TQ-ST segment mapping: critical review and analysis of current concepts

Tipping the scales of understanding: An engineering approach to design and implement whole-body cardiac electrophysiology experimental models

The study of cardiac electrophysiology is built on experimental models that span all scales, from ion channels to whole-body preparations. Novel discoveries made at each scale have contributed to our fundamental understanding of human cardiac electrophysiology, which informs clinicians as they detect, diagnose, and treat complex cardiac pathologies. This expert review describes an engineering approach to developing experimental models that is applicable across scales. The review also outlines how we applied the approach to create a set of multiscale whole-body experimental models of cardiac electrophysiology, models that are driving new insights into the response of the myocardium to acute ischemia. Specifically, we propose that researchers must address three critical requirements to develop an effective experimental model: 1) how the experimental model replicates and maintains human physiological conditions, 2) how the interventions possible with the experimental model capture human pathophysiology, and 3) what signals need to be measured, at which levels of resolution and fidelity, and what are the resulting requirements of the measurement system and the access to the organs of interest. We will discuss these requirements in the context of two examples of whole-body experimental models, a closed chest in situ model of cardiac ischemia and an isolated-heart, torso-tank preparation, both of which we have developed over decades and used to gather valuable insights from hundreds of experiments.

Cardioprotective Potential of Aqueous Extract of Fumaria indica on Isoproterenol-Induced Myocardial Infarction in SD Rats

Ischemic heart disease (IHD) treatments and preventions by using plant extract and its phytochemical constituents have achieved considerable attention globally due to its cardioprotective effects. This study is aimed at investigating the cardioprotective and vascular effects of Fumaria indica (F. indica) crude extract on isoproterenol- (ISO-) induced myocardial infarction (MI) in Sprague-Dawley (SD) rats. Rats treated with isoproterenol (85 mg/kg, s.c), administered. Twice at an interval of 24 h showed a significant ST-segment elevation in ECG, edema, and necrosis in histopathology and also in troponin I (cTnI), creatine phosphokinase (CPK), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST). Pretreatment with F. indica (10, 30, and 100 mg/kg, p.o) for 21 days significantly reversed the effects of isoproterenol-induced ischemic changes in the ECG, levels of cTnI, CPK, LDH, and AST, and histopathological changes. In isolated rat atrial strips, F. indica induced negative chronotropic and inotropic effects which were not affected by pretreatment with atropine, excluding role of cardiac muscarinic receptors. Cumulative addition of the extract induced a vasorelaxant effect on phenylephrine-evoked contractions in isolated rat aortic rings, which remained unchanged when challenged with _L-NAME, excluding role of endothelial NO. However, extract of F. indica concentration dependently reversed contractions evoked with high K⁺, indicating calcium entry blocking effect. In conclusion, the F. indica extract is a cardioprotective remedy that ameliorates the isoproterenol-induced cardiotoxic effects and reverses cardiac ischemia, and the calcium antagonistic effect might be of useful in the treatment of MI.

Ethyl pyruvate attenuates isoproterenol-induced myocardial infarction in rats: Insight to TNF-α-mediated apoptotic and necroptotic signaling interplay

The current study investigated the prophylactic effect of ethyl pyruvate (EP) in Isoproterenol (ISO) - induced myocardial infarction (MI). Ethyl pyruvate (EP) was given at a dose of 100 mg/kg i.p for 7 days, while isoproterenol (ISO) was administered at a dose of 10 mg/kg s.c. on the 6th and 7th days to induce MI. All parameters were assessed 24 and 48 h following treatment. Interestingly, EP pre-treatment significantly improved ISO-induced hemodynamic alterations and remarkably ameliorated serum levels of cardiac injury markers, Cardiac Troponin I (cTnI) and Cardiac Creatine Kinase (CK-MB). Also, EP notably suppressed levels of oxidative stress markers, total antioxidants (TAO) and malondialdehyde (MDA) as compared to ISO-treated group. Cardioprotective effects of EP were confirmed by histopathological examination. Moreover, EP remarkably attenuated ISO-induced elevation in Tumor Necrosis Factor Alpha (TNF-α) and Nuclear factor kappa-B p65 (NF-κB) expression, along with Interleukin-6 (IL-6), Monocyte chemoattractant protein 1 (MCP-1) and Inducible nitric oxide synthase (i-NOS) levels. Also, EP significantly diminished expression of apoptotic markers; caspase 8, cleaved caspase 3 and apoptotic regulator; cellular FLICE-like inhibitory protein (cFLIP). Finally, EP notably mitigated necroptotic mediators, phosphorylated receptor-interacting serine/threonine protein kinase 1 and 3 (p-RIPK1 and p-RIPK3), phosphorylated mixed lineage kinase domain-like protein (p-MLKL) and heat shock protein 70 (HSP 70) expression as compared to the ISO-treated group. Our study was the first to investigate the effect of EP on the necroptotic signaling. Taken together, EP conferred its cardioprotective effect against ISO-induced MI partially through mitigation of TNF-α and its downstream inflammatory, apoptotic and necroptotic signaling pathways.

Transient recovery of epicardial and torso ST-segment ischemic signals during cardiac stress tests: A possible physiological mechanism

BACKGROUND

Acute myocardial ischemia has several characteristic ECG findings, including clinically detectable ST-segment deviations. However, the sensitivity and specificity of diagnosis based on ST-segment changes are low. Furthermore, ST-segment deviations have been shown to be transient and spontaneously recover without any indication the ischemic event has subsided.

OBJECTIVE

Assess the transient recovery of ST-segment deviations on remote recording electrodes during a partial occlusion cardiac stress test and compare them to intramyocardial ST-segment deviations.

METHODS

We used a previously validated porcine experimental model of acute myocardial ischemia with controllable ischemic load and simultaneous electrical measurements within the heart wall, on the epicardial surface, and on the torso surface. Simulated cardiac stress tests were induced by occluding a coronary artery while simultaneously pacing rapidly or infusing dobutamine to stimulate cardiac function. Postexperimental imaging created anatomical models for data visualization and quantification. Markers of ischemia were identified as deviations in the potentials measured at 40% of the ST-segment. Intramural cardiac conduction speed was also determined using the inverse gradient method. We assessed changes in intramyocardial ischemic volume proportion, conduction speed, clinical presence of ischemia on remote recording arrays, and regional changes to intramyocardial ischemia. We defined the peak deviation response time as the time interval after onset of ischemia at which maximum ST-segment deviation was achieved, and ST-recovery time was the interval when ST deviation returned to below thresholded of ST elevation.

