Molecular basis of electrocardiographic ST-segment elevation

Hydroethanolic extract of Cirsium setidens ameliorates doxorubicin-induced cardiotoxicity by AMPK-PGC-1α-SOD-mediated mitochondrial protection

BACKGROUND

Doxorubicin (DOX) is an effective anticancer agent. However, the clinical outcomes of DOX-based therapies are severely hampered by their significant cardiotoxicity.

PURPOSE

We investigated the beneficial effects of an ethanol extract of Cirsium setidens (CSE) on DOX-induced cardiomyotoxicity (DICT).

METHODS

UPLC-TQ/MS analysis was used to identify CSE metabolite profiles. H9c2 rat cardiomyocytes and MDA-MB-231 human breast cancer cells were used to evaluate the effects of CSE on DICT-induced cell death. To elucidate the mechanism underlying it, AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma co-activator l-alpha (PGC1-α), nuclear respiratory factor 1 (NRF1), NRF2, superoxide dismutase (SOD1), and SOD2 expression was detected using western blot analysis. The oxygen consumption rate (OCR), cellular ROS, and mitochondrial membrane potential were measured. Finally, we confirmed the cardioprotective effect of CSE against DICT in both C57BL/6 mice and human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs) by observing various parameters, such as electrophysiological changes, cardiac fibrosis, and cardiac cell death.

RESULTS

Chlorogenic acid and nicotiflorin were the major compounds in CSE. Our data demonstrated that CSE blocked DOX-induced cell death of H9c2 cells without hindrance of its apoptotic effects on MDA-MB-231 cells. DOX-induced defects of OCR and mitochondrial membrane potential were recovered in a CSE through upregulation of the AMPK-PGC1-α-NRF1 signaling pathway. CSE accelerated NRF1 translocation to the nucleus, increased SOD activity, and consequently blocked apoptosis in H9c2 cells. In mice treated with 400 mg/kg CSE for 4 weeks, electrocardiogram data, creatine kinase and lactate dehydrogenase levels in the serum, and cardiac fibrosis, were improved. Moreover, various electrophysiological features indicative of cardiac function were significantly enhanced following the CSE treatment of hiPSCCMs.

CONCLUSION

Our findings demonstrate CSE that ameliorates DICT by protecting mitochondrial dysfunction via the AMP- PGC1α-NRF1 axis, underscoring the therapeutic potential of CSE and its underlying molecular pathways, setting the stage for future investigations into its clinical applications.

Potential protective effects of L-carnitine against myocardial ischemia/reperfusion injury in a rat model

Myocardial ischemia/reperfusion (I/R) injury is a growing concern for global public health. This study seeks to explore the potential protective effects of L-carnitine (LC) against heart ischemia-reperfusion injury in rats. To induce I/R injury, the rat hearts underwent a 30-min ligation of the left anterior descending coronary artery, followed by 24 h of reperfusion. We evaluated cardiac function through electrocardiography and heart rate variability (HRV) and conducted pathological examinations of myocardial structure. Additionally, the study investigated the influence of LC on myocardial apoptosis, inflammation, and oxidative stress in the context of I/R injury. The results show that pretreatment with LC led to improvements in the observed alterations in ECG waveforms and HRV parameters in the nontreated ischemic reperfusion model group, although most of these changes did not reach statistical significance. Similarly, although without a significant difference, LC reduced the levels of proinflammatory cytokines when compared to the values in the nontreated ischemic rat group. Furthermore, LC restored the reduced expressions of SOD1, SOD2, and SOD3. Additionally, LC significantly reduced the elevated Bax expressions and showed a nonsignificant increase in Bcl-2 expression, resulting in a favorable adjustment of the Bcl-2/Bax ratio. We also observed a significant enhancement in the histological appearance of cardiac muscles, a substantial reduction in myocardial fibrosis, and suppressed CD3 + cell proliferation in the ischemic myocardium. This small-scale, experimental, in vivo study indicates that LC was associated with enhancements in the pathological findings in the ischemic myocardium in the context of ischemia/reperfusion injury in this rat model. Although statistical significance was not achieved, LC exhibits potential and beneficial protective effects against I/R injury. It does so by modulating the expression of antioxidative and antiapoptotic genes, inhibiting the inflammatory response, and enhancing autonomic balance, particularly by increasing vagal tone in the heart. Further studies are necessary to confirm and elaborate on these findings.

De Winter electrocardiographic pattern in a young patient with acute myocardial infarction

A significant number of patients with acute coronary occlusion present with atypical electrocardiographic features in the emergency department. The de Winter pattern is suggestive of proximal left anterior descending coronary artery occlusion. Timely identification and immediate reperfusion is of utmost importance in these cases. The electrocardiographic pattern and its evolution in a young patient with acute myocardial infarction is described here.

The impact of ST-segment elevation on the prognosis of patients with Takotsubo cardiomyopathy

INTRODUCTION

Takotsubo cardiomyopathy (TC) has a variety of electrocardiographic expressions such as ST-segment elevation (STE), T-wave inversion, QTc-prolongation, left bundle branch block, presence of anterior Q waves and rarely ST-segment depression. In contrast to acute myocardial infarction, the impact of STE on the initial electrocardiogram (EKG), on TC outcomes, remains largely unknown.

OBJECTIVE

To evaluate the significance of STE on the index EKG of patients with takotsubo cardiomyopathy (TC) in terms of prognosis.

METHODS

We examined retrospectively the data of 436 patients diagnosed with TC who were admitted to the Minneapolis Heart Institute between August 2001 and November 2019.

RESULTS

Of 436 patients, 145 (33%) presented with STE on the index EKG. Typical apical ballooning pattern was encountered more frequently in the STE group (66% vs 51%; p = 0.005), on the contrary to the mid-ventricular ballooning which was more common in the non-STE group (31% vs 45%; p = 0.005) while initial left ventricular ejection fraction was similar between the two groups (31% ± 9 vs 33% ± 11; p = 0.163). The composite endpoint of TC-related complications, defined as left ventricular outflow tract obstruction (LVOTO), left ventricular (LV) thrombus, hemodynamic instability requiring mechanical or intravenous vasopressor support, cardiac arrest or in-hospital death, was higher for the STE group (37% vs 24%; p = 0.006). Left ventricular outflow obstruction (LVOTO) was more frequent in patients with STE (13% vs 3%; p < 0.001) while there was a trend toward higher rates of LV thrombus formation in the same group (5% vs 1%; p = 0.057). On multivariable analysis, STE remained an independent predictor of TC-related complications. In-hospital mortality (2.8% vs 3.4%; p = 1.000) and five-year mortality were similar between the two groups (23% vs 20%; p = 0.612).

