Antiplatelet therapy in patients with myocardial infarction without obstructive coronary artery disease

OBJECTIVE

Approximately 10% of patients with myocardial infarction (MI) have no obstructive coronary artery disease. The prognosis and role of intensified antiplatelet therapy in those patients were evaluated.

METHODS

We analysed data from the Clopidogrel and Aspirin Optimal Dose Usage to Reduce Recurrent Events-Seventh Organisation to Assess Strategies in Ischaemic Symptoms trial randomising patients with ACS referred for early intervention to receive either double-dose (600 mg, day 1; 150 mg, days 2-7; then 75 mg/day) or standard-dose (300 mg, day 1; then 75 mg/day) clopidogrel. Outcomes in patients with myocardial infarction with non-obstructive coronary arteries (MINOCA) versus those with obstructive coronary artery disease (CAD) and their relation to standard-dose versus double-dose clopidogrel were evaluated. The primary outcome was cardiovascular (CV) death, MI or stroke at 30 days.

RESULTS

We included 23 783 patients with MI and 1599 (6.7%) with MINOCA. Patients with MINOCA were younger, presented more frequently with non-ST-segment elevation MI and had fewer comorbidities. All-cause mortality (0.6% vs 2.3%, p=0.005), CV mortality (0.6% vs 2.2%, p=0.006), repeat MI (0.5% vs 2.3%, p=0.001) and major bleeding (0.6% vs 2.4%, p<0.0001) were lower among patients with MINOCA than among those with obstructive CAD. Among patients with MINOCA, 2.1% of patients in the double-dose clopidogrel group and 0.6% in the standard-dose group experienced a primary outcome (HR 3.57, 95% CI 1.31 to 9.76), whereas in those with obstructive CAD, rates were 4.3% and 4.7%, respectively (HR 0.91, 95% CI 0.80 to 1.03; p value for interaction=0.011).

CONCLUSIONS

Patients with MINOCA are at lower risk of recurrent CV events compared with patients with MI with obstructive CAD. Compared with a standard clopidogrel-based dual antiplatelet therapy (DAPT) regimen, an intensified dosing strategy appears to offer no additional benefit with a signal of possible harm. Further randomised trials evaluating the effects of potent DAPT in patients with MINOCA are warranted.

TRIAL REGISTRATION NUMBER

NCT00335452.

2387Recurrent cardiovascular events and mortality in relation to antiplatelet therapy in patients with myocardial infarction without obstructive coronary artery disease (MINOCA)

Background

Approximately 10% of patients presenting with myocardial infarction (MI) do not have obstructive coronary artery disease (MINOCA). The role of antiplatelet therapy and outcomes in this group remain unclear. We assessed prognosis and the effect of an intensified clopidogrel regimen in MINOCA patients.

Methods

We analyzed data from the CURRENT-OASIS 7 trial, which randomized 25,086 patients with acute coronary syndromes (ACS) referred for early intervention to receive either double-dose (600mg day 1; 150mg days 2–7; then 75mg daily) or standard-dose (300mg day 1; then 75mg daily) clopidogrel. We evaluated clinical outcomes at 30-days in patients with versus without obstructive CAD and in relation to standard versus double-dose clopidogrel.

Results

Overall, 23,783 MI patients were included, of which 1,599 (6.7%) had MINOCA. MINOCA patients were younger, more frequently presented with non-ST-segment elevation MI and had fewer comorbidities. Rates of all-cause mortality (0.7% versus 2.4%, p=0.0046), cardiovascular mortality (0.6 versus 2.2%, p=0.0056), repeat MI (0.5% versus 2.3%, p=0.0009) and major bleedings (0.7% versus 2.5%, p=0.0001) were significantly lower among patients with MINOCA versus those with obstructive CAD. Compared with the standard-dose clopidogrel regimen, the double-dose regimen appeared to increase the risk of cardiovascular death, MI or stroke in MINOCA patients (0.8% versus 2.1%, hazard ratio (HR) 2.74, P=0.033). There was no difference in those with obstructive CAD (4.7% versus 4.4%, HR 0.93, P=0.226; P-for-interaction=0.023) (see Figure 1A). Major bleeding did not occur more frequently in MINOCA patients with double- versus standard-dose clopidogrel regimen (0.7% versus 0.6%, (HR 1.16 (95% CI 0.35–3.80), p=0.805), but their rate was higher In MI patients with obstructive CAD (2.7% versus 2.2% (HR 1.26 (95% CI 1.06–1.49), p=0.008) (Figure 1B).

