A Single High-Sensitivity Cardiac Troponin T Strategy for Ruling Out Myocardial Infarction

Background

Ruling out acute myocardial infarction (AMI) in the emergency department (ED) is challenging. Studies have shown that a high-sensitivity cardiac troponin T (hs-cTnT) <5 ng/L or <6 ng/L at presentation (0 h) can be used to rule out AMI. The objective of this study was to identify whether an even higher hs-cTnT threshold can be used for a safe rule out of AMI in the ED.

Methods

The derivation cohort consisted of 24,973 ED patients with a primary complaint of chest pain. In this cohort, we identified the highest concentration of 0 h hs-cTnT that corresponded to a negative predictive value (NPV) of ≥99.5% for the primary endpoint of AMI/all-cause death within 30 days and the secondary endpoint of all-cause death within one year. The results were validated in two cohorts consisting of 132,021 and 1167 ED chest pain patients.

Results

The 0 h hs-cTnT threshold corresponding to a NPV of ≥99.5% for the primary endpoint was <9 ng/L (NPV: 99.6% and 95% CI: 99.5-99.7). This cutoff provided a sensitivity of 96.2% (95% CI: 95.2-97.1) and identified 59.7% of the patients as low risk compared to 35.8% and 43.9% with a 0 h hs-cTnT <5 ng/L and <6 ng/L, respectively. The results were similar in the validation cohorts and seemed to perform even better in patients where the 0 h hs-cTnT was measured >3 h after symptom onset and in those with a nonischemic ECG and nonhigh risk history.

Conclusions

A 0 h hs-cTnT cutoff of <9 ng/L safely rules out AMI/death within 30 days in a majority of chest pain patients and is a more effective strategy than the currently recommended <5 ng/L and <6 ng/L cutoffs. This trial is registered with NCT03421873.

Sex differences in potential triggers of myocardial infarction

Aims

Internal and external triggers affect seasonal and circadian variations of myocardial infarction (MI). We aimed to assess sex differences in common triggers of MI.

Methods

A nationwide, retrospective cross-sectional postal survey study was conducted. Individuals who experienced a MI during holidays and weekdays were identified through the SWEDEHEART registry. 27 potential MI-triggers were rated in regards of occurring more or less than usual during the last 24 hours before the MI. Three areas were covered: activities, emotions and food- or alcohol consumption. A logistic regression model was used to identify sex differences for each trigger and odds ratios (OR) were reported.

Results

451 patients, of whom 317 were men responded. The most common reported triggers were stress (35.3%), worry (26.2 %), depression (21.1%) and insomnia (20.0%). Women reported emotional triggers including sadness (OR 3.52, 95% CI 1,92-6,45), stress (OR 2.38, 95% CI 1.52-3.71), insomnia (OR 2.31, 95% CI 1,39-3,81) and upset (OR 2.69, 95% CI 1.47-4.95) to a greater extent than men. Outdoor activity was less reported by women, OR 0.35, 95% CI 0.14-0.87. No significant sex differences were found in other activities or food and alcohol consumption.

Conclusion

Self-experienced stress and distress were higher among women prior to myocardial infarction compared to men. Understanding sex perspectives in acute triggers may help us find preventive strategies and to reduce the excess numbers of MI.

Pretreatment with heparin in patients with ST-segment elevation myocardial infarction: a report from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR)

BACKGROUND

Unfractionated heparin (UFH) is frequently administered before percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI).

AIMS

The aim of the study was to investigate if pretreatment with UFH prior to arrival at the catheterisation laboratory affects coronary artery occlusion, mortality, and in-hospital major bleeding in patients with STEMI undergoing PCI.

METHODS

Patients with a first STEMI event undergoing PCI between 2008 and 2016 were extracted from the Swedish Coronary Angiography and Angioplasty Registry. Risk ratios for UFH pretreatment versus no pretreatment regarding coronary artery occlusion at presentation in the catheterisation laboratory, 30-day mortality, and bleeding were obtained using adjusted Poisson regression models with robust standard errors. Analyses of propensity score (PS)-matched groups were performed to obtain absolute risk differences.

RESULTS

In all, 41,631 patients were included, 16,026 (38%) with and 25,605 (62%) without UFH pretreatment. Adjusted risk ratios were 0.89 (95% confidence interval [CI]: 0.87 to 0.90) for coronary artery occlusion, 0.87 (0.77 to 0.99) for mortality, and 1.01 (0.86 to 1.18) for bleeding. In the PS-matched analyses, the absolute risk differences were -0.087 (-0.074 to -0.099) for coronary artery occlusion, -0.011 (-0.017 to -0.0041) for mortality, and 0 (-0.0052 to 0.0052) for bleeding.

CONCLUSIONS

Pretreatment with UFH was associated with a reduction in coronary artery occlusion among patients with STEMI, with a number needed to treat (NNT) of 12, without increasing the risk of major in-hospital bleeding. Regarding mortality, a reduction was found with UFH pretreatment, with an NNT of 94, but this effect was not robust over all sensitivity analyses and residual confounding cannot be excluded.

Comparison between ticagrelor and clopidogrel in high bleeding risk patients with acute coronary syndrome

Background

Potent antiplatelet agents such as ticagrelor are associated with a lower risk of ischemic events than clopidogrel in patients with acute coronary syndrome (ACS). However, it is uncertain whether the benefits of more intensive anti-ischemic therapy outweigh the risks of major bleeding in individuals who have a high bleeding risk (HBR). This study aimed to assess treatment outcomes following dual antiplatelet therapy (DAPT) using either ticagrelor or clopidogrel in ACS patients with HBR.

Methods

All HBR patients enrolled in the SWEDEHEART registry who were discharged with DAPT using ticagrelor or clopidogrel following ACS between 2010 and 2017 were included in this study. Bleeding risk was assessed using the 4-item PRECISE-DAPT score, which consists of age, prior bleeding, haemoglobin concentration and creatinine clearance. HBR was defined as a PRECISE-DAPT score ≥25. Inverse-probability of treatment weighting was used to adjust for baseline differences between the treatment groups. The main analysis consisted of a doubly robust estimation of causal effect using Cox proportional hazards models. Data on major bleeding, recurrent myocardial infarction (MI), ischemic stroke and all-cause mortality was obtained from national registries, with 365 days of follow-up. Additional outcomes include major adverse cardiovascular events (MACE), a composite of MI, ischemic stroke and all-cause mortality, and net adverse clinical events (NACE), a composite of MACE and major bleeding.

