Detection Of Acute Myocardial Ischemia Research Articles

A Low-Power Single-Path Bio-Impedance Measurement System Using an Analog-to-Digital Converter for I/Q Demodulation.

In this paper, a low power single-path bio-impedance (Bio-Z) measurement system for early detection of acute myocardial ischemia is presented. The fully integrated system consists of a current source, an amplifier, and an analog-to-digital converter (ADC). The system utilizes the in-phase and quadrature (I/Q) components to obtain the real and imaginary parts of the tissue impedance. To achieve this goal, the ADC has been used to separate the I/Q components in addition to digitizing the samples. This can lead to power and silicon area reduction. The proposed circuit exploits the benefits of capacitively-coupled instrumentation amplifier, including inherent DC cancellation, low power, low noise, and high linearity and is implemented in 0.18 µm CMOS technology with a 1 V power supply. This system is designed and tested using a pseudo-sine 2 µAP-P current with a frequency of 1 kHz. The system can measure an input impedance that varies over a range from 0.03-7.5 kΩ with a resolution of 0.766 Ωrms while consuming 2 µW power from the supply. The operation of the system is also shown in the recording of impedance variation with respiration and heartbeat.

An initial exploration of subtraction electrocardiography to detect myocardial ischemia in the prehospital setting.

BackgroundIn the prehospital triage of patients presenting with symptoms suggestive of acute myocardial ischemia, reliable myocardial ischemia detection in the electrocardiogram (ECG) is pivotal. Due to large interindividual variability and overlap between ischemic and nonischemic ECG‐patterns, incorporation of a previous elective (reference) ECG may improve accuracy. The aim of the current study was to explore the potential value of serial ECG analysis using subtraction electrocardiography.MethodsSUBTRACT is a multicenter retrospective observational study, including patients who were prehospitally evaluated for acute myocardial ischemia. For each patient, an elective previously recorded reference ECG was subtracted from the ambulance ECG. Patients were classified as myocardial ischemia cases or controls, based on the in‐hospital diagnosis. The diagnostic performance of subtraction electrocardiography was tested using logistic regression of 28 variables describing the differences between the reference and ambulance ECGs. The Uni‐G ECG Analysis Program was used for state‐of‐the‐art single‐ECG interpretation of the ambulance ECG.ResultsIn 1,229 patients, the mean area‐under‐the‐curve of subtraction electrocardiography was 0.80 (95%CI: 0.77–0.82). The performance of our new method was comparable to single‐ECG analysis using the Uni‐G algorithm: sensitivities were 66% versus 67% (p‐value > .05), respectively; specificities were 80% versus 81% (p‐value > .05), respectively.ConclusionsIn our initial exploration, the diagnostic performance of subtraction electrocardiography for the detection of acute myocardial ischemia proved equal to that of state‐of‐the‐art automated single‐ECG analysis by the Uni‐G algorithm. Possibly, refinement of both algorithms, or even integration of the two, could surpass current electrocardiographic myocardial ischemia detection.

Reintroducing Heart Sounds for Early Detection of Acute Myocardial Ischemia in a Porcine Model - Correlation of Acoustic Cardiography With Gold Standard of Pressure-Volume Analysis.

BackgroundAcoustic cardiography is a hybrid technique that couples heart sounds recording with ECG providing insights into electrical-mechanical activity of the heart in an unsupervised, non-invasive and inexpensive manner. During myocardial ischemia hemodynamic abnormalities appear in the first minutes and we hypothesize a putative diagnostic role of acoustic cardiography for prompt detection of cardiac dysfunction for future patient management improvement.Methods and ResultsTen female Swiss large white pigs underwent permanent distal coronary occlusion as a model of acute myocardial ischemia. Acoustic cardiography analyses were performed prior, during and after coronary occlusion. Pressure-volume analysis was conducted in parallel as an invasive method of hemodynamic assessment for comparison. Similar systolic and diastolic intervals obtained with the two techniques were significantly correlated [Q to min dP/dt vs. Q to second heart sound (r2 = 0.9583, p < 0.0001), PV diastolic filling time vs. AC perfusion time (r2 = 0.9686, p < 0.0001)]. Indexes of systolic and diastolic impairment correlated with quantifiable features of heart sounds [Tau vs. fourth heart sound Display Value (r2 = 0.2721, p < 0.0001) cardiac output vs. third heart sound Display Value (r2 = 0.0791 p = 0.0023)]. Additionally, acoustic cardiography diastolic time (AUC 0.675, p = 0.008), perfusion time (AUC 0.649, p = 0.024) and third heart sound Display Value (AUC 0.654, p = 0.019) emerged as possible indicators of coronary occlusion. Finally, these three parameters, when joined with heart rate into a composite joint-index, represent the best model in our experience for ischemia detection (AUC 0.770, p < 0.001).ConclusionIn the rapidly evolving setting of acute myocardial ischemia, acoustic cardiography provided meaningful insights of mechanical dysfunction in a prompt and non-invasive manner. These findings should propel interest in resurrecting this technique for future translational studies as well as reconsidering its reintroduction in the clinical setting.

Criteria for ECG detection of acute myocardial ischemia: Sensitivity versus specificity

BackgroundCriteria for electrocardiographic detection of acute myocardial ischemia recommended by the Consensus Document of ESC/ACCF/AHA/WHF consist of two parts: The ST elevation myocardial infarction (STEMI) criteria based on ST elevation (ST↑) in 10 pairs of contiguous leads and the other on ST depression (ST↓) in the same 10 contiguous pairs. Our aim was to assess sensitivity (SE) and specificity (SP) of these criteria—and to seek their possible improvements—in three databases of 12‑lead ECGs. MethodsWe used (1) STAFF III data of controlled ischemic episodes recorded from 99 patients (pts) during percutaneous coronary intervention (PCI) involving either left anterior descending (LAD) coronary artery, right coronary artery (RCA), or left circumflex (LCx) coronary artery. (2) Data from the University of Glasgow for 58 pts with acute myocardial infarction (AMI) and 58 pts without AMI, as confirmed by MRI. (3) Data from Lund University retrieved from a centralized ECG management system for 100 pts with various pathological ST changes—other than acute coronary occlusion—including ventricular pre-excitation, acute pericarditis, early repolarization syndrome, left ventricular hypertrophy, and left bundle branch block. ST measurements at J-point in ECGs of all 315 pts were obtained automatically on the averaged beat with manual review and the recommended criteria as well as their proposed modifications, were applied. Performance measures included SE, SP, positive predictive value (PPV), and benefit-to-harm ratio (BHR), defined as the ratio of true-positive vs. false-positive detections. ResultsWe found that the SE of widely-used STEMI criteria can be indeed improved by the additional ST↓ criteria, but at the cost of markedly decreased SP. In contrast, using ST↑ in only 3 additional contiguous pairs of leads (STEMI13) can boost SE without any loss of SP. In the STAFF III database, SE/SP/PPV were 56/98/97% for the STEMI, 79/79/79% for the STEMI with added ST↓ and 67/97/96% for the STEMI13. In the Glasgow database, corresponding SE/SP/PPV were 43/98/96%, 84/90/89%, and 55/98/97%. For the Lund database, SP was 56% for the STEMI, 24% for the STEMI with ST↓, and 56% for the STEMI13. ConclusionCurrent recommended criteria for detecting acute myocardial ischemia, involving ST↓, boost SE of widely-used STEMI criteria, at the cost of SP. To keep the SP high, we propose either the adjustment of threshold for the added ST↓ criteria or a selective use of ST↓ only in contiguous leads V2 and V3 plus ST↑ in lead pairs (aVL, –III) and (III, –aVL).

Unshielded magnetocardiography: Repeatability and reproducibility of automatically estimated ventricular repolarization parameters in 204 healthy subjects.