Figure 1A & B

Conclusions

Compared to MI patients with obstructive CAD, patients presenting with MINOCA represent a distinct cohort, which is generally younger, has a higher NSTEMI prevalence and fewer comorbidities. Their risk for adverse events, especially repeat MI, stroke, death, and bleeding, is low (<1%) at 30 days. Applying an intensified clopidogrel regimen in MINOCA patients appears to be related to a higher risk for CV death, MI and stroke. Accordingly, more potent antiplatelet regimens might be harmful among MINOCA patients and should not be administered routinely. Nevertheless, there is a need for more prospective studies evaluating the role of dual antiplatelet therapies in MINOCA patients.

Acknowledgement/Funding

The CURRENT-OASIS 7 trial was sponsored by Sanofi-Aventis and Bristol-Myers Squibb.

[The DISC tool improves communication and results in pulmonary rehabilitation]

INTRODUCTION

Competence in personal relationships is essential for a caregiver, especially in pulmonary rehabilitation (PR). Considering the behavioral profile of patients might help to optimize their management and the results of PR.

METHODS

We evaluated eight hundred and thirty-two consecutive patients with chronic respiratory disease who received eight weeks of home-based PR. Their exercise tolerance (six-minute stepper test, 6MST), mood (HAD), and quality of life (VSRQ, MRF28) were evaluated at the beginning and end of PR. For six hundred and ninety patients, a behavioral approach was implemented at the beginning of PR by using the DISC tool to identify four behavioral profiles: dominance, influence, steadiness, conscientiousness. The remaining 142 patients served as the control group.

RESULTS

Subjectively, the therapeutic alliance was more easily established with the behavioral approach. Compared with the control group, patients with the "steadiness" profile were younger (60.7±12 years) and mostly female (52.8%), whereas patients with the "conscientiousness" profile were older (67.5±10.6 years) and mostly male (85.5%). The four behaviorally profiled groups showed no differences in exercise tolerance, mood, or quality of life scores at baseline. Globally, all patients improved their exercise tolerance, mood and quality of life. The percentage of responders to 6MST and VSRQ (>MCID) was 7.5% and 5.3% higher with the behavioral approach. For non-responders to 6MST and VSRQ (<MCID), only patients benefiting from the behavioral approach improved the other parameters studied, patients from control group having exhibited no improvement at all.

CONCLUSIONS

The DISC-guided behavioral approach improves the patient-caregiver relationship and achieves better results at the end of PR.

Effect of radial versus femoral access on radiation dose and the importance of procedural volume: a substudy of the multicenter randomized RIVAL trial

OBJECTIVES

The authors sought to compare the radiation dose between radial and femoral access.

BACKGROUND

Small trials have shown an increase in the radiation dose with radial compared with femoral access, but many were performed during the operators' learning curve of radial access.

METHODS

Patients were randomized to radial or femoral access, as a part of the RIVAL (RadIal Vs. femorAL) trial (N = 7,021). Fluoroscopy time was prospectively collected in 5740 patients and radiation dose quantified as air kerma in 1,445 patients and dose-area product (DAP) in 2,255 patients.

RESULTS

Median fluoroscopy time was higher with radial versus femoral access (9.3 vs. 8.0 min, p < 0.001). Median air kerma was nominally higher with radial versus femoral access (1,046 vs. 930 mGy, respectively, p = 0.051). Median DAP was not different between radial and femoral access (52.8 Gy-cm(2) vs. 51.2 Gy·cm(2), p = 0.83). When results are stratified according to procedural volume, air kerma was increased only in the lowest tertile of radial volume centers (low 1,425 vs. 1,045 mGy, p = 0.002; middle 987 vs. 958 mGy, p = 0.597; high 652 vs. 621 mGy, p = 0.403, interaction p = 0.026). Multivariable regression showed procedural volume was the greatest independent predictor of lower air kerma dose (ratio of geometric means 0.55; 95% confidence interval 0.49 to 0.61 for highest-volume radial centers).

CONCLUSIONS

Radiation dose as measured by air kerma was nominally higher with radial versus femoral access, but differences were present only in lower-volume centers and operators. High-volume centers have the lowest radiation dose irrespective of which access site approach that they use. (A Trial of Trans-radial Versus Trans-femoral Percutaneous Coronary Intervention (PCI) Access Site Approach in Patients With Unstable Angina or Myocardial Infarction Managed With an Invasive Strategy [RIVAL]; NCT01014273).