Results

Of all ACS patients, 36% (n=25,042) had a PRECISE-DAPT score ≥25. Approximately half of the study participants were treated with ticagrelor (n=11,848). Ticagrelor reduced the risk of MI (hazard ratio [HR], 0.82 [95% CI 0.74–0.91]), ischemic stroke (HR, 0.73 [95% CI 0.60–0.88]) and MACE (HR, 0.90 [95% CI 0.84–0.97]), while also increasing the risk of major bleeding compared to clopidogrel (HR, 1.30 [95% CI 1.16–1.47]). We found no significant differences in all-cause mortality (HR 1.02 [95% CI 0.92–1.12]) and NACE (HR 0.98 [95% CI 0.92–1.05]).

Conclusions

Ticagrelor was associated with a lower risk of recurrent ischemic events, but a higher risk of major bleeding compared to clopidogrel. There were no significant differences in all-cause mortality and NACE between the treatment groups. These results suggest that more potent antiplatelet agents might not be superior to clopidogrel in ACS patients with HBR.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Stockholm county council

Trends in Clinical Practice and Outcomes After Percutaneous Coronary Intervention of Unprotected Left Main Coronary Artery

Background

The use of percutaneous coronary intervention (PCI) to treat unprotected left main coronary artery disease has expanded rapidly in the past decade. We aimed to describe nationwide trends in clinical practice and outcomes after PCI for left main coronary artery disease.

Methods and Results

Patients (n=4085) enrolled in the SCAAR (Swedish Coronary Angiography and Angioplasty Registry) as undergoing PCI for left main coronary artery disease from 2005 to 2017 were included. A count regression model was used to analyze time‐related differences in procedural characteristics. The 3‐year major adverse cardiovascular and cerebrovascular event rate defined as death, myocardial infarction, stroke, and repeat revascularization was calculated with the Kaplan‐Meier estimator and Cox proportional hazard model. The number of annual PCI procedures grew from 121 in 2005 to 589 in 2017 (389%). The increase was greater for men (479%) and individuals with diabetes (500%). Periprocedural complications occurred in 7.9%, decreasing from 10% to 6% during the study period. A major adverse cardiovascular and cerebrovascular event occurred in 35.7% of patients, falling from 45.6% to 23.9% (hazard ratio, 0.56; 95% CI, 0.41–0.78; P=0.001). Radial artery access rose from 21.5% to 74.2% and intracoronary diagnostic procedures from 14.0% to 53.3%. Use of bare‐metal stents and first‐generation drug‐eluting stents fell from 19.0% and 71.9%, respectively, to 0, with use of new‐generation drug‐eluting stents increasing to 95.2%.

Conclusions

Recent changes in clinical practice relating to PCI for left main coronary artery disease are characterized by a 4‐fold rise in procedures conducted, increased use of evidence‐based adjunctive treatment strategies, intracoronary diagnostics, newer stents, and more favorable outcomes.

Adding historical high-sensitivity troponin T results to rule out acute myocardial infarction

AIMS

The clinical usefulness of historical concentrations of high-sensitivity cardiac troponin T (hs-cTnT) is unknown. This study investigated the ability to rule out myocardial infarction (MI) with the use of historical hs-cTnT concentrations among patients with chest pain in the emergency department (ED).

METHODS AND RESULTS

The derivation cohort consisted of patients presenting with chest pain to nine different EDs (n = 60 071), where we included those with ≥1 hs-cTnT analysed at the index visit and ≥1 hs-cTnT results prior to the visit. We developed an algorithm to rule out MI within 30 days with a pre-specified target negative predictive value (NPV) of ≥99.5%. The performance was then validated in a separate cohort of ED chest pain patients (n = 10 994). A historical hs-cTnT < 12 ng/L and a < 3 ng/L absolute change between the historical and the index visit hs-cTnT had the best performance and ruled out 24 862 (41%) patients in the derivation cohort. In the validation cohort, these criteria identified 4764 (43%) low-risk patients in whom 18 (0.4%) MIs within 30 days occurred, and had an NPV for MI of 99.6% (99.4-99.8), a sensitivity of 96.9% (95.2-.2), and an LR- of 0.11 (0.07-0.14).

CONCLUSION

Combining a historical hs-cTnT with a single new hs-cTnT may safely rule out MI and thereby reduce the need for serial hs-cTnT measurements in ED patients with chest pain.

Safety of early hospital discharge following admission with ST-elevation myocardial infarction treated with percutaneous coronary intervention: a nationwide cohort study

BACKGROUND

The Second Primary Angioplasty in Myocardial Infarction (PAMI-II) risk score is recommended by guidelines to identify low-risk patients with ST-elevation myocardial infarction (STEMI) for an early discharge strategy.

AIMS

We aimed to assess the safety of early discharge (≤2 days) for low-risk STEMI patients treated with primary percutaneous coronary intervention (PCI).

METHODS

Using nationwide data from the SWEDEHEART registry, we identified patients with STEMI treated with primary PCI during the period 2009-2017, of whom 8,092 (26.4%) were identified as low risk with the PAMI-II score. Low-risk patients were stratified according to their length of hospital stay (≤2 days vs >2 days). The primary endpoint was major adverse cardiovascular events (MACE, including death, reinfarction treated with PCI, stroke or heart failure hospitalisation) at one year, assessed using a Cox proportional hazards model with propensity score as well as an inverse probability weighting propensity score of average treatment effect to adjust for confounders.

RESULTS

A total of 1,449 (17.9%) patients were discharged ≤2 days from admission. After adjustment, the one-year MACE rate was not higher for patients discharged at >2 days from admission than for patients discharged ≤2 days (4.3% vs 3.2%; adjusted HR 1.31, 95% confidence interval [CI]: 0.92-1.87, p=0.14), and no difference was observed regarding any of the individual components of the main outcome. Results were consistent across all subgroups with no difference in MACE between early and late discharge patients.

CONCLUSIONS

Nationwide observational data suggest that early discharge of low-risk patients with STEMI treated with PCI is not associated with an increase in one-year MACE.

Development and validation of an artificial neural network algorithm to predict mortality and admission to hospital for heart failure after myocardial infarction: a nationwide population-based study

BACKGROUND

Patients have an estimated mortality of 15-20% within the first year following myocardial infarction and one in four patients who survive myocardial infarction will develop heart failure, severely reducing quality of life and increasing the risk of long-term mortality. We aimed to establish the accuracy of an artificial neural network (ANN) algorithm in predicting 1-year mortality and admission to hospital for heart failure after myocardial infarction.