RESULTS

In both epicardial and torso recordings, the peak ST-segment deviation response time was 4.9±1.1 min and the ST-recovery time was approximately 7.9±2.5 min, both well before the termination of the ischemic stress. At peak response time, conduction speed was reduced by 50% and returned to near baseline at ST-recovery. The overall ischemic volume proportion initially increased, on average, to 37% at peak response time; however, it recovered to only 30% at the ST-recovery time. By contrast, the subepicardial region of the myocardial wall showed 40% ischemic volume at peak response time and recovered much more strongly to 25% as epicardial ST-segment deviations returned to baseline.

CONCLUSION

Our data show that remote ischemic signal recovery correlates with a recovery of the subepicardial myocardium, whereas subendocardial ischemic development persists.

Utility of a Smartphone Based System (cvrPhone) to Predict Short-term Arrhythmia Susceptibility

Repolarization alternans (RA) has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death. We developed a 12-lead, blue-tooth/Smart-Phone (Android) based electrocardiogram (ECG) acquisition and monitoring system (cvrPhone), and an application to estimate RA, in real-time. In in-vivo swine studies (N = 17), 12-lead ECG signals were recorded at baseline and following coronary artery occlusion. RA was estimated using the Fast Fourier Transform (FFT) method using a custom developed algorithm in JAVA. Underlying ischemia was detected using a custom developed ischemic index. RA from each lead showed a significant (p < 0.05) increase within 1 min of occlusion compared to baseline (n = 29). Following myocardial infarction, spontaneous ventricular tachycardia episodes (n = 4) were preceded by significant (p < 0.05) increase of RA prior to the onset of the tachy-arrhythmias. Similarly, the ischemic index exhibited a significant increase following myocardial infarction (p < 0.05) and preceding a tachy-arrhythmic event. In conclusion, RA can be effectively estimated using surface lead electrocardiograms by analyzing beat-to-beat variability in ECG morphology using a smartphone based platform. cvrPhone can be used to detect myocardial ischemia and arrhythmia susceptibility using a user-friendly, clinically acceptable, mobile platform.

Summation and Cancellation Effects on QRS and ST-Segment Changes Induced by Simultaneous Regional Myocardial Ischemia

Simultaneous ischemia in two myocardial regions is a potentially lethal clinical condition often unrecognized whose corresponding electrocardiographic (ECG) patterns have not yet been characterized. Thus, this study aimed to determine the QRS complex and ST-segment changes induced by concurrent ischemia in different myocardial regions elicited by combined double occlusion of the three main coronary arteries. For this purpose, 12 swine were randomized to combination of 5-min single and double coronary artery occlusion: Group 1: left Circumflex (LCX) and right (RCA) coronary arteries (n = 4); Group 2: left anterior descending artery (LAD) and LCX (n = 4) and; Group 3: LAD and RCA (n = 4). QRS duration and ST-segment displacement were measured in 15-lead ECG. As compared with single occlusion, double LCX+RCA blockade induced significant QRS widening of about 40 ms in nearly all ECG leads and magnification of the ST-segment depression in leads V1-V3 (maximal 228% in lead V3, p < 0.05). In contrast, LAD+LCX or LAD+RCA did not induce significant QRS widening and markedly attenuated the ST-segment elevation in precordial leads (maximal attenuation of 60% in lead V3 in LAD+LCX and 86% in lead V5 in LAD+RCA, p < 0.05). ST-segment elevation in leads V7-V9 was a specific sign of single LCX occlusion. In conclusion, concurrent infero-lateral ischemia was associated with a marked summation effect of the ECG changes previously elicited by each single ischemic region. By contrast, a cancellation effect on ST-segment changes with no QRS widening was observed when the left anterior descending artery was involved.

Mangifera indica L. leaf extract alleviates doxorubicin induced cardiac stress

AIM

The study was undertaken to evaluate the cardioprotective effect of the alcoholic leaf extract of Mangifera indica L. against cardiac stress caused by doxorubicin (DOX).

MATERIALS AND METHODS

Rats were treated with 100 mg/kg of M. indica leaf extract (MILE) in alone and interactive groups for 21 days. Apart from the normal and MILE control groups, all the groups were subjected to DOX (15 mg/kg, i.p.) toxicity for 21 days and effects of different treatments were analyzed by changes in serum biomarkers, tissue antioxidant levels, electrocardiographic parameters, lipid profile, and histopathological evaluation.

RESULTS

The MILE treated group showed decrease in serum biomarker enzyme levels and increase in tissue antioxidants levels. Compared to DOX control group, MILE treated animals showed improvement in lipid profile, electrocardiographic parameters, histological score, and mortality.

CONCLUSION

These findings clearly suggest the protective role of alcoholic leaf extract of M. indica against oxidative stress induced by DOX.

A novel method to capture the onset of dynamic electrocardiographic ischemic changes and its implications to arrhythmia susceptibility

Background

This study investigates the hypothesis that morphologic analysis of intracardiac electrograms provides a sensitive approach to detect acute myocardial infarction or myocardial infarction‐induced arrhythmia susceptibility. Large proportions of irreversible myocardial injury and fatal ventricular tachyarrhythmias occur in the first hour after coronary occlusion; therefore, early detection of acute myocardial infarction may improve clinical outcomes.

Methods and Results

We developed a method that uses the wavelet transform to delineate electrocardiographic signals, and we have devised an index to quantify the ischemia‐induced changes in these signals. We recorded body‐surface and intracardiac electrograms at baseline and following myocardial infarction in 24 swine. Statistically significant ischemia‐induced changes after the initiation of occlusion compared with baseline were detectable within 30 seconds in intracardiac left ventricle (P<0.0016) and right ventricle–coronary sinus (P<0.0011) leads, 60 seconds in coronary sinus leads (P<0.0002), 90 seconds in right ventricle leads (P<0.0020), and 360 seconds in body‐surface electrocardiographic signals (P<0.0022). Intracardiac leads exhibited a higher probability of detecting ischemia‐induced changes than body‐surface leads (P<0.0381), and the right ventricle–coronary sinus configuration provided the highest sensitivity (96%). The 24‐hour ECG recordings showed that the ischemic index is statistically significantly increased compared with baseline in lead I, aVR, and all precordial leads (P<0.0388). Finally, we showed that the ischemic index in intracardiac electrograms is significantly increased preceding ventricular tachyarrhythmic events (P<0.0360).

Conclusions

We present a novel method that is capable of detecting ischemia‐induced changes in intracardiac electrograms as early as 30 seconds following myocardial infarction or as early as 12 minutes preceding tachyarrhythmic events.

ST-segment deviation behavior during acute myocardial ischemia in opposite ventricular regions: observations in the intact and perfused heart

BACKGROUND

Acute myocardial ischemia in opposite regions may attenuate ST-segment changes, but whether this effect is expressed differently in extracardiac compared to direct intramyocardial recordings is not well known.

OBJECTIVE

The purpose of this study was to characterize ST-segment changes induced by opposite ischemic regions in intact and isolated perfused pig hearts.

METHODS

Left anterior descending (LAD) and right coronary arteries (RCA) were occluded in 7 closed chest pigs and in 5 isolated pig hearts. ST-segment changes were analyzed in 12-lead ECG and in local extracellular electrograms.

RESULTS

Isolated LAD or RCA occlusion induced maximal ST-segment elevation in leads V4 (0.84 ± 0.30 mV, P = .003) and III (0.16 ± 0.11 mV, P = .04), respectively. RCA occlusion also induced reciprocal ST-segment depression maximal in lead V4 (-0.40 ± 0.16 mV, P = .005). Simultaneous LAD and RCA occlusion reduced ST-segment elevation by about 60% and blunted reciprocal ST-segment changes. Reperfusion of 1 of the 2 occluded arteries induced immediate regional reversion of ST-segment elevation with concurrent beat-to-beat re-elevation in the opposite ischemic region and reappearance of reciprocal ST-segment changes. In the isolated heart, single LAD or RCA ligature induced regional transmural ST-segment elevation that was maximal in endocardial electrograms with no appreciable reciprocal ST-segment depression. Simultaneous LAD and RCA ligature reduced ST-segment elevation by about 30% with no appreciable re-elevation after 1-vessel selective reperfusion.

CONCLUSION

Acute myocardial ischemia in opposite ventricular regions attenuated ST-segment elevation and blunted reciprocal depression in conventional ECG leads but not in direct local myocardial electrograms.

Cardioprotective potential of Korean Red Ginseng extract on isoproterenol-induced cardiac injury in rats

The present study was designed to investigate the cardioprotective effects of Korean Red Ginseng extract (KRG) on isoproterenol (ISO)-induced cardiac injury in rats, particularly in regards to electrocardiographic changes, hemodynamics, cardiac function, serum cardiac enzymes, components of the myocardial antioxidant defense system, as well as inflammatory markers and histopathological changes in heart tissue. ISO (150 mg/kg, subcutaneous, two doses administered at 24-hour intervals) treatment induced significant decreases in P waves and QRS complexes (p<0.01), as well as a significant increase in ST segments. Moreover, ISO-treated rats exhibited decreases in left-ventricular systolic pressure, maximal rate of developed left ventricular pressure (+dP/dt_max) and minimal rate of developed left ventricular pressure (−dP/dt_max), in addition to significant increases in lactate dehydrogenase, aspartate transaminase, alanine transaminase and creatine kinase activity. Heart rate, however, was not significantly altered. And the activities of superoxide dismutase, catalase and glutathione peroxidase were decreased, whereas the activity of malondialdehyde was increased in the ISO-treated group. ISO-treated group also showed increased caspase-3 level, release of inflammatory markers and neutrophil infiltration in heart tissue. KRG pretreatment (250 and 500 mg/kg, respectively) significantly ameliorated almost all of the parameters of heart failure and myocardial injury induced by ISO. The protective effect of KRG on ISO-induced cardiac injury was further confirmed by histopathological study. In this regard, ISO treatment induced fewer morphological changes in rats pretreated with 250 or 500 mg/kg of KRG. Compared with the control group, all indexes in rats administered KRG (500 mg/kg) alone were unaltered (p>0.05). Our results suggest that KRG significantly protects against cardiac injury and ISO-induced cardiac infarction by bolstering antioxidant action in myocardial tissue.

Combined effects of quercetin and atenolol in reducing isoproterenol-induced cardiotoxicity in rats: possible mediation through scavenging free radicals

In this investigation, combined effects of quercetin and atenolol in the regulation of isoproterenol (ISO)-induced cardiotoxicity have been evaluated in rats. While ISO administration increased the levels of serum creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH) and glutamate pyruvate transaminase (SGPT) as well as cardiac malondialdehyde (MDA); it reduced the activities of superoxide dismutase, catalase, glutathione peroxidase and the level of reduced glutathione. ISO-induced rats also exhibited ST-segment elevation and tachycardia. Oral administration of atenolol (6 mg/kg) and quercetin (5 mg/kg), along with ISO (5 mg/kg, subcutaneously) every day for 10 days markedly reduced the serum CK-MB, LDH and SGPT levels. Concomitantly the test drugs improved the status of antioxidative enzymes, decreased the cardiac MDA and nearly normalized the electrocardiogram. Electron paramagnetic resonance study also revealed a decrease in 5,5'-dimethyl-1-pyroline-N-oxide-hydroxyl radicals signal intensity when atenolol and quercetin were administered together to ISO-treated rats. In conclusion, the combined treatment of atenolol and quercetin appears to produce a better cardioprotective effect in ISO-induced animals as compared to their individual treatments, and possibly the beneficial actions are associated with the free radical scavenging action of quercetin.

Cardioprotective effect of methanolic extract of Ixora coccinea Linn. leaves on doxorubicin-induced cardiac toxicity in rats

OBJECTIVES

To investigate the effect of methanolic extract of Ixora coccinea Linn. (MEIC) leaves against doxorubicin-induced cardiac toxicity in rats.