Magnetocardiographic mapping (MCG) provides quantitative assessment of the magnetic field (MF) induced by cardiac ionic currents, is more sensitive to tangential currents, and measures vortex currents undetectable by ECG, with higher reported sensitivity of MCG ventricular repolarization (VR) parameters for earlier detection of acute myocardial ischemia. Aims of this study were to validate the feasibility of in-hospital unshielded MCG and to assess repeatability and reproducibility of quantitative VR parameters, considering also possible gender- and age-related variability. MCG of 204 healthy subjects [114 males-mean age 43.4±17.3 and 90 females-mean age 40.2±15.7] was retrospectively analyzed, with a patented proprietary software automatically estimating twelve VR parameters derived from the analysis of the dynamics of the T-wave MF extrema (five parameters) and from the inverse solution with the effective magnetic dipole model giving the effective magnetic vector components (seven parameters). MCG repeatability was calculated as coefficient of variation (CV) ±standard error of the mean (SEM). Reproducibility was assessed as intraclass correlation coefficient (ICC). The repeatability of all MCG parameters was 16±1.2 (%) (average CV±SEM). Optimal (ICC>0.7) reproducibility was found for 11/12 parameters (mean values) and in 8/12 parameters (single values). No significant gender-related difference was observed; six parameters showed a strong/moderate correlation with age. Reliable MCG can be performed into an unshielded hospital ambulatory, with repeatability and reproducibility of quantitative assessment of VR adequate for clinical purposes. Wider clinical use is foreseen with the development of multichannel optical magnetometry.

Left ventricular endocardial and epicardial strain changes with apical myocardial ischemia in an open-chest porcine model.

Early detection of acute myocardial ischemia is critical to prevent permanent myocardial damage. The impact of apical ischemia on global left ventricular (LV) function can be difficult to characterize using traditional volume‐based echocardiography measures. Myocardial strain imaging is a sensitive, quantitative marker of myocardial deformation that can measure ventricular function. Recent advances allow layer‐specific measurement of endo‐ and epicardial strain, enhancing the ability to evaluate myocardial ischemia. This study investigates the effects of apical ischemia on LV function using epi‐ and endocardial strain. We hypothesize that myocardial strain will identify changes in regional and global myocardial function associated with focal apical ischemia as compared to ejection fraction (EF), and that longitudinal strain will be a better indicator of myocardial dysfunction compared to circumferential or radial strain. In a porcine model (n = 9), acute ischemia was induced by left anterior descending coronary artery occlusion. Echocardiograms were performed at baseline, during 15‐min ischemia, and after reperfusion. Global longitudinal strain decreased with acute focal ischemia of the left ventricular apical region (baseline: −16.4% vs. ischemia: −12.2%; P = 0.010), with no change observed in global circumferential and radial strain or EF. Both endocardial and epicardial longitudinal strain decreased by 68% (P < 0.001) in the ischemic and peri‐ischemic zone, while circumferential and radial strain only decreased in endocardium of the ischemic zone. Longitudinal strain was more sensitive to ischemia, being able to detect changes in global LV function and thus may confer clinical diagnostic advantage in the evaluation of acute LV apical ischemia.

The Olson method for detection of acute myocardial ischemia in patients with coronary occlusion

An automated ECG-based method may provide diagnostic support in the management of patients with acute coronary syndrome. The Olson method has previously proved to accurately identify the culprit artery in patients with acute coronary occlusion. MethodsThe Olson method was applied to 360 patients without acute myocardial ischemia and 52 patients with acute coronary occlusion. ResultsThis study establishes the normal variation of the Olson wall scores in patients without acute myocardial ischemia, which provides the basis for implementation of the Olson method for triage of patients with acute coronary syndrome. All patients with acute occlusion had Olson wall scores above the upper limit of normal. ConclusionThe Olson method can be used for ischemia detection with very high sensitivity. Future studies are needed to explore specificity in patients with non-ischemic ST elevation.