CONCLUSION

Patients with TC presenting with STE on the initial EKG, were more likely to develop disease related complications, thus, careful in-hospital monitoring including imaging evaluation for LVOTO and LV thrombus may be warranted for these patients. Nevertheless, both groups had similar in-hospital and five-year mortality.

Atypical de Winter Presentation of Critical Left Anterior Descending Coronary Artery Occlusion

A 69-year-old male presented with substernal chest pain that started a few hours earlier. On arrival, the patient was hemodynamically stable, and the physical examination was unrevealing. Laboratory workup revealed an elevated high-sensitivity troponin, and an initial electrocardiogram (ECG) revealed tall, symmetric T-waves with preceding minor concave ST-segment elevations less than 1 mm in the precordial leads (V1-V6) and 0.5 mm ST elevation in the aVR. Due to concerning ECG changes, the patient was treated for a possible non-ST-segment elevation myocardial infarction. A loading dose of aspirin and clopidogrel was given and a heparin drip was initiated. However, the patient's chest pain persisted requiring multiple sublingual nitroglycerin tablets. Later, on further review of the ECGs, the presence of de Winter T-waves was noted and led to activation of the catheterization laboratory, and an urgent left heart catheterization (LHC) was done. LHC revealed a critical 90% occlusion of the left anterior descending artery, and a drug-eluting stent was placed. The patient had a good recovery thereafter. This case emphasizes the rarity of the case and lack of awareness about the atypical de Winter pattern that is considered to be an ST-segment elevation myocardial infarction equivalent. Failure to recognize this can potentially lead to delayed intervention.

Beneficial effects of PEGylated graphene quantum dot on arrhythmias induced by myocardial infarction

Arrhythmias are one of the leading causes of early death following myocardial infarction (MI) and heart failure. Graphene derivatives have emerged as an therapeutic target that have electrical conductivity. The study aimed to evaluate the impacts of polyethylene glycol-graphene quantum dots (GQDs-PEG) on arrhythmias created by MI in the rat. Animals were randomly assigned to five groups of sham, MI, and MI + GQDs-PEG at doses of 5, 10, and 20 mg/kg. MI was induced by the closure of the left anterior descending artery. The day after MI, animals were administered vehicle (phosphate buffered saline) or GQDs-PEG at different doses every other day for 2 weeks. On day 15, electrocardiogram (ECG), mean arterial pressure (MAP), and heart contractility indices were recorded by the PowerLab data acquisition system. GQDs-PEG 20 mg/kg increased contractility and improved the reduction of MAP in the MI group. The prolonged QT and QTc intervals, inverted T wave, and deviated ST segment were modified by GQDs-PEG 10 and 20 mg/kg in rats with MI. The amplitude of the Q wave was also decreased in a dose-dependent manner in the GQDs-PEG-treated rats. The results demonstrated that 2 weeks of treatment with GQDs-PEG normalized ECG abnormalities and improved left ventricular dysfunction in rats with MI.

A case of de Winter syndrome presenting with chest tightness

de Winter syndrome, also termed anterior ST-segment elevation myocardial infarction (STEMI) equivalent, is estimated to be present in approximately 2% of patients with acute myocardial infarction, but is often under-recognized by clinicians. Therefore, de Winter syndrome is associated with increased morbidity and mortality. We report a 51-year-old man with typical chest tightness and a characteristic electrocardiographic pattern without classic ST-segment elevation, but with acute nearly total occlusion of the left anterior descending coronary artery. Although the patient presented as a non-STEMI case, the definite diagnosis of de Winter syndrome was made on the basis of clinical and electrocardiographic findings. The patient's symptom of chest tightness was relieved immediately after acute percutaneous coronary intervention and the left ventricular ejection fraction had not deteriorated at 1 month of follow-up.

The rare presentation of the de Winter's pattern: Case report and literature review

Although not classified as a ST elevated myocardial infarction (STEMI), the patterns known as equivalents also require prompt recognition and treatment. A 50-year-old male with no pertinent history presented to the emergency department for chest pain that radiated to his left shoulder. An electrocardiogram (EKG) revealed findings consistent with the de Winter's pattern, which were greater than 1 mm upsloping ST depressions at the J point in leads V3-V6 (maximally in leads V3-V5), tall, peaked T waves in leads II, III, and V3-V5, ST elevations in lead aVR, and 1 mm ST elevation in V1 and V2. The physical exam, troponins, and other laboratory investigations were unrevealing. Urgent, diagnostic coronary angiography revealed complete occlusion of the proximal left anterior descending (LAD) artery, which was successfully treated with percutaneous coronary intervention (PCI) and two drug-eluting stents. After the stent placement, arterial blood flow was re-established and the ECG normalized. The patient was started on guideline based treatment and discharged home once medically stable. The de Winter's pattern on electrocardiogram indicates a significant coronary artery disease. This pattern requires urgent intervention, typically percutaneous stent placement.

Novel cholesterol-dependent regulation of cardiac KATP subunit expression revealed using histone deacetylase inhibitors

We recently discovered that the histone deacetylase inhibitor, trichostatin A (TSA), increases expression of the sulfonylurea receptor 2 (SUR2; Abcc9) subunit of the ATP-sensitive K+ (KATP ) channel in HL-1 cardiomyocytes. Interestingly, the increase in SUR2 was abolished with exogenous cholesterol, suggesting that cholesterol may regulate channel expression. In the present study, we tested the hypothesis that TSA increases SUR2 by depleting cholesterol and activating the sterol response element binding protein (SREBP) family of transcription factors. Treatment of HL-1 cardiomyocytes with TSA (30 ng/ml) caused a time-dependent increase in SUR2 mRNA expression that correlates with the time course of cholesterol depletion assessed by filipin staining. Consistent with the cholesterol-dependent regulation of SREBP increasing SUR2 mRNA expression, we observe a significant increase in SREBP cleavage and translocation to the nucleus following TSA treatment that is inhibited by exogenous cholesterol. Further supporting the role of SREBP in mediating the effect of TSA on KATP subunit expression, SREBP1 significantly increased luciferase reporter gene expression driven by the upstream SUR2 promoter. Lastly, HL-1 cardiomyocytes treated with the SREBP inhibitor PF429242 significantly suppresses the effect of TSA on SUR2 gene expression. These results demonstrate that SREBP is an important regulator of KATP channel expression and suggest a novel method by which hypercholesterolemia may exert negative effects on the cardiovascular system, namely, by suppressing expression of the KATP channel.

