Thaler's The Only EKG Book You'll Ever Need

  • Publisher: Wolters Kluwer
  • Author: Malcolm S. Thