National Heart Foundation of Australia and Cardiac Society of Australia and New Zealand: Australian clinical guidelines for the management of acute coronary syndromes 2016

INTRODUCTION

The modern care of suspected and confirmed acute coronary syndrome (ACS) is informed by an extensive and evolving evidence base. This clinical practice guideline focuses on key components of management associated with improved clinical outcomes for patients with chest pain or ACS. These are presented as recommendations that have been graded on both the strength of evidence and the likely absolute benefit versus harm. Additional considerations influencing the delivery of specific therapies and management strategies are presented as practice points.

MAIN RECOMMENDATIONS

This guideline provides advice on the standardised assessment and management of patients with suspected ACS, including the implementation of clinical assessment pathways and subsequent functional and anatomical testing. It provides guidance on the: diagnosis and risk stratification of ACS; provision of acute reperfusion therapy and immediate post-fibrinolysis care for patients with ST segment elevation myocardial infarction; risk stratification informing the use of routine versus selective invasive management for patients with non-ST segment elevation ACS; administration of antithrombotic therapies in the acute setting and considerations affecting their long term use; and implementation of an individualised secondary prevention plan that includes both pharmacotherapies and cardiac rehabilitation. Changes in management as a result of the guideline: This guideline has been designed to facilitate the systematic integration of the recommendations into a standardised approach to ACS care, while also allowing for contextual adaptation of the recommendations in response to the individual's needs and preferences. The provision of ACS care should be subject to continuous monitoring, feedback and improvement of quality and patient outcomes.

National Heart Foundation of Australia and Cardiac Society of Australia and New Zealand: Australian clinical guidelines for the management of acute coronary syndromes 2016

INTRODUCTION

The modern care of suspected and confirmed acute coronary syndrome (ACS) is informed by an extensive and evolving evidence base. This clinical practice guideline focuses on key components of management associated with improved clinical outcomes for patients with chest pain or ACS. These are presented as recommendations that have been graded on both the strength of evidence and the likely absolute benefit versus harm. Additional considerations influencing the delivery of specific therapies and management strategies are presented as practice points.

MAIN RECOMMENDATIONS

This guideline provides advice on the standardised assessment and management of patients with suspected ACS, including the implementation of clinical assessment pathways and subsequent functional and anatomical testing. It provides guidance on the: diagnosis and risk stratification of ACS; provision of acute reperfusion therapy and immediate post-fibrinolysis care for patients with ST segment elevation myocardial infarction; risk stratification informing the use of routine versus selective invasive management for patients with non-ST segment elevation ACS; administration of antithrombotic therapies in the acute setting and considerations affecting their long term use; and implementation of an individualised secondary prevention plan that includes both pharmacotherapies and cardiac rehabilitation. Changes in management as a result of the guideline: This guideline has been designed to facilitate the systematic integration of the recommendations into a standardised approach to ACS care, while also allowing for contextual adaptation of the recommendations in response to the individual's needs and preferences. The provision of ACS care should be subject to continuous monitoring, feedback and improvement of quality and patient outcomes.

The potential role of anticoagulant therapy for the secondary prevention of ischemic events post-acute coronary syndrome

Abstract The use of dual antiplatelet therapy has led to a substantial reduction in ischemic events post-acute coronary syndrome (ACS). Despite this, recurrent event rates remain high. Recent research has combined antiplatelet with anticoagulant therapy to reduce recurrent event rates further. Compared with standard medical therapy, rivaroxaban demonstrated improved efficacy outcomes and significantly reduced mortality after an ACS. Although clear benefits of novel oral anticoagulants post-ACS have been proven, concerns regarding bleeding are still a barrier to widespread use. This review explores key trials of dual antiplatelet therapy and examines the latest research in anticoagulation aiming to optimize clinical outcomes post-ACS.

New ST-depression: an under-recognized high-risk category of 'complete' ST-resolution after reperfusion therapy

AIM

It is not known if there is an association between resolution of ST-elevation to ST-depression following fibrinolysis and 30-day mortality.

METHODS

In an ECG substudy of HERO-2, which compared bivalirudin to unfractionated heparin following streptokinase in 12,556 patients with ST-elevation myocardial infarction ECGs were recorded at baseline and at 60 minutes after commencing fibrinolysis. The main outcome measure was 30-day mortality.

RESULTS

Using summed ST-segment elevation and five categories of changes in the infarct leads, further ST-elevation, 0-30% ST-resolution, >30-70% (partial) ST-resolution, >70% (complete) ST-resolution, and new ST-depression occurred in 21.7, 24.9, 36.8, 14.8, and 1.8% of patients, with 30-day mortality of 12.3, 11.7, 8.0, 4.2, and 8.1%, respectively. For the comparison of new ST-depression with complete ST-resolution and no ST-depression, p<0.01 with 24-hour mortality 4.5 vs. 1.3%, respectively (p=0.0003). Patients with new ST-depression had similar peak cardiac enzyme elevations as patients with complete ST-resolution without ST-depression. On multivariate analysis including summed ST-elevation at baseline, age, sex, and infarct location, new ST-depression was a significant predictor of 30-day mortality (OR 1.82, 95% CI 1.42-4.29).

CONCLUSIONS

In patients with complete ST-resolution following fibrinolysis, new ST-depression at 60 minutes developed in 10.8% of patients. These patients had higher mortality than patients with complete ST-resolution without ST-depression and represent a high-risk group which could benefit from rapid triage to early angiography and revascularization as appropriate.

Slowed ST segment recovery despite early infarct artery patency in patients with Q waves at presentation with a first acute myocardial infarction. Implications of initial Q waves on myocyte reperfusion

BACKGROUND

The presence of Q waves at presentation with a first acute myocardial infarction reflects a more advanced stage of the infarction process. When infarct-related artery patency (Thrombolysis in Myocardial Infarction 2 or 3 flow) is restored, resolution of ST segment elevation indicating successful myocyte reperfusion may differ according to how far the infarction process has progressed.

METHODS AND RESULTS

In 144 patients with a first acute myocardial infarction treated with streptokinase in the first Hirulog Early Reperfusion Occlusion trial, information was obtained from continuous ST segment monitoring, the presenting electrocardiogram and early angiography performed at a median time of 99 min after the commencement of streptokinase (interquartile range 89-108 min). We determined how many patients had 50% ST recovery within 120 min and in how many cases it was sustained over 4h. In the 109 patients with patent infarct-related arteries, 50% ST recovery occurred in 95% of patients without vs 80% of those with initial Q waves (P=0.03), and sustained ST recovery occurred in 67% of patients without vs 47% of those with initial Q waves (P=0.03). On multivariate analysis including the time from symptom onset to streptokinase therapy, the presence of Q waves at presentation was the only predictor of failure to achieve 50% ST recovery (odds ratio 5.08, 95% confidence interval 1.29-20.01, P=0.02). TIMI 2 flow, as opposed to TIMI 3 flow, was the only predictor of failure to achieve stable ST recovery (odds ratio 2.63, 95% confidence interval 1.15-5.88,P =0.02).

CONCLUSION

The presence of initial Q waves predicts slower and less complete ST recovery, reflecting reduced myocyte reperfusion, even in those with early infarct artery patency. These patients may be targeted for new therapeutic strategies to improve microvascular reperfusion.

Usefulness of the presenting electrocardiogram in predicting myocardial salvage with thrombolytic therapy in patients with a first acute myocardial infarction

AIMS

Patients with Q waves and T-wave inversion are generally at a later stage of the infarction process than patients without these changes. Our aim was to investigate whether a single assessment of electrocardiographic parameters at presentation would predict the proportion of myocardium salvageable by thrombolytic therapy.

METHODS AND RESULTS

Electrocardiographic algorithms to calculate the potential and final infarct size have been developed and allow the proportion of myocardium salvageable with therapy to be calculated. This was measured in 146 patients with acute myocardial infarction who had angiography at a median of 91 min after streptokinase. The relationship between myocardial salvage and the electrocardiographic parameters at presentation (Q waves, T-wave inversion, quantitative ST segment changes, and the initial QRS score), was examined together with the 90-min angiographic parameters (TIMI flow grade and collateral grade), clinical parameters (haemodynamics and age), and time to therapy. Parameters that correlated with myocardial salvage included the initial QRS score (r=-0.56, P<0.0001), Q wave grade (r=-0.36, P<0.0001), number of leads with ST depression (r=0.28, P<0.001), maximum ST depression (r=0.27, P<0.01), T-inversion grade (r=-0.26, P<0.01), and TIMI flow grade at 90 min (r=0.21, P<0.02). The time from symptom onset to thrombolytic therapy did not correlate with salvage (r=-0.09). On multivariate analysis, only the initial QRS score and T-inversion grade on the initial electrocardiogram were independent predictors of salvage (multivariate r using both variables combined=0.57, P<0.001).

CONCLUSIONS

The QRS score and T-wave inversion grade on the presenting electrocardiogram provide important information in predicting myocardial salvage. These parameters may help triage patients to appropriate therapies.