Performance of ST and ventricular gradient difference vectors in electrocardiographic detection of acute myocardial ischemia

IntroductionSerial analysis could improve ECG diagnosis of myocardial ischemia caused by acute coronary occlusion. MethodsWe analyzed ECG pairs of 84 cases and 398 controls. In case-patients, who underwent elective percutaneous coronary intervention, ischemic ECGs during balloon occlusion were compared with preceding non-ischemic ECGs. In control-patients, two elective non-ischemic ECGs were compared. In each ECG the ST vector at the J point and the ventricular gradient (VG) vector was computed, after which difference vectors ΔST and ΔVG were computed within patients. Finally, receiver operating characteristic analysis was done. ResultsAreas under the curve were 0.906 (P<0.001; CI 0.862–0.949; SE 0.022) for ΔST and 0.880 (P<0.001; CI 0.833–0.926; SE 0.024) for ΔVG. Sensitivity and specificity of conventional ST-elevation myocardial infarction (STEMI) criteria were 70.2% and 89.1%, respectively. At matched serial analysis specificity and STEMI specificity, serial analysis sensitivity was 78.6% for ΔST and 71.4% for ΔVG (not significantly different from STEMI sensitivity). At matched serial analysis sensitivity and STEMI sensitivity, serial analysis specificity was 96.5% for ΔST and 89.3% for ΔVG; ΔST and STEMI specificities differed significantly (P<0.001). ConclusionDetection of acute myocardial ischemia by serial ECG analysis of ST and VG vectors has equal or even superior performance than the STEMI criteria. This concept should be further evaluated in triage ECGs of patients suspected from having acute myocardial ischemia.

Detection and quantification of acute myocardial ischemia by morphologic evaluation of QRS changes by an angle-based method

ObjectiveIn acute myocardial ischemia changes within the QRS complex can add valuable information to that from the repolarization phase. This study evaluates three angles obtained from the main slopes of the R-wave within the QRS complex to assess acute myocardial ischemia. MethodsThe QRS angles, denoted by ØR (R-wave angle), ØU (up-stroke angle) and ØD (down-stroke angle), were evaluated in 12-lead electrocardiogram (ECG) recordings of 79 patients before and during coronary occlusion by elective percutaneous coronary intervention (PCI). In a subset of 38 patients, ischemia was quantified by myocardial scintigraphy. ResultsAt baseline the QRS angles presented low variations. During occlusion, ØU and ØD developed a fast and abrupt change, whereas ØR showed a smaller and gradual change. There were significant correlations between both maximal and sum of positive change in ØR and ischemia: r=0.67; p<0.001 and r=0.78; p<0.001, for extent, and r=0.60; p<0.001 and r=0.73; p<0.001, for severity, respectively. Prediction of extent and severity of ischemia increased by 50% by adding ØR changes to ST-segment changes, for LCX occlusions, whereas increased by 12.1% and 24.6% for LAD and RCA occlusions, respectively. No significant correlation was seen between ØU and ØD angles and ischemia. ConclusionsEvaluation of QRS angles from the standard 12-lead ECG represents a sensitive marker for detection of acute myocardial ischemia, whereas, ØR changes can be used for prediction of its extent and severity.

Abstract 29: A New Biomarker for Diagnosis of Ischemic Stroke: Plasma Glycogen Phosphorylase-BB

Background: Glycogen phosphorylase-BB (GPBB) is the key enzyme that breaks down glycogen to yield glucose-1-phosphate in order to meet the emergent ATP need during cerebral ischemia. GPBB is one of the most sensitive and specific plasma markers for early detection of acute myocardial ischemia. GPBB concentration is about 100 times higher in brain than in heart. We hypothesized that plasma levels of GPBB might elevate following cerebral ischemia. Methods: We measured plasma GPBB levels in 172 patients with imaging-confirmed brain infarction at two time points (within 9 hours of symptom onset and at 48 hours). The control group consisted of 97 age-matched subjects without stroke. GPBB levels were determined blind to case/control assignment using a commercially available ELISA kit (Diagenics, Germany). Results: Baseline mean (±SD) GPBB level was 46.3 ng/ml (± 38.6 ng/ml) in cases and 4.8 ng/ml (±8.0 ng/ml) in controls (p &lt; 0.001, Figure). GPBB levels slightly decreased from baseline to 48 hours in patients with stroke (38.7 ± 36.5 ng/ml, p = 0.02). The discriminative ability of GPBB between cases and controls as measured by the area under the Receiver Operating Characteristic (ROC) curve was high (0.95, 95% CI 0.93-0.98). GPBB level corresponding to optimal operating point on the ROC curve was 6 ng/ml. Based on the 6 ng/dl cut-off, baseline plasma GPBB showed 94% sensitivity and 90% specificity for diagnosis of ischemic stroke. Conclusion: Plasma GPBB appears to be a sensitive and specific marker for early diagnosis of brain ischemia. Its high proportional rise with respect to the discriminator value suggests that GPBB may find utility particularly in the diagnosis of mild ischemic syndromes associated with trace amounts of brain injury.

Human &amp; swine studies of concurrent 12-lead ECG &amp; MRI

Background 12-lead Electrocardiogram (ECG) is a clinical standard for patient physiological monitoring. An MRI-conditional 12-lead ECG should permit detection of acute myocardial ischemia during MR imaging or MRI-guided therapy, which may improve the handling of patients with ischemic histories. MRI visualization of ischemic episodes can also enhance the understanding of ischemic progression. Previously an MR-conditional 12-lead ECG system was presented. The system was equipped with GradientRampR (2) detect S-wave to T-wave (ST) ECG elevation & perform MR imaging of a Left Anterior Descending (LAD) balloon occlusion from the onset of ischemia to death in a swine model.

Detection of acute myocardial ischemia by vessel-specific leads derived from the 12-lead electrocardiogram

Detection of acute myocardial ischemia by vessel-specific leads derived from the 12-lead electrocardiogram

Interpreting 12-Lead Electrocardiograms for Acute ST-Elevation Myocardial Infarction

In patients with acute myocardial infarction, early reperfusion and sustained patency of the culprit artery are important determinants of survival. The 12-lead electrocardiogram (ECG) is considered the noninvasive gold standard for identification of acute ST-elevation myocardial infarction. Nurses play a critical role in the process of obtaining, interpreting, and communicating ECG findings. This study evaluates nurses' ability to differentiate ischemic from nonischemic ECG patterns, to detect affected ECG leads and location of ischemia, and assesses skill level by hospital unit type. Seventy-five nurses were given a set of 6 patient scenarios, each with a corresponding 12-lead ECG, and asked to identify the presence or absence of ischemia. Fourteen (19%) of the 75 nurses correctly identified the presence or absence of ischemia in all 6 scenarios. Of the 3 ECGs with a myocardial infarction pattern, 59 (79%) of the nurses identified all 3 as ischemic; however, no one was able to determine the correct leads, location, or amplitude of ST-segment elevation. For the 3 nonischemic ECGs, 37 (49%) of the nurses identified a normal ECG as ischemic, 47 (63%) determined that an early repolarization pattern was ischemic, and 34 (45%) indicated that a left bundle branch block pattern was ischemic. These results not only identify educational opportunities but also provide important information for researchers implementing clinical trials evaluating the use of bedside ECG monitoring systems for detection of acute myocardial ischemia.

Added value of new acute coronary syndrome computer algorithm for interpretation of prehospital electrocardiograms

A new computerized acute coronary syndrome (ACS) computer algorithm has been developed with the aim of improving the electrocardiographic detection of acute myocardial ischemia and infarction in the emergency department (ED). The purpose of this study was to determine the added value of the new ACS algorithm in assisting ED physicians to obtain a more accurate diagnosis in patients with ACS. The new algorithm combines a rule-based decision tree, which uses well-known clinical criteria and a data-centered neural network model for more robust pattern recognition. Input parameters of the neural network model consist of morphology features of derived Frank X, Y, Z waveforms and the patient’s gender and age. The neural network model was trained with electrocardiograms obtained from documented acute myocardial infarction patients at the Mayo Clinic who were a part of a research ACS database, which includes electrocardiograms (ECGs) of more than 5,000 individuals at hospital admission (1 st ECG in the ED). The test set portion of the study was conducted in 2 steps: 1) One emergency physician and 1 cardiologist classified 1,902 clinically correlated out-of-hospital ECGs without seeing the interpretation statement from the algorithm into 1 of the following categories: 1) acute myocardial infarction, acute ischemia, or nonischemic; 2) After 9 months, the same 2 physicians classified the same group of ECGs but with the interpretation statement of the algorithm printed on the tracing. The results demonstrated that with the assistance of the new algorithm, the emergency physician and cardiologist improved their sensitivity of interpreting acute myocardial infarction by 50% and 26%, respectively, without a loss of specificity. The new algorithm also improved the emergency physician’s acute ischemia interpretation sensitivity by 53% and still maintained a reasonable specificity (91%). The new ACS algorithm provides added value for improving acute ischemia and infarction detection in the ED.