MATERIAL AND METHODS

Albino Wistar rats were pretreated with the methanolic extract of Ixora coccinea Linn. leaves (200 and 400 mg/kg, orally) for 1 week followed with the simultaneous treatment with doxorubicin (cumulative dose of 15 mg/kg in six divided doses for 2 weeks) along with the extracts for the next 14 days. On the 22(nd) day hemodynamic parameters such as blood pressure and ECG were recorded. Biochemical study including biomarkers like creatine kinase - MB (CK - MB), lactate dehydrogenase (LDH), SGOT and SGPT, tissue antioxidant markers viz. catalase (CAT), superoxide dismutase (SOD) and extent of lipid peroxidation viz. malondialdehyde (MDA) was estimated. Histopathology of heart was also done to assess the cardioprotective effect.

RESULTS

Pretreatment with MEIC significantly reduced (P<0.01) the ST segment elevation and also maintained the BP (P<0.01) close to normal. The MEIC significantly reduced the elevated level of biomarkers like CK - MB, LDH, SGOT, SGPT (P<0.01) near to normal, the MEIC also increased the tissue antioxidant markers viz. CAT, SOD and decreased the level of MDA (P<0.01) in cardiac tissue by dose-dependant manner. The histopathology of heart also further confirmed the cardioprotection provided by the methanolic extract of Ixora coccinea Linn. leaves.

CONCLUSION

The results suggest a cardioprotective effect of Ixora coccinea Linn. leaves due to its antioxidant properties.

Ellagic acid ameliorates isoproterenol induced oxidative stress: Evidence from electrocardiological, biochemical and histological study

The present study was designed to evaluate the cardioprotective effects of ellagic acid against isoproterenol induced myocardial infarction in rats by studying electrocardiography, blood pressure, cardiac markers, lipid peroxidation, antioxidant defense system and histological changes. Male Wistar rats were treated orally with ellagic acid (7.5 and 15mg/kg) daily for a period of 10 days. After 10 days of pretreatment, isoproterenol (100mg/kg) was injected subcutaneously to rats at an interval of 24h for 2 days to induce myocardial infarction. Isoproterenol administered rats showed significant changes in the electrocardiogram pattern, arterial pressure, and heart rate. Isoproterenol-induced rats also showed significant (P<0.05) increase in the levels of serum troponin-I, creatine kinase, lactate dehydrogenase, C-reactive protein, plasma homocysteine, heart tissue thiobarbituric acid reactive substances and lipid hydro peroxides. The activities/levels of antioxidant system were decreased in isoproterenol-induced rats. The histopathological findings of the myocardial tissue evidenced myocardial damage in isoproterenol induced rats. The oral pretreatment of ellagic acid restored the pathological electrocardiographic patterns, regulated the arterial blood pressures and heart rate in the isoproterenol induced myocardial infarcted rats. The ellagic acid pretreatment significantly reduced the levels of biochemical markers, lipid peroxidation and significantly increased the activities/levels of the antioxidant system in the isoproterenol induced rats. An inhibited myocardial necrosis was evidenced by the histopathological findings in ellagic acid pretreated isoproterenol induced rats. Our study shows that oral pretreatment of ellagic acid prevents isoproterenol induced oxidative stress in myocardial infarction.

Cardioprotective effect of melatonin against isoproterenol induced myocardial infarction in rats: A biochemical, electrocardiographic and histoarchitectural evaluation

The present study was designed to investigate the cardioprotective effect of melatonin against isoproterenol induced myocardial infarction in rats by studying myocyte injury markers, antioxidant defense system, serum and heart lipid profile, inflammatory markers, electrocardiographic and histopathological changes. Male Sprague Dawley (SD) rats were randomly divided into four groups, namely control, melatonin, isoproterenol and melatonin+isoproterenol treated group. Melatonin treatment group received melatonin (10mg/kg/day, i.p.) for 7days. Myocardial infarction in rats was induced by isoproterenol administration (150mg/kg, s.c.) at an interval of 24h on 6th and 7th day. On 8th day ECG, gravimetric, biochemical and histopathological parameters were assessed. Isoproterenol administration showed changes in ECG pattern, including ST-segment elevation (diagnostic of myocardial infarction) increase in the serum levels of cardiac injury markers (creatine kinase-MB, lactate dehydrogenase, aspartate transaminase and alanine transaminase), decreased antioxidant defense system in the heart and altered lipid profile in the serum and heart. Isoproterenol administration also resulted in release of inflammatory markers and neutrophil infiltration along with histopathological changes. Melatonin pre-co-treatment prevented almost all the parameters of isoproterenol induced myocardial infarction in rats. The above finding was confirmed by the histopathological examination. In the baseline group (melatonin alone treated group) no significant change was observed. Results of the present study suggest that melatonin has a significant effect on the protection of the heart against isoproterenol induced myocardial infarction through maintaining endogenous antioxidant enzyme activities.

Cardioprotective potential of myricetin in isoproterenol-induced myocardial infarction in Wistar rats

The study aimed to evaluate the protective role of myricetin obtained from Vitis vinifera (Vitaceae) on heart rate, electrocardiographic (ECG) patterns, vascular reactivity to catecholamines, cardiac marker enzymes, antioxidant enzymes together with morphological and histopathological changes in isoproterenol (ISO) induced myocardial infarction (MI) in male Wistar rats. Rats treated with isoproterenol (85 mg/kg, administered subcutaneously twice at an interval of 24 h) showed a significant increase in heart rate and ST elevation in ECG, and a significant increase in the levels of cardiac marker enzymes - lactate dehydrogenase (LDH), creatine kinase (CK) and aspartate aminotransferase (AST) in serum. Isoproterenol significantly reduced superoxide dismutase (SOD) and catalase (CAT) activity and increased vascular reactivity to various catecholamines. Pretreatment with myricetin (100 mg/kg, p.o. and 300 mg/kg, p.o.) for a period of 21 days significantly inhibited the effects of ISO on heart rate, levels of LDH, CK, AST, SOD, CAT, vascular reactivity changes and ECG patterns. Treatment with myricetin (100 mg/kg and 300 mg/kg) alone did not alter any of the parameters compared with vehicle treated Wistar rats. Myricetin treated animals showed a lesser degree of cellular infiltration in histopathological studies. Thus, myricetin (100 mg/kg and 300 mg/kg) ameliorates the cardiotoxic effects of isoproterenol and may be of value in the treatment of MI.