Prophylactic lidocaine use in acute myocardial infarction: incidence and outcomes from two international trials. The GUSTO-I and GUSTO-IIb Investigators

BACKGROUND

Early meta-analyses suggested that prophylactic lidocaine use reduces ventricular fibrillation but increases mortality rates after acute myocardial infarction. We determined the frequency and effect on clinical outcomes with its use in the thrombolytic era.

METHODS AND RESULTS

We studied 43,704 patients enrolled in GUSTO-I or GUSTO-IIb who had ST-segment elevation, underwent thrombolysis, and survived at least 1 hour after enrollment. Odds ratios (OR) and confidence intervals (CI) were calculated for the risk of asystole, atrioventricular block, ventricular fibrillation, and ventricular tachycardia during hospitalization; for 24-hour, in-hospital, and 30-day mortality rates; and for 24-hour and 30-day mortality rates after adjustment for baseline predictors of death. In GUSTO-I and GUSTO-IIb, 16% and 3.5% of patients, respectively, received prophylactic lidocaine. They had a lower risk of death at 24 hours (OR 0.81, 95% CI 0.67 to 0.97) and trends toward lower odds of in-hospital death (OR 0.90, 95% CI 0.81 to 1.01) and death at 30 days (OR 0.92, 95% CI 0.82 to 1. 02). After adjustment for baseline characteristics, however, the odds of death were similar with or without lidocaine (OR 0.90 and 0. 97, respectively). Outside the United States, lidocaine was associated with higher incidences of all serious arrhythmias, but in US patients it conferred a lower likelihood of ventricular fibrillation and no increase in asystole, atrioventricular block, or mortality rates.

CONCLUSIONS

Prophylactic lidocaine use has decreased with the advent of thrombolysis, although its use may not be associated with increased mortality rates.

One-year survival among patients with acute myocardial infarction complicated by cardiogenic shock, and its relation to early revascularization: results from the GUSTO-I trial

BACKGROUND

Although 30-day survival is increased in patients with acute myocardial infarction complicated by cardiogenic shock who undergo coronary revascularization, the longer-term outcome in such patients and the duration of benefit from revascularization are unknown.

METHODS AND RESULTS

We analyzed 30-day survivors of acute myocardial infarction in the Global Utilization of Streptokinase and Tissue-Plasminogen Activator for Occluded Coronary Arteries (GUSTO-I) trial and identified 36 333 who had not had cardiogenic shock (systolic blood pressure <90 mm Hg for >/=1 hour, group 1) and 1321 patients who had shock (group 2). Group 2 patients were older and sicker. At 1 year, 97.4% of group 1 patients were alive versus 88.0% of group 2 (P=0.0001). Among group 2 patients, 578 (44%) had undergone revascularization within 30 days (group 2A) and 728 (56%) had not (group 2B). Revascularization was not required by protocol but was selected by the attending physicians. At 1 year, 91.7% of group 2A patients were alive versus 85.3% of group 2B (P=0.0003). With the use of multivariable logistic regression analysis to adjust for differences in baseline characteristics of shock patients alive at 30 days, revascularization within 30 days was independently associated with reduced 1-year mortality (odds ratio 0.6, [95% confidence interval 0.4, 0.9], P=0.007).

CONCLUSIONS

Most patients (88%) with acute myocardial infarction complicated by cardiogenic shock who are alive at 30 days survived at least 1 year. Shock patients who underwent revascularization within 30 days had improved survival at 1 year compared with shock patients who did not receive revascularization, even after adjustment for differences in baseline characteristics between the 2 groups.

Angiographic frame counts 90 minutes after streptokinase predict left ventricular function at 48 hours following myocardial infarction

OBJECTIVE

To assess whether the 90 minute corrected thrombolysis in myocardial infarction frame count (CTFC) in the infarct related artery predicts left ventricular function at 48 hours in patients with myocardial infarction treated with aspirin, streptokinase, and either heparin or Hirulog.

DESIGN AND SETTING

Analysis of 251 patients with acute myocardial infarction enrolled in the international, multicentre Hirulog early reperfusion/occlusion (HERO-1) trial, who underwent both 90 minute coronary angiography and 48 hour left ventriculography.

MAIN OUTCOME VARIABLES

The CTFC was determined in the infarct related artery 90 minutes after starting intravenous streptokinase (1.5 x 106 U over 30 to 60 minutes), and compared with indices of left ventricular function assessed by contrast ventriculography at 48 hours.

RESULTS

A CTFC of </= 27 frames (previously reported mean + 2 SD in coronary arteries of patients without acute infarction) occurred in 29% of infarct related arteries, and was associated with a lower infarct zone mean chord score (-2.06 v -2.54, p = 0.01), a lower fraction of chords > 2 SD below normal (37% v 51%, p = 0.005), and trends towards higher left ventricular ejection fractions (60.9% v 58.2%, p = 0.11) and lower end systolic volumes (50.1 ml v 55.9 ml, p = 0.23). A CTFC of </= 40 at 90 minutes occurred in 50% of infarct related arteries, and was associated with a significantly lower mean chord score (-2.20 v -2.60, p = 0.02), a smaller fraction of chords > 2 SD below normal (41% v 52%, p = 0.025), a smaller end systolic volume (49.1 ml v 59.3 ml, p = 0.02), and a higher left ventricular ejection fraction (60.4% v 56.5%, p = 0.03).

CONCLUSIONS

The 90 minute CTFC predicts left ventricular function at 48 hours following streptokinase. The CTFC associated with better ventricular function may be higher than values determined from a non-infarct population.

Usefulness of the presenting electrocardiogram in predicting successful reperfusion with streptokinase in acute myocardial infarction

The presenting electrocardiogram may contain information indicating the probability of successful reperfusion. The relation between 3 parameters in the presenting electrocardiogram (pathologic Q waves, T-wave inversion, and the slope of ST elevation) and Thrombolysis in Myocardial Infarction trial (TIMI) grade 3 flow in the infarct-related artery was assessed angiographically 90 minutes after beginning streptokinase in 362 patients. TIMI grade 3 flow was more common in patients without Q waves (55%) than in those with Q waves (35%; p <0.001), and more common in patients without T-wave inversion (50%) than in those with T-wave inversion (30%; p <0.002). There was no relation between the slope of the ST segment or the magnitude of its deviation and the achievement of TIMI grade 3 flow. Only 20% of the 59 patients with both Q waves and T-wave inversion had TIMI grade 3 flow, compared with 50% of the remaining patients (p <0.0001). Among patients treated within 3 hours, TIMI grade 3 flow was seen in 68% of those without versus 44% of those with Q waves (p <0.01), and in 62% of those without versus 43% of those with T-wave inversion (p = 0.06). Among patients treated after 3 hours, TIMI grade 3 flow was seen in 38% of those without versus 30% of those with Q waves (p = NS), and in 38% of those without versus 23% of those with T-wave inversion (p <0.05). On multivariate analysis, the absence of Q waves, the time from the onset of chest pain to treatment, and age were independent predictors of TIMI grade 3 flow. Pathologic Q waves in the presenting electrocardiogram provide valuable information as to the probability of achieving successful reperfusion following administration of streptokinase, and may be helpful for triage of patients to alternative reperfusion strategies, including percutaneous revascularization.

Use of bedside activated partial thromboplastin time monitor to adjust heparin dosing after thrombolysis for acute myocardial infarction: results of GUSTO-I. Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries

BACKGROUND

The safety and efficacy of bedside monitors of activated partial thromboplastin time (aPTT) have not been examined in a large population receiving intravenous heparin after thrombolytic treatment for acute myocardial infarction. We compared outcomes among patients monitored with these devices versus standard monitoring methods.

METHODS AND RESULTS

Investigators chose the bedside device (n = 1713 patients) or their standard method (n = 26,162) for all aPTT measurements at their sites. Clinical outcomes at 30 days, 1-year mortality rate, and aPTT levels at 6, 12, and 24 hours were compared. Bedside-monitored patients had significantly less moderate/severe bleeding (10% vs 12%, P < .01), fewer transfusions (7% vs 11%, P < .001), and a smaller decrease in hematocrit (5.5% vs 6.7%, P < .001) but significantly more recurrent ischemia (22% vs 20%, P = .01). Fewer bedside-monitored patients had subtherapeutic aPTT levels at 12 and 24 hours. Among patients with subtherapeutic levels at 6 and 12 hours, more bedside-monitored patients had therapeutic levels when next monitored. After adjustment for baseline differences, no significant difference in mortality rate was observed in bedside-monitored patients at 30 days (4.3% vs 4.8%, P = .27) and at 1 year (7.1% vs 7.7%, P = .38). The groups had similar rates of reinfarction, shock, heart failure, and stroke.

CONCLUSIONS

This prospective substudy supports the use of bedside monitoring of heparin anticoagulation after thrombolysis.

Intervention with PTCA and CABG following thrombolysis for acute myocardial infarction. Australian data from GUSTO 1 (1991-3) and International Study Group r-TPA-Streptokinase Mortality (1989) trials. Global Utilisation of Streptokinase and Tissue

The patterns of revascularisation with percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass graft (CABG) surgery in the GUSTO 1 trial patients in Australia are described. In comparison with rates documented in earlier trials of thrombolytic therapy in Australia, the rates of revascularisation post-thrombolysis increased by 50%, primarily due to a doubling in the rate of use of PTCA. However, the rates were low by international comparisons. There were marked variations in the rates of revascularisation between States, but no correlation with differences in mortality between States. The main predictors of post thrombolysis PTCA were prior angina, mild infarction and access to PTCA facilities.

