaction bands on IgG immunoblots. The correlation between chronic B19 infection and persistence of antilinear VP2 epitopes requires further study.

A randomized study of the prevention of sudden death in patients with coronary artery disease. Multicenter Unsustained Tachycardia Trial Investigators

BACKGROUND

Empirical antiarrhythmic therapy has not reduced mortality among patients with coronary artery disease and asymptomatic ventricular arrhythmias. Previous studies have suggested that antiarrhythmic therapy guided by electrophysiologic testing might reduce the risk of sudden death.

METHODS

We conducted a randomized, controlled trial to test the hypothesis that electrophysiologically guided antiarrhythmic therapy would reduce the risk of sudden death among patients with coronary artery disease, a left ventricular ejection fraction of 40 percent or less, and asymptomatic, unsustained ventricular tachycardia. Patients in whom sustained ventricular tachyarrhythmias were induced by programmed stimulation were randomly assigned to receive either antiarrhythmic therapy, including drugs and implantable defibrillators, as indicated by the results of electrophysiologic testing, or no antiarrhythmic therapy. Angiotensin-converting-enzyme inhibitors and beta-adrenergic-blocking agents were administered if the patients could tolerate them.

RESULTS

A total of 704 patients with inducible, sustained ventricular tachyarrhythmias were randomly assigned to treatment groups. Five-year Kaplan-Meier estimates of the incidence of the primary end point of cardiac arrest or death from arrhythmia were 25 percent among those receiving electrophysiologically guided therapy and 32 percent among the patients assigned to no antiarrhythmic therapy (relative risk, 0.73; 95 percent confidence interval, 0.53 to 0.99), representing a reduction in risk of 27 percent). The five-year estimates of overall mortality were 42 percent and 48 percent, respectively (relative risk, 0.80; 95 percent confidence interval, 0.64 to 1.01). The risk of cardiac arrest or death from arrhythmia among the patients who received treatment with defibrillators was significantly lower than that among the patients discharged without receiving defibrillator treatment (relative risk, 0.24; 95 percent confidence interval, 0.13 to 0.45; P<0.001). Neither the rate of cardiac arrest or death from arrhythmia nor the overall mortality rate was lower among the patients assigned to electrophysiologically guided therapy and treated with antiarrhythmic drugs than among the patients assigned to no antiarrhythmic therapy.

CONCLUSIONS

Electrophysiologically guided antiarrhythmic therapy with implantable defibrillators, but not with antiarrhythmic drugs, reduces the risk of sudden death in high-risk patients with coronary disease.

Effect of the implantable atrial defibrillator on the natural history of atrial fibrillation

INTRODUCTION

The purpose of our study was to evaluate the effect of repeated cardioversion with an implantable atrial defibrillator on the clinical outcome of patients with atrial fibrillation.

METHODS AND RESULTS

The effects of the implantable atrial defibrillator on the total duration of atrial fibrillation, number of atrial fibrillation recurrences, and left atrial size were evaluated prospectively in 16 patients with atrial fibrillation (13 men and 3 women; mean age 58 +/- 11 years). Seven patients had no cardiovascular disease, 5 patients had hypertension, 3 patients had coronary heart disease, and 1 patient had congenital heart disease. Eight patients had paroxysmal atrial fibrillation for a mean duration of 80 +/- 61 months, and eight patients had persistent atrial fibrillation for a mean duration of 68 +/- 119 months. Except for one patient who received digoxin throughout the study, all patients received the same Class I or III antiarrhythmic agent throughout the study. The implantable atrial defibrillator successfully converted 50 (93%) of 54 spontaneous episodes of atrial fibrillation in 12 patients. During the initial 3 months of clinical follow-up, the atrial defibrillator documented 261 +/- 270 hours of atrial fibrillation compared with 126 +/- 172 hours (P = 0.01) during the subsequent 3 months. The left atrial size decreased from 4.4 +/- 0.7 cm at the time of atrial defibrillator implantation to 4.1 +/- 0.6 cm (P = 0.02) 6 months later. The number of atrial fibrillation recurrences did not change. These findings were observed in the absence of changes in drug therapy. No complications were observed.