METHODS

In this nationwide population-based study, we used data for all patients admitted to hospital for myocardial infarction and discharged alive from a coronary care unit in Sweden (n=139 288) between Jan 1, 2008, and April 1, 2017, from the Swedish Web system for Enhancement and Development of Evidence-based care in Heart disease Evaluated According to Recommended Therapies (SWEDEHEART) nationwide registry; these patients were randomly divided into training (80%) and testing (20%) datasets. We developed an ANN using 21 variables (including age, sex, medical history, previous medications, in-hospital characteristics, and discharge medications) associated with the outcomes of interest with a back-propagation algorithm in the training dataset and tested it in the testing dataset. The ANN algorithm was then validated in patients with incident myocardial infarction enrolled in the Western Denmark Heart Registry (external validation cohort) between Jan 1, 2008, and Dec 31, 2016. The predictive ability of the model was evaluated using area under the receiver operating characteristic curve (AUROC) and Youden's index was established as a means of identifying an empirical dichotomous cutoff, allowing further evaluation of model performance.

FINDINGS

139 288 patients who were admitted to hospital for myocardial infarction in the SWEDEHEART registry were randomly divided into a training dataset of 111 558 (80%) patients and a testing dataset of 27 730 (20%) patients. 30 971 patients with myocardial infarction who were enrolled in the Western Denmark Heart Registry were included in the external validation cohort. A first event, either all-cause mortality or admission to hospital for heart failure 1 year after myocardial infarction, occurred in 32 308 (23·2%) patients in the testing and training cohorts only. For 1-year all-cause mortality, the ANN had an AUROC of 0·85 (95% CI 0·84-0·85) in the testing dataset and 0·84 (0·83-0·84) in the external validation cohort. The AUROC for admission to hospital for heart failure within 1 year was 0·82 (0·81-0·82) in the testing dataset and 0·78 (0·77-0·79) in the external validation dataset. With an empirical cutoff the ANN algorithm correctly classified 73·6% of patients with regard to all-cause mortality and 61·5% of patients with regard to admission to hospital for heart failure in the external validation cohort, ruling out adverse outcomes with 97·1-98·7% probability in the external validation cohort.

INTERPRETATION

Identifying patients at a high risk of developing heart failure or death after myocardial infarction could result in tailored therapies and monitoring by the allocation of resources to those at greatest risk.

FUNDING

The Swedish Heart and Lung Foundation, Swedish Scientific Research Council, Swedish Foundation for Strategic Research, Knut and Alice Wallenberg Foundation, ALF Agreement on Medical Education and Research, Skane University Hospital, The Bundy Academy, the Märta Winkler Foundation, the Anna-Lisa and Sven-Eric Lundgren Foundation for Medical Research.

Validation of the 4-Item PRECISE-DAPT Score: A SWEDEHEART Study

Background

The Predicting Bleeding Complications in Patients Undergoing Stent Implantation and Subsequent Dual Antiplatelet Therapy (PRECISE‐DAPT) score has been shown to predict out‐of‐hospital major bleeding after myocardial infarction treated with percutaneous coronary intervention and dual antiplatelet therapy (DAPT). However, large validation studies have been scarce and the discriminative ability for patients with a preexisting bleeding risk factor (elderly, underweight, women, anemia, kidney dysfunction, or cancer) in a real‐world setting is unknown.

Methods and Results

Patients undergoing percutaneous coronary intervention for myocardial infarction between 2008 and 2017 were included from the SWEDEHEART (Swedish Web System for Enhancement of Evidence‐Based Care in Heart Disease Evaluated According to Recommended Therapies) registry (n=66 295). The predictive value of the PRECISE‐DAPT score for rehospitalization with major bleeding during dual antiplatelet therapy was evaluated using receiver operating characteristic analyses. A high PRECISE‐DAPT score (≥25; n=13 894) was associated with increased risk of major bleeding (3.9% versus 1.8%; hazard ratio [HR], 2.2; 95% CI, 2.0–2.5; P<0.001) compared with a non‐high score (<25; n=52 401). The score demonstrated a c‐statistic of 0.64 (95% CI, 0.63–0.66). The discriminative ability of the score to further stratify bleeding risk in patients with preexisting bleeding risk factors was poor, especially in patients who are elderly (c‐statistic=0.57; 95% CI, 0.55–0.60) or underweight (c‐statistic=0.56; 95% CI, 0.51–0.61), for whom a non‐high PRECISE‐DAPT score was associated with similar bleeding risk as a high PRECISE‐DAPT score in the general myocardial infarction population.

Conclusions

In this nationwide population‐based study, the PRECISE‐DAPT score performed moderately in the general myocardial infarction population and poorly in patients with preexisting bleeding risk factors, where its usefulness seems limited.

Christmas holiday triggers of myocardial infarction

Objectives: Christmas holidays have been associated with the highest incidence of myocardial infarction (MI). We wanted to assess possible triggers of MI during Christmas. Design: A nationwide, retrospective postal survey with case-control design. All individuals suffering an MI during the Christmas holidays 2018 and 2019 in Sweden were identified through the SWEDEHEART registry and a control group matched in age and gender with chronic coronary syndrome who did not seek medical attention during Christmas were asked for participation. Subjects completed a questionnaire asking them to rate 27 potential MI-triggers as having occurred more or less than usual. Results: A total of 189 patients suffering an MI on Christmas Eve, Christmas Day, or Boxing Day, and 157 patients in the control group responded to the questionnaire, representing response rates of 66% and 62%, respectively. Patients with MI on Christmas experienced more stress (37% vs. 21%, p = .002), depression (21% vs. 11%, p = .024), and worry (26% vs. 10%, p < .001) compared to the control group. The food and sweets consumption was increased in both groups, but to a greater extent in the control group (33% vs. 50%, p = .002 and 32% vs. 43%, p = .031). There were no increases in quarrels, anger, economic worries, or reduced compliance with medication. Conclusions: Patients suffering MI on Christmas holiday experienced higher levels of stress and emotional distress compared to patients with chronic coronary syndrome, possibly contributing to the phenomenon of holiday heart attack. Understanding what factors increase the number of MI on Christmas may help reduce the excess number of MIs and cardiovascular burden.

Prevalence of Subclinical Coronary Artery Atherosclerosis in the General Population

Supplemental Digital Content is available in the text.

Background:

Early detection of coronary atherosclerosis using coronary computed tomography angiography (CCTA), in addition to coronary artery calcification (CAC) scoring, may help inform prevention strategies. We used CCTA to determine the prevalence, severity, and characteristics of coronary atherosclerosis and its association with CAC scores in a general population.

Methods:

We recruited 30 154 randomly invited individuals age 50 to 64 years to SCAPIS (the Swedish Cardiopulmonary Bioimage Study). The study includes individuals without known coronary heart disease (ie, no previous myocardial infarctions or cardiac procedures) and with high-quality results from CCTA and CAC imaging performed using dedicated dual-source CT scanners. Noncontrast images were scored for CAC. CCTA images were visually read and scored for coronary atherosclerosis per segment (defined as no atherosclerosis, 1% to 49% stenosis, or ≥50% stenosis). External validity of prevalence estimates was evaluated using inverse probability for participation weighting and Swedish register data.