Recurrent ischemia after thrombolysis: importance of associated clinical findings. GUSTO-I Investigators. Global Utilization of Streptokinase and t-PA [tissue-plasminogen activator] for Occluded Coronary Arteries

OBJECTIVES

We sought to assess the incidence and clinical relevance of examination data to recurrent ischemia within an international randomized trial.

BACKGROUND

Ischemic symptoms commonly recur after thrombolysis for acute myocardial infarction.

METHODS

Patients (n = 40,848) were prospectively evaluated for recurrent angina and transient electrocardiographic (ECG) or hemodynamic changes. Five groups were developed: Group 1, patients with no signs or symptoms of recurrent ischemia; Group 2, patients with angina only; Group 3, patients with angina and ST segment changes; Group 4, patients with angina and hemodynamic abnormalities; and Group 5, patients with angina, ST segment changes and hemodynamic abnormalities. Baseline clinical and outcome variables were compared among the five groups.

RESULTS

Group 1 comprised 32,717 patients, and Groups 2 to 5 comprised 20% of patients (4,488 in Group 2; 3,021 in Group 3; 337 in Group 4; and 285 in Group 5). Patients with recurrent ischemia were more often female, had more cardiovascular risk factors and less often received intravenous heparin. Significantly more extensive and more severe coronary disease, antianginal treatment, angioplasty and coronary bypass surgery were observed as a function of ischemic severity. The 30-day reinfarction rate was 1.6% in Group 1, 6.5% in Group 2, 21.7% in Group 3, 13.1% in Group 4 and 36.5% in Group 5 (p < 0.0001); in contrast, the 30-day mortality rate was significantly lower (p < 0.0001) in Groups 1, 2 and 3 (6.6%, 5.4% and 7.7%, respectively) than in Groups 4 and 5 (21.8% and 29.1%).

CONCLUSIONS

Postinfarction angina greatly increases the risk of reinfarction, especially when accompanied by transient ECG changes. However, mortality is markedly increased only in the presence of concomitant hemodynamic abnormalities.

Randomized, double-blind comparison of hirulog versus heparin in patients receiving streptokinase and aspirin for acute myocardial infarction (HERO). Hirulog Early Reperfusion/Occlusion (HERO) Trial Investigators

BACKGROUND

Thrombolytic therapy improves survival after myocardial infarction through reperfusion of the infarct-related artery. Thrombin generated during thrombolytic administration may reduce the efficacy of thrombolysis. A direct thrombin inhibitor may improve early patency rates.

METHODS AND RESULTS

Four hundred twelve patients presenting within 12 hours with ST-segment elevation were given aspirin and streptokinase and randomized in a double-blind manner to receive up to 60 hours of either heparin (5000 U bolus followed by 1000 to 1200 U/h), low-dose hirulog (0.125 mg/kg bolus followed by 0.25 mg x kg(-1) x h(-1) for 12 hours then 0.125 mg x kg(-1) x h(-1)), or high-dose hirulog (0.25 mg/kg bolus followed by 0.5 mg x kg(-1) x h(-1) for 12 hours then 0.25 mg x kg(-1) x h(-1)). The primary outcome was Thrombolysis In Myocardial Infarction trial (TIMI) grade 3 flow of the infarct-related artery at 90 to 120 minutes. TIMI 3 flow was 35% (95% CI, 28% to 44%) with heparin, 46% (95% CI, 38% to 55%) with low-dose hirulog, and 48% (95% CI, 40% to 57%) with high-dose hirulog (heparin versus hirulog, P=.023; heparin versus high-dose hirulog, P=.03). At 48 hours, reocclusion had occurred in 7% of heparin, 5% of low-dose hirulog, and 1% of high-dose hirulog patients (P=NS). By 35 days, death, cardiogenic shock, or reinfarction had occurred in 25 heparin (17.9%), 19 low-dose hirulog (14%), and 17 high-dose hirulog patients (12.5%) (P=NS). Two strokes occurred with heparin, none with low-dose hirulog, and two with high-dose hirulog. Major bleeding (40% from the groin site) occurred in 28% of heparin, 14% of low-dose hirulog, and 19% of high-dose hirulog patients (heparin versus low-dose hirulog, P<.01).

CONCLUSIONS

Hirulog was more effective than heparin in producing early patency in patients treated with aspirin and streptokinase without increasing the risk of major bleeding. Direct thrombin inhibition may improve clinical outcome.

Coronary revascularization surgery after myocardial infarction: impact of bypass surgery on survival after thrombolysis. GUSTO Investigators. Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries

OBJECTIVES

This study sought to investigate the impact of surgical revascularization on outcome after myocardial infarction.

BACKGROUND

Small variations in rates of coronary artery bypass graft surgery (CABG) were noted among thrombolytic regimens in the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO) trial, prompting the question of whether survival differences were partly related to differences in CABG rates.

METHODS

Patients in the GUSTO trial were randomized to one of four thrombolytic strategies. Of 40,861 patients with complete data, 3,526 underwent surgical revascularization during their initial hospital admission. Thirty-day and 1-year mortality rates were estimated using Kaplan-Meier techniques, and the impact of CABG as a time-dependent covariate on death was evaluated using a Cox survival model, adjusting for baseline prognostic factors.

RESULTS

The median time from study enrollment to CABG was 7 days across treatment groups. A 15% reduction in mortality for the tissue-type plasminogen activator (t-PA)-treated group was evident by the seventh day. Bypass surgery was a significant independent predictor of 30-day mortality (risk ratio 1.87) and a weaker predictor of 1-year mortality (risk ratio 1.21). Operative mortality was highest in patients with acute mitral regurgitation, ventricular septal defect or poor left ventricular function and in those undergoing CABG within the first 4 days of randomization.

CONCLUSIONS

The survival benefit of accelerated t-PA was not related to surgical revascularization. Bypass surgery was associated with excess mortality in the first year, but the added short-term mortality associated with CABG may be balanced by anticipated long-term benefit in specific groups of patients.

Relation of increased arterial blood pressure to mortality and stroke in the context of contemporary thrombolytic therapy for acute myocardial infarction. A randomized trial. GUSTO-I Investigators

BACKGROUND

Despite concern that hypertension increases the risk for intracranial hemorrhage during thrombolysis for acute myocardial infarction, the exact nature of the risk remains unclear.

OBJECTIVE

To assess the effects of previous hypertension and blood pressure at study entry on the outcomes of patients who had acute myocardial infarction and received thrombolysis.

DESIGN

Randomized trial.

SETTING

1081 hospitals in 15 countries.

PATIENTS

41,021 patients who had myocardial infarction accompanied by ST-segment elevation and who presented to hospitals within 6 hours of symptom onset.

INTERVENTION

One of four thrombolytic regimens.

MAIN OUTCOME MEASURES

Mortality, stroke subtypes, and death plus disabling stroke in patients with previous hypertension and as functions of blood pressure at entry. Logistic regression analysis of relations among blood pressure at entry, baseline characteristics, and treatment effects.

RESULTS

The incidence of total stroke and intracranial hemorrhage increased as systolic blood pressure at entry increased and was particularly high for systolic pressures of about 175 mm Hg or more (incidence of total stroke, 3.4% compared with 1.17% for pressures between 100 and 124 mm Hg). Patients who had systolic blood pressure of 175 mm Hg or more at entry and who received accelerated alteplase therapy had a lower rate of death within 30 days (4.3% compared with 7.8%; P = 0.044) and a lower rate of death plus disabling stroke (4.9% compared with 8.9%; P = 0.031) than patients treated with streptokinase, despite having higher rates of total and hemorrhagic stroke (incidence of hemorrhagic stroke, 2.3% compared with 1.5%). Assumptions based on previous trials and rates of stroke from the GUSTO-1 (Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries) trial suggest that in hypertensive patients with low risk for death from cardiac causes (no previous infarction, Killip class I), the risk-to-benefit ratio with thrombolysis is about unity, with about 13 lives saved per 1000 persons treated at the risk of about 13 intracranial hemorrhages.

CONCLUSIONS

Patients with myocardial infarction and very elevated blood pressure who have thrombolysis and risk for stroke is higher in the former group. Future studies should assess 1) the risk-to-benefit ratio of thrombolysis in these patients, especially those at low risk for death from cardiac causes, and 2) whether decreasing elevated blood pressure before thrombolysis reduces the incidence of stroke without increasing mortality rates.

Age and outcome with contemporary thrombolytic therapy. Results from the GUSTO-I trial. Global Utilization of Streptokinase and TPA for Occluded coronary arteries trial

BACKGROUND

Elderly patients with acute myocardial infarction have much to gain from reperfusion with thrombolytic therapy but are also at increased risk of adverse events. We examined outcomes according to age of patients receiving thrombolysis in an international trial.