Radial versus femoral access for coronary angiography and intervention in patients with acute coronary syndromes (RIVAL): a randomised, parallel group, multicentre trial

BACKGROUND

Small trials have suggested that radial access for percutaneous coronary intervention (PCI) reduces vascular complications and bleeding compared with femoral access. We aimed to assess whether radial access was superior to femoral access in patients with acute coronary syndromes (ACS) who were undergoing coronary angiography with possible intervention.

METHODS

The RadIal Vs femorAL access for coronary intervention (RIVAL) trial was a randomised, parallel group, multicentre trial. Patients with ACS were randomly assigned (1:1) by a 24 h computerised central automated voice response system to radial or femoral artery access. The primary outcome was a composite of death, myocardial infarction, stroke, or non-coronary artery bypass graft (non-CABG)-related major bleeding at 30 days. Key secondary outcomes were death, myocardial infarction, or stroke; and non-CABG-related major bleeding at 30 days. A masked central committee adjudicated the primary outcome, components of the primary outcome, and stent thrombosis. All other outcomes were as reported by the investigators. Patients and investigators were not masked to treatment allocation. Analyses were by intention to treat. This trial is registered with ClinicalTrials.gov, NCT01014273.

FINDINGS

Between June 6, 2006, and Nov 3, 2010, 7021 patients were enrolled from 158 hospitals in 32 countries. 3507 patients were randomly assigned to radial access and 3514 to femoral access. The primary outcome occurred in 128 (3·7%) of 3507 patients in the radial access group compared with 139 (4·0%) of 3514 in the femoral access group (hazard ratio [HR] 0·92, 95% CI 0·72-1·17; p=0·50). Of the six prespecified subgroups, there was a significant interaction for the primary outcome with benefit for radial access in highest tertile volume radial centres (HR 0·49, 95% CI 0·28-0·87; p=0·015) and in patients with ST-segment elevation myocardial infarction (0·60, 0·38-0·94; p=0·026). The rate of death, myocardial infarction, or stroke at 30 days was 112 (3·2%) of 3507 patients in the radial group compared with 114 (3·2%) of 3514 in the femoral group (HR 0·98, 95% CI 0·76-1·28; p=0·90). The rate of non-CABG-related major bleeding at 30 days was 24 (0·7%) of 3507 patients in the radial group compared with 33 (0·9%) of 3514 patients in the femoral group (HR 0·73, 95% CI 0·43-1·23; p=0·23). At 30 days, 42 of 3507 patients in the radial group had large haematoma compared with 106 of 3514 in the femoral group (HR 0·40, 95% CI 0·28-0·57; p<0·0001). Pseudoaneurysm needing closure occurred in seven of 3507 patients in the radial group compared with 23 of 3514 in the femoral group (HR 0·30, 95% CI 0·13-0·71; p=0·006).

INTERPRETATION

Radial and femoral approaches are both safe and effective for PCI. However, the lower rate of local vascular complications may be a reason to use the radial approach.

FUNDING

Sanofi-Aventis, Population Health Research Institute, and Canadian Network for Trials Internationally (CANNeCTIN), an initiative of the Canadian Institutes of Health Research.

Design and rationale of the radial versus femoral access for coronary intervention (RIVAL) trial: a randomized comparison of radial versus femoral access for coronary angiography or intervention in patients with acute coronary syndromes

BACKGROUND

Major bleeding in acute coronary syndromes (ACS) is associated with an increased risk of subsequent mortality and recurrent ischemic events. Observational data and small randomized trials suggest that radial instead of femoral access for coronary angiography/intervention results in fewer bleeding complications, with preserved and possibly improved efficacy. Radial access versus femoral access has yet to be formally evaluated in a randomized trial adequately powered for the comparison of clinically important outcomes.

OBJECTIVES

The aim of this study is to evaluate the efficacy and safety of radial versus femoral access for coronary angiography/intervention in patients with ACS managed with an invasive strategy.

DESIGN

This was a multicenter international randomized trial with blinded assessment of outcomes. 7021 patients with ACS (with or without ST elevation) have been randomized to either radial or femoral access for coronary angiography/intervention. The primary outcome is the composite of death, myocardial infarction, stroke, or non-coronary artery bypass graft-related major bleeding up to day 30. The key secondary outcomes are (1) death, myocardial infarction, or stroke up to day 30 and (2) non-coronary artery bypass graft-related major bleeding up to day 30. Percutaneous coronary intervention (PCI) success rates will also be compared between the two access sites.