Results:

In total, 25 182 individuals without known coronary heart disease were included (50.6% women). Any CCTA-detected atherosclerosis was found in 42.1%; any significant stenosis (≥50%) in 5.2%; left main, proximal left anterior descending artery, or 3-vessel disease in 1.9%; and any noncalcified plaques in 8.3% of this population. Onset of atherosclerosis was delayed on average by 10 years in women. Atherosclerosis was more prevalent in older individuals and predominantly found in the proximal left anterior descending artery. Prevalence of CCTA-detected atherosclerosis increased with increasing CAC scores. Among those with a CAC score >400, all had atherosclerosis and 45.7% had significant stenosis. In those with 0 CAC, 5.5% had atherosclerosis and 0.4% had significant stenosis. In participants with 0 CAC and intermediate 10-year risk of atherosclerotic cardiovascular disease according to the pooled cohort equation, 9.2% had CCTA-verified atherosclerosis. Prevalence estimates had excellent external validity and changed marginally when adjusted to the age-matched Swedish background population.

Conclusions:

Using CCTA in a large, random sample of the general population without established disease, we showed that silent coronary atherosclerosis is common in this population. High CAC scores convey a significant probability of substantial stenosis, and 0 CAC does not exclude atherosclerosis, particularly in those at higher baseline risk.

Clinical Impact of Intraprocedural Stent Thrombosis During Percutaneous Coronary Intervention in Patients Treated With Potent P2Y12 inhibitors - a VALIDATE-SWEDEHEART Substudy

Background

The clinical importance of intraprocedural stent thrombosis (IPST) during percutaneous coronary intervention in the contemporary era of potent oral P2Y12 inhibitors is not established. The aim of this study was to assess IPST and its association with clinical outcome in patients with myocardial infarction undergoing percutaneous coronary intervention with contemporary antithrombotic medications.

Methods and Results

The VALIDATE‐SWEDEHEART study (Bivalirudin Versus Heparin in ST‐Segment and Non–ST‐Segment Elevation Myocardial Infarction in Patients on Modern Antiplatelet Therapy in the Swedish Web System for Enhancement and Development of Evidence‐Based Care in Heart Disease Evaluated According to Recommended Therapies Registry Trial) included 6006 patients with myocardial infarction, treated with potent P2Y12 inhibitors during percutaneous coronary intervention. IPST, defined as a new or worsening thrombus related to a stent deployed during the procedure, was reported by the interventional cardiologist in 55 patients (0.9%) and was significantly associated with ST‐segment elevation myocardial infarction presentation, longer stents, bailout glycoprotein IIb/IIIa inhibitors, and final Thrombolysis in Myocardial Infarction flow <3. The primary composite end point included cardiovascular death, myocardial infarction, out‐of‐laboratory definite stent thrombosis and target vessel revascularization within 30 days. Secondary end points were major bleeding and the individual components of the primary composite end point. Patients with versus without IPST had significantly higher rates of the primary composite end point (20.0% versus 4.4%), including higher rates of cardiovascular death, target vessel revascularization, and definite stent thrombosis, but not myocardial infarction or major bleeding. By multivariable analysis, IPST was independently associated with the primary composite end point (hazard ratio, 3.82; 95% CI, 2.05–7.12; P<0.001).

Conclusions

IPST is a rare but dangerous complication during percutaneous coronary intervention, independently associated with poor prognosis, even in the current era of potent antiplatelet agents. Future treatment studies are needed to reduce the rate of IPST and to improve the poor outcome among these patients.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02311231.

The association of mode of location activity and mobility with acute coronary syndrome: a nationwide ecological study

BACKGROUND

We aimed to study the effect of social containment mandates on ACS presentation during COVID-19 pandemic using location activity and mobility data from mobile phone map services.

METHODS

We conducted a cross-sectional study using data from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR) including all ACS presentations during the pandemic until 7 May 2020. Using a count regression model, we adjusted for day of the week, daily weather and incidence of COVID-19.

RESULTS

A 10% increase in activity around areas of residence was associated with 38% lower rates of ACS hospitalizations, whereas increased activity relating to retail and recreation, grocery stores and pharmacies, workplaces and mode of mobility was associated with 10-20% higher rates of ACS hospitalizations.

CONCLUSION

Government policy regarding social containment mandates has important public health implications for medical emergencies such as ACS and may explain the decline in ACS presentations observed during COVID-19 pandemic.

Usefulness of High Sensitivity Troponin T to Predict Long-Term Left Ventricular Dysfunction After ST-Elevation Myocardial Infarction

Guidelines recommend the use of transthoracic echocardiography (TTE) and clinical scores to risk stratify patients after ST-elevation myocardial infarction (STEMI). High sensitivity troponin T (hs-cTnT) is predictive of outcome after STEMI but the predictive value of hs-cTnT relative to other risk assessment tools has not been established. We aimed to compare the predictive value of hs-cTnT to other risk assessment tools in patients with STEMI. A subset of 578 patients with STEMI were included in this post-hoc study from the Third DANish Study of Optimal Acute Treatment of Patients with ST-segment Elevation Myocardial Infarction trial. Patients underwent cardiac magnetic resonance imaging (CMR) during index hospitalization as well as TTE at 1 year after their STEMI. The predictive value of hs-cTnT was compared with CKMB, infarct size (IS)/left ventricular ejection fraction (LVEF) assessed with CMR, LVEF assessed at discharge with TTE and the Global Registry of Acute Coronary Events (GRACE) and Thrombolysis in Myocardial Infarction (TIMI) risk-scores. The primary outcome was LV systolic dysfunction defined as LVEF ≤40% after 1 year on TTE. The area under the receiver operating characteristic curve analyses showed no significant difference between hs-cTnT and early CMR-assessed IS or LVEF in predicting subsequent LVEF ≤40%. Area under the curve for hs-cTnT was 0.82, 0.85 for IS (p = 0.22), and 0.87 for LVEF (p = 0.23). For predischarge TTE-assessed LVEF, the value was 0.85 (p = 0.45), 0.63 for creatine kinase-MB (p <0.001), 0.61 for the GRACE score (p <0.001), and 0.70 for the TIMI score (p = 0.02). A peak hs-cTnT value <3,500 ng/L ruled out LVEF ≤40% with probability of 98%. In conclusion, in patients presenting with STEMI undergoing PCI, hs-cTnT level strongly predicted long-term LV dysfunction and could be used as a clinical risk stratification tool to identify patients at high risk of progressing to LV dysfunction due to its general availability and high-predictive accuracy.