The de Winter's pattern revisited: a case series

BACKGROUND

The de Winter's electrocardiogram (ECG) pattern signifying proximal left anterior descending (LAD) artery occlusion was first described in 2008. The ECG changes were thought to be static and mechanisms for this were suggested. In addition, the optimal management of these patients was reported to be via a primary percutaneous coronary intervention (PCI) strategy.

CASE SUMMARY

Case 1: A 48-year-old gentleman presented with a 2-h history of ischaemic chest pain with initial de Winter's pattern on ECG. This progressed to anterior ST-elevation myocardial infarction (STEMI) complicated by ventricular fibrillation. Emergency angiography revealed a mid-vessel LAD occlusion which was successfully reperfused. Case 2: A 34-year-old female presented with a 2-h history of ischaemic chest pain with initial ECG showing a de Winter's pattern. Due to concerns of performing PCI timeously, a pharmacoinvasive strategy of reperfusion was adopted with resolution of the de Winter's pattern. Urgent angiography revealed a proximal LAD lesion which was successfully stented.

DISCUSSION

The two cases highlight that the de Winter's pattern may in fact not be static, but rather lie along the continuum of ischaemia and may evolve into STEMI. In addition, we provide further evidence that if primary PCI cannot be offered in a timeous manner, thrombolytic therapy may be considered in such patients. The de Winter's pattern remains a high-risk ECG pattern that requires early recognition and intervention.

Elevations in High-Sensitive Cardiac Troponin T and N-Terminal Prohormone Brain Natriuretic Peptide Levels in the Serum Can Predict the Development of Anthracycline-Induced Cardiomyopathy

BACKGROUND

Anthracyclines remain the cornerstone of the treatment in many cancers including lymphomas, leukemia and sarcomas, and breast cancer. The cardiomyopathy that develops from anthracyclines can lead to heart failure and decreased survival. Multiple mechanisms are involved in the pathophysiology of anthracycline-induced heart failure.

STUDY QUESTION

We hypothesize that anthracycline-induced cardiac (AIC) pathology can be monitored using a panel of blood biomarkers including high-sensitive cardiac troponin T (hs-cTnT) for myocyte necrosis and N-terminal prohormone brain natriuretic peptide (NT-proBNP) for parietal stress.

STUDY DESIGN

A prospective, institutionally approved study recruited all patients with cancer scheduled to start anthracycline chemotherapy in the Transylvania University cancer clinics.

MEASURES AND OUTCOMES

Transthoracic 2D echocardiography and the measurements of NT-proBNP and hs-cTnT plasma levels were performed at the beginning of the study and 3 months and 6 months after anthracycline treatment initiation.

RESULTS

The plasma levels of hs-cTnT at 3 months (rho = 0.439, P = 0.0001) and 6 months (rho = 0.490, P = 0.0001) are correlated with AIC occurrence. For a cutoff value of hs-cTnT at 3 months > 0.008 ng/mL, we obtained 66.7% sensitivity and 67.9% specificity for developing AIC at 6 months, with a 54.5% positive predictive value and a 87.8% negative predictive value. The NT-proBNP serum levels at 3 months (rho = 0.495, P = 0.0001) and 6 months (rho = 0.638, P = 0.0001) are correlated with an AIC diagnosis at 6 months. For a cutoff value of NT-proBNP at 3 months >118.5 pg/mL, we obtained 80% sensitivity and 79.2% specificity for evolution to AIC at 6 months, with 52.2% positive predictive value and 93.3% negative predictive value.

CONCLUSIONS

In anthracycline-treated cancer patients, the increase in plasma levels of NT-proBNP and of hs-cTnT can predict the development of anthracycline-induced cardiomyopathy. Early identification of at-risk patients will potentially allow for targeted dose reductions and will diminish the number of patients developing cardiac pathology.

[High-risk electrocardiographic patterns in Patients with acute coronary syndrome]

Acute myocardial infarction is the leading cause of death in the world and the electrocardiogram remains the diagnostic tool for determining an acute myocardial infarction with ST-segment elevation. In spite of this, only half of the patients present classic electrocardiogram findings compatible with the ST-elevation infarction criteria. There is a spectrum of electrocardiographic findings that may reflect a phenomenon of acute coronary occlusion, which should be promptly recognized by the clinician to offer early reperfusion therapy.

The De Winter-like electrocardiogram pattern in inferior and lateral leads associated with left circumflex coronary artery occlusion

The aim of this report was to investigate coronary artery occlusion related to De Winter-like electrocardiogram (ECG) pattern. A patient admitted to Zhongshan Hospital who was diagnosed with acute coronary syndrome with De Winter-like ECG pattern was reviewed in our case report. In this case, we found that a De Winter-like ECG change in the inferior and lateral leads was associated with left circumflex coronary artery occlusion. After a timely reperfusion therapy, the symptom was obviously alleviated with a normalization of upsloping ST-segment. Doctors should be aware that De Winter-like ECG changes can also predict acute occlusion in any coronary artery, not only in the left anterior descending artery and right coronary artery but also in the left circumflex coronary artery.

[de Winter syndrome, an easily ignored but life-threatening disease: a case report]

de Winter syndrome is a special equivalent of anterior ST-segment elevation myocardial infarction (STEMI) characterized by the absence of overt ST-elevation with upsloping ST-segment depression followed by tall symmetrical T-waves in the precordial leads, often associated with total occlusion of the proximal left anterior descending coronary artery. Herein we present a case of de Winter syndrome in a 63-year-old man, whose initial ECG showed no ST-segment elevation, but subsequent coronary angiography confirmed total occlusion of the proximal LAD coronary artery. The patient was successfully treated via mechanical reperfusion therapy and stenting through percutaneous coronary intervention (PCI). de Winter syndrome is associated with a high mortality often due to insufficient awareness of this condition by clinicians. Immediate reperfusion therapy by PCI is the life-saving treatment for the patients diagnosed with this syndrome, and prompt recognition of the ECG pattern is critical to ensure the timely administration of the therapy.

Implications of Localized ST Depression in a Vascular Territory and Altered Precordial T-Wave Balance in Ischemic Heart Disease

The incidence of acute coronary syndrome (ACS) is rising globally. Electrocardiography is still one of the best diagnostic modalities for it. Although some of the ECG changes of ACS are well known among medical practitioners, there are a handful of ECG changes that do not get the recognition they deserve. Among these are localized ST-segment depressions in a vascular territory and altered precordial T-wave balance. The urgency of management varies among the various subtypes of ACS, especially in low resource settings. ST-segment depression localized to a vascular territory is a sign of ST-elevation myocardial infarction (MI) in the reciprocal lead which may not always be evident and hence, requires emergent reperfusion therapy. On the other hand, altered precordial T-wave balance (T1 > T6, T-wave in V1 > 1.5 mm and upright T-wave in V1) may be predictive of significant coronary artery disease (CAD).