S-propargyl-cysteine protects both adult rat hearts and neonatal cardiomyocytes from ischemia/hypoxia injury: the contribution of the hydrogen sulfide-mediated pathway

In this study, we determined the cardioprotective effects of S-propargyl-cysteine (SPRC), a structural analog of S-allylcysteine (SAC), using in vivo models of acute myocardial infarction (MI) and in vitro hypoxic cardiomyocytes models. MI was created in rats by ligating the left anterior descending coronary artery. Plasma enzymes levels and cystathionine-gamma-lyase (CSE) activities were determined. Primary cultures of newborn rats' cardiomyocytes were injured by hypoxia for 6 h. Cell viabilities were measured with the thiazolyl blue assay. RT-PCR and western blot analysis revealed the expression of CSE in both models. The protective effects of SPRC were associated with an observed reduction in infarct size (20.8 +/- 2.4% vs. 36.0 +/- 1.3%), decreased plasma enzymes levels and reduced malondialdehyde levels when compared to the MI vehicle group (P < 0.05); cardiac function was also improved. SPRC increased CSE activity and plasma H2S concentration by 1.6-fold and 1.3-fold, respectively, in MI rats. Decreased cell viability (64.5 +/- 5.4%) in hypoxic cardiomyocytes could be rescued with use of SPRC (81.0 +/- 3.1%). Similarly, mRNA and protein expression of CSE were upregulated in the SPRC group. Treatment with the CSE inhibitor propargylglycine abolished the protective effects of SPRC. Our study provides novel evidence that SPRC is protective in myocardial infarctions via a H2S-related pathway.

Electrocardiographic criteria for predicting total occlusion of the proximal left anterior descending coronary artery in anterior wall acute myocardial infarction

BACKGROUND

Patients with occlusion of the left anterior descending coronary artery (LAD) proximal to both the first septal branch and the first diagonal branch may benefit most from early reperfusion therapy due to extensive area at risk.

HYPOTHESIS

The aim of the study was to examine whether 12-lead electrocardiograms (ECGs) in the acute phase of acute myocardial infarction (AMI) could identify total occlusion of the LAD proximal to both the first septal and the first diagonal branch.

METHODS

A 12-lead electrocardiogram was recorded on admission in 128 patients with anterior AMI within 12 h from symptom onset. Patients were divided into three groups according to the culprit lesion: 33 patients had total occlusion of the LAD proximal to both the first septal perforator and the first diagonal branch (Group P), in 51 it was proximal to either the first septal perforator or the first diagonal branch (Group D-a), and in 44 it was distal to both the first septal perforator and the first diagonal branch (Group D-b).

RESULTS

Sensitivity and specificity of a greater degree of ST-segment depression in lead III than that of ST-segment elevation in lead aVL were 85 and 95%, respectively, which was better than the results derived by all other ECG criteria (p< 0.001).

CONCLUSIONS

We conclude that a greater degree of ST-segment depression in lead III than that of ST-segment elevation in lead aVL is a useful predictor of proximal LAD occlusion in patients with anterior AMI.

ST-Segment Deviation Analysis of the Admission 12-Lead Electrocardiogram as an Aid to Early Diagnosis of Acute Myocardial Infarction With a Cardiac Magnetic Resonance Imaging Gold Standard

OBJECTIVES

The purpose of this study was to validate existing 12-lead electrocardiographic (ECG) ST-segment elevation myocardial infarction (STEMI) criteria in the diagnosis of acute myocardial infarction (AMI) and the application of similar ST-segment depression (STEMI-equivalent) criteria with contrast-enhanced cardiac magnetic resonance imaging (ceMRI) as the diagnostic gold standard.

BACKGROUND

The admission ECG is the cornerstone in the diagnosis of AMI, and ceMRI is a new diagnostic gold standard that can be used to validate existing and novel 12-lead ECG criteria.

METHODS

One hundred fifty-one consecutive patients with their first hospital admission for chest pain underwent ceMRI. The 116 patients without ECG confounding factors were included in this study, and AMI was confirmed in 58 (50%). The admission ECG was evaluated on the basis of the lead distribution of ST-segment deviation according to current American College of Cardiology/European Society of Cardiology (ACC/ESC) guidelines.

RESULTS

A sensitivity of 50% and specificity of 97% for AMI were achieved with the currently applied ST-segment elevation criteria. Consideration of ST-segment depression in addition to elevation increased sensitivity for detection of AMI from 50% to 84% (p < 0.0001) but only decreased specificity from 97% to 93% (p = 0.50). There were no significant differences in AMI location or size between patients meeting the 12-lead ACC/ESC ST-segment elevation criteria and those only meeting the ST-segment depression criteria.

CONCLUSIONS

In patients admitted to hospital with possible AMI, the consideration of both ST-segment elevation and depression in the standard 12 lead-ECG recording significantly increases the sensitivity for the detection of AMI with only a slight decrease in the specificity.

Thoughts about the abnormalities in the electrocardiogram of patients with acute myocardial infarction with emphasis on a more accurate method of interpreting ST-segment displacement: part I

The QRS, S-T, and T wave abnormalities produced by the usual myocardial infarction are discussed in Part I of this manuscript. The recent guidelines supplied by the ACC/AHA Practice Guidelines divide primary S-T segment displacement into S-T segment elevated myocardial infarction (STEMI) and non S-T segment elevated myocardial infarction (NSTEMI). Accordingly, the electrophysiologic mechanisms responsible for epicardial and subendocardial injury that produce the S-T segment abnormalities are discussed in this manuscript. In this regard, the author suggests that the Grant method of interpreting the 12 lead electrocardiogram, which uses basic principles and vector concepts, is a more accurate method of identifying epicardial injury and subendocardial injury than memorizing the rules provided by the guidelines. An electrocardiogram is shown to illustrate this point. In Addition, the author expresses his personal view that labeling an electrocardiogram as NSTEMI but not stating what is actually present in the tracing is a cumbersome method of communication. The author believes it is better communication to state what is present rather than to state what is not present. At best, the result of both assessments should be stated in the interpretation. Part II of the manuscript is devoted to a discussion as to why treatment with thrombolytic or percutaneous coronary intervention is more effective in patients whose electrocardiograms reveal epicardial injury than it is in patients whose electrocardiograms reveal subendocardial injury or no injury.