Incidence and outcome of myocardial infarction treated with percutaneous coronary intervention during COVID-19 pandemic

Objective

Most reports on the declining incidence of myocardial infarction (MI) during the COVID-19 have either been anecdotal, survey results or geographically limited to areas with lockdowns. We examined the incidence of MI during the COVID-19 pandemic in Sweden, which has remained an open society with a different public health approach fighting COVID-19.

Methods

We assessed the incidence rate (IR) as well as the incidence rate ratios (IRRs) of all MI referred for coronary angiography in Sweden using the nationwide Swedish Coronary Angiography and Angioplasty Registry (SCAAR), during the COVID-19 pandemic in Sweden (1 March 2020–7 May 2020) in relation to the same days 2015–2019.

Results

A total of 2443 MIs were referred for coronary angiography during the COVID-19 pandemic resulting in an IR 36 MIs/day (204 MIs/100 000 per year) compared with 15 213 MIs during the reference period with an IR of 45 MIs/day (254 MIs/100 000 per year) resulting in IRR of 0.80, 95% CI (0.74 to 0.86), p<0.001. Results were consistent in all investigated patient subgroups, indicating no change in patient category seeking cardiac care. Kaplan-Meier event rates for 7-day case fatality were 439 (2.3%) compared with 37 (2.9%) (HR: 0.81, 95% CI (0.58 to 1.13), p=0.21). Time to percutaneous coronary intervention (PCI) was shorter during the pandemic and PCI was equally performed, indicating no change in quality of care during the pandemic.

Conclusion

The COVID-19 pandemic has significantly reduced the incidence of MI referred for invasive treatment strategy. No differences in overall short-term case fatality or quality of care indicators were observed.

Association of acute myocardial infarction with influenza: A nationwide observational study

Introduction

Influenza may precipitate cardiovascular disease, but influenza typically peaks in winter, coinciding with other triggers of myocardial infarction (MI) such as low air temperature, high wind velocity, low atmospheric pressure, and short sunshine duration.

Objective

We aimed to determine the relationship of week-to-week variation in influenza cases and acute MI, controlling for meteorological factors in a nationwide population.

Methods

Weekly laboratory-confirmed influenza case reports were obtained from the Public Health Agency of Sweden from 2009 to 2016 and merged with the nationwide SWEDEHEART MI registry. Weekly incidence of MI was studied with regard to number of influenza cases stratified into tertiles of 0–16, 17–164, and >164 cases/week. Incidence rate ratios (IRR) were calculated using a count regression model for each category and compared to a non-influenza period as reference, controlling for air temperature, atmospheric pressure, wind velocity, and sunshine duration.

Results

A total of 133562 MI events was reported to the registry during the study period. Weeks with influenza cases were associated with higher incidence of MI than those without in unadjusted analysis for overall MI, ST-elevation MI and non ST-elevation MI independently. During the influenza season, weeks with 0–16 reported cases/week were not associated with MI incidence after adjusting for weather parameters, adjusted IRR for MI was 1.03 (95% CI 1.00–1.06, P = 0.09). However, weeks with more cases reported were associated with MI incidence: 17–163 reported cases/week, adjusted IRR = 1.05 (95% CI 1.02–1.08, P = 0.003); and for ≥164 cases/week, the IRR = 1.06 (95% CI 1.02–1.09, P = 0.002). Results were consistent across a large range of subgroups.

Conclusions

In this nationwide observational study, we found an association of incidence of MI with incidence of influenza cases beyond what could be explained by meteorological factors.

Bivalirudin Versus Heparin Monotherapy in Elderly Patients With Myocardial Infarction: A Prespecified Subgroup Analysis of the VALIDATE-SWEDEHEART Trial

BACKGROUND

Elderly patients with acute myocardial infarction undergoing percutaneous coronary intervention are at increased risk of both ischemic and bleeding complications. The optimal anticoagulation strategy in these patients is uncertain. Therefore, we compared bivalirudin to heparin monotherapy in a contemporary cohort of such patients.

METHODS

A prespecified subgroup analysis of elderly patients with myocardial infarction (≥75 years) from the VALIDATE-SWEDEHEART trial (Bivalirudin Versus Heparin in ST-Segment and Non-ST-Segment Elevation Myocardial Infarction in Patients on Modern Antiplatelet Therapy in the Swedish Web System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies Registry Trial) was performed. In the trial, patients were randomized to either bivalirudin or heparin monotherapy during percutaneous coronary intervention, with mandatory potent P2Y12 inhibition, routine radial artery access, and only bail-out glycoprotein IIb/IIIa inhibition. Kaplan-Meier event rates were assessed for the primary end point, consisting of a composite of all-cause death, myocardial reinfarction, or major bleeding, within 180 days.

RESULTS

The elderly (n=1592) had more than twice the risk of all events compared with younger patients (n=4406). Baseline and periprocedural characteristics were equal between bivalirudin (n=799) and heparin (n=793) treated patients ≥75 years. No differences were found in the elderly between bivalirudin and heparin monotherapy regarding the primary end point (180-day all-cause death, myocardial reinfarction, or major bleeding), the individual components of the primary end point, definite stent thrombosis, or stroke.

CONCLUSIONS

In this prespecified subgroup analysis of the VALIDATE-SWEDEHEART trial, elderly patients with myocardial infarction had a highly increased risk of all events. However, no difference in outcomes could be observed with an anticoagulation strategy with either bivalirudin or heparin as monotherapy in this patient group.

Association of Weather With Day-to-Day Incidence of Myocardial Infarction: A SWEDEHEART Nationwide Observational Study

Importance

Whether certain weather conditions modulate the onset of myocardial infarction (MI) is of great interest to clinicians because it could be used to prevent MIs as well as guide allocation of health care resources.

Objective

To determine if weather is associated with day-to-day incidence of MI.

Design, Setting, and Participants

In this prospective, population-based and nationwide setting, daily weather data from the Swedish Meteorological and Hydrological Institute were extracted for all MIs reported to the Swedish nationwide coronary care unit registry, Swedish Web-System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies (SWEDEHEART), during 1998 to 2013 and then merged with each MI on date of symptom onset and coronary care unit. All patients admitted to any coronary care unit in Sweden owing to MI were included. A total of 280 873 patients were included, of whom 92 044 were diagnosed as having ST-elevation MI. Weather data were available for 274 029 patients (97.6%), which composed the final study population. Data were analyzed between February 2017 and April 2018.

Exposures

The nationwide daily mean air temperature, minimum air temperature, maximum air temperature, wind velocity, sunshine duration, atmospheric air pressure, air humidity, snow precipitation, rain precipitation, and change in air temperature.

Main Outcomes and Measures

The nationwide daily counts of MI as outcome.

