EKG Myocardial infarction and EKG Myocardial infarction and other ischemic statesother ischemic states

Sandra Rodriguez, M.D.Sandra Rodriguez, M.D.

Internal MedicineInternal Medicine

TTHSCTTHSC

BackgroundBackgroundRupture of an atherosclerotic plaque followed by acute coronary Rupture of an atherosclerotic plaque followed by acute coronary thrombosis is the usual mechanism of acute MI.thrombosis is the usual mechanism of acute MI.

Two-thirds of MI's presenting to emergency rooms evolve Two-thirds of MI's presenting to emergency rooms evolve to non-Q wave MI's, most having ST segment depression or to non-Q wave MI's, most having ST segment depression or T wave inversion.T wave inversion.

In the TIMI III Registry of patients with UA/NSTEMI, independent In the TIMI III Registry of patients with UA/NSTEMI, independent predictors of 1-year death or MI included left bundle branch block predictors of 1-year death or MI included left bundle branch block (risk ratio 2.8); ST segment deviation >0.05 mV (risk ratio 2.45); (risk ratio 2.8); ST segment deviation >0.05 mV (risk ratio 2.45); both both pp< 0.001.< 0.001.

The left anterior descending coronary artery (LAD) and it's The left anterior descending coronary artery (LAD) and it's branches usually supply the anterior and anterolateral walls of the branches usually supply the anterior and anterolateral walls of the left ventricle and the anterior two-thirds of the septum. left ventricle and the anterior two-thirds of the septum.

BackgroundBackgroundThe left circumflex coronary artery (LCX) The left circumflex coronary artery (LCX) and its branches usually supply the and its branches usually supply the posterolateral wall of the left ventricle. posterolateral wall of the left ventricle. The right coronary artery (RCA) supplies The right coronary artery (RCA) supplies the right ventricle, the inferior the right ventricle, the inferior (diaphragmatic) and true posterior walls of (diaphragmatic) and true posterior walls of the left ventricle, and the posterior third of the left ventricle, and the posterior third of the septum. the septum. The RCA also gives off the AV nodal The RCA also gives off the AV nodal coronary artery in 85-90% of individuals; coronary artery in 85-90% of individuals; in the remaining 10-15%, this artery is a in the remaining 10-15%, this artery is a branch of the LCX.branch of the LCX.

Progression of wave changesProgression of wave changesHyperacute T wave changes - increased T wave Hyperacute T wave changes - increased T wave amplitude and width; may also see ST elevation.amplitude and width; may also see ST elevation.

Marked ST elevation with hyperacute T wave Marked ST elevation with hyperacute T wave changes (transmural injury)changes (transmural injury)

Pathologic Q waves, less ST elevation, terminal T Pathologic Q waves, less ST elevation, terminal T wave inversion (necrosis)  (Pathologic Q waves wave inversion (necrosis)  (Pathologic Q waves are usually defined as duration are usually defined as duration >>0.04 s or >25% 0.04 s or >25% of R-wave amplitude) of R-wave amplitude)

Pathologic Q waves, T wave inversion (necrosis Pathologic Q waves, T wave inversion (necrosis and fibrosis) and fibrosis)

Pathologic Q waves, upright T waves (fibrosisPathologic Q waves, upright T waves (fibrosis) )

Inferior MIInferior MI

Pathologic Q waves and evolving ST-Pathologic Q waves and evolving ST-T changes in leads II, III, aVF.T changes in leads II, III, aVF.

Q waves usually largest in lead III, Q waves usually largest in lead III, next largest in lead aVF, and smallest next largest in lead aVF, and smallest in lead II in lead II

Inferior MIInferior MI

Inferoposterior MIInferoposterior MIECG changes are seen in anterior precordial leads ECG changes are seen in anterior precordial leads V1-3, but are the V1-3, but are the mirror imagemirror image of an anteroseptal of an anteroseptal MI,  MI,  Increased R wave amplitude and duration (i.e., a Increased R wave amplitude and duration (i.e., a "pathologic R wave" is a mirror image of a "pathologic R wave" is a mirror image of a pathologic Q).pathologic Q).R/S ratio in V1 or V2 >1 (i.e., prominent anterior R/S ratio in V1 or V2 >1 (i.e., prominent anterior forces).forces).Hyperacute ST-T wave changes: i.e., ST depression Hyperacute ST-T wave changes: i.e., ST depression and large, inverted T waves in V1-3.and large, inverted T waves in V1-3.Late normalization of ST-T with symmetrical upright Late normalization of ST-T with symmetrical upright T waves in V1-3. T waves in V1-3. Often seen with inferior MI (i.e., "inferoposterior Often seen with inferior MI (i.e., "inferoposterior MI") MI")

Inferoposterior MIInferoposterior MI

Inferoposterior MIInferoposterior MI

Right Ventricular MIRight Ventricular MIRight Ventricular MI (only seen with Right Ventricular MI (only seen with proximal right coronary occlusion; proximal right coronary occlusion; i.e., with inferior family MI's)  i.e., with inferior family MI's)  ECG findings usually require ECG findings usually require additional leads on right chest (V1R additional leads on right chest (V1R to V6R, analogous to the left chest to V6R, analogous to the left chest leads) leads) ST elevation, ST elevation, >>1mm, in right chest 1mm, in right chest leads, especially V4R.leads, especially V4R.