De Winter T-wave Electrocardiogram Pattern Due to Thromboembolic Event: A Rare Phenomenon

De winter pattern on the ECG is associated with occlusion of proximal left anterior descending artery. It is an atypical presentation of acute myocardial infarction due to LAD occlusion. We report a case due to thromboembolic occlusion of LAD after chemical cardioversion. It is imperative for cardiologists and physicians to instantly identify the De Winter pattern on ECG to appropriately triage these patients without delay.

The presence of De Winter electrocardiogram pattern following elective percutaneous coronary intervention in a patient without coronary artery occlusion: A case report

RATIONALE

The De Winter electrocardiogram (ECG) pattern is considered as a ST elevated myocardial infarction (STEMI)-equivalent pattern. Due to its rare nature, it is unclear whether this ECG pattern suggests the presence of some other condition.

PATIENT CONCERNS

We reported a 47-year-old man with new-onset chest discomfort several hours after the second-stage percutaneous coronary intervention (PCI).

DIAGNOSES

An emergency coronary angiogram (CAG) did not show any abnormality. However, the dynamic changes in the ECG and myocardial biomarkers indicated perioperative myocardial infarction.

INTERVENTION

The patient was monitored in the cardiac care unite (CCU), and was administered an intravenous infusion of diltiazem and subcutaneous injection of low molecular weight heparin.

OUTCOMES

After a few hours, his symptoms were alleviated. The patient was discharged after 6 days of hospitalization without any complications.

LESSONS

The De Winter ECG pattern can be observed in patients without significantly coronary arteries occlusion. The newly onset De Winter ECG pattern after PCI procedure may indicate perioperative myocardial infarction caused by impaired microvascular perfusion.

Is early invasive management as ST elevation myocardial infarction warranted in de Winter's sign?-a "peak" into the widow-maker

de Winter's sign was first described by de Winter et al. in 2008 as a new electrocardiographic (EKG) pattern of acute proximal left anterior descending coronary artery (LAD) occlusion. Instead of the normal presentation of ST elevation, it is described as depression of ST segment at the J point in the precordial leads V1-V6, which are upsloping leading to hyper-acute T waves, with ST elevation in aVR. The initial retrospective systematic analysis proved this sign to be present in about 2% of anterior myocardial infarction. This review aims to address the important question of mode and urgency of intervention, on detection of de Winter's sign. In this review, we take a look at the de Winter's sign EKG characteristics, accuracy in diagnosis, typical patient presentation, and the outcomes of early intervention. We conducted a Medline search using various combinations of "de Winter's sign," "STEMI equivalent," "cardiac catheterization," and "thrombolysis" to identify pivotal research articles published before June 1, 2019, for inclusion in this review. Concurrently, major practice guidelines, trial bibliographies, and pertinent reviews were examined to ensure inclusion of relevant trials. A consensus among the authors was used to choose items for narrative inclusion. The following section reviews data from pivotal trials to determine the need for early invasive management in de Winter's sign. Research articles reviewed evaluating cardiac catheterization in de Winter's sign. de Winter's sign, although rare (~2%), should be promptly recognized, as it reveals underlying severe coronary artery pathology, frequently involving the LAD which is associated with a high rate of mortality. This systematic review emphasizes awareness and strong consideration of early activation of the cardiac catheterization lab with PPCI; which may yield better treatment outcomes. The evidence suggests that de Winter's sign, presenting with ST depression and T wave elevation, should indeed be treated as ST-elevation myocardial infarction (STEMI) equivalent, with prompt recognition and early intervention.

Tpeak-Tend/QT interval predicts ST-segment resolution and major adverse cardiac events in acute ST-segment elevation myocardial infarction patients undergoing percutaneous coronary intervention

Elevated ST-segment and increased Tpeak-Tend interval (Tp-e) were prognostic predictors in major adverse cardiac events (MACEs) in ST-segment elevation myocardial infarction (STEMI). The electrophysiologic relationship between them during percutaneous coronary intervention (PCI) needs to elucidate.Patients with STEMI admitted to hospital were prospectively evaluated. ST-segment resolution (STR) (defined as ≥50% reduction as the complete-STR [CSTR] group, <50% as incomplete-STR [ISTR] group), Tp-e interval, and ratio of Tp-e to QT interval (Tp-e/QT) were measured, calculated and analyzed with MACEs.Tp-ec interval (corrected Tp-e interval, P < .001) and Tp-e/QT ratio (P < .001) were significantly increased by myocardial infarction and partly recovered post-PCI. Patients with ISTR showed more increased Tp-ec interval (P < .001) and Tp-e/QT ratio (P < .001) than those in CSTR groups post-PCI. In multivariate analysis and receiver operating characteristic curves analysis, Tp-e/QT was an independent and strongest predictor for STR. STR and electrocardiogram parameters with a cutoff value for predicting STR showed prognostic value for MACE in STEMI in Kaplan-Meier survival analysis.Both STR and change of Tp-e parameters were not only predictors of arrhythmia, but also prognostic factors of MACE in patients with STEMI after PCI.

The de winter electrocardiogram pattern is a transient electrocardiographic phenomenon that presents at the early stage of ST-segment elevation myocardial infarction

BACKGROUND

The de Winter electrocardiogram (EKG) pattern is a novel sign that indicates left anterior descending coronary artery (LAD) occlusion in patients with chest pain. This study aimed to assess the prevalence and clinical characteristics of patients with this pattern.

HYPOTHESIS

The de Winter EKG pattern is an special anterior ST-segment elevation myocardial infarction (STEMI) equivalents without obvious ST-segment elevation.

METHODS

This retrospective study included all patients with anterior myocardial infarction admitted between January 2011 and December 2017. Patients were categorized into two groups: those with the de Winter EKG pattern and those with typical STEMI.

RESULTS

Of 441 patients, 15 (3.4%) with anterior myocardial infarction had the de Winter EKG pattern. Similar to those with typical STEMI, the majority of patients with the de Winter EKG pattern had ST-segment elevation, pathologic Q wave, and absence of R wave at follow-up. The median time from recognition of this pattern until its evolution was 114 minutes. The ST-segment in leads V3R to V5R and leads V7 to V9 were normal or slightly depressed when a typical de Winter EKG pattern was noted in leads V1 to V6. The culprit lesion was mainly in the proximal LAD or the diagonal branch. Patients with this EKG pattern responded poorly to thrombolytic therapy.

CONCLUSIONS

We believe that the de Winter EKG pattern may be a sign of ischemia and presents at the early stage of STEMI rather than being an independent pattern. In patients with this pattern, a percutaneous coronary intervention rather than follow-up and thrombolytic strategy should be performed.