Results

In 274 029 patients, mean (SD) age was 71.7 (12) years. Incidence of MI increased with lower air temperature, lower atmospheric air pressure, higher wind velocity, and shorter sunshine duration. The most pronounced association was observed for air temperature, where a 1-SD increase in air temperature (7.4°C) was associated with a 2.8% reduction in risk of MI (unadjusted incidence ratio, 0.972; 95% CI, 0.967-0.977; P <.001). Results were consistent for non-ST-elevation MI as well as ST-elevation MI and across a large range of subgroups and health care regions.

Conclusions and Relevance

In this large, nationwide study, low air temperature, low atmospheric air pressure, high wind velocity, and shorter sunshine duration were associated with risk of MI with the most evident association observed for air temperature.

P6392Under the weather: acute myocardial infarction and subsequent case fatality with influenza burden - a nationwide observational study

Background

Influenza may precipitate cardiovascular disease but influenza typically peaks in winter coinciding with other triggers of myocardial infarction (MI) such as low air temperature, high wind velocity, low air pressure and short sunshine duration. We aimed to study week-to-week variation in influenza cases and acute MI after meteorological confounder adjustment in a nationwide setting.

Methods

Weekly laboratory-confirmed influenza case reports were obtained from the Public Health Agency of Sweden from 2009 to 2016 and merged with the nationwide SWEDEHEART MI registry. Weekly counts of MI were studied with regard to influenza cases stratified into tertiles, 0–16, 17–164 and >164 influenza cases/week. Incidence rate ratios were calculated for each category and compared to a reference period of the year with no influenza. A negative binomial regression model was applied to adjust for weather parameters.

Results

A total of 133 562 MIs were reported to the registry during the study period of which 44 055 were ST-elevation MIs. Weeks with influenza cases were associated with higher risk of MI. For 0–16 influenza cases/week the unadjusted incidence rate ratio (IRR) for MI was 1.04 (95% confidence interval [CI] 1.01–1.07, p=0.007); for 17–163 cases/week the IRR=1.07 (95% CI 1.04–1.10, p≤0.001) and for ≥164 cases/week the IRR=1.08 (95% CI 1.05–1.11, p≤0.001). Results were consistent across a large range of subgroups and after adjusting for confounders. In addition, all-cause mortality was higher in weeks with highest reported rates of influenza cases.

Conclusion

In this nationwide observational study, we found an association between occurrence of MI and number of influenza cases beyond what could be explained by meteorological factors.

Development and evaluation of nanoemulsion and microsuspension formulations of curcuminoids for lung delivery with a novel approach to understanding the aerosol performance of nanoparticles

Extensive research has demonstrated the potential effectiveness of curcumin against various diseases, including asthma and cancers. However, few studies have used liquid-based vehicles in the preparation of curcumin formulations. Therefore, the current study proposed the use of nanoemulsion and microsuspension formulations to prepare nebulised curcuminoid for lung delivery. Furthermore, this work expressed a new approach to understanding the aerosol performance of nanoparticles compared to microsuspension formulations. The genotoxicity of the formulations was also assessed. Curcuminoid nanoemulsion formulations were prepared in three concentrations (100, 250 and 500 µg/ml) using limonene and oleic acid as oil phases, while microsuspension solutions were prepared by suspending curcuminoid particles in isotonic solution (saline solution) of 0.02% Tween 80. The average fine particle fraction (FPF) and mass median aerodynamic diameter (MMAD) of the nebulised microsuspension formulations ranged from 26% and 7.1 µm to 40% and 5.7 µm, for 1000 µg/ml and 100 µg/ml respectively. In a comparison of the low and high drug concentrations of the nebulised nanoemulsion, the average FPF and MMAD of the nebulised nanoemulsion formulations prepared with limonene oil ranged from 50% and 4.6 µm to 45% and 5.6 µm, respectively; whereas the FPF and MMAD of the nebulised nanoemulsion prepared with oleic acid oil ranged from 46% and 4.9 µm to 44% and 5.6 µm, respectively. The aerosol performance of the microsuspension formulations were concentration dependent, while the nanoemulsion formulations did not appear to be dependent on the curcuminoids concentration. The performance and genotoxicity results of the formulations suggest the suitability of these preparations for further inhalation studies in animals.

Christmas, national holidays, sport events, and time factors as triggers of acute myocardial infarction: SWEDEHEART observational study 1998-2013

OBJECTIVES

To study circadian rhythm aspects, national holidays, and major sports events as triggers of myocardial infarction.

DESIGN

Retrospective observational study using the nationwide coronary care unit registry, SWEDEHEART.

SETTING

Sweden.

PARTICIPANTS

283 014 cases of myocardial infarction reported to SWEDEHEART between 1998 and 2013. Symptom onset date was documented for all cases, and time to the nearest minute for 88%.

INTERVENTIONS

Myocardial infarctions with symptom onset on Christmas/New Year, Easter, and Midsummer holiday were identified. Similarly, myocardial infarctions that occurred during a FIFA World Cup, UEFA European Championship, and winter and summer Olympic Games were identified. The two weeks before and after a holiday were set as a control period, and for sports events the control period was set to the same time one year before and after the tournament. Circadian and circaseptan analyses were performed with Sunday and 24:00 as the reference day and hour with which all other days and hours were compared. Incidence rate ratios were calculated using a count regression model.

MAIN OUTCOME MEASURES

Daily count of myocardial infarction.

RESULTS

Christmas and Midsummer holidays were associated with a higher risk of myocardial infarction (incidence rate ratio 1.15, 95% confidence interval 1.12 to 1.19, P<0.001, and 1.12, 1.07 to 1.18, P<0.001, respectively). The highest associated risk was observed for Christmas Eve (1.37, 1.29 to 1.46, P<0.001). No increased risk was observed during Easter holiday or sports events. A circaseptan and circadian variation in the risk of myocardial infarction was observed, with higher risk during early mornings and on Mondays. Results were more pronounced in patients aged over 75 and those with diabetes and a history of coronary artery disease.

CONCLUSIONS

In this nationwide real world study covering 16 years of hospital admissions for myocardial infarction with symptom onset documented to the nearest minute, Christmas, and Midsummer holidays were associated with higher risk of myocardial infarction, particularly in older and sicker patients, suggesting a role of external triggers in vulnerable individuals.