CONCLUSION

Restoration and maintenance of sinus rhythm in patients with atrial fibrillation by repeated cardioversion with an implantable atrial defibrillator was associated with a reduction in the total arrhythmia duration and a reduction in left atrial size. These results suggest that maintenance of sinus rhythm with the atrial defibrillator may reverse the remodeling process associated with atrial fibrillation.

Autologous blood use in percutaneous nephrolithotomy

OBJECTIVES

Preoperative autologous blood (AUB) donation has decreased patient exposure to allogenic blood (ALB) products and associated infectious risk. The risk of contracting hepatitis C and human immunodeficiency virus is 1 in 103,000 and 1 in 678,000, respectively, after receiving 1 U ALB. Elective surgical procedures require surgeons to offer preoperative AUB donation in California. Unused AUB is discarded. We report our use of AUB obtained for percutaneous nephrolithotomy.

METHODS

A retrospective study of 144 consecutive patients who underwent 193 percutaneous nephrolithotomies between January 1994 and April 1998 at one of four teaching hospitals at the University of California, San Francisco was performed. Preoperative AUB donation, transfusion rates, hemoglobin levels, blood use, and costs were analyzed.

RESULTS

Ninety-six units of blood were collected from 63 patients (44%) and were available for 70 procedures (36%). The overall transfusion rate per procedure was 7%, with 13 patients receiving a total of 24 U, 7 AUB and 17 ALB. Eighty-nine units (92.7%) of AUB were discarded, and the transfusion rate in donors and nondonors was similar. There was no significant difference in preoperative hemoglobin or operative blood loss between donors and nondonors. The 13 transfused patients had a lower preoperative hemoglobin ( 11.5 versus 12.8 g/dL; P = 0.029) and higher operative blood loss as measured by hemoglobin level (3.2 versus 1.6 g/dL; P <0.001). Blood bank charges for ALB and AUB were $ 119/U and $244 to $498/U, respectively, depending on transportation and thawing charges.

CONCLUSIONS

Routine preoperative blood donation adds substantial cost for minimal benefit, given the low infectious risk of ALB and the two- to fourfold higher cost of AUB. In our series, women had an increased incidence of blood transfusion compared with men. AUB donation may provide peace of mind but is rarely used and is discarded 93% of the time.

Effect of adenosine and verapamil in catecholamine-induced accelerated atrioventricular junctional rhythm: insights into the underlying mechanism

Accelerated AV junctional rhythm is postulated to be due to enhanced automaticity of a high AV junctional focus. The adenosine response of this rhythm was tested in 17 patients (7 males, 12-83 years). The indications of electrophysiology study were nonspecific palpitation (n = 5), unexplained syncope (n = 6), postablation of accessory pathways (n = 4), and postmodification of AV nodal reentry tachycardia (n = 2). The sinus node and AV nodal functions were normal. Pacing and programmed electrical stimulation failed to induce any arrhythmia at baseline. The accelerated junctional rhythm (cycle length = 553 +/- 134 ms) was initiated spontaneously in all patients after isoproterenol infusion (1-2 micrograms/min). It was not suppressible by overdrive pacing. Cessation of isoproterenol infusion terminated the rhythm in all patients. Adenosine (6 mg) reproducibly terminated the accelerated junctional rhythm in all patients. In six patients, adenosine suppressed the junctional rhythm without producing AV nodal block. In the other 11 patients, the junctional rhythm was terminated prior to the occurrence of AV nodal block. Verapamil was tested in ten patients and 5 mg of intravenous verapamil terminated the junctional rhythm in all patients. In conclusion, the mechanism of catecholamine-induced accelerated AV junctional rhythm is most likely enhanced automaticity, and catecholamine-induced accelerated AV junctional automaticity is sensitive to adenosine and verapamil. Adenosine appears to have differential effects on catecholamine-enhanced AV junctional automaticity and AV nodal conduction. This suggests that, under catecholamine stimulation, adenosine may have different mechanisms of action on AV nodal conduction and automaticity.

Prediction of sustained ventricular tachycardia inducible by programmed stimulation in patients with coronary artery disease. Utility of clinical variables

BACKGROUND

Cardiologists often use clinical variables to determine the need for electrophysiological studies to stratify patients for risk of sudden death. It is not clear whether this is rational in patients with coronary artery disease, left ventricular dysfunction, and nonsustained ventricular tachycardia.