The de Winter electrocardiographic pattern of proximal left anterior descending occlusion

Prompt recognition of electrocardiographic signs of acute left anterior descending (LAD) occlusion is essential for timely restoration of flow. However, some patients may present with atypical electrocardiographic signs, and early diagnosis of these patients may constitute a clinical challenge. Here, we report two cases presenting with an atypical electrocardiographic manifestation despite angiographically confirmed acute thrombotic occlusion of proximal LAD. These cases highlight the importance of recognizing the de Winter electrocardiogram pattern in cases of suspected acute myocardial infarction (AMI). An emergency percutaneous coronary intervention (PCI) should be performed in suspected AMI patients as early as possible.

Remote Liver Ischemic Preconditioning Protects against Sudden Cardiac Death via an ERK/GSK-3β-Dependent Mechanism

BACKGROUND

Preconditioning stimuli conducted in remote organs can protect the heart against subsequent ischemic injury, but effects on arrhythmogenesis and sudden cardiac death (SCD) are unclear. Here, we investigated the effect of remote liver ischemia preconditioning (RLIPC) on ischemia/reperfusion (I/R)-induced cardiac arrhythmia and sudden cardiac death (SCD) in vivo, and determined the potential role of ERK/GSK-3βsignaling.

METHODS/RESULTS

Male Sprague Dawley rats were randomized to sham-operated, control, or RLIPC groups. RLIPC was induced by alternating four 5-minute cycles of liver ischemia with 5-minute intermittent reperfusions. To investigate I/R-induced arrhythmogenesis, hearts in each group were subsequently subjected to 5-minute left main coronary artery ligation followed by 20-minute reperfusion. RLIPC reduced post-I/R ventricular arrhythmias, and decreased the incidence of SCD >threefold. RLIPC increased phosphorylation of cardiac ERK1/2, and GSK-3β Ser9 but not Tyr216 post-I/R injury. Inhibition of either GSK-3β (with SB216763) or ERK1/2 (with U0126) abolished RLIPC-induced antiarrhythmic activity and GSK-3β Ser9 and ERK1/2 phosphorylation, leaving GSK-3β Tyr216 phosphorylation unchanged.

CONCLUSIONS

RLIPC exerts a powerful antiarrhythmic effect and reduces predisposition to post-IR SCD. The underlying mechanism of RLIPC cardioprotection against I/R-induced early arrhythmogenesis may involve ERK1/2/GSK-3β Ser9-dependent pathways.

The de Winter Electrocardiographic Pattern of Proximal Left Anterior Descending Coronary Artery Occlusion

An example of the electrocardiographic pattern of acute anterior myocardial infarction described by deWinter et al is presented, and its implications is discussed.

Non-cell autonomous cues for enhanced functionality of human embryonic stem cell-derived cardiomyocytes via maturation of sarcolemmal and mitochondrial KATP channels

Human embryonic stem cells (hESCs) is a potential unlimited ex vivo source of ventricular (V) cardiomyocytes (CMs), but hESC-VCMs and their engineered tissues display immature traits. In adult VCMs, sarcolemmal (sarc) and mitochondrial (mito) ATP-sensitive potassium (K_ATP) channels play crucial roles in excitability and cardioprotection. In this study, we aim to investigate the biological roles and use of sarcK_ATP and mitoK_ATP in hESC-VCM. We showed that SarcI_{K, ATP} in single hESC-VCMs was dormant under baseline conditions, but became markedly activated by cyanide (CN) or the known opener P1075 with a current density that was ~8-fold smaller than adult; These effects were reversible upon washout or the addition of GLI or HMR1098. Interestingly, sarcI_{K, ATP} displayed a ~3-fold increase after treatment with hypoxia (5% O₂). MitoI_{K, ATP} was absent in hESC-VCMs. However, the thyroid hormone T3 up-regulated mitoI_{K, ATP,} conferring diazoxide protective effect on T3-treated hESC-VCMs. When assessed using a multi-cellular engineered 3D ventricular cardiac micro-tissue (hvCMT) system, T3 substantially enhanced the developed tension by 3-folds. Diazoxide also attenuated the decrease in contractility induced by simulated ischemia (1% O₂). We conclude that hypoxia and T3 enhance the functionality of hESC-VCMs and their engineered tissues by selectively acting on sarc and mitoI_{K, ATP}.

Reduced acute myocardial ischemia-reperfusion injury in IL-6-deficient mice employing a closed-chest model

Objective and design

We examined the role of IL-6 in the temporal development of cardiac ischemia–reperfusion injury employing a closed-chest I/R model.

Materials/methods

Infarction, local and systemic inflammation, neutrophil infiltration, coagulation and ST elevation/resolution were compared between wild-type (WT) and IL-6-deficient (IL-6^−/−) mice after 1 h ischemia and 0, ½, 3, and 24 h reperfusion.

Results

IL-6 deficiency reduced infarct size at 3 h reperfusion (28.8 ± 4.5 % WT vs 17.6 ± 2.5 % IL-6^−/−), which reduction persisted and remained similar at 24 h reperfusion (25.1 ± 3.0 % WT vs 14.6 ± 4.4 % IL-6^−/−). Serum Amyloid A was reduced at 24 h reperfusion only (57.5 ± 4.9 WT vs 24.8 ± 5.6 ug/ml IL-6^−/− mice). Cardiac cytokines (IL-6, IL-1β and TNFα) peaked at 3 h reperfusion, but IL-1β and TNFα levels were unaffected by IL-6 deficiency. Significant neutrophil influx was only detected at 24 h reperfusion and was similar for WT and IL-6^−/−. Tissue factor peaked at 24 h reperfusion, whereas fibrin/fibrinogen peaked at 3 h reperfusion and was completely resolved at 24 h reperfusion; both coagulation factors were unaltered by IL-6 deficiency. Prolonged ST elevation was observed during ischemia that completely resolved for both genotypes at early reperfusion.

Conclusions

The data suggest that, in the absence of major surgical intervention, IL-6 contributes to the development of infarct size in the early phase of reperfusion; this contribution did not depend on neutrophil influx, IL-1β and TNFα, tissue factor and fibrin.

Sulfonylurea use is associated with larger infarct size in patients with diabetes and ST-elevation myocardial infarction

BACKGROUND

Animal models have demonstrated that sulfonylureas increase the size of myocardial infarction; however, data in humans is scarce. This study evaluated the association between sulfonylurea use and infarct size in diabetes patients with ST-elevation myocardial infarction (STEMI).

