Ischemia and Infarction07

Ischemia and Infarction07 - Ischemia and Infarction...

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Unformatted text preview: Ischemia and Infarction Ischemia and Infarction Ischemia – lack of blood flow leading to a lack of Ischemia oxygen in an area of the myocardium Subendocardial Subendocardial Transmural Transmural Myocardial Infarction Myocardial Diagnosed via Diagnosed History and Physical Exam History Cardiac Enzymes Cardiac ECG ECG Ischemia and Exercise Ischemia ECG analysis of the ST segment in particular ECG is used during exercise testing (GXT) for DIAGNOSTIC DIAGNOSTIC PROGNOSTIC PROGNOSTIC EXERCISE PRESCRIPTION EXERCISE 1 Types of Ischemia Subendocardial Subendocardial Manifested as ST segment depression on an ECG Manifested but MI can not be diagnosed from this finding Transmural Transmural Ischemia affecting the entire thickness of the Ischemia myocardium Manifested as ST segment elevation on an ECG Manifested In most cases, acute MI can be diagnosed from In ECG findings Coronary Artery Anatomy Blocked Coronary Artery 2 Measuring the ST segment Accurate and precise measure of the ST segment is critical in not only evaluating acute MI but also changes in during exercise 1. Identify the PQ junction, mark this as the baseline for at least 2 adjacent cycles 2. Identify the J-point J3. Measure 0.08 seconds from the J-point J4. Measure the distance from the J-point to the Jbaseline Measure up, depression; Measure down, elevation Measure Changes in ECG during MI 1. T wave peaking and/or ST segment elevation 0 – 12 hours 2. T wave inversion 24 – 96 hours 24 3. Appearance of new Q waves 2 weeks to 1 year weeks Must be 1/3 the size of the R wave and at least 0.04 Must seconds in length to be considered significant 3 ST segment: Acute V. Old MI Acute MI Acute ST segment signifies myocardial injury and/or ST transmural ischemia ST segment elevation (usually at least 2 mm) ST Old MI Old Significant Q waves over areas of nonSignificant nonrecoverable myocardium Localization of old MI: Q wave infarction Views Views Anterior – V1 – V4 (LAD) Anterior Left Lateral – I, avL, V5 and V6 (LCA) Left Inferior – II, III, and avF (LAD) Inferior Posterior – avR, reciprocal changes in V1 Posterior (RCA) ST segment depression: Subendocardial Ischemia Subendocardial This type of ST segment depression is specifically This analyzed in the presence of ischemia due to exercise stress Types of ST segment depression (>1.0mm) Types Upsloping Upsloping Horizontal Horizontal Downsloping Downsloping Note: Can NOT localize ischemia when ST segment depression is present ! 4 ST segment depression Horizontal and downsloping depression are Horizontal more sensitive indicator of disease If upsloping ST depression, other clinical If indicators of disease should be used. The more leads with apparent shifts, the more The severe the disease ST segment depression ST Significant (1 mm) ST segment depression Significant occurring during recovery should be considered an important diagnostic finding Normalization of ST segment and T wave Normalization with exercise may also be indicative of disease. Special Cases: ST segment Ventricular Aneurysm/ Wall motion Ventricular abnormalities ST segment elevation in leads with Significant Q ST waves Digitalis Effect Digitalis Toxicity will create a “scooping” of the ST Toxicity scooping” segment which should not be confused with ST segment depression 5 Diagnostic Use of the GXT Sensitivity (pg 125 - 129, ACSM Guidelines) ACSM Sensitivity (pg TP/(TP +FN) TP/(TP Specificity Specificity TN/(TN + FP) TN/(TN ECG related causes of False Negative Tests Insufficient number of ECG leads Insufficient ECG related causes of False Positive Tests Left bundle-branch block Left bundleWPW WPW Hypokalemia Hypokalemia Female gender Female Prognostic Use of GXT Exercise ST-segment deviation, angina Exercise STsymptoms, and functional capacity are used to determine annual mortality rate. ST-segment devaition – extent of change in mm STAngina – none, limiting, or non-limiting Angina nonExercise – METs Exercise Page 94, ACSM Guidelines ACSM Clinical Significance of ECG Responses to Exercise Testing ST segment depression ST ST segment elevation ST Supraventricular arrythmias (usually O.K.) Supraventricular Ventricular arrythmias (malignant) Ventricular Heart rate Heart Page 128, ACSM Guidelines 6 ...
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