CONCLUSIONS

The RIVAL trial will help define the optimal access site for coronary angiography/intervention in patients with ACS.

Influence of renal function on the efficacy and safety of fondaparinux relative to enoxaparin in non ST-segment elevation acute coronary syndromes

BACKGROUND

A recent randomized, controlled trial, the Fifth Organization to Assess Strategies in Acute Ischemic Syndromes (OASIS 5) trial, reported that major bleeding was 2-fold less frequent with fondaparinux than with enoxaparin in acute coronary syndromes (ACS). Renal dysfunction increases the risk for major bleeding.

OBJECTIVE

To compare the efficacy and safety of fondaparinux and enoxaparin over the spectrum of renal dysfunction observed in the OASIS 5 trial.

DESIGN

Subgroup analysis of a randomized, controlled trial.

SETTING

Patients presenting to the hospital with non-ST-segment elevation ACS.

PATIENTS

19,979 of the 20,078 patients in the OASIS 5 trial in whom creatinine was measured at baseline.

MEASUREMENTS

Death, myocardial infarction, refractory ischemia, and major bleeding were evaluated separately and as a composite end point at 9, 30, and 180 days. Glomerular filtration rate (GFR) was calculated by using the Modification of Diet in Renal Disease formula.

RESULTS

The absolute differences in favor of fondaparinux (efficacy and safety) were most marked in patients with a GFR less than 58 mL/min per 1.73 m2; the largest differences occurred in major bleeding events. At 9 days, death, myocardial infarction, or refractory ischemia occurred in 6.7% of patients receiving fondaparinux and 7.4% of those receiving enoxaparin (hazard ratio, 0.90 [95% CI, 0.73 to 1.11]); major bleeding occurred in 2.8% and 6.4%, respectively (hazard ratio, 0.42 [CI, 0.32 to 0.56]). Statistically significant differences in major bleeding persisted at 30 and 180 days. The rates of the composite end point were lower with fondaparinux than with enoxaparin in all quartiles of GFR, but the differences were statistically significant only among patients with a GFR less than 58 mL/min per 1.73 m2.

LIMITATIONS

Subgroup analyses warrant caution; the study was powered to detect noninferiority at 9 days. Fondaparinux is not approved for use in patients with ACS in the United States.

CONCLUSIONS

The benefits of fondaparinux over enoxaparin when administered for non-ST-segment elevation ACS are most marked among patients with renal dysfunction and are largely explained by lower rates of major bleeding with fondaparinux.

Tobacco use and risk of myocardial infarction in 52 countries in the INTERHEART study: a case-control study

BACKGROUND

Tobacco use is one of the major avoidable causes of cardiovascular diseases. We aimed to assess the risks associated with tobacco use (both smoking and non-smoking) and second hand tobacco smoke (SHS) worldwide.

METHODS

We did a standardised case-control study of acute myocardial infarction (AMI) with 27,089 participants in 52 countries (12,461 cases, 14,637 controls). We assessed relation between risk of AMI and current or former smoking, type of tobacco, amount smoked, effect of smokeless tobacco, and exposure to SHS. We controlled for confounders such as differences in lifestyles between smokers and non-smokers.

FINDINGS

Current smoking was associated with a greater risk of non-fatal AMI (odds ratio [OR] 2.95, 95% CI 2.77-3.14, p<0.0001) compared with never smoking; risk increased by 5.6% for every additional cigarette smoked. The OR associated with former smoking fell to 1.87 (95% CI 1.55-2.24) within 3 years of quitting. A residual excess risk remained 20 or more years after quitting (1.22, 1.09-1.37). Exclusion of individuals exposed to SHS in the never smoker reference group raised the risk in former smokers by about 10%. Smoking beedies alone (indigenous to South Asia) was associated with increased risk (2.89, 2.11-3.96) similar to that associated with cigarette smoking. Chewing tobacco alone was associated with OR 2.23 (1.41-3.52), and smokers who also chewed tobacco had the highest increase in risk (4.09, 2.98-5.61). SHS was associated with a graded increase in risk related to exposure; OR was 1.24 (1.17-1.32) in individuals who were least exposed (1-7 h per week) and 1.62 (1.45-1.81) in people who were most exposed (>21 h per week). Young male current smokers had the highest population attributable risk (58.3%; 95% CI 55.0-61.6) and older women the lowest (6.2%, 4.1-9.2). Population attributable risk for exposure to SHS for more than 1 h per week in never smokers was 15.4% (12.1-19.3).