METHODS AND RESULTS

Patients were randomized to streptokinase plus subcutaneous heparin, streptokinase plus intravenous heparin, accelerated tissue plasminogen activator (TPA) plus intravenous heparin, or streptokinase and TPA plus intravenous heparin. Clinical outcomes at 30 days (death, stroke, and nonfatal, disabling stroke) and 1-year mortality were summarized descriptively for patients aged < 65 (n = 24,708), 65 to 74 (n = 11,201), 75 to 85 (n = 4625), and > 85 years (n = 412) and assessed as continuous functions of age. Older patients had a higher-risk profile with regard to baseline clinical and angiographic characteristics. Mortality at 30 days increased markedly with age (3.0%, 9.5%, 19.6%, and 30.3% in the four groups, respectively), as did stroke, cardiogenic shock, bleeding, and reinfarction. Combined death or disabling stroke occurred less often with accelerated TPA in all but the oldest patients, who showed a weak trend toward a lower incidence with streptokinase plus subcutaneous heparin: odds ratio 1.13; 95% confidence interval 0.6, 2.1. Similarly, accelerated TPA treatment resulted in lower 1-year mortality in all but the oldest patients (47% TPA versus 40.3% streptokinase).

CONCLUSIONS

Lower mortality and greater net clinical benefit were seen with accelerated TPA in patients aged < or = 85 years. Because data are limited for patients aged > 85 years, the relative superiority of a given thrombolytic regimen cannot be determined. The interactions of stroke and mortality with newer thrombolytic strategies must be examined explicitly in older patients.

Time from symptom onset to treatment and outcomes after thrombolytic therapy. GUSTO-1 Investigators

OBJECTIVES

This study sought to examine the relations among patient characteristics, time to thrombolysis and outcomes in the international GUSTO-I trial.

BACKGROUND

Studies have shown better left ventricular function and decreased infarct size as well as increased survival with earlier thrombolysis, but the relative benefits of various thrombolytic agents with earlier administration are uncertain.

METHODS

We evaluated the relations of baseline characteristics to three prospectively defined time variables: symptom onset to treatment, symptom onset to hospital arrival (presentation delay) and hospital arrival to treatment (treatment delay). We also examined the relations of delays to clinical outcomes and to the relative 30-day mortality benefit with accelerated tissue-type plasminogen activator (t-PA) versus streptokinase.

RESULTS

Female, elderly, diabetic and hypertensive patients had longer delays at all stages. Previous infarction or bypass surgery was an additional risk factor for treatment delay. Early thrombolysis was associated with lower overall mortality rate (< 2 h, 5.5%; > 4 h, 9.0%), but no additional relative benefit resulted from earlier treatment with accelerated t-PA versus streptokinase (p = 0.38). Longer presentation and treatment delays were both associated with increased mortality rate (presentation delay < 1 h, 5.6% and > 4 h, 8.6%; treatment delay < 1 h, 5.4%, and > 90 min, 8.1%). As time to treatment increased, the incidence of recurrent ischemia or reinfarction decreased, but the rates of shock, heart failure and stroke increased.

CONCLUSIONS

Earlier treatment resulted in better outcomes, regardless of thrombolytic strategy. Elderly, female and diabetic patients were treated later, adding to their already substantial risk.

Comparisons of characteristics and outcomes among women and men with acute myocardial infarction treated with thrombolytic therapy. GUSTO-I investigators

OBJECTIVE

To compare baseline characteristics, complications, and treatment-specific outcomes of women and men with acute myocardial infarction treated with thrombolytic therapy.

DESIGN

Randomized controlled trial.

PATIENTS AND SETTING

A total of 10315 women and 30706 men with acute myocardial infarction treated in 1081 hospitals in 15 countries as part of the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO-I).

INTERVENTION

One of four thrombolytic regimens: (1) streptokinase with subcutaneous heparin; (2) streptokinase with intravenous heparin; (3) streptokinase plus alteplase (tissue-type plasminogen activator) with intravenous heparin; or (4) accelerated alteplase with intravenous heparin.

MAIN OUTCOME MEASURES

Mortality, stroke, and nonfatal complications during 30-day follow-up.

RESULTS

Women were on average 7 years older than men and delayed 18 minutes (median) longer after symptom onset before presenting to the hospital. After adjustment for age, women more often had a history of diabetes, hypertension, and smoking than men. Time to treatment was significantly longer in women (1.2 vs 1.0 hours; P<.001). Women had more nonfatal complications after treatment, including shock (9% vs 5%; P<.001), congestive heart failure (22% vs 14%; P<.001), serious bleeding (15% vs 7%; P<.001), and reinfarction (5.1% vs 3.6%; P<.001). Women had twice as many total strokes as men (2.1% vs 1.2%; P<.001), secondary to their older age at presentation. The unadjusted mortality rate was twice as high in women as men (11.3% vs 5.5%; P<.001); the relative risk (RR) of death was greater among women than men after adjustment for differences in baseline characteristics (RR=1.15; 95% confidence interval, 1.0 to 1.31). Although women and men underwent angiography at similar rates, there were small but significant differences in their rates of revascularization procedures (angioplasty: 35% of women and 32% of men; bypass surgery: 7% of women and 9% of men; P<.001 for both). The higher rate of stroke in women after treatment with alteplase (2.0% vs 1.9% with streptokinase and intravenous heparin) was offset by a greater relative reduction in mortality (10.3% vs 11.1%).

CONCLUSION

Women who received thrombolytic therapy for treatment of acute myocardial infarction were at greater risk for both fatal and nonfatal complications than men.

Stroke after thrombolysis. Mortality and functional outcomes in the GUSTO-I trial. Global Use of Strategies to Open Occluded Coronary Arteries

BACKGROUND

Stroke is the most feared complication of thrombolysis for acute myocardial infarction because of the resulting mortality and disability. We analyzed the incidence, timing, and outcomes of stroke in an international trial.

METHODS AND RESULTS

Patients were randomly assigned to one of four thrombolytic strategies. Neurological events were confirmed clinically and anatomically and were adjudicated by a blinded committee. Stroke survivors, categorized by residual deficit and disability, assessed their quality of life with a time trade-off technique. Multivariable regression identified patient characteristics associated with intracranial hemorrhage. Over-all, 1.4% of the patients had a stroke (93% anatomic documentation). The risk ranged from 1.19% with streptokinase/subcutaneous heparin therapy to 1.64% with combination thrombolytic therapy (P = .007). Primary intracranial hemorrhage rates ranged from 0.46% with streptokinase/subcutaneous heparin to 0.88% with combination therapy (P < .001). Of all strokes, 41% were fatal, 31% were disabling, and 24% were nondisabling, with no significant treatment-related differences. Stroke subtype affected prognosis: 60% of patients with primary intracranial hemorrhage died and 25% were disabled versus 17% dead and 40% disabled with nonhemorrhagic infarctions. Patients with moderate or severe residual deficits showed significantly decreased quality of life. Advanced age, lower weight, prior cerebrovascular disease or hypertension, systolic and diastolic blood pressures, randomization to tissue plasminogen activator, and an interaction between age and hypertension were significant predictors of intracranial hemorrhage.

CONCLUSIONS

Stroke remains a rare but catastrophic complication of thrombolysis. Additional studies should assess the net clinical benefit of thrombolysis in high-risk subgroups, particularly the elderly and patients with prior cerebrovascular events.

Streptokinase morbidity--more common than previously recognised

Streptokinase is the thrombolytic agent most commonly used for the treatment of acute myocardial infarction. We report eight patients who developed late uncommon adverse reactions to streptokinase probably due to immune complex disease. The clinical manifestations included vasculitic rashes, abnormal renal and liver function tests and a syndrome resembling adult respiratory distress syndrome. Major adverse events with streptokinase such as stroke, bleeding and other allergic reactions, have been previously documented but the morbidity related to delayed reactions has not been widely recognised. These reactions produced significant morbidity resulting in prolonged hospital stay and may need to be considered in the decision to use streptokinase.

A randomized comparison of intravenous heparin with oral aspirin and dipyridamole 24 hours after recombinant tissue-type plasminogen activator for acute myocardial infarction. National Heart Foundation of Australia Coronary Thrombolysis Group

BACKGROUND

This study addressed the need for heparin administration to be continued for more than 24 hours after coronary thrombolysis with recombinant tissue-type plasminogen activator (rt-PA).

METHODS AND RESULTS

A total of 241 patients with acute myocardial infarction were treated with 100 mg rt-PA and a bolus of 5,000 units i.v. heparin followed by 1,000 units/hr i.v. heparin for 24 hours. At 24 hours, 202 patients were randomized to continue intravenous heparin therapy (n = 99) in full dosage or to discontinue heparin therapy and begin an oral antiplatelet regimen of aspirin (300 mg/day) and dipyridamole (300 mg/day) (n = 103). On prospective recording, there were no differences in the pattern of chest pain, reinfarction, or bleeding complications. Coronary angiography on cardiac catheterization at 7-10 days showed no differences in patency of the infarct-related artery. The proportion of patients with total occlusion (TIMI grade 0-1) of the infarct-related artery was 18.9% in the heparin group and 19.8% in the aspirin and dipyridamole group. In the patients with an incompletely occluded infarct-related artery, the lumen was reduced by 69 +/- 2% of normal in the heparin group and 67 +/- 2% in the aspirin and dipyridamole group. Left ventricular function assessed on cardiac catheterization and radionuclide study at day 2 and at 1 month showed no differences between the two groups. Left ventricular ejection fraction on radionuclide ventriculography at 1 month was 52.4 +/- 1.2% in the heparin group and 51.9 +/- 1.2% in the aspirin and dipyridamole group.