METHODS AND RESULTS

We analyzed the first 1721 patients enrolled in the Multicenter UnSustained Tachycardia Trial to determine whether clinical variables could predict which patients would have inducible sustained monomorphic ventricular tachycardia. The rate of inducibility of sustained ventricular tachycardia was significantly higher in patients with a history of myocardial infarction and in men compared with women. There was a progressively increased rate of inducibility with increasing numbers of diseased coronary arteries. There was a significantly lower rate of inducibility in patients with prior coronary artery bypass surgery and in patients who also had noncoronary cardiac disease. The rate of inducibility was higher in patients of white race, patients with recent (</=6 weeks) angina, left ventricular dyskinesis, and in patients with greater numbers of fixed thallium defects. Inducibility was more likely in patients who had a prior myocardial infarction complicated by congestive heart failure, ventricular tachycardia, or fibrillation </=48 hours after the onset of infarction. Although these associations are statistically significant, the accuracy of the clinical variables in discriminating between patients with and those without inducible ventricular tachycardia is only modest (receiver operator characteristic area <0.70).

CONCLUSIONS

Multiple clinical variables are independently associated with inducible sustained ventricular tachycardia. However, they have limited utility to guide clinical decisions regarding the use of electrophysiological testing for risk stratification in this patient population.

Acute coronary syndromes in the GUSTO-IIb trial: prognostic insights and impact of recurrent ischemia. The GUSTO-IIb Investigators

BACKGROUND

Recurrent ischemia after an acute coronary syndrome portends an unfavorable outcome and has major resource-use implications. This issue has not been studied systematically among the spectrum of patients with acute coronary presentations, encompassing those with and without ST-segment elevation.

METHODS AND RESULTS

We assessed the 1-year prognosis of the 12 142 patients enrolled in the GUSTO-IIb trial by the presence (n=4125) or absence (n=8001) of ST-segment elevation. This latter group was further categorized into those with baseline myocardial infarction (n=3513) or unstable angina (n=4488). We also assessed the incidence of recurrent ischemia and its impact on outcomes. Recurrent ischemia was significantly rarer in those with ST-segment elevation (23%) than in those without (35%; P<0.001). Mortality at 30 days was greater among patients with ST-segment elevation (6.1% versus 3.8%; P<0.001) but less so at 6 months; by 1 year, mortality did not differ significantly (9.6% versus 8.8%). Patients with non-ST-segment-elevation infarction had higher rates of reinfarction at 6 months (9.8% versus 6.2%) and higher 6-month (8.8% versus 5.0%) and 1-year mortality rates (11.1% versus 7.0%) than such patients who had unstable angina.

CONCLUSIONS

Refractory ischemia was associated with an approximate doubling of mortality among patients with ST-segment elevation and a near tripling of risk among those without ST elevation. This study highlights not only the substantial increase in late mortality and reinfarction with non-ST-segment-elevation infarction but also the opportunities for better triage and application of therapeutic strategies for patients with recurrent ischemia.

Value of serial troponin T measures for early and late risk stratification in patients with acute coronary syndromes. The GUSTO-IIa Investigators

BACKGROUND

The baseline cardiac troponin T (cTnT) level strongly predicts short-term mortality in acute coronary syndromes, but the added value of later measures to predict short- and long-term outcome and in the context of baseline clinical characteristics is unclear.

METHODS AND RESULTS

Relations between baseline, peak, and 8- and 16-hour (late) cTnT results and outcomes were assessed in 734 patients in a GUSTO-IIa substudy. Proportional-hazards models assessed the prognostic information gained from late cTnT when added to a mortality model containing the baseline cTnT result and clinical factors. At baseline, 260 patients were cTnT-positive (>0.1 ng/mL), 323 became positive later, and 151 remained negative (</=0.1 ng/mL). Mortality at 30 days was 10% in the baseline-positive group, 5% in late-positive patients, and 0% in negative patients. After adjustment for baseline characteristics, any positive cTnT result predicted 30-day mortality (baseline, chi2=8.96, P=0.0113; 8-hour, chi2=6.51, P=0.0107; 16-hour, chi2=8.40, P=0.0038). Both the 8- and the 16-hour results added to the strength of the baseline result (baseline+8-hour, chi2=12.04, P=0.0072; baseline+16-hour, chi2=13.52, P=0.0036). Only age and ST-segment elevation were stronger predictors of 30-day mortality than baseline cTnT; results were similar for prediction of 1-year mortality. Most of the mortality difference between cTnT-positive and -negative patients occurred within the first 30 days.

