ECG Pearls
The three irregularly irregular rhythms are atrial fibrillation, atrial flutter with variable conduction and multifocal atrial tachycardia (similar to wandering atrial pacemaker).
Atrioventricular (AV) dissociation occurs in complete heart block (third-degree AV block) and ventricular tachycardia.
Treat a wide-complex tachycardia like ventricular tachycardia until proven otherwise. Use the Brugada criteria to distinguish ventricular tachycardia from supraventricular tachycardia (SVT) with aberrancy.
If no P waves can be seen and the QRS complexes are irregularly irregular, then atrial fibrillation is present.
ST segment elevation from pericarditis is diffuse (all leads except aVR and V1) and concave upward.
PR segment depression can be from acute pericarditis or an atrial infarction.
Diffuse T wave inversion is stage III of the ECG changes in pericarditis.
Pericarditis can be distinguished from early repolarization by the ratio of the T wave to the ST elevation. If the ratio is > 4, then early repolarization is present (the ST elevation is < 25% of the T wave amplitude).
The ST elevation from early repolarization resolves with exercise, while that of pericarditis does not.
Acute myocardial infarction can be diagnosed on an ECG in the setting of a left bundle branch block (LBBB) on occasion using Sgarbossa criteria or identifying Chapman’s sign or Cabrera’s sign.
The causes of the R wave in lead V1 greater in amplitude than the S wave include right bundle branch block (RBBB), posterior myocardial infarction, Wolff-Parkinson-White syndrome type A, right ventricular hypertrophy, ventricular tachycardia with right bundle morphology and isolated posterior wall hypertrophy occurring in Duchenne’s muscular dystrophy.
An Epsilon wave in lead V1 occurs in arrhythmogenic right ventricular dysplasia (ARVD) and is described as a “grassy knoll” appearance just after the QRS complex.
An Osborne wave classically occurs in the setting of hypothermia and is seen as a spike at the end of the QRS complex. An Osborne wave can also occur from hypercalcemia.
Hypercalcemia shortens the QT interval.
Dextrocardia shows negative QRS complex in lead I with negative P and T wave in this lead. There is low voltage in leads V4 through V6 (unlike limb lead reversal which has normal voltage in these leads, but negative QRS in lead I).
Hypokalemia causes U waves in the ECG seen as a positive wave just after the T wave.
Hyperkalemia causes peaked T waves initially, then an intraventricular conduction delay with a widened QRS complex, then bradycardia. Eventually a “sine wave” pattern ensues.
Hyperacute T waves are large and broadly shaped, occurring in the first few minutes of an acute myocardial infarction.
Delta waves occur in Wolff-Parkinson-White syndrome
Hypertrophic obstructive cardiomyopathy (HOCM) is characterized by sharp, dagger-like Q waves in the lateral leads in the setting of left ventricular hypertrophy.
The most common ECG finding of an acute pulmonary embolism is sinus tachycardia; however, the classic finding is an S wave in lead I, Q wave in lead III and inverted T waves in lead III (S1Q3T3 pattern).
A bifascicular block is a combination of a right bundle branch block with a left anterior or posterior fascicular block.
A trifascicular block is a bifascicular block with a first-degree AV block.
2:1 AV block is a form of second-degree AV block that can be type I or type II. If the PR interval of the conducted beat is prolonged and the QRS complex is narrow, then it is most likely second-degree type I AV nodal block (Wenckebach). Alternatively, if the PR interval is normal and the QRS duration is prolonged, then it is most likely second-degree type II
Carotid massage, atropine administration or exercise can help determine if 2:1 AV block is from second-degree type I or second-degree type II AV block (see 2:1 AV block ECG Review).
A posterior wall MI shows ST depression, not elevation in leads V1 and V2 with an R:S ratio greater that 1 in lead V1.
Blocked premature atrial contractions occurring in a pattern of bigeminy can mimic sinus bradycardia.
Coarse “fibrillatory waves” can be seen during atrial fibrillation.
Clockwise atrial flutter causes positively deflected P waves in the inferior leads while counterclockwise atrial flutter causes negative deflected P waves in the inferior leads.
Multifocal atrial tachycardia (MAT) requires three different P wave morphologies in one ECG with a QRS complex rate of > 100.
Wandering atrial pacemaker (WAP) requires three different P wave morphologies in one ECG with a QRS complex rate of < 100.
Idioventricular rhythms meet criteria for ventricular tachycardia, but have a heart rate of < 100.
Massive left atrial enlargement causes a notch in the P wave and is termed “P-mitrale.”
A left ventricular aneurysm results in chronic ST elevation in the anterior precordial leads.
Low voltage on the ECG can be caused by obesity, chronic obstructive pulmonary disease (COPD), pericardial effusion, severe hypothyroidism, subcutaneous emphysema, massive myocardial damage/infarction, or infiltrative/restrictive diseases such as amyloid cardiomyopathy.
Electrical alternans occurs when every other QRS complex has varying amplitudes and is from the heart swaying within a large pericardial effusion.
Sinus arrhythmia requires a variation of at least 120 milliseconds of the PP interval.
A prolonged QT interval from hypocalcemia has a lengthened ST segment, then normal-appearing T wave.
Wellen’s phenomenon occurs from a proximal left anterior descending subtotal occlusion and has two types. Type I is deep inverted T waves in the precordial leads and type II is biphasic T waves in V1 through V3.
Digoxin can cause ST depression appearing as a “reverse tick” or “reverse check.”
Bidirectional ventricular tachycardia occurs when every other beat has a different QRS morphology and each morphology meets VT criteria. This is caused most commonly by digoxin toxicity.
Atrial tachycardia with 2:1 AV block is a common rhythm in the setting of digoxin toxicity.
An acute intracranial process (hemorrhage, trauma, carotid endarterectomy, etc.) can cause dramatic T wave inversions and a prolonged QT interval on the ECG.
Ostium primum atrial septal defects cause an incomplete right bundle branch block with left axis deviation. Ostium secundum atrial septal defects cause an incomplete right bundle branch block with right axis deviation.