Predictive Value of High-Sensitivity Troponin T for Systolic Dysfunction and Infarct Size (Six Months) After ST-Elevation Myocardial Infarction

The association of markers of myocardial injury and dysfunction with infarct size (IS) and ejection fraction (EF) are well documented. However, limited data are available on the newer high-sensitivity troponin assays and comparison with morphologic and functional assessment with cardiac magnetic resonance imaging. We aimed to examine the associations of high-sensitivity cardiac Troponin-T (hs-cTnT), creatine kinase MB iso-enzyme (CKMB), and N-terminal pro B-type Natriuretic Peptide (NT-proBNP) to IS and EF at 6 months. Blood samples from 119 ST-segment elevation myocardial infarction patients from the Rapid Endovascular Catheter Core Cooling Combined With Cold Saline solution as an Adjunct to Percutaneous Coronary Intervention for the Treatment of Acute Myocardial Infarction trial were collected at baseline, 6, 24, and 48 hours after admission. Cardiac magnetic resonance was performed at 4 ± 2 days and 6 months. The association of biomarker levels to IS and EF was tested with Pearson's correlation coefficients and linear regression models with bootstrap resampling. The correlation coefficient of biomarker to IS was (CKMB: r = 0.71); (NT-proBNP: r = 0.55); (hs-cTnT: r = 0.80); and for EF (CKMB: r = 0.57); (NT-proBNP: r = 0.48); and (peak hs-cTnT: r = 0.68). IS and EF at 4 ± 2 days had the strongest correlations with IS and EF at 6 months respectively (IS: r = 0.84) and (EF: r = 0.74). Receiver operating characteristic of peak hs-cTnT for predicting EF ≤40% at 6 months was 0.87 compared with 0.75 for early IS. Early EF was a negative predictor of late EF <40%, 1-area under curve = 0.93. In conclusion, high-sensitivity Troponin T is a rapid, cheap, generally available tool for accurate prediction of systolic dysfunction in patients 6 months after first-time ST-segment elevation myocardial infarction.

Editor’s Choice- Heparin pre-treatment in patients with ST-segment elevation myocardial infarction and the risk of intracoronary thrombus and total vessel occlusion. Insights from the TASTE trial

Background:

Pre-treatment with unfractionated heparin is common in ST-segment elevation myocardial infarction (STEMI) protocols, but the effect on intracoronary thrombus burden is unknown. We studied the effect of heparin pre-treatment on intracoronary thrombus burden and Thrombolysis in Myocardial Infarction (TIMI) flow prior to percutaneous coronary intervention in patients with STEMI.

Methods:

The Thrombus Aspiration in ST-Elevation Myocardial Infarction in Scandinavia (TASTE) trial angiographically assessed intracoronary thrombus burden and TIMI flow, prior to percutaneous coronary intervention, in patients with STEMI. In this observational sub-study, patients pre-treated with heparin were compared with patients not pre-treated with heparin. Primary end points were a visible intracoronary thrombus and total vessel occlusion prior to percutaneous coronary intervention. Secondary end points were in-hospital bleeding, in-hospital stroke and 30-day all-cause mortality.

Results:

Heparin pre-treatment was administered in 2898 out of 7144 patients (41.0%). Patients pre-treated with heparin less often presented with an intracoronary thrombus (61.3% vs. 66.0%, p<0.001) and total vessel occlusion (62.9% vs. 71.6%, p<0.001). After adjustments, heparin pre-treatment was independently associated with a reduced risk of intracoronary thrombus (odds ratio (OR) 0.73, 95% confidence interval (CI)=0.65–0.83) and total vessel occlusion (OR 0.64, 95% CI=0.56–0.73), prior to percutaneous coronary intervention. There were no significant differences in secondary end points of in-hospital bleeding (OR 0.84, 95% CI=0.55–1.27), in-hospital stroke (OR 1.17, 95% CI=0.48–2.82) or 30-day all-cause mortality (hazard ratio 0.88, 95% CI=0.60–1.30).

Conclusions:

Heparin pre-treatment was independently associated with a lower risk of intracoronary thrombus and total vessel occlusion before percutaneous coronary intervention in patients with STEMI, without evident safety concerns, in this large multi-centre observational study.

Intravascular Ultrasound Guidance Is Associated With Better Outcome in Patients Undergoing Unprotected Left Main Coronary Artery Stenting Compared With Angiography Guidance Alone

Background—

Small observational studies have indicated better outcome with intravascular ultrasound (IVUS) guidance when performing unprotected left main coronary artery (LMCA) percutaneous coronary intervention (PCI), but the overall picture remains inconclusive and warrants further investigation. We studied the impact of IVUS guidance on outcome in patients undergoing unprotected LMCA PCI in a Swedish nationwide observational study.

Methods and Results—

Patients who underwent unprotected LMCA PCI between 2005 and 2014 because of stable coronary artery disease or acute coronary syndrome were included from the nationwide SCAAR (Swedish Coronary Angiography and Angioplasty Registry). Of 2468 patients, IVUS guidance was used in 621 (25.2%). The IVUS group was younger (median age, 70 versus 75 years) and had fewer comorbidities but more complex lesions. IVUS was associated with larger stent diameters (median, 4 mm versus 3.5 mm). After adjusting for potential confounders, IVUS was associated with significantly lower occurrence of the primary composite end point of all-cause mortality, restenosis, or definite stent thrombosis (hazard ratio, 0.65; 95% confidence interval, 0.50–0.84) and all-cause mortality alone (hazard ratio, 0.62; 95% confidence interval, 0.47–0.82). In 340 propensity score–matched pairs, IVUS was also associated with significantly lower occurrence of the primary end point (hazard ratio, 0.54; 95% confidence interval, 0.37–0.80).

Conclusions—

IVUS was associated with an independent and significant outcome benefit when performing unprotected LMCA PCI. Potential mediators of this benefit include larger and more appropriately sized stents, perhaps translating into lower risk of subsequent stent thrombosis. Although residual confounding cannot be ruled out, our findings indicate a possible hazard when performing unprotected LMCA PCI without IVUS guidance.

Cangrelor in combination with ticagrelor provides consistent and potent P2Y12-inhibition during and after primary percutaneous coronary intervention in real-world patients with ST-segment-elevation myocardial infarction

Patients pretreated with ticagrelor with less than 1 hour from percutaneous coronary intervention (PCI) or receiving ticagrelor in cath lab were prospectively included and received cangrelor. Cangrelor was infused for 2 hours and platelet function was assessed as P2Y12 reactivity units (PRU) with the VerifyNow P2Y12 function assay before start of infusion, 15 min after the start of infusion, and 30 min after the end of infusion. A total of n = 32 patients with an average age of 68 (±13) years with n = 22 (69%) males were included. The level of P2Y12 inhibition before cangrelor infusion was started was 249 PRU (IQR 221-271). After 15 min of cangrelor infusion the P2Y12 reactivity was markedly decreased to 71 PRU (IQR 52-104, p < 0.001). At 30 min after end of infusion PRU remained within the therapeutic range, 89 PRU (IQR 50-178; p < 0.001 for comparison with preinfusion) with only n = 4 (12.5%) patients with PRU >225. Results were consistent between patients receiving ticagrelor prehospital or in the cath lab and no statistical differences in PRU were noted between the two groups in any of the three measurements. In conclusion, cangrelor in combination with ticagrelor results in consistent and strong P2Y12 inhibition during and after infusion and cangrelor may bridge the gap until oral P2Y12 inhibitors achieve effect in real-world STEMI patients undergoing primary PCI.