CONCLUSIONS

The cTnT level is a strong, independent predictor of short-term outcome in acute coronary syndromes. The addition of later samples to a baseline level is useful to evaluate the risk of serious cardiac events.

In vitro bovine ciliary body/epithelium in a small continuously perfused Ussing type chamber

Our goal is to assess the viability of an in vitro preparation of bovine ciliary body/epithelium (CBE) in a small volume Ussing-type chamber. A new small volume Ussing-type chamber with continuous perfusion was developed for bovine CBE. The trans-CBE electrical parameters were monitored and the electrical responses of the CBE to ouabain (1 and 0.01 mM) were recorded. The trans-CBE fluxes of [14C]-L-ascorbate and [3H]-L-glucose were also studied. The bovine CBE preparation was stable inside the chamber in terms of its potential difference (PD), short circuit current (SCC) and trans-CBE resistance. They were -0.51+/-0.05 mV (aqueous side negative), -5.43+/-0.04 microAcm-2 and 94+/-2 Q.cm2 (mean s.e.m., n=35), respectively. The preparation hyperpolarised when 0.01 mM ouabain was administered to the aqueous side, depolarised when ouabain was applied to the stromal side. [3H]-L-glucose diffusion was about 74 nEq h(-1)cm(-2) in either direction (n=12). Taking the area magnification factor of the CBE into consideration, the diffusional L-glucose flux across the bovine CBE was comparable to other tight epithelia. A significant net ascorbate flux (0.26+/-0.05 nEq h(-1)cm(-2), n=4, p<0.01) was found in the stroma to aqueous direction. We have developed a viable in vitro bovine CBE preparation which was (1) electrically stable, (2) responsive to ouabain, (3) tight to L-glucose diffusion, and (4) capable of actively secreting ascorbate. A net trans-CBE chloride transport (0.81+/-0.30 microEq h(-1)cm(-2), n=12, p=0.01) from stromal to aqueous side was found in the present in vitro model under short-circuited conditions.

Chloride and sodium transport across bovine ciliary body/epithelium (CBE)

PURPOSE

To study the chloride and sodium ion transports across the bovine ciliary body/epithelium (CBE) by a modified Ussing-Zerahn type chamber.

METHODS

Isolated bovine CBE preparations were mounted in a modified Ussing-type chamber and the transepithelial electrical parameters were monitored. The inward (stroma to aqueous) and outward (aqueous to stroma) fluxes of 36[Cl] chloride and 22[Na] sodium ions across the CBE were measured under short-circuited conditions. The effect of 0.1 mM of furosemide and bumetanide on the chloride transport were studied.

RESULTS

The potential difference (PD), the resistance and the short-circuit current (SCC) across the isolated bovine ciliary body were found to be -0.20+/-0.01 mV (aqueous negative), 75+/-1 omegacm2 and -2.70+/-0.17 microAcm(-2) (mean+/-SEM, n=50) respectively. A statistically significant net inward chloride ion flux of 1.12+/-0.41 microEq h(-1)cm(-2) (p < 0.01) was found (n=15). The net chloride transport was abolished when 0.1 mM furosemide (82% inhibition) and 0.1 mM bumetanide (100% inhibition) were applied bilateral. No significant net sodium ion flux was detected.

CONCLUSIONS

Electrolyte and fluid transport across the bovine CBE may be via a bumetanide and furosemide-sensitive chloride transport mechanism. The Na-K-2Cl cotransporter plays a significant role in the trans-CBE chloride transport. The net chloride flux/current was about 12 times higher than the measured SCC, suggesting that the chloride ion transport may be coupled to other ion species.