Combined effects of reduced connexin 43, depressed active generator properties and energetic stress on conduction disturbances in canine failing myocardium

To show that reductions in connexin43 (Cx43) can contribute, in association with electrophysiological alterations identified from unipolar recordings, to conduction disturbances in a realistic model of heart failure, canines were subjected to chronic rapid pacing (240/min for 4 weeks) and progressive occlusion of the left coronary circumflex artery (LCx) by an ameroid constrictor. Alterations identified from 191 epicardial recordings included abrupt activation delay, functional block, ST segment potential elevation, and reduced maximum negative slope (-dV/dt (max)). The LCx territory was divided into apical areas with depressed conduction velocity (LCx1: 0.06 +/- 0.04 m/s, mean +/- SD) and basal areas with relatively preserved conduction (LCx2: 0.28 +/- 0.01 m/s). Subepicardial Cx43 immunoblot measurements (percent of corresponding healthy heart measurements) were reduced in LCx1 ( approximately 40%) and LCx2 ( approximately 60%). In addition, -dV/dt (max) was significantly depressed (-3.8 +/- 3.3 mV/ms) and ST segment potential elevated (23.3 +/- 14.6 mV) in LCx1 compared to LCx2 (-9.5 +/- 3.4 mV/ms and 0.3 +/- 1.4 mV). Anisotropic conduction, Cx43 and ST segment potential measurements from the left anterior descending coronary artery territory, and interstitial collagen from all regions were similar to the healthy. Thus, moderate Cx43 reduction to "clinically relevant" levels can, in conjunction with regional energetic stress and depression of sarcolemmal active generator properties, provide a substrate for conduction disturbances.

Effect of clinical variables on the correlation between amount of ST elevation and myocardial scintigraphic perfusion defect during coronary occlusion

PURPOSE

We investigated if the correlation between the amount of ST elevation (STE) and myocardial ischemia could be altered by variables such as hypertension or body mass index (BMI).

METHODS

A 12-lead electrocardiogram and a technetium-99m tetrofosmin injection were performed during balloon coronary occlusion in 34 patients with single-vessel disease.

RESULTS

The sum of STE correlated with scintigraphic extent of ischemia (r = 0.441; P = .009), but this correlation improved significantly in men and patients with BMI of 28 kg/m2 or less and was highest in nonhypertensive patients (r = 0.763; P < .001). In contrast, it was poor in women and patients with BMI greater than 28 kg/m2 or arterial hypertension, being lowest in the latter subset (r = 0.110; P = .664). Moreover, 8 (80%) of 10 patients with extensive hypoperfusion but with low SigmaSTE (< or =20 mm) were hypertensive.

CONCLUSIONS

If confirmed by larger studies, electrocardiographic underestimation of transmural ischemia during coronary occlusion in patients with hypertension or increased BMI may lead to adjustments in STE criteria for reperfusion therapy.

S-allylcysteine ameliorates isoproterenol-induced cardiac toxicity in rats by stabilizing cardiac mitochondrial and lysosomal enzymes

This study was aimed to evaluate the preventive role of S-allylcysteine (SAC) on mitochondrial and lysosomal enzymes in isoproterenol (ISO)-induced rats. Male albino Wistar rats were pretreated with SAC (50, 100 and 150 mg/kg) daily for a period of 45 days. After the treatment period, ISO (150 mg/kg) was subcutaneously injected to rats at an interval of 24 h for two days. The activities of heart mitochondrial enzymes (isocitrate dehydrogenase, succinate dehydrogenase, malate dehydrogenase and alpha-ketoglutarate dehydrogenase) and respiratory chain enzymes (NADH dehydrogenase and cytochrome C oxidase) were decreased significantly (p<0.05) in ISO-induced rats. The activities of lysosomal enzymes (beta-glucuronidase, beta-N-acetyl glucosaminidase, beta-galactosidase, cathepsin-D and acid phosphatase) were increased significantly (p<0.05) in serum and heart of ISO-induced rats. Pretreatment with SAC (100 mg/kg and 150 mg/kg) for a period of 45 days increased significantly (p<0.05) the activities of mitochondrial and respiratory chain enzymes and decreased the activities of lysosomal enzymes significantly (p<0.05) in ISO-induced rats. Oral administration of SAC (50, 100 and 150 mg/kg) for a period of 45 days to normal rats did not show any significant (p<0.05) effect in all the parameters studied. The altered electrocardiogram (ECG) of ISO-treated rats was also restored to near normal by treatment with SAC (100 and 150 mg/kg). These results confirm the efficacy of SAC in alleviating ISO-induced cardiac damage.

Preventive effect of naringin on cardiac markers, electrocardiographic patterns and lysosomal hydrolases in normal and isoproterenol-induced myocardial infarction in Wistar rats

Diets rich in natural antioxidants are associated with reduced risk of heart diseases. This study was aimed to evaluate the preventive role of naringin on cardiac troponin T (cTnT), lactate dehydrogenase (LDH)-isoenzyme, cardiac marker enzymes, electrocardiographic (ECG)-patterns and lysosomal enzymes in isoproterenol (ISO)-induced myocardial infarction (MI) in male Wistar rats. Rats subcutaneously injected with ISO (85mg/kg) at an interval of 24h for 2 days showed a significant increase in the levels of cTnT, intensity of the bands of LDH-isoenzyme (LDH1 and LDH2) and the activities of cardiac marker enzymes such as creatine kinase-MB (CK-MB), creatine kinase (CK), LDH, aspartate transaminase (AST) and alanine transaminase (ALT) in serum with subsequent decrease in the activities of CK, LDH, AST and ALT in the heart and alterations in ECG-patterns. The activities of lysosomal enzymes (beta-glucuronidase, beta-N-acetyl glucosaminidase, beta-galactosidase, cathepsin-B and cathepsin-D) were increased significantly in serum and the heart of ISO-induced rats, but the activities of beta-glucuronidase and cathepsin-D were decreased significantly in the lysosomal fraction of the heart. Pretreatment with naringin (10, 20 or 40mg/kg) daily for a period of 56 days positively altered the levels of cTnT, intensity of the bands of the LDH1 and LDH2-isoenzyme and the activities of cardiac marker enzymes, ECG-patterns and lysosomal hydrolases in ISO-induced rats. Thus, naringin possess cardioprotective effect in ISO-induced MI in rats.