METHODS

Consecutive STEMI patients admitted in Edmonton, Canada between 2006 and 2011 were enrolled in a regional prospective registry program. Patients with type 2 diabetes were identified from this group and the maximum recorded troponin I (max cTnI) within the first 48 h of chest pain onset was used as the primary outcome to quantify infarct size. The relationship between preadmission sulfonylurea use and max cTnI was assessed using multivariable linear regression to adjust for patient demographics, cardiovascular risk factors, clinical data on admission, ischemia time, reperfusion therapy and preadmission drugs.

RESULTS

There were 560 STEMI patients with type 2 diabetes; mean (standard deviation; SD) age was 63.3 (12.8) years, 395 (70.5%) were male, 216 (38.6%) received primary percutaneous intervention, and 211 (37.7%) received thrombolysis. The max cTnI was higher in 146 sulfonylurea users compared to 414 non-sulfonylurea users (mean (SD): 49.8 (74.3) ng/mL versus 39.9 (50.4) ng/mL, respectively; adjusted between-group difference: 12.9 ng/mL; 95% CI 0.3-25.5; p=0.044).

CONCLUSION

This study adds further evidence to the proposed causal relationship between sulfonylureas and adverse cardiovascular events by observing a significant difference in infarct size among type 2 diabetes patients presenting with STEMI. Clinicians should consider this association when prescribing sulfonylureas to manage patients with type 2 diabetes.

Histone deacetylase inhibitors modulate KATP subunit transcription in HL-1 cardiomyocytes through effects on cholesterol homeostasis

Histone deacetylase inhibitors (HDIs) are under investigation for the treatment of a number of human health problems. HDIs have proven therapeutic value in refractory cases of cutaneous T-cell lymphoma. Electrocardiographic ST segment morphological changes associated with HDIs were observed during development. Because ST segment morphology is typically linked to changes in ATP sensitive potassium (K_ATP) channel activity, we tested the hypothesis that HDIs affect cardiac K_ATP channel subunit expression. Two different HDIs, romidepsin and trichostatin A, caused ~20-fold increase in SUR2 (Abcc9) subunit mRNA expression in HL-1 cardiomyocytes. The effect was specific for the SUR2 subunit as neither compound causes a marked change in SUR1 (Abcc8) expression. Moreover, the effect was cell specific as neither HDI markedly altered K_ATP subunit expression in MIN6 pancreatic β-cells. We observe significant enrichment of the H3K9Ac histone mark specifically at the SUR2 promoter consistent with the conclusion that chromatin remodeling at this locus plays a role in increasing SUR2 gene expression. Unexpectedly, however, we also discovered that HDI-dependent depletion of cellular cholesterol is required for the observed effects on SUR2 expression. Taken together, the data in the present study demonstrate that K_ATP subunit expression can be epigenetically regulated in cardiomyocytes, defines a role for cholesterol homeostasis in mediating epigenetic regulation and suggests a potential molecular basis for the cardiac effects of the HDIs.

The role of ATP-sensitive potassium channels in cellular function and protection in the cardiovascular system

ATP-sensitive potassium channels (K(ATP)) are widely distributed and present in a number of tissues including muscle, pancreatic beta cells and the brain. Their activity is regulated by adenine nucleotides, characteristically being activated by falling ATP and rising ADP levels. Thus, they link cellular metabolism with membrane excitability. Recent studies using genetically modified mice and genomic studies in patients have implicated K(ATP) channels in a number of physiological and pathological processes. In this review, we focus on their role in cellular function and protection particularly in the cardiovascular system.

Acute myocardial ischemia: cellular mechanisms underlying ST segment elevation

The electrocardiogram (ECG) is an essential tool for the diagnosis of acute myocardial ischemia in the emergency department, as well as for that of an evolving acute myocardial infarction (AMI). Changes in the surface ECG in leads whose positive poles face the ischemic region are known to be related to injury currents flowing across the boundaries between the ischemic and the surrounding normal myocardium. Although experimental studies have also shown an endocardium to epicardium differential sensitivity to the effect of acute ischemia, the important contribution of this transmural heterogeneous response to the changes observed in the surface ECG is less appreciated by the clinical cardiologist. This review briefly discusses our current knowledge regarding the electrophysiology of the ischemic myocardium focusing primarily on the electrophysiologic changes underlying the ECG alterations observed at the onset of a transmural AMI.

Are users of sulphonylureas at the time of an acute coronary syndrome at risk of poorer outcomes?

AIMS

Adenosine triphosphate sensitive potassium (K(ATP)) channel activity is cardioprotective during ischaemia. One of the purported mechanisms for sulphonylurea adverse effects is through inhibition of these channels. The purpose of this study is to examine whether patients using K(ATP) channel inhibitors at the time of an acute coronary syndrome are at greater risk of death or heart failure (HF) than those not exposed.

METHODS

Using linked administrative databases we identified all adults who had an acute coronary syndrome between April 2002 and October 2006 (n = 21 023).

RESULTS

Within 30 days of acute coronary syndrome, 5.3% of our cohort died and 15.6% were diagnosed with HF. Individuals with diabetes exhibited significantly higher risk of death (adjusted OR: 1.20, 95% CI: 1.03-1.40) and death or HF (aOR: 1.73, 95% CI: 1.59-1.89) than individuals without diabetes. However, there was no significantly increased risk of death (aOR: 1.00, 95% CI: 0.76-1.33) or death/HF (aOR: 1.06, 95% CI: 0.89-1.26) in patients exposed to K(ATP) channel inhibitors versus patients not exposed to K(ATP) channel inhibitors prior to their acute coronary syndrome.

CONCLUSIONS

Diabetes is associated with an increased risk of death or HF within 30 days of an acute coronary syndrome. However, we did not find any excess risk of death or HF associated with use of K(ATP) channel inhibitors at the time of an acute coronary syndrome, raising doubts about the hypothesis that sulphonylureas inhibit the cardioprotective effects of myocardial K(ATP) channels.

Transcriptome-guided functional analyses reveal novel biological properties and regulatory hierarchy of human embryonic stem cell-derived ventricular cardiomyocytes crucial for maturation

Human (h) embryonic stem cells (ESC) represent an unlimited source of cardiomyocytes (CMs); however, these differentiated cells are immature. Thus far, gene profiling studies have been performed with non-purified or non-chamber specific CMs. Here we took a combinatorial approach of using systems biology to guide functional discoveries of novel biological properties of purified hESC-derived ventricular (V) CMs. We profiled the transcriptomes of hESCs, hESC-, fetal (hF) and adult (hA) VCMs, and showed that hESC-VCMs displayed a unique transcriptomic signature. Not only did a detailed comparison between hESC-VCMs and hF-VCMs confirm known expression changes in metabolic and contractile genes, it further revealed novel differences in genes associated with reactive oxygen species (ROS) metabolism, migration and cell cycle, as well as potassium and calcium ion transport. Following these guides, we functionally confirmed that hESC-VCMs expressed I_KATP with immature properties, and were accordingly vulnerable to hypoxia/reoxygenation-induced apoptosis. For mechanistic insights, our coexpression and promoter analyses uncovered a novel transcriptional hierarchy involving select transcription factors (GATA4, HAND1, NKX2.5, PPARGC1A and TCF8), and genes involved in contraction, calcium homeostasis and metabolism. These data highlight novel expression and functional differences between hESC-VCMs and their fetal counterparts, and offer insights into the underlying cell developmental state. These findings may lead to mechanism-based methods for in vitro driven maturation.