Early brain natriuretic peptide increase reflects acute myocardial ischemia in patients with ongoing chest pain

Background: Plasma brain natriuretic peptide levels increase during acute ischemic events. In this study we tested the diagnostic performance of brain natriuretic peptide measurements in the detection of acute myocardial ischemia. Methods: Blood brain natriuretic peptide was measured in 101 patients with ongoing chest pain but no heart failure or an ST-segment elevation myocardial infarction on arrival at the emergency department (baseline) and at 2 and 6 h later. After diagnostic testing and 1-month follow-up for ischemia, patients were classified as either ischemic or non-ischemic. Results: In the ischemic group median (25th, 75th percentiles) brain natriuretic peptide values (pg/ml) were 122 (20, 349) at baseline, 116 (36, 347) at 2 h, increasing to 148 (52, 428) at 6 h ( p<0.001 vs. baseline). Non-ischemic patients had 12 (5, 32) at baseline, 9 (6, 30) at 2 h, and 13 (5, 29) at 6 h ( p<0.001 vs. corresponding values of the ischemic group). Receiver operator characteristic curves were constructed for brain natriuretic peptide values at baseline 2 and 6 h and for the increase of peptide levels from baseline to 6 h. All areas under curve indicated a significant diagnostic ability for the detection of ischemia. The 6-h measurement had better diagnostic performance than baseline and 2-h measurements. The subgroup of ischemic patients without myocardial necrosis also had higher brain natriuretic peptide values and could thus be discriminated from non-ischemic subjects. Conclusions: Brain natriuretic peptide values may detect acute myocardial ischemia in patients with ongoing chest pain but without ST-segment elevation, and distinguish ischemic patients from those with pain of non-ischemic origin.

Detection of acute myocardial ischemia during percutaneous transluminal coronary angioplasty by endocardial acceleration.

The first heart sound is generated by vibrations from the myocardium during isovolumic contraction. Peak endocardial acceleration (PEA) has been used previously to measure these vibrations in humans and correlates with myocardial contractility during inotropic interventions. It is unknown if changes in PEA can be used to characterize a reduction in contractility during ischemic episodes. This study was designed to evaluate the use of an endocardial accelerometer for the detection of acute myocardial ischemia. Thirteen patients undergoing routine percutaneous transluminal coronary angioplasty (PTCA) consented to having a single-axis, lead-based accelerometer positioned in the right ventricular apex. PEA was defined as the maximum peak-to-peak amplitude during a window 50 ms before to 200 ms following the peak R wave. Time of endocardial acceleration (TEA) was defined as the time from the peak R wave to the maximum accelerometer signal within this window. To obtain a more robust estimate of the strength of vibrations, a 100-beat template of the accelerometer signal was constructed at baseline and applied as a matched filter during ischemia. The peak magnitude of the filtered endocardial accelerometer signal (Max Filtered EA) was used as an index of signal intensity. Median baseline PEA, TEA, and Max Filtered EA were 0.91 +/- 0.35 g, 75.2 +/- 16.2 ms, and 0.40 +/- 0.20 g, respectively. PEA and Max Filtered EA significantly decreased by 7% during ischemia (0.91 to 0.85 g and 0.40 to 0.37 g, both P < 0.05, respectively). TEA did not significantly change from baseline (77.0 ms, P = ns). The results of this study suggest that acute ischemia can be detected with an endocardial accelerometer in humans.