Mechanisms of ischemia-induced ST-segment changes

Many aspects of ischemia-induced changes in the electrocardiogram lack solid biophysical underpinnings although variations in ST segments form the predominant basis for diagnostic and monitoring of patients. This incomplete knowledge certainly plays a role in the poor performance of some forms of electrocardiogram-based detection and characterization of ischemia, especially when it is limited to the subendocardium. The focus of our recent studies has been to develop a comprehensive mechanistic model of the electrocardiographic effects of ischemia. The computational component of this model is based on highly realistic heart geometry with anisotropic fiber structure and allows us to assign ischemic action potentials to contiguous regions that can span a prescribed thickness of the ventricles. A separate, high-resolution model of myocardial tissue provides us with a means of setting electrical characteristics of the heart, including the status of gap junctional coupling between cells. The experimental counterpart of this model consists of dog hearts, either in situ or isolated and perfused with blood, in which we control coronary blood flow by means of a cannula and blood pump. By reducing blood flow through the cannula for various durations, we can replicate any phase of ischemia from hyper acute to early infarction. Based on the results of these models, there is emerging a mechanism of the electrocardiographic response to ischemia that depends strongly on the anisotropic conductivity of the myocardium. Ischemic injury currents flow across the boundary between healthy and ischemic tissue, but it is their interaction with local fiber orientation and the associated conductivity that generates secondary currents that determine epicardial ST-segment potentials. Results from experiments support qualitatively the findings of the simulations and underscore the role of myocardial anisotropy in electrocardiography.

The effect of simplifying assumptions in the bidomain model of cardiac tissue: application to ST segment shifts during partial ischaemia

In this study various electrical conductivity approximations used in bidomain models of cardiac tissue are considered. Comparisons are based on epicardial surface potential distributions arising from regions of subendocardial ischaemia situated within the cardiac tissue. Approximations studied are a single conductivity bidomain model, an isotropic bidomain model and equal and reciprocal anisotropy ratios both with and without fibre rotation. It is demonstrated both analytically and numerically that the approximations involving a single conductivity bidomain, an isotropic bidomain or equal anisotropy ratios (ignoring fibre rotation) results in identical epicardial potential distributions for all degrees of subendocardial ischaemia. This result is contrary to experimental observations. It is further shown that by assuming reciprocal anisotropy ratios, epicardial potential distributions vary with the degree of subendocardial ischaemia. However, it is concluded that unequal anisotropy ratios must be used to obtain the true character of experimental observations.

Mechanism for ST depression associated with contiguous subendocardial ischemia

INTRODUCTION

A mechanism for ST depression arising on the epicardial surface over the border between normal and ischemic tissue is proposed. Depression is caused by current flowing in a transmural loop that begins and ends at the lateral boundary between healthy and ischemic tissue and passes through the transmural boundary between healthy and ischemic tissue. The result is ST depression at the epicardium over the lateral boundary. The size and direction of current flow are dictated by differences in the magnitude and orientation of anisotropic conductivity between those boundaries.

METHODS AND RESULTS

Computer simulations verified and quantified the relationship between ST depression and conductivity differences. We used computer simulations based on an anatomically accurate, anisotropic model of canine ventricles and a bidomain representation of the effects of ischemia to verify the biophysical basis of this mechanism.

CONCLUSION

ST depression at the epicardium appears over a lateral boundary between healthy and ischemic tissue.

Spinal cord activation differentially modulates ischaemic electrical responses to different stressors in canine ventricles

Spinal cord stimulation (SCS) represents an acceptable treatment modality for patients with chronic angina pectoris refractory to standard therapy, but its mechanism of action remains unclear. To develop an experimental paradigm to study this issue, ameroid (AM) constrictors were implanted around the left circumflex coronary artery (LCx) in canines. Six weeks later, unipolar electrograms were recorded from 191 sites in the LCx territory in the open-chest, anesthetized state under basal pacing at 150 beats/min. We investigated the effect of SCS on ST segment displacements induced in the collateral-dependent myocardium in response to two stressors: (i) transient bouts of rapid ventricular pacing (TRP: 240/min for 1 min) and (ii) angiotensin II administered to right atrial neurons via their coronary artery blood supply. ST segment responses to TRP consisted of ST segment elevation in central areas of the LCx territory and ST depression at more peripheral areas. Such responses were unchanged when TRP was applied under SCS. Shortening of repolarization intervals in the metabolically compromised myocardium in response to TRP was also unaffected by SCS. In contrast, ST segment responses to intracoronary angiotensin II, which consisted of increased ST elevation, were attenuated by SCS in 6/8 preparations. The modulator effects of SCS were greatest at sites at which the greatest responses to angiotensin II occurred in the absence of SCS. These data indicate that spinal cord stimulation may attenuate the deleterious effects that stressors exert on the myocardium with reduced coronary reserve, particularly stressors associated with chemical activation of the intrinsic cardiac nervous system.

Linear furanocoumarin protects rat myocardium against lipidperoxidation and membrane damage during experimental myocardial injury

The antioxidant activity and the membrane effects of linear furanocoumarin marmesinin isolated from Aegle marmelose was evaluated during experimental myocardial injury. Isoproterenol (150 mg kg(-1) intraperitonially twice at an interval of 24 h) caused increase in the levels of serum marker enzymes via creatinekinase (CK), creatinekinase-MB (CK-MB) isoenzyme, lactatedehydrogenase (LDH) and lactatedehydrogenase isoenzyme (LDH1). It also produced electrocardiographic changes such as increased heart rate, reduced R amplitude and ST elevation. Marmesinin at a dose of 200 mg kg(-1), when administered orally, demonstrated a decrease in serum enzyme levels and restored the electrocardiographic changes towards normalcy. Myocardial injury was accompanied by the disintegration of lipidperoxides and the impairment of natural scavengers. Marmesinin oral treatment for 2 days before and during isoproterenol administration decreased the effect of lipidperoxidation. It was also shown to have a membrane stabilizing action by inhibiting the release of beta-glucuronidase from the subcellular fractions. Thus, linear furanocoumarin marmesinin could have the protective effect against the damage caused by experimental myocardial injury.