KATP channels and cardiovascular disease: suddenly a syndrome

ATP-sensitive potassium (KATP) channels were first discovered in the heart 30 years ago. Reconstitution of KATP channel activity by coexpression of members of the pore-forming inward rectifier gene family (Kir6.1, KCNJ8, and Kir6.2 KCNJ11) with sulfonylurea receptors (SUR1, ABCC8, and SUR2, ABCC9) of the ABCC protein subfamily has led to the elucidation of many details of channel gating and pore properties. In addition, the essential roles of Kir6.x and SURx subunits in generating cardiac and vascular KATP(2) and the detrimental consequences of genetic deletions or mutations in mice have been recognized. However, despite this extensive body of knowledge, there has been a paucity of defined roles of KATP subunits in human cardiovascular diseases, although there are reports of association of a single Kir6.1 variant with the J-wave syndrome in the ECG, and 2 isolated studies have reported association of loss of function mutations in SUR2 with atrial fibrillation and heart failure. Two new studies convincingly demonstrate that mutations in the SUR2 gene are associated with Cantu syndrome, a complex multi-organ disorder characterized by hypertrichosis, craniofacial dysmorphology, osteochondrodysplasia, patent ductus arteriosus, cardiomegaly, pericardial effusion, and lymphoedema. This realization of previously unconsidered consequences provides significant insight into the roles of the KATP channel in the cardiovascular system and suggests novel therapeutic possibilities.

Electrocardiographic studies of romidepsin demonstrate its safety and identify a potential role for K(ATP) channel

PURPOSE

Romidepsin is a histone deacetylase inhibitor (HDI) approved for the treatment of both cutaneous and peripheral T-cell lymphoma (CTCL and PTCL). During development, a thorough assessment of cardiac toxicity was conducted.

EXPERIMENTAL DESIGN

A phase II single-agent nonrandomized study of romidepsin was conducted in patients with CTCL or PTCL who had progressed after at least 1 prior systemic therapy.

RESULTS

Results for the first 42 patients enrolled on the NCI 1312 phase II study of romidepsin in CTCL or PTCL showed no cardiac toxicity based on serial electrocardiograms (ECG), troponins, and MUGA scans/echocardiograms. The cardiac assessments reported herein confirm the safety of romidepsin among 131 enrolled patients, while supporting a role for electrolyte replacement. Heart rate increased an average 11 bpm following romidepsin infusion; there was no evidence of increased arrhythmia. Criteria for potassium/magnesium replacement were met before 55% of 1365 romidepsin doses; an association with hypoalbuminemia was confirmed. We propose a mechanism for ST segment flattening and depression, the most common ECG abnormalities observed: HDI-induced alteration of the activity or expression of KATP channels. In addition, examination of the variants of the active transporter of romidepsin, ABCB1, showed a trend toward smaller heart rate changes in the peri-infusion period among wild-type than variant diplotypes.

CONCLUSIONS

We conclude that in the context of appropriate attention to electrolyte levels, the data support the cardiac safety of romidepsin.

Promoter DNA methylation regulates murine SUR1 (Abcc8) and SUR2 (Abcc9) expression in HL-1 cardiomyocytes

Two mammalian genes encode the SURx (SUR1, Abcc8 and SUR2, Abcc9) subunits that combine with Kir6.2 (Kcnj11) subunits to form the ATP-sensitive potassium (KATP) channel in cardiac myocytes. Different isoform combinations endow the channel with distinct physiological and pharmacological properties, and we have recently reported that the molecular composition of sarcolemmal KATP channels is chamber specific in the mouse heart. KATP channel composition is determined by what subunits are expressed in a cell or tissue. In the present study, we explore the role of CpG methylation in regulating SUR1 and SUR2 expression. In HL-1 cardiomyocytes, as in atrial myocytes, SUR1 expression is markedly greater than SUR2. Consistent with CpG methylation-dependent silencing of SUR2 expression, bisulfite sequencing of genomic DNA isolated from HL-1 cells demonstrates that 57.6% of the CpGs in the promoter region of the SUR2 gene are methylated, compared with 0.14% of the the CpG residues in the SUR1 sequence. Moreover, treatment with 10 µM 5-aza-2'-deoxycytidine (Aza-dC) significantly increased both the unmethylated fraction of the SUR2 CpG island and mRNA expression. However, we cannot rule out additional mechanisms of Aza-dC action, as Aza-dC also causes a decrease in SUR1 expression and lower doses of Aza-dC do not alter the unmethylated DNA fraction but do elicit a small increase in SUR2 expression. The conclusion that DNA methylation alone is not the only regulator of SUR subunit expression is also consistent with observations in native myocytes, where the CpG islands of both SUR genes are essentially unmethylated in both atrial and ventricular myocytes. Collectively, these data demonstrate the potential for CpG methylation to regulate SURx subunit expression and raises the possibility that regulated or aberrant CpG methylation might play a role in controlling channel structure and function under different physiological conditions or different species.

Treatment for ST-elevation myocardial infarction--bronchoscopy!

ST elevation is usually treated in cardiac catheterization laboratory with an aim for myocardial salvage by restoration of adequate coronary blood flow enhancing both early and long-term survival. Maximum benefit is achieved if therapy is initiated in the first hour after treatment onset, thus ushering the concept of door-to-balloon time. We present an interesting case of a patient whose ST elevation resolved after bronchoscopy for a lung whiteout.