CONCLUSIONS

We conclude that heparin therapy can be discontinued 24 hours after rt-PA therapy and replaced with an oral antiplatelet regimen without any adverse effects on chest pain, reinfarction, coronary patency, or left ventricular function.

Adrenaline facilitates neurogenic vasoconstriction in borderline hypertensive subjects

Adrenaline facilitates the neural release of endogenous noradrenaline by stimulating prejunctional beta-receptors on adrenergic nerve endings. Recently, we demonstrated the functional significance of this action in the control of vascular resistance in young subjects with normal blood pressure. In the present study, we tested the hypothesis that the effects of adrenaline on neurogenic vasoconstriction are exaggerated in humans with borderline hypertension. Forearm blood flow was measured simultaneously in the experimental and contralateral arms of seven young men with borderline hypertension. We compared forearm vasoconstrictor responses to a reflex stimulus to noradrenaline release (lower-body negative pressure, LBNP) and to intra-arterial infusion of noradrenaline before and 30 min after brachial artery infusion of adrenaline (50 ng/min). These doses had no systemic effects. In the experimental arm, the vasoconstrictor response to LBNP was 65% greater 30 min after the adrenaline infusion (P = 0.075), whereas the response to intra-arterial noradrenaline decreased by 36% (P greater than 0.1). Forearm vascular responses to LBNP in the contralateral control arm that did not receive adrenaline were similar before and after the adrenaline infusion. The ratio of forearm vasoconstrictor responses (i.e. the increase in forearm vascular resistance) with LBNP to the forearm vasoconstrictor response to noradrenaline in the experimental arm was used as an index of neural release of the neurotransmitter noradrenaline. This ratio increased from 0.8 to 2.1 (P less than 0.05) after the adrenaline infusion. These facilitatory neural after-effects of adrenaline were similar in magnitude to our previous observation in young normotensive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Automated non-invasive measurement of cardiac output by the carbon dioxide rebreathing method: comparisons with dye dilution and thermodilution

The accuracy and reproducibility of indirect measurement of cardiac output at rest by the carbon dioxide rebreathing (indirect Fick) method with an automated respiratory analysis system (Gould 9000IV) were compared with simultaneous measurements made in duplicate by dye dilution and thermodilution in 25 patients having cardiac catheterisation studies. Measurements of cardiac output by the carbon dioxide rebreathing method were not significantly different from those obtained with dye dilution (mean difference -0.3 l/min, SD 0.76, 95% confidence interval -0.7 to 0.1). Thermodilution significantly over-estimated cardiac output by a mean of 2.2 l/min or 39% (SD 1.5, 95% confidence interval 1.6 to 2.8) compared with the carbon dioxide rebreathing method and significantly overestimated cardiac output by 1.9 l/min or 31% (SD 1.2, 95% confidence interval 1.2 to 2.5) compared with dye dilution. The reproducibility of measurements of cardiac output in individual patients was satisfactory with the dye dilution method but was poor with carbon dioxide rebreathing and thermodilution. Indirect measurement of resting cardiac output by the Gould 9000IV automated carbon dioxide rebreathing method is more accurate but the variability inherent with this method requires that multiple measurements be taken for each determination. Measurement of cardiac output by the thermodilution method by a commercially available cardiac output computer was not satisfactory because not only was there considerable variability between repeat measurements but the method also consistently overestimated cardiac output compared with the dye dilution method.

Role of vasopressin in cardiovascular and blood pressure regulation

At low concentrations and in physiologic states vasopressin is a potent antidiuretic hormone. Its cardiovascular effects have been more complex and their role in circulatory adjustments to hypovolemia and hypotension difficult to define with precision. Although recognized as a powerful vasoconstrictor, its pressor effect in intact animals, even at high concentrations, is minimal. The reasons for this blunted pressor response have been explored. This report is a review of previously published work from our laboratories which highlights the direct and indirect vasodilator actions of this hormone in animals and humans. The indirect vasodilator effect is caused by inhibition of sympathetic efferents, and facilitation of the baroreflex through a central action of the hormone and its sensitization of arterial baroreceptors as well as cardiac afferents.

Optimal size of cuff bladder for indirect measurement of arterial pressure in adults

This study tested the hypothesis that a sphygmomanometer cuff bladder long enough to encircle the arm in most adults ('obese cuff') would provide a more accurate and precise estimate of intra-arterial pressure than the usual 'standard' cuff bladder. In 53 patients undergoing diagnostic coronary angiography (35 males, 18 females, aged 36-79 years), indirect blood pressure, measured in the left arm with a random-zero sphygmomanometer, was compared with simultaneously measured femoral intra-arterial pressure. Duplicate indirect measurements were made with each of two cuffs containing bladders measuring 39 x 15 cm ('obese') and 23 x 12 cm ('standard'). The obese cuff bladder encircled 80% or more of the arm circumference in all subjects, whereas the standard cuff bladder met this requirement in only 19% of the subjects. For both systolic and diastolic pressure there was marked interindividual variability in the differences between indirect and direct measurements with both cuffs. With the obese cuff there was no systematic error in the diastolic blood pressure measurement. The standard cuff consistently overestimated diastolic pressure by 7.7 +/- 8.3 mmHg (mean +/- s.d.). For both cuffs, the difference between indirect and direct diastolic pressure increased with arm size (P less than 0.05). Both cuffs underestimated systolic blood pressure, the obese cuff by 15.5 +/- 11.7 mmHg and the standard cuff by 7.6 +/- 12.1 mmHg. These systolic blood pressure underestimates were greater at higher blood pressures (P less than 0.01) and with smaller arms (P less than 0.05). Age was not related to measurement error with either cuff.(ABSTRACT TRUNCATED AT 250 WORDS)

Postexercise hypotension and sympathoinhibition in borderline hypertensive men

To determine if there would be a decrease in blood pressure after exercise in patients with borderline hypertension and if this decrease would be accompanied by a decrease in sympathetic nerve activity to muscle, we recorded multifiber postganglionic muscle sympathetic activity from the peroneal nerve at rest in nine men with borderline hypertension (age 25 +/- 1 years, mean +/- SEM) before and 60 minutes after 45 minutes of submaximal treadmill exercise. In addition, responses to a cold pressor test, handgrip, and the Valsalva maneuver were recorded before and after exercise. Four subjects were also studied before and after "sham" exercise. Sham exercise had no effect on blood pressure or sympathetic nerve activity whereas resting systolic blood pressure was lower after treadmill exercise in seven subjects (from 136 +/- 4 before to 123 +/- 2 mm Hg 60 minutes after exercise; p less than 0.01). Sixty minutes after exercise, sympathetic nerve activity was lower in all seven subjects (from 19 +/- 2 to 11 +/- 2 bursts/min, p less than 0.015; or from 27 +/- 3 to 14 +/- 2 bursts/100 heartbeats, p less than 0.005) but was slightly increased in the two subjects without postexercise hypotension. Heart rate and pressor and sympathoneural responses to the cold pressor test, handgrip, and the Valsalva maneuver were not altered by prior exercise. When nitroprusside was infused in five subjects to produce a reduction in systolic blood pressure similar to that seen 60 minutes after exercise, this drug increased sympathetic discharge from 37 +/- 6 to 57 +/- 4 bursts/100 heartbeats (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of the Takeda TM-2420 ambulatory blood pressure monitor

1. The accuracy of blood pressure measurement with the Takeda TM-2420 ambulatory blood pressure monitor and the TM-2020 data recorder have been assessed by comparison with simultaneous measurements taken using auscultation and direct femoral artery measurements. 2. Systolic blood pressure was underestimated by the TM-2420 by a mean of 10 mmHg (s.d. = 6, 95% confidence interval (CI) = -13 to -7) over the range of pressures measured by auscultation. It was underestimated by 23 mmHg (s.d. = 12, 95% CI = -28 to -18) compared with direct femoral artery measurements. 3. Diastolic pressure measurements were similar to those obtained by auscultation. When compared with direct femoral artery recordings, diastolic pressure was overestimated by about 5 mmHg (s.d. = 4, 95% CI = 3.4-6.6), which is consistent with indirect readings, taken with a 'standard' cuff (inflatable bladder 23 cm X 12 cm). 4. The TM-2420/2020 is thus suitable for ambulatory measurements of blood pressure when diastolic pressure is the criterion of interest.

Transmitral velocities measured by pulsed Doppler in healthy volunteers: effects of acute changes in blood pressure and heart rate

The effect of a two minute cold pressor test on transmitral velocities measured by pulsed Doppler was studied in 11 healthy volunteers. Blood pressure increased significantly during cold immersion but peak atrial and peak early diastolic transmitral velocities and their ratio (A:E) were unchanged. There was no correlation between changes in Doppler variables and changes in calculated mean arterial blood pressure during the test. Heart rate changes were variable and not related to changes in blood pressure. In individual people the change in pulse interval during cold immersion was significantly and inversely correlated with the change in the A:E ratio. The large acute increase in arterial pressure seen during the cold pressor test in normal volunteers had no consistent effect on the transmitral velocity profile although small changes in heart rate were associated with large changes in A:E ratio. The effect of small changes in heart rate may be of considerable importance in determining transmitral velocity profiles. Thus in clinical and experimental studies in which the heart rate is not controlled, Doppler data on transmitral flow should be interpreted with caution.