Myocardial electrical alteration in canine preparations with combined chronic rapid pacing and progressive coronary artery occlusion

Our objective was to create an animal preparation displaying long-term electrical alterations after chronic regional energetic stress without myocardial scarring. An Ameroid (AM) constrictor was implanted around the left circumflex coronary artery (LCx) 2 wk before chronic rapid ventricular pacing (CRP) was initiated at 240 beats/min for 4 wk (CRP-AM). Comparisons were made with healthy canines and canines with either AM or CRP. Unipolar electrograms were recorded from 191 sites in the LCx territory in open-chest, anesthetized animals during sinus rhythm and while pacing at 120–150 beats/min, with bouts of transient rapid pacing (TRP; 240/min). In CRP-AM and AM, ST segment elevation was identified at central sites and ST depression at peripheral sites, both increasing with TRP. In CRP-AM and CRP, the maximum negative slope of unipolar activation complexes was significantly depressed and activation-recovery intervals prolonged. Areas of inexcitability as well as irregular isocontour patterns displaying localized activation-recovery intervals shortening and gradients >20 ms between neighboring sites were identified in one-third of CRP-AM at slow rate, with increasing incidence and magnitude in response to TRP. In CRP-AM, programmed stimulation-induced marked conduction delay and block as well as polymorphic ventricular tachycardias, which stabilized into monomorphic tachycardias with the use of lidocaine or procainamide. Whole cell Na+ current and channel protein expression were reduced in CRP-AM and CRP. Despite complete constrictor closure, small areas of necrosis were detected in a minority of CRP-AM. Long-term electrical alterations and their exacerbation by TRP contribute to arrhythmia formation in collateral-dependent myocardium subjected to chronic tachycardic stress.

Sarpogrelate, a 5-HT2 Receptor Blocker, may Have a Preconditioning-Like Effect in Patients With Coronary Artery Disease

BACKGROUND

Sarpogrelate, a serotonin receptor blocker, increases collaterals via a platelet anti-aggregation effect and/or vasodilatation. However, a recent report showed a preconditioning effect of sarpogrelate that enhances the translocation of PKC-epsilon of cardiomyocytes, followed by opening of the mitochondrial K(ATP) channel via inhibition of serotonin release from platelets during ischemia, protecting against cellular injury in rabbit hearts without collaterals. The present study used a percutaneous coronary intervention (PCI) model to define the protective effect of sarpogrelate against ischemic injury and its mechanism in human coronary artery disease.

METHODS AND RESULTS

The study enrolled 20 patients with single vessel disease of 75% or 90% stenosis in the proximal left anterior descending (LAD) artery on coronary angiography (CAG). Patients were randomly divided into a control group (n=10) and a sarpogrelate group (n=10). The Delta STmax (maximum ST elevation) and Sigma ST (sum of ST elevation) on the 12-lead ECG recorded in the late stages (ie, 90 s and 120 s) after inflation were significantly smaller in the sarpogrelate group than in the controls. There was no significant difference in collaterals on the right and left CAG or between the 2 groups.

CONCLUSIONS

Sarpogrelate improves ischemic injury during PCI and may be related to a preconditioning-like mechanism rather than to stimulating collateral development.

Mechanisms of ST change in partial thickness ischemia

The origin of ST depression in ischemia remains poorly understood. The accepted source is of intracellular current flowing between the ischemic and non ischaemic muscle both in systole and diastole such that the AC recorded electrocardiogram shows ST elevation over the ischemic area. The difficulty comes with partial thickness ischemia where the body surface changes do not allow localisation of the ischemic region. In an animal model we have shown that the reason one cannot see the region on the body surface is that the epicardial distribution of ST segment is almost identical for partial thickness ischaemia in the left anterior descending coronary artery, (LAD) and circumflex coronary artery (Cx) territories. Dissection of the reasons for this finding has lead to 3 contributing factors. The first is the role of the right ventricular blood mass, the second the boundary between ischemia and normal and the third the presence of anisotropy and its contribution. In a block of myocardium with anisotropy included we have shown marked differences between the distributions depending on the anisotropy. We have also shown that the published values of conductivity for use in the bidomain model produce unacceptably disparate results.

The importance of anisotropy in modeling ST segment shift in subendocardial ischaemia

In this paper, a simple mathematical model of a slab of cardiac tissue is presented in an attempt to better understand the relationship between subendocardial ischaemia and the resulting epicardial potential distributions. The cardiac tissue is represented by the bidomain model where tissue anisotropy and fiber rotation have been incorporated with a view to predicting the epicardial surface potential distribution. The source of electric potential in this steady-state problem is the difference between plateau potentials in normal and ischaemic tissue, where it is assumed that ischaemic tissue has a lower plateau potential. Simulations with tissue anisotropy and no fiber rotation are also considered. Simulations are performed for various thicknesses of the transition region between normal and ischaemic tissue and for various sizes of the ischaemic region. The simulated epicardial potential distributions, based on an anisotropic model of the cardiac tissue, show that there are large potential gradients above the border of the ischaemic region and that there are dips in the potential distribution above the region of ischaemia. It could be concluded from the simulations that it would be possible to predict the region of subendocardial ischaemia from the epicardial potential distribution, a conclusion contrary to observed experimental data. Possible reasons for this discrepancy are discussed. In the interests of mathematical simplicity, isotropic models of the cardiac tissue are also considered, but results from these simulations predict epicardial potential distributions vastly different from experimental observations. A major conclusion from this work is that tissue anisotropy and fiber rotation must be included to obtain meaningful and realistic epicardial potential distributions.

Computing and visualizing electric potentials and current pathways in the thorax

The long-term goal of electrocardiography is to relate electric potentials on the body surface with activities in the heart. Many previously reported studies have focused on direct links between heart and body surface potentials. The goals of this study were first to validate computational methods of determining volume potentials and currents with high-resolution experimental measurements and then to use interactive visualization of thoracic currents to understand features of the electrocardiographic fields from measured cardiac sources. We developed both simulation and experimental studies based on a realistic shaped torso phantom containing an isolated, perfused dog heart. Interventions included atrial pacing, single pacing and simultaneously pacing at multiple locations on the ventricles. Simulated torso volume potentials closely matched measured potentials in the torso-tank preparation (mean correlation coefficients of 0.95). Simulation further provided a means of estimating the current field in the torso from the computed torso volume potentials and the local geometric and conductive properties of the medium. Applying these techniques to the torso electric fields under a variety of pacing conditions, we have further demonstrated that thoracic current can provide many insights into the relationship between heart surface potential and body surface potentials. Specifically, we have shown that geometric factors including cardiac source configuration and location play an important role in determining to what extent electric activity in the heart is directly visible on the body surface electrocardiogram. The computation and visualization toolkit we developed in this study to explore current fields associated with cardiac events may provide new insights into electrocardiology.