Extracellular proton depression of peak and late Na⁺ current in the canine left ventricle

Cardiac ischemia reduces excitability in ventricular tissue. Acidosis (one component of ischemia) affects a number of ion currents. We examined the effects of extracellular acidosis (pH 6.6) on peak and late Na(+) current (I(Na)) in canine ventricular cells. Epicardial and endocardial myocytes were isolated, and patch-clamp techniques were used to record I(Na). Action potential recordings from left ventricular wedges exposed to acidic Tyrode solution showed a widening of the QRS complex, indicating slowing of transmural conduction. In myocytes, exposure to acidic conditions resulted in a 17.3 ± 0.9% reduction in upstroke velocity. Analysis of fast I(Na) showed that current density was similar in epicardial and endocardial cells at normal pH (68.1 ± 7.0 vs. 63.2 ± 7.1 pA/pF, respectively). Extracellular acidosis reduced the fast I(Na) magnitude by 22.7% in epicardial cells and 23.1% in endocardial cells. In addition, a significant slowing of the decay (time constant) of fast I(Na) was observed at pH 6.6. Acidosis did not affect steady-state inactivation of I(Na) or recovery from inactivation. Analysis of late I(Na) during a 500-ms pulse showed that the acidosis significantly reduced late I(Na) at 250 and 500 ms into the pulse. Using action potential clamp techniques, application of an epicardial waveform resulted in a larger late I(Na) compared with when an endocardial waveform was applied to the same cell. Acidosis caused a greater decrease in late I(Na) when an epicardial waveform was applied. These results suggest acidosis reduces both peak and late I(Na) in both cell types and contributes to the depression in cardiac excitability observed under ischemic conditions.

Characterization of an ATP-sensitive K(+) channel in rat carotid body glomus cells

Carotid body glomus (CB) cells express different types of K(+) channels such as TASK, BK, and Kv channels, and hypoxia has been shown to inhibit these channels. Here we report the presence of a ∼72-pS channel that has not been described previously in CB cells. In cell-attached patches with 150 mM K(+) in the pipette and bath solutions, TASK-like channels were present (∼15 and ∼36-pS). After formation of inside-out patches, a 72-pS channel became transiently active in ∼18% of patches. The 72-pS channel was K(+)-selective, inhibited by 2-4 mM ATP and 10-100 μM glybenclamide. The 72-pS channel was observed in CB cells isolated from newborn, 2-3 week and 10-12 week-old rats. Reverse transcriptase-PCR and immunocytochemistry showed that Kir6.1, Kir6.2, SUR1 and SUR2 were expressed in CB glomus cells as well as in non-glomus cells. Acute hypoxia (∼15 mmHg O(2)) inhibited TASK-like channels but failed to activate the 72-pS channel in cell-attached CB cells. K(+) channel openers (diazoxide, pinacidil, levcromakalim), sodium cyanide and removal of extracellular glucose also did not activate the 72-pS channel in the cell-attached state. The hypoxia-induced elevation of intracellular [Ca(2+)] was unchanged by glybenclamide or diazoxide. NaCN-induced increase in [Ca(2+)] was not affected by 10 μM glybenclamide but inhibited by 100 μM glybenclamide. Acute glucose deprivation did not elevate [Ca(2+)] in the presence or absence of glybenclamide. These results show that an ATP-sensitive K(+) channel is expressed in the plasma membrane of CB cells, but is not activated by short-term metabolic inhibition. The functional relevance of the 72-pS channel remains to be determined.

Automaticity in acute ischemia: bifurcation analysis of a human ventricular model

Acute ischemia (restriction in blood supply to part of the heart as a result of myocardial infarction) induces major changes in the electrophysiological properties of the ventricular tissue. Extracellular potassium concentration ([K(o)(+)]) increases in the ischemic zone, leading to an elevation of the resting membrane potential that creates an "injury current" (I(S)) between the infarcted and the healthy zone. In addition, the lack of oxygen impairs the metabolic activity of the myocytes and decreases ATP production, thereby affecting ATP-sensitive potassium channels (I(Katp)). Frequent complications of myocardial infarction are tachycardia, fibrillation, and sudden cardiac death, but the mechanisms underlying their initiation are still debated. One hypothesis is that these arrhythmias may be triggered by abnormal automaticity. We investigated the effect of ischemia on myocyte automaticity by performing a comprehensive bifurcation analysis (fixed points, cycles, and their stability) of a human ventricular myocyte model [K. H. W. J. ten Tusscher and A. V. Panfilov, Am. J. Physiol. Heart Circ. Physiol. 291, H1088 (2006)] as a function of three ischemia-relevant parameters [K(o)(+)], I(S), and I(Katp). In this single-cell model, we found that automatic activity was possible only in the presence of an injury current. Changes in [K(o)(+)] and I(Katp) significantly altered the bifurcation structure of I(S), including the occurrence of early-after depolarization. The results provide a sound basis for studying higher-dimensional tissue structures representing an ischemic heart.

Muscle KATP channels: recent insights to energy sensing and myoprotection

ATP-sensitive potassium (K(ATP)) channels are present in the surface and internal membranes of cardiac, skeletal, and smooth muscle cells and provide a unique feedback between muscle cell metabolism and electrical activity. In so doing, they can play an important role in the control of contractility, particularly when cellular energetics are compromised, protecting the tissue against calcium overload and fiber damage, but the cost of this protection may be enhanced arrhythmic activity. Generated as complexes of Kir6.1 or Kir6.2 pore-forming subunits with regulatory sulfonylurea receptor subunits, SUR1 or SUR2, the differential assembly of K(ATP) channels in different tissues gives rise to tissue-specific physiological and pharmacological regulation, and hence to the tissue-specific pharmacological control of contractility. The last 10 years have provided insights into the regulation and role of muscle K(ATP) channels, in large part driven by studies of mice in which the protein determinants of channel activity have been deleted or modified. As yet, few human diseases have been correlated with altered muscle K(ATP) activity, but genetically modified animals give important insights to likely pathological roles of aberrant channel activity in different muscle types.

In vivo studies of Scn5a+/- mice modeling Brugada syndrome demonstrate both conduction and repolarization abnormalities

Objectives

We investigate the extent to which the electrocardiographic (ECG) properties of intact Scn5a+/− mice reproduce the corresponding clinical Brugada syndrome phenotype and use this model to investigate the role of conduction and repolarization abnormalities in the arrhythmogenic mechanism.

Methods and Results

The ECGs were obtained from anesthetized wild-type and Scn5a+/− mice, before and after administration of the known pro- and antiarrhythmic agents flecainide and quinidine. The ECG intervals were measured and their dispersions calculated. Scn5a+/− hearts showed ventricular arrhythmias, ST elevation, and conduction disorders including increased QT dispersion, accentuated by flecainide. Quinidine did not cause ventricular arrhythmias but exerted variable effects on ST segments and worsened conduction abnormalities.

Conclusions

The ECG features in an Scn5a+/− mouse establish it as a suitable model for Brugada syndrome and demonstrate abnormal conduction and repolarization phenomena. Altered QT dispersion, taken to indicate increased transmural repolarization gradients, may be useful in clinical risk stratification.