CONCLUSION

Tobacco use is one of the most important causes of AMI globally, especially in men. All forms of tobacco use, including different types of smoking and chewing tobacco and inhalation of SHS, should be discouraged to prevent cardiovascular diseases.

Rationale and design of ACTIVE: the atrial fibrillation clopidogrel trial with irbesartan for prevention of vascular events

BACKGROUND

Atrial fibrillation (AF) is the most frequently occurring cardiac arrhythmia with often serious clinical consequences. Many patients have contraindications to anticoagulation, and it is often underused in clinical practice. The addition of clopidogrel to aspirin (ASA) has been shown to reduce vascular events in a number of high-risk populations. Irbesartan is an angiotensin receptor-blocking agent that reduces blood pressure and has other vascular protective effects.

METHODS AND RESULTS

ACTIVE W is a noninferiority trial of clopidogrel plus ASA versus oral anticoagulation in patients with AF and at least 1 risk factor for stroke. ACTIVE A is a double-blind, placebo-controlled trial of clopidogrel in patients with AF and with at least 1 risk factor for stroke who receive ASA because they have a contraindication for oral anticoagulation or because they are unwilling to take an oral anticoagulant. ACTIVE I is a partial factorial, double-blind, placebo-controlled trial of irbesartan in patients participating in ACTIVE A or ACTIVE W. The primary outcomes of these studies are composites of vascular events. A total of 14000 patients will be enrolled in these trials.

CONCLUSIONS

ACTIVE is the largest trial yet conducted in AF. Its results will lead to a new understanding of the role of combined antiplatelet therapy and the role of blood pressure lowering with an angiotensin II receptor blocker in patients with AF.

Effects of aspirin dose when used alone or in combination with clopidogrel in patients with acute coronary syndromes: observations from the Clopidogrel in Unstable angina to prevent Recurrent Events (CURE) study

BACKGROUND

We studied the benefits and risks of adding clopidogrel to different doses of aspirin in the treatment of patients with acute coronary syndrome (ACS).

METHODS AND RESULTS

In the Clopidogrel in Unstable angina to prevent Recurrent Events (CURE) trial, 12 562 patients with ACS using aspirin, 75 to 325 mg daily, were randomized to clopidogrel or placebo for up to 1 year. In this analysis, patients were divided into the following 3 aspirin dose groups: < or =100 mg, 101 through 199 mg, and > or =200 mg. The combined incidence of cardiovascular death, myocardial infarction, or stroke was reduced by clopidogrel regardless of aspirin dose, as follows: < or =100 mg, 10.5% versus 8.6% (relative risk [RR], 0.81 [95% CI, 0.68 to 0.97]); 101 to 199 mg, 9.8% versus 9.5% (RR, 0.97 [95% CI 0.77 to 1.22]); and > or =200 mg, 13.6% versus 9.8% (RR, 0.71 [95% CI, 0.59 to 0.85]). The incidence of major bleeding increased with increasing aspirin dose both in the placebo group (1.9%, 2.8%, and 3.7%, respectively; P=0.0001) and the clopidogrel group (3.0%, 3.4%, and 4.9%, respectively; P=0.0009); thus, the excess risk with clopidogrel was 1.1%, 1.2%, and 1.2%, respectively. The adjusted hazard ratio for major bleeding for the highest versus the lowest dose of aspirin was 1.9 (95% CI 1.29 to 2.72) in the placebo group, 1.6 (95% CI 1.19 to 2.23) in the clopidogrel group, and 1.7 (95% CI 1.36 to 2.20) in the combined group.

CONCLUSIONS

In patients with ACS, adding clopidogrel to aspirin is beneficial regardless of aspirin dose. Bleeding risks increase with increasing aspirin dose, with or without clopidogrel, without any increase in efficacy. Our findings suggest that the optimal daily dose of aspirin may be between 75 and 100 mg, with or without clopidogrel.