Detection of acute myocardial ischemia during pharmacological stress in graded coronary artery stenosis: Analysis of left ventricular asynchrony using fourier phase imaging

Background: Stress echocardiography is increasingly used to identify coronary artery disease, but quantitative techniques are required to improve the accuracy of this method. Current algorithms used to analyze wall motion usually neglect motion asynchrony that is found in acute ischemia. Fourier phase imaging of echocardiographic images may offer the possibility to detect asynchrony, but its feasibility with dobutamine stress echocardiography (DSE) is undefined. The aim of this study was to investigate whether the extent of left ventricular asynergy can be used to quantify the severity of regional myocardial dysfunction and to detect functionally significant coronary artery stenoses during DSE. Methods: Regional wall motion abnormalities were induced by graded coronary stenoses (mild and severe) of the left anterior descending coronary artery (LAD) in seven open-chest anesthetized pigs. DSE (10–40 μg/kg/min) was performed under control conditions and during sustained ischemia. Coronary flow was measured under resting conditions and during maximal hyperemic response due to intravenous infusion of adenosine. Functional significance of stenoses was defined as mild when coronary flow reserve (CFR) was reduced but > 1.5 and severe when CFR was ≤ 1.5. Echocardiographic cine loops were mathematically transformed using a first-harmonic Fourier algorithm displaying the sequence of wall motion as phase angles in parametric images and regional phase histograms. The phase difference (PD) of the first Fourier harmonic of posterior vs. anterior myocardial wall motion was calculated as an index of left ventricular asynchrony. Segmental fractional area shortening (FAS) and wall thickening (WT) as ratio of stress to rest served as a reference method of regional wall motion. Results: The increase in FAS (1.62 ± 0.6 vs. 0.42 ± 0.2, p = 0.0002) and WT (1.92 ± 0.5 to 0.3 ± 1.1; p = 0.004) in anterior regions during DSE was significantly higher in the control group compared to severe ischemia but not compared to mild ischemia. During graded ischemia, profiles of phase angles were consistently modified, showing a delayed onset in regional contraction. The mean PD during DSE in the control group was 10.4 ± 7°. PD rose in mild ischemic segments (CFR>1.5) to 28.9 ± 10° (p = 0.003) and to 89.6 ± 25° (p = 0.0002) in severely ischemic segments (CFR ≤ 1.5). There was a significant inverse correlation between the PDs and WT (r = −0.87, p < 0.0001). Normal WT ratios yielded low phase angles while segmental phase angles increased with decreased WT. The intraobserver variability of phase analysis was 2.7 ± 24° (mean ± 2SD). Conclusions: These results suggest that left ventricular asynchrony is an indicator of acute ischemia. Echocardiographic Fourier phase imaging is feasible to quantify wall motion displaying contraction sequence in a simple and objective format and is a␣promising approach for the clinical interpretation of stress echocardiograms.

Identification of acutely ischemic myocardium using ultrasonic strain measurements: A clinical study in patients undergoing coronary angioplasty

ObjectivesThe goal of this study was to investigate whether the changes in myocardial deformation measured with ultrasonic strain could accurately identify acutely ischemic myocardium during coronary angioplasty. BackgroundEarly identification of acute myocardial ischemia has important clinical implications. The accuracy of ultrasonic strain for the detection of acute myocardial ischemia has been validated in animal experiments but has not been investigated in the clinical setting. MethodsIn 73 patients (64 ± 12 years), either radial or longitudinal strain values were monitored in the “at-risk” segments before, during, and early after right, circumflex, and left anterior descending coronary angioplasty. Based on the visual wall motion assessed before the angioplasty, segments were divided into normokinetic (group I) and hypo/akinetic (group II). Strain data in the “at-risk ” segments were compared with values derived from the adjacent nonischemic segments and normal values in 20 controls. ResultsCoronary occlusion induced a marked reduction in the systolic strain both in the radial (from 49 ± 6.9% to 23 ± 4.6% in group I and from 21.9 ± 11% to 11.3 ± 8.4% in group II, p < 0.001) and longitudinal directions. Concomitantly, postsystolic strain increased (from 3.8 ± 3.1% to 14.6 ± 9.5% in group I, and from 4.4 ± 3.7% to 11.3 ± 7.8% in group II in radial direction, p < 0.001). Upon reperfusion, all deformation parameters returned to near preocclusion values. In comparison with control, baseline, and reperfusion data, the systolic and postsystolic strain parameters measured during total coronary occlusion identified acutely ischemic myocardium with a sensitivity of 86% to 95% and a specificity of 83% to 89%. ConclusionsIn this model of acute ischemia, ultrasonic strain indexes differentiate acutely ischemic segments from both normal and dysfunctional myocardium. This should be a promising new approach to the bedside monitoring of acute ischemic changes in regional myocardial function.