The distribution of heavy-chain isoforms of myosin in airways smooth muscle from adult and neonate humans

Changes in the expression of heavy chains of myosin during development determine the functional characteristics of striated muscles. The distribution of heavy-chain isoforms of smooth-muscle myosin was determined in the airways of adult and infant humans to see whether it might underlie the hyperreactivity of human airways. The protein bands corresponding to myosin were separated using SDS/polyacrylamide-gel electrophoresis (4% gels) and identified by immunoblotting using both monoclonal and polyclonal antibodies against smooth-muscle myosin and non-muscle myosin. The relative proportion of each heavy chain stained by Coomassie Blue was measured by densitometric scanning. Three major bands corresponding to myosin heavy-chain isoforms were found; the two slower migrating bands (MHC1 and MHC2) were smooth-muscle myosin, and the third band was non-muscle myosin. The MHC1/MHC2 ratio was 0.69:1 in adult bronchus, and in infant bronchus and trachea. This contrasted with the airway smooth muscle in pigs, which was run concurrently, where the smooth-muscle heavy-chain ratio changed with development [Mohammad & Sparrow (1988) FEBS Lett. 228, 109-112]. The non-muscle myosin heavy chain comprised 63% of the smooth-muscle myosin. In both adult and infant lungs an additional putative myosin heavy chain which migrated slightly more rapidly than non-muscle myosin heavy chain was identified using the monoclonal smooth-muscle myosin antibody BF 48. This was unique to the human species.

Ivermectin, levamisole and thymic extract for chemotherapy and immunostimulation of visceral leishmaniasis in hamsters and mice

The anti-leishmanial activity of ivermectin, pentostam or combination of pentostam with either levamisole or thymic extract was tested against Leishmania donovani infection in hamsters and mice. In vitro peritoneal macrophage-parasite interaction, the effect of splenic cells on the interaction of macrophages and parasites, spleen weight, parasite burden in spleen tissue as well as the antibody titers using micro-ELISA were used as parameters for evaluating the efficacy of these chemotherapeutic regimens. Treatment with ivermectin and immunoenhancement with pentostam combined with levamisole gave best results in both animal models. Furthermore, regimens used in this work were all active in reducing phagocytosis of promastigotes by macrophages in vitro.

Myosin composition and functional properties of smooth muscle from the uterus of pregnant and non-pregnant rats

The myosin heavy chain stoichiometry and the force-velocity relation have been determined in the myometrium of the non-pregnant and pregnant rat. The relative proportions of the slower migrating heavy chain (MHC1) greatly exceeded that of the faster migrating heavy chain (MHC2) as shown by electrophoresis on SDS 4%-polyacrylamide gels. The ratios of MHC1/MHC2 were 2.2/1 in the non-pregnant rats, 2.6/1 in the pregnant rat, and contrasted with 0.8/1 in the rat portal vein. This stoichiometry was unchanged by extracting the myosin from the smooth muscle as native myosin in a salt extract, as dissociated myosin using sodium dodecyl sulphate (SDS) or by isolating the native myosin first by a non-dissociating (pyrophosphate) electrophoresis step and subsequently analysing the protein bands on the SDS 4%-polyacrylamide gel. Although the unequal proportions of the heavy chains suggested the possibility that the native myosin molecule may be arranged as homodimeric heavy chains, no evidence for or against the existence of native myosin isoforms could be obtained by electrophoresing native myosin extracts on pyrophosphate-polyacrylamide gels. The force-velocity relations of the intact electrically stimulated myometrium from the non-pregnant and pregnant rats gave isometric force of 45 and 135 mN/mm2 and Vmax of 0.71 and 0.52 lengths/s (37 degrees C) when measured at 95% of optimal length, whereas in chemically skinned uterine strips at 22 degrees C Vmax was 0.09 and 0.13 lengths/s, respectively. The length-force relationship was of similar shape in the non-gravid and gravid skinned tissues. The energetic tension cost (ATP-turnover/active stress) in skinned fibres was also similar. The mechanical and metabolic characteristics of the gravid and non-gravid uterus found in the present study do not suggest an obvious difference in the intrinsic properties of the myosin, although significant functional alterations in the tissue appear during pregnancy. This corresponds to the lack of a difference in the pattern of the heavy chains.

Changes in myosin heavy chain stoichiometry in pig tracheal smooth muscle during development

The stoichiometry of the myosin heavy chains (MHCs) has been measured in the tracheal smooth muscle of the pig after electrophoresis on SDS 4% polyacrylamide gel. The ratio of slower migrating MHC to the faster migrating MHC was 2.1 neonates, 1.5 in young and 0.95 in old pigs (P less than 0.01) showing that MHC composition changes with development. The unequal proportion of MHCs was not compatible with a heterodimeric arrangement of the MHCs in the native molecule as proposed earlier by Rovner et al. [(1986) Am. J. Physiol. 250, C861-870] and it is suggested that native molecules may be composed of homodimer heavy chains.

The heavy-chain stoichiometry of smooth muscle myosin is a characteristic of smooth muscle tissues

The stoichiometry of the two heavy chains of myosin in smooth muscle was determined by electrophoresing extracts of native myosin and of dissociated myosin on sodium dodecyl sulfate (SDS) 4%-polyacrylamide gels. The slower migrating heavy chain was 3.6 times more abundant in toad stomach, 2.3 in rabbit myometrium, 2.0 in rat femoral artery, 1.3 in guinea pig ileum, 0.93 in pig trachea and 0.69 in human bronchus, than the more rapidly migrating chain. Both heavy chains were identified as smooth muscle myosin by immunoblotting using antibodies to smooth muscle and non-muscle myosin. The unequal proportion of heavy chains suggested the possibility of native isoforms of myosin comprised of heavy-chain homodimers. To test this, native myosin extracts wer electrophoresed on non-dissociating (pyrophosphate) gels. When each band was individually analysed on SDS-polyacrylamide gel the slowest was found to be filamin and the other bands were myosin in which the relative proportion of the heavy chains was unchanged from that found in the original tissue extracts. Since this is incompatible with either a heterodimeric or a homodimeric arrangement it suggests that pyrophosphate gel electrophoresis is incapable of separating putative isoforms of native myosin.