High-dose mitoxantrone and cyclophosphamide without stem cell support in high-risk and advanced solid tumors: a phase I trial

This phase I study was designed to develop a high-dose combination of two cycles of mitoxantrone and cyclophosphamide in patients with solid tumors, as an alternative to single-cycle high-dose regimens that use only alkylating agents. Treatment was delivered with granulocyte colony-stimulating factor (G-CSF), but without stem cell support, in order to avoid potential tumor cell reinfusion. Thirty-one patients with advanced solid tumors received two cycles of high-dose mitoxantrone (20-30 mg/m2) plus high-dose cyclophosphamide (3000-4000 mg/m2). All patients received G-CSF until hematologic recovery. Dose-escalation was performed when less than 50% of cycles per level had dose-limiting toxicity (DLT). The maximum tolerated dose (MTD) achieved was mitoxantrone 25 mg/m2 and cyclophosphamide 4000 mg/m2. Main dose-limiting toxicities (DLTs) were hematological: grade IV neutropenia lasting more than 7 days and thrombopenia below 20 x 10(9)/l requiring more than one platelet transfusion. Non-hematological DLT consisted predominantly of grade III emesis and asthenia. Follow-up after each cycle was performed in an outpatient setting and there were no toxic deaths. In conclusion, the administration of two cycles of high-dose mitoxantrone and cyclophosphamide with G-CSF support is safe and feasible. MTD was mitoxantrone 25 mg/m2 and cyclophosphamide 4000 mg/m2. Evaluation of this regimen is being done in a phase II trial.

Effects of atrial impulse timing on AV concealed conduction in the rabbit heart

The influence of the timing of a nontransmitted or transmitted atrial impulse on the atrioventricular (AV) conduction time of the subsequent impulse was studied in nine isolated rabbit hearts. AV conduction curves were determined by applying the atrial extrastimulus test. The extrastimulus was delivered preceded or not by an interposed atrial impulse whose coupling interval with respect to the last atrial beat of a basic train was kept constant at 100, 120, 140, 160, 175, 200, 225, 250, and 300 msec. In all experiments, there was a "concealment interval," i.e., the AV effective refractory period was longer than the atrial functional refractory period, and in seven experiments was comprised between 100 and 160 msec. For any given extrastimulus coupling interval in the presence of an interposed nontransmitted atrial impulse, AV conduction time was significantly greater than in its absence; the increase was greater than the longer the nontransmitted atrial impulse coupling interval, i.e., the shorter the subsequent transmitted impulse coupling interval with respect to the previous interposed nontransmitted impulse. The AV conduction curves relating the extrastimulus AV conduction time to its coupling interval with respect to the last atrial impulse of the basic train fitted to a hyperbolic model both in the absence of the interposed atrial impulse and in its presence (mean square residual 31 +/- 23 msec2), and the interposed atrial impulse modified the constants of the functions; the slope of the linear transformations was progressively more negative as the interposed atrial impulse was delayed. Furthermore, the effects of the interposed atrial impulse--transmitted or not--on AV conduction time of the subsequent impulse were qualitatively similar, their magnitude depending on the time elapsed were qualitatively similar, their magnitude depending on the time elapsed between the two.

Closed chest radiofrequency ablation of the sinoatrial node in dogs

Transcatheter ablation of the sinoatrial node with radiofrequency energy (0.6 MHZ, 2.5-5 watts) was performed in 10 dogs under fluoroscopic monitoring and autonomic blockade. Sinus function was previously studied in terms of cycle length, recovery time and atrial activation pattern by catheter mapping. Several discharges (8-22) were applied for variable periods of time (maximum 1 minute). Sinus tachycardia and/or sinus arrest during ablation confirmed correct catheter position. Sinus rhythm was abolished in eight dogs. The ectopic rhythm was atrial in six and AV nodal in two dogs. Ectopic atrial cycle length and recovery time were longer than the baseline sinus values: 724 +/- 321 versus 509 +/- 147, P less than 0.05; 1103 +/- 775 versus 618 +/- 151, P less than 0.05 (values in msec). The study was repeated 10-14 days later in six dogs; three maintained the same atrial rhythm, one persisted in sinus rhythm, and one dog changed from atrial to sinus rhythm, whereas another changed from sinus to atrial rhythm. Gross findings revealed transmural lesions in all dogs, without perforation. Histology in chronic dogs showed sinus cell necrosis and its replacement by granulation tissue.

IN CONCLUSION

sinus function may be abolished by closed chest radiofrequency ablation.

Clinical use of the arterial/alveolar oxygen tension ratio

A prospective study to verify the behavior of the arterial/alveolar oxygen tension ratio (PaO2/PAO2) at different fractions of inspired oxygen (FIO2), was performed in 15 adult hypoxemic patients. This index was useful not only for predicting the arterial oxygen tension but also for choosing the necessary oxygen supplementary levels. PaO2/PAO2 was a less reliable index in patients with mild intrapulmonary shunts, probably because of changes in the distribution of alveolar ventilation/perfusion ratios.