Detection of acute myocardial ischemia during pharmacological stress in graded coronary artery stenosis: analysis of left ventricular asynchrony using Fourier phase imaging in pigs.

Stress echocardiography is increasingly used to identify coronary artery disease, but quantitative techniques are required to improve the accuracy of this method. Current algorithms used to analyze wall motion usually neglect motion asynchrony that is found in acute ischemia. Fourier phase imaging of echocardiographic images may offer the possibility to detect asynchrony, but its feasibility with dobutamine stress echocardiography (DSE) is undefined. The aim of this study was to investigate whether the extent of left ventricular asynergy can be used to quantify the severity of regional myocardial dysfunction and to detect functionally significant coronary artery stenoses during DSE. Regional wall motion abnormalities were induced by graded coronary stenoses (mild and severe) of the left anterior descending coronary artery (LAD) in seven open-chest anesthetized pigs. DSE (10-40 microg/kg/min) was performed under control conditions and during sustained ischemia. Coronary flow was measured under resting conditions and during maximal hyperemic response due to intravenous infusion of adenosine. Functional significance of stenoses was defined as mild when coronary flow reserve (CFR) was reduced but > 1.5 and severe when CFR was < or = 1.5. Echocardiographic cine loops were mathematically transformed using a first-harmonic Fourier algorithm displaying the sequence of wall motion as phase angles in parametric images and regional phase histograms. The phase difference (PD) of the first Fourier harmonic of posterior vs. anterior myocardial wall motion was calculated as an index of left ventricular asynchrony. Segmental fractional area shortening (FAS) and wall thickening (WT) as ratio of stress to rest served as a reference method of regional wall motion. The increase in FAS (1.62 +/- 0.6 vs. 0.42 +/- 0.2, p = 0.0002) and WT (1.92 +/- 0.5 to 0.3 +/- 1.1; p = 0.004) in anterior regions during DSE was significantly higher in the control group compared to severe ischemia but not compared to mild ischemia. During graded ischemia, profiles of phase angles were consistently modified, showing a delayed onset in regional contraction. The mean PD during DSE in the control group was 10.4 +/- 7 degrees. PD rose in mild ischemic segments (CFR > 1.5) to 28.9 +/- 10 degrees (p = 0.003) and to 89.6 +/- 25 degrees (p = 0.0002) in severely ischemic segments (CFR < or = 1.5). There was a significant inverse correlation between the PDs and WT (r = -0.87, p < 0.0001). Normal WT ratios yielded low phase angles while segmental phase angles increased with decreased WT. The intraobserver variability of phase analysis was 2.7 +/- 24 degrees (mean +/- 2SD). These results suggest that left ventricular asynchrony is an indicator of acute ischemia. Echocardiographic Fourier phase imaging is feasible to quantify wall motion displaying contraction sequence in a simple and objective format and is a promising approach for the clinical interpretation of stress echocardiograms.

Detection of acute myocardial ischemia by analysis of ultrasonic gray levels in dogs

In conclusion, this study demonstrates, in an animal model, that analysis of the digitized two-dimensional echocardiogram may detect the acute changes in mean gray level (occurring as early as 30 minutes after coronary artery ligation) caused by myocardial ischemia. The clinical application of our findings to humans requires further study.