Right Ventricular MIRight Ventricular MI

Anterior MIAnterior MI

High Lateral MIHigh Lateral MI

What is the diagnosis?What is the diagnosis?

MI plus LBBBMI plus LBBBQ waves of any size in Q waves of any size in twotwo or more of leads I, aVL, V5, or V6 or more of leads I, aVL, V5, or V6 (See below: one of the most reliable signs and probably (See below: one of the most reliable signs and probably indicates indicates septalseptal infarction, because the septum is activated infarction, because the septum is activated early from the right ventricular side in LBBB). early from the right ventricular side in LBBB).

Reversal of the usual R wave progression in precordial Reversal of the usual R wave progression in precordial leads.leads.

Notching of the downstroke of the S wave in precordial Notching of the downstroke of the S wave in precordial leads to the right of the transition zone (i.e., before QRS leads to the right of the transition zone (i.e., before QRS changes from a predominate S wave complex to a changes from a predominate S wave complex to a predominate R wave complex); this may be a Q-wave predominate R wave complex); this may be a Q-wave equivalent.equivalent.

MI plus LBBBMI plus LBBBNotching of the upstroke of the S wave in precordial leads Notching of the upstroke of the S wave in precordial leads to the right of the transition zone (another Q-wave to the right of the transition zone (another Q-wave equivalent). equivalent).

rSR' complex in leads I, V5 or V6 (the S is a Q-wave rSR' complex in leads I, V5 or V6 (the S is a Q-wave equivalent occurring in the middle of the QRS complex) equivalent occurring in the middle of the QRS complex)

RS complex in V5-6 rather than the usual monophasic R RS complex in V5-6 rather than the usual monophasic R waves seen in uncomplicated LBBB; (the S is a Q-wave waves seen in uncomplicated LBBB; (the S is a Q-wave equivalent). equivalent).

"Primary" ST-T wave changes (i.e., ST-T changes in the "Primary" ST-T wave changes (i.e., ST-T changes in the same direction as the QRS complex rather than the usual same direction as the QRS complex rather than the usual "secondary" ST-T changes seen in uncomplicated LBBB); "secondary" ST-T changes seen in uncomplicated LBBB); these changes may reflect an acute, evolving MI. these changes may reflect an acute, evolving MI.

Old MI plus LBBOld MI plus LBB

Non-Q wave MINon-Q wave MIRecognized by evolving ST-T changes over time without the Recognized by evolving ST-T changes over time without the formation of pathologic Q waves (in a patient with typical chest pain formation of pathologic Q waves (in a patient with typical chest pain symptoms and/or elevation in myocardial-specific enzymes)symptoms and/or elevation in myocardial-specific enzymes)

Although it is tempting to localize the non-Q MI by the particular Although it is tempting to localize the non-Q MI by the particular leads showing ST-T changes, this is probably only valid for the ST leads showing ST-T changes, this is probably only valid for the ST segment elevation pattern.segment elevation pattern.

Evolving ST-T changes may include any of the following patterns: Evolving ST-T changes may include any of the following patterns:

Convex downward ST segment depression only (common) Convex downward ST segment depression only (common)

Convex upwards or straight ST segment elevation only.Convex upwards or straight ST segment elevation only.

Symmetrical T wave inversion only (common) Symmetrical T wave inversion only (common)

   

Non-Q wave MINon-Q wave MI

Differential MI patternDifferential MI patternWPW preexcitation (WPW preexcitation (negativenegative delta wave delta wave may mimic pathologic Q waves) may mimic pathologic Q waves) IHSS (septal hypertrophy may make IHSS (septal hypertrophy may make normal septal Q waves "fatter" thereby normal septal Q waves "fatter" thereby mimicking pathologic Q waves) mimicking pathologic Q waves) LVH (may have QS pattern or poor R wave LVH (may have QS pattern or poor R wave progression in leads V1-3) progression in leads V1-3) RVH (tall R waves in V1 or V2 may mimic RVH (tall R waves in V1 or V2 may mimic true posterior MI) true posterior MI) Complete or incomplete LBBB (QS waves Complete or incomplete LBBB (QS waves or poor R wave progression in leads V1-3) or poor R wave progression in leads V1-3)

Differential MI patternDifferential MI patternPneumothorax (loss of right precordial R waves) Pneumothorax (loss of right precordial R waves) Pulmonary emphysema and cor pulmonale (loss Pulmonary emphysema and cor pulmonale (loss of R waves V1-3 and/or inferior Q waves with right of R waves V1-3 and/or inferior Q waves with right axis deviation) axis deviation) Left anterior fascicular block (may see small q-Left anterior fascicular block (may see small q-waves in anterior chest leads) waves in anterior chest leads) Acute pericarditis (the ST segment elevation may Acute pericarditis (the ST segment elevation may mimic acute transmural injury) mimic acute transmural injury) Central nervous system disease (may mimic non-Central nervous system disease (may mimic non-Q wave MI by causing diffuse ST-T wave changes Q wave MI by causing diffuse ST-T wave changes