Feasibility of identifying amyloid and hypertrophic cardiomyopathy with the use of computerized quantitative texture analysis of clinical echocardiographic data

Ultrasound tissue characterization, the evaluation of certain physical properties of a tissue based on its acoustic properties, is an evolving application in echocardiography. The ability to identify acutely and chronically injured tissue has been demonstrated in a number of animal studies, but data in humans are limited. The present study tested the hypothesis that quantitative echocardiographic texture analysis, a method of evaluating the spatial pattern of echoes in echocardiographic images, would differentiate amyloid and hypertrophic cardiomyopathy from normal myocardium. Routine clinical echocardiographic data were obtained on 34 subjects at the Mayo Clinic (10 normal subjects, 10 patients with amyloid heart disease, 8 patients with hypertrophic cardiomyopathy and 6 patients with left ventricular hypertrophy due to hypertension). Standard videotape recordings of these echocardiograms were analyzed at the University of Iowa. Echocardiographic data were digitized with use of a calibrated, 256 gray level digitization system. Quantitative texture analysis was performed on data from the ventricular septum and posterior left ventricular wall in end-diastolic and end-systolic, short-axis and long-axis echocardiographic images. The gray level run length texture variables were able to discriminate hypertrophic cardiomyopathy and amyloid heart disease from normal myocardium and from each other (p less than 0.0083 for comparisons of the quantitative texture features of amyloid versus hypertrophic cardiomyopathy versus normal by multivariate analysis of variance). The texture of the myocardium in hypertensive left ventricular hypertrophy not associated with amyloid or hypertrophic cardiomyopathy was in general not significantly different from that of normal myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma neuropeptide Y and atrial natriuretic peptide concentrations in man

1. In order to examine the concentration of neuropeptide Y-like immunoreactivity (NPY-LI) and atrial natriuretic peptide (ANP) in the circulation in man, blood was sampled from the iliac vein, the inferior vena cava, the superior vena cava, the pulmonary artery and the femoral artery in 13 patients undergoing cardiac catheterization. 2. Plasma NPY-LI levels were similar at all points sampled and no arteriovenous differences were found. Plasma ANP concentration in the pulmonary artery was greater than in peripheral venous blood but there was a strong correlation between the two. 3. The concentration of NPY-LI and ANP in peripheral venous blood reflects central venous and arterial concentrations.

Epinephrine facilitates neurogenic vasoconstriction in humans

Numerous studies have suggested that epinephrine may facilitate neural release of NE. There have been no studies in humans that demonstrate the functional significance of this action. To determine whether epinephrine facilitates neurogenic vasoconstriction in humans, we contrasted forearm vasoconstrictor responses to a reflex stimulus (lower body negative pressure [LBNP]) and to intraarterial NE before, during, and 30 min after infusion of epinephrine (50 ng/min) or isoproterenol (10 or 25 ng/min) into a brachial artery. These doses had no systemic effects. We reasoned that if prejunctional stimulation of beta receptors by epinephrine and isoproterenol had functional significance, the vasoconstrictor response to LBNP would be potentiated in comparison to the response to NE (postjunctional mechanism). Studies were done on 23 normal male volunteers. Forearm blood flow was measured with a strain gauge plethysmograph and intraarterial pressure was recorded. The ratio of vasoconstrictor responses to LBNP/NE was used as an index of neural release of the neurotransmitter NE. This ratio increased during infusions of both epinephrine and isoproterenol. 30 min after epinephrine the vasoconstrictor response to LBNP (n = 15) was augmented from +9.9 +/- 2.2 (SE) resistance units (RU) before epinephrine to +16.4 +/- 3.2 RU (P less than 0.05); whereas the response to NE (n = 8) tended to decrease from +8.8 +/- 3.1 RU before to +4.2 +/- 1.2 RU after epinephrine (P greater than 0.05). In contrast, 30 min after isoproterenol the vasoconstrictor responses to LBNP and NE were the same as before isoproterenol. The augmented ratio of responses to LBNP/NE after epinephrine and not after isoproterenol supports the concept that epinephrine, but not isoproterenol, is taken up by the adrenergic terminal, is released subsequently during reflex stimulation, and augments the release of the neurotransmitter NE. These experiments provide the first hemodynamic evidence in humans that epinephrine and isoproterenol facilitate neurogenic vasoconstriction. The sustained effect of epinephrine in contrast to isoproterenol suggests that the late facilitation by epinephrine is related to its neural uptake and subsequent release.

The effect of coronary angioplasty on coronary flow reserve

To determine the effects of coronary angioplasty on coronary flow reserve (CFR), we studied 32 patients before and immediately after single-vessel coronary angioplasty and 31 patients evaluated late after angioplasty (7.5 +/- 1.2 months, mean +/- SEM). The geometry (percent area stenosis and minimal cross-sectional area) of each lesion was determined by quantitative coronary angiography (Brown/Dodge method) and the integrated optical density was measured by videodensitometry. CFR was measured with a No. 3F coronary Doppler catheter placed immediately proximal to the lesion and a maximally vasodilating dose of intracoronary papaverine. The translesional pressure gradient was obtained in all lesions before and immediately after angioplasty and in 18 of 31 vessels late after angioplasty. CFR immediately after angioplasty returned to normal levels (greater than 3.5 peak/resting velocity ratio) in 14 of 31 patients and was improved, although not normalized, in the remaining 17 patients. CFR immediately after dilation was not significantly correlated with any of the angiographic variables of arterial stenosis nor the resting pressure gradient. Moreover, the pressure gradient and absolute distal coronary pressure at peak hyperemia were not significantly different in vessels with normal and those with abnormal flow reserve immediately after dilation, suggesting that the residual stenosis did not significantly limit hyperemia. Late after angioplasty, however, a significant relationship emerged between CFR and all four indexes of residual arterial stenosis (percent area stenosis r = .70, p less than .01; minimum arterial cross-sectional area r = .70, p less than .01; integrated optical density r = .60, p less than .01; and translesional pressure gradient r = .77, p less than .01). Furthermore, in the absence of restenosis, CFR eventually normalized in all patients. These findings demonstrate that in one-half of patients there is a transient reduction in coronary flow reserve immediately after angioplasty. In the absence of restenosis, coronary flow reserve later normalizes. Consequently, measurements of coronary flow reserve immediately after angioplasty may not reflect the eventual success of the procedure in removing physiologic obstruction to coronary blood flow.

Inhibition of muscle sympathetic nerve activity in humans by arginine vasopressin

Arginine vasopressin, a potent vasoconstrictor, does not raise arterial pressure in normal humans even at pathophysiological plasma levels. To examine whether the pressor effect of vasopressin in humans is buffered by baroreceptor reflex inhibition of sympathetic nerve activity, we recorded postganglionic muscle sympathetic nerve activity directly from the peroneal nerve in 12 normal men before, during, and after a 20-minute intravenous infusion of vasopressin, 4 ng/kg/min, that increased mean plasma concentrations from 6.2 +/- 0.6 to 320 +/- 68 (SE) pg/ml. During the first 5 minutes (n = 8), mean arterial pressure increased from 91 +/- 3 to 97 +/- 4 mm Hg (p less than 0.05) and integrated sympathetic nerve activity decreased from 271 +/- 45 to 156 +/- 33 units (p less than 0.05). At 15 minutes (n = 12), arterial pressure did not differ from control values whereas forearm vascular resistance fell (p less than 0.05) and central venous pressure and heart rate increased (p less than 0.05). Sympathetic nerve activity remained below control levels throughout the infusion (202 +/- 31 vs 254 +/- 40 units before infusion; p less than 0.05). An effect of vasopressin on ganglionic transmission was excluded, since the sympathoexcitatory response to apnea was not attenuated during vasopressin. Thus, pathophysiologic levels of vasopressin in humans cause inhibition of muscle sympathetic nerve activity that is not due to a ganglionic blocking action. The sympathoinhibition may be caused in part by the modest increases in mean arterial and central venous pressures and attendant stimulation of arterial and cardiac baroreceptors. The reflex decrease in sympathetic nerve activity would be expected to buffer the direct vasoconstrictor effects of vasopressin.

Modulation of cardiovascular reflexes by arginine vasopressin

Arginine vasopressin (AVP), a potent vasoconstrictor, does not raise arterial pressure in normal humans or neurally intact animals, even during infusions that achieve pathophysiological plasma concentrations. It has been proposed that this is because AVP facilitates the baroreflex control of the circulation. We performed a series of investigations to test this hypothesis, and to determine sites at which AVP might act to augment the baroreflex. In anesthetized rabbits, vasopressin (36 pmol.kg-1.min-1) increased discharge from both medullated and nonmedullated single fibres from aortic baroreceptor nerves during elevations in aortic arch pressure. Similarly, vasopressin (36 pmol.kg-1.min-1) increased the response of left ventricular mechanoreceptor single fibre discharge to elevations of left ventricular end-diastolic pressure. These observations suggest that sensitization of high and low pressure baroreceptors is one mechanism by which vasopressin may facilitate baroreflexes. In a further series of experiments in sinoaortic denervated anesthetized rabbits, vasopressin (18 pmol.kg-1.min-1) facilitated vagally mediated reflex inhibition of renal sympathetic nerve activity during volume expansion. In humans, AVP (0.37 pmol.kg-1.min-1) raised plasma AVP to an antidiuretic level (22 +/- 4 fmol/mL), but did not change blood pressure or the baroreflex control of heart rate or forearm vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin facilitates inhibition of renal nerve activity mediated through vagal afferents

We measured the effect of vasopressin (8 mU X kg-1 X min-1) on reflex inhibition of renal sympathetic nerve activity induced by volume expansion in 13 sinoaortic-denervated anesthetized rabbits. Volume expansion increased left ventricular end-diastolic pressure (LVEDP) from 5.1 +/- 0.7 to 14.1 +/- 1.4 mmHg and decreased renal nerve activity (RNA) from 57.4 +/- 6.9 to 30.2 +/- 5.6 impulses/s. Infusion of vasopressin elevated LVEDP from 6.0 +/- 1.0 to 7.3 +/- 1.1 mmHg and decreased RNA from 61.8 +/- 7.2 to 47.1 +/- 6.3 impulses/s. Heart rate fell from 243 +/- 7 to 231 +/- 9 beats/min; no other significant hemodynamic changes were seen. During the infusion of vasopressin, volume expansion increased LVEDP to 13.7 +/- 1.2 mmHg and decreased RNA to 17.0 +/- 4.2 impulses/s. The slopes relating the percent decrease in RNA to the rise in LVEDP were calculated from values of RNA recorded at several levels of LVEDP. The slope averaged -6.2 +/- 1.1%/mmHg before vasopressin and nearly doubled (-11.9 +/- 1.8%/mmHg) during vasopressin. Infusion of placebo (saline) instead of vasopressin did not alter the reflex inhibition of nerve activity. Bilateral vagotomy abolished the decrease in resting nerve activity that occurred during infusion of vasopressin as well as the reflex inhibition of RNA. These data demonstrate that vasopressin facilitates the reflex inhibition of renal sympathetic nerve activity associated with increases in LVEDP and mediated through vagal afferents.

Paroxysmal hypertension due to sinoaortic baroreceptor denervation in humans

A 41-year-old man with a remote history of neck and mediastinal radiation was seen with severe paroxysms of hypertension, headache, and cutaneous flushing after bilateral carotid bypass surgery. Investigation revealed marked parallel fluctuations in blood pressure and heart rate and elevation of plasma norepinephrine to 1164 pg/ml during a paroxysm. We systematically evaluated his arterial and cardiopulmonary baroreceptor reflex function by assessing changes in heart rate, arterial pressure, and efferent muscle sympathetic nerve activity, which was measured directly by the microneurographic technique. Elevating resting arterial pressure from 130/88 to 164/100 mm Hg with phenylephrine or lowering it to 88/56 mm Hg with nitroprusside produced no reflex changes in heart rate or efferent sympathetic nerve activity. In contrast, decreases in cardiac filling pressures with lower body negative pressure produced a marked increase in sympathetic nerve activity. These findings indicate complete loss of the afferent limb of the arterial baroreceptor reflex but preservation of the cardiopulmonary baroreceptor reflex. They suggest that both carotid and aortic baroreceptors were impaired by the previous radiation and surgery. Despite the loss of arterial baroreceptor function, the patient did not have sustained hypertension. The paroxysms of hypertension appear to be due to spontaneous fluctuations in central sympathetic drive not buffered by arterial baroreceptors in a manner similar to that seen in sinoaortic-denervated animals.

Sensitization of aortic and cardiac baroreceptors by arginine vasopressin in mammals

Vasopressin facilitates the baroreflex control of the circulation. The peptide may act at several sites to augment the baroreflex. In this study we examined the effect of vasopressin on aortic baroreceptors in anaesthetized rabbits and on left ventricular mechanoreceptors in anaesthetized cats. Vasopressin (16 mu./kg. min) did not change resting nerve discharge in single fibres from aortic baroreceptors. Vasopressin (16 mu./kg. min) significantly enhanced the response of single aortic nerve fibre discharge to elevation in arterial pressure. The slope relating nerve activity to mean arterial pressure increased from 0.24 +/- 0.05 (mean +/- S.E. of mean) to 0.50 +/- 0.16 impulses/cardiac cycle. mmHg (P less than 0.05) in ten aortic medullated fibres and from 0.06 +/- 0.03 to 0.18 +/- 0.04 impulses/cardiac cycle. mmHg (P less than 0.05) in three non-medullated fibres. Vasopressin (16 mu./kg. min) did not change resting nerve discharge in single fibres from left ventricular mechanoreceptors. Vasopressin (16 mu./kg. min) significantly enhanced the response of single nerve fibre discharge from left ventricular mechanoreceptors in response to elevation of left ventricular end-diastolic pressure. The slope relating nerve activity to left ventricular end-diastolic pressure increased from 0.24 +/- 0.07 to 0.32 +/- 0.07 impulses/cardiac cycle. mmHg (P less than 0.05) in six medullated fibres and from 0.10 +/- 0.01 to 0.15 +/- 0.02 impulses/cardiac cycle. mmHg (P less than 0.05) in four non-medullated fibres. These data show that vasopressin sensitizes high and low pressure baroreceptors and suggest a mechanism by which vasopressin may facilitate the baroreflex control of the circulation.

Effects of vasopressin on the circulation and its baroreflex control in healthy men

Information on the hemodynamic effects of vasopressin (AVP) in healthy humans is very limited despite its known importance in body fluid homeostasis and release in pathologic states such as hemorrhage and trauma. Although it is a potent vasoconstrictor in vitro, it does not cause the expected rise in arterial pressure when given systemically to animals with intact baroreflexes. It has been proposed that this is because AVP facilitates baroreflex control of the circulation. In this study, we assessed the effect of infusion of AVP on resting circulatory variables and on the baroreflex control of forearm vascular resistance and heart rate in healthy men. AVP in a dose of 0.4 ng/kg/min, which raised plasma level of AVP to 24 +/- 4 pg/ml, a value known to have a significant antidiuretic effect, had little hemodynamic effect, producing only mild bradycardia and a slight increase in central venous pressure. Reflex changes in heart rate during neck suction (-15 and -30 mm Hg) and neck pressure (+15 and +30 mm Hg) were not altered. Reflex responses to lower body negative pressure and to its release were also unchanged by this dose of AVP. In contrast, a higher dose of AVP (4 ng/kg/min), which raised plasma levels to 290 +/- 41 pg/ml, a concentration known to occur as a result of hemorrhagic hypotension and circulatory stresses, did cause hemodynamic changes. There was tachycardia (from 63 +/- 2 to 68 +/- 2 beats/min), a decrease in pulse pressure (from 62 +/- 2 to 53 +/- 2 mm Hg), an increase in central venous pressure (from 2.6 +/- 0.5 to 4.1 +/- 0.4 mm Hg), and surprisingly in view of the known vasoconstrictor effect of AVP, an increase in forearm flow (from 4.4 +/- 0.7 to 5.9 +/- 1.2 ml/min/100 ml tissue) and a decrease in forearm vascular resistance (from 24 +/- 4 to 18 +/- 3 U); there was no significant change in mean arterial pressure (from 83 +/- 2 to 83 +/- 3 mm Hg). Reflex changes in heart rate were unaltered. The maximal vasoconstrictor response in the forearm attained during lower body negative pressure was not influenced by AVP, but the reflex vasodilator response to the sudden release of lower body negative pressure was significantly augmented, vascular resistance falling to 23 +/- 4 U before and 13 +/- 2 U during AVP. The unanticipated findings in this study include the biphasic changes in heart rate with increasing doses of AVP, the absence of a pressor response, and the vasodilatation in forearm vessels.(ABSTRACT TRUNCATED AT 400 WORDS)

Direct evidence from intraneural recordings for increased central sympathetic outflow in patients with heart failure

Patients with heart failure have increased vascular resistance and evidence for increased neurohumoral drive. High levels of circulating norepinephrine are found in patients with heart failure, but it is not known whether they reflect increased sympathetic neural activity or result from altered synthesis, release, or metabolism of norepinephrine. We used microneurography (peroneal nerve) to directly record sympathetic nerve activity to muscle (mSNA) and also measured plasma norepinephrine levels in patients with heart failure and in normal control subjects. Our goal was to determine whether sympathetic nerve activity is increased in patients with heart failure and whether plasma norepinephrine levels correlate with levels of mSNA in heart failure. Resting muscle sympathetic nerve activity in 16 patients with moderate to severe heart failure (54 +/- 5 bursts/min, mean +/- SE) was significantly higher (p less than .01) than the levels of activity in either nine age-matched normal control subjects (25 +/- 4 bursts/min) or 19 "young" normal control subjects (24 +/- 2 bursts/min). We found a significant correlation between plasma norepinephrine levels and mSNA (r = .73, p less than .05). Neither mSNA nor plasma norepinephrine levels correlated with total systemic vascular resistance, cardiac index, left ventricular ejection fraction, or heart rate. However, both mSNA and plasma norepinephrine levels showed significant positive correlations (p less than .05) with left ventricular filling pressures (r = .80, mSNA vs filling pressures; r = .82, norepinephrine levels vs filling pressures) and mean right atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Defibrillator electrode-chest wall coupling agents: influence on transthoracic impedance and shock success

The purpose of this study was to determine if the difference in transthoracic impedance produced by different coupling agents affects the success of shocks for defibrillation. Three different coupling agents, Harco pads (Hewlett-Packard), Littman pads (3M) and Redux paste (Hewlett-Packard), were assessed in 10 anesthetized dogs in which ventricular fibrillation was induced by electrical stimulation of the right ventricle. Defibrillation was attempted 15 seconds later, using 50, 100 and 150 joules (selected energy). Actual delivered energy, current, impedance and the percent of the shocks that achieved defibrillation were determined for the three coupling agents. Redux paste gave significantly lower impedance and higher current than the two disposable performed coupling pads tested. Despite this, there were no significant differences in shock success among the three coupling agents. Thus, in this experimental model, over a three-fold energy range, disposable coupling pads were as effective as electrode paste for defibrillation despite the slightly higher impedance of the disposable pads.

Relative roles of vagal and sympathetic effector mechanisms in the baroreflex control of myocardial contractility in conscious rabbits

The relative roles of vagal and sympathetic effector mechanisms in the baroreflex control of myocardial contractility have been assessed in the conscious normotensive and hypertensive rabbit. Graded increases in mean arterial pressure (MAP) were produced by inflation of a balloon occluder around the abdominal aorta. Stimulus response curves relating the change in MAP to the induced change in peak rate of change of left ventricular pressure (peak LV dP/dt) were produced when heart rate was allowed to change and when it was held constant by atrial pacing. These curves were repeated after sympathetic blockade with propranolol, vagal blockade with methylscopolamine and combined blockade with the two drugs together. Increase in MAP produced a reflex fall in peak LV dP/dt which was due to two components. There was a reflex negative inotropic effect which was independent of heart rate, occurring in animals in whom heart rate was held constant by atrial pacing, and there was also a reduction in peak LV dP/dt which was caused by the reflex bradycardia when the heart rate was allowed to change. Both sympathetic and vagal efferents contributed to the reflex fall in peak LV dP/dt seen after elevation of MAP, the sympathetic being primarily responsible for the direct negative inotropic effect and the vagus for the bradycardia and hence the secondary effects on peak LV dP/dt. The slope of the stimulus response curves relating the fall in peak LV dP/dt to the increase in MAP was similar in intact normotensive and hypertensive rabbits, both with and without atrial pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of cardiac pacing in the analysis of vagal and sympathetic contributions to baroreflex control of cardiac performance in the conscious rabbit

The baroreflex control of myocardial contractility has been assessed in the conscious normotensive and hypertensive rabbit. Stimulus response curves relating graded changes in mean arterial pressure (MAP) to induced changes in peak rate of change of left ventricular pressure (peak LV dP/dt) were compared during constant heart rate controlled by atrial pacing and when heart rate was uncontrolled. The experiments were repeated after beta-block, cholinergic block and during combined block in both A rise in MAP produced a fall in peak LV dP/dt which was due to two components. There was a reflex negative inotropic effect which was independent of heart rate and a reduction in peak LV dP/dt due to reflex bradycardia. The sympathetic nerves were primarily responsible for the direct negative inotropic effect and the vagus for the indirect effect, secondary to the bradycardia. The slope of the stimulus response curves relating the baroreflex fall in peak LV dP/dt to rises in MAP were similar in normotensive and hypertensive animals, in contrast to the sensitivity of the baroreflex heart rate response which is impaired in animals with chronic hypertension.

Cardiac performance in the conscious rabbit with acute hypertension following brainstem lesions coinciding with the A1 group of catecholamine neurons

Electrolytic lesions of the ventrolateral medulla, coinciding with the A1 catecholamine cells of the conscious rabbit (A1 lesions) cause acute hypertension and bradycardia and in some animals, pulmonary oedema. We have assessed the change in cardiac performance after an A1 lesion, the role of cardiac autonomic effectors in this change; and the mechanism of the pulmonary oedema. Following A1 lesions there was a profound (over 100%) rise in total peripheral resistance and a fall in cardiac output which was mainly due to a fall in stroke volume since it occurred even in animals in which the heart rate was held constant by atrial pacing. This reduced stroke volume occurred despite a 40% increase in myocardial contractility (peak LV dP/dt) and elevation of left ventricular end diastolic pressure. beta-Adrenoceptor blockade with propranolol abolished the rise in peak LV dP/dt, while vagal blockade with methylscopolamine abolished the bradycardia and combined blockade with propranolol and methylscopolamine abolished the rise in peak LV dP/dt and reduced the bradycardia. In rabbits which developed pulmonary oedema, left ventricular end diastolic pressure rose to 35 +/- 3.5 compared to 16 +/- 2.7 mmHg in those which did not, suggesting that the pulmonary oedema was due to raised left ventricular filling pressure.

Comparative haemodynamic effects of lidocaine, mexiletine, and disopyramide

The effect of intravenous boluses of lidocaine (5 mg/kg), mexiletine (3.5 mg/kg), and disopyramide (5 mg/kg) on mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), total peripheral resistance, left ventricular end-diastolic pressure, and peak rate of change of left ventricular pressure (peak LV dP/dt) were assessed in the conscious rabbit. Plasma levels for the three drugs corresponded to the human therapeutic range 3 min after administration. All three drugs had negative inotropic effects and reduced HR. Lidocaine reduced peak LV dP/dt by 26%, mexiletine by 41%, and disopyramide by 53%. The three drugs had quite different effects on CO as a result of differences in their actions on peripheral blood vessels: disopyramide caused a 21% fall in CO, associated with a significant vasoconstriction; mexiletine did not lower CO, as it caused a substantial vasodilation; and lidocaine did not produce any substantial change in either CO or vascular resistance. Cardiac autonomic blockade did not alter these changes. These results confirm that disopyramide has a marked cardiodepressant effect, and demonstrate that, although lidocaine depresses myocardial contractility in the conscious rabbit, it has little effect on other haemodynamic parameters. The experiments also show that mexiletine is a more profound negative inotrope than lidocaine, but that, as it produces a significant fall in MAP and thus a reduction in afterload, the CO is maintained.

Baroreflex control of myocardial contractility in conscious normotensive and renal hypertensive rabbits

We have assessed resting myocardial contractility and its baroreflex control in normotensive and hypertensive conscious rabbits. Hypertension was induced by bilateral cellophane wrapping of the kidneys with experiments performed 6 weeks later during the established phase of hypertension. The peak rate of change of left ventricular pressure (peak LV dP/dt) was used as the index of myocardial contractility. Baroreflex control of contractility and heart period (HP) was assessed by constructing stimulus response curves relating change in mean arterial pressure (MAP), induced by balloon occluders around the abdominal aorta and inferior vena cava, to change in peak LV dP/dt and HP. These stimulus response curves were obtained in normotensive rabbits with and without cardiac pacing, and in both normotensive and hypertensive animals after cardiac beta sympathetic blockade with propranolol, vagal blockade with methylscopolamine, and combined cardiac autonomic blockade with propranolol and scopolamine, as well as in rabbits with intact autonomic effectors. Resting MAP was significantly higher in the hypertensive rabbits (119 +/- 2 mm Hg) compared to normotensive controls (76 +/- 1 mm Hg). Resting peak LV dP/dt was also greater by 51% in the hypertensive animals (7054 +/- 287 mm Hg sec-1) compared to controls (4690 +/- 223 mm Hg sec-1). There was no significant difference in the resting heart period or resting left ventricular end diastolic pressure. Transient changes in MAP induced by occlusion of the aortic or venous balloons produced significant alterations in peak LV dP/dt in normotensive animals with and without pacing and in hypertensive control animals. In animals with cardiac sympathetic block, the range and slope or sensitivity of the stimulus response curves were not significantly changed but in animals with vagal blockade the sensitivity was reduced by 90% and the range at 30 mm Hg by 88%. After propranolol and methylscopolamine were administered together, the stimulus no longer evoked a response. These experiments demonstrate that myocardial contractility is under baroreflex control and suggest that this is mediated principally via parasympathetic nerves to the heart. There was no significant difference between the sensitivity of baroreflex control of myocardial contractility in the normotensive (-84 +/- 14 mm Hg sec-1 per mm Hg) and the hypertensive (-110 +/- 14 mm Hg sec-1 per mm Hg) rabbits, unlike the baroreflex control of heart period where sensitivity was markedly impaired in the hypertensive (sensitivity 3.8 +/- 0.8 msec/mm Hg) compared to the normotensive (6.9 +/- 1.0 msec/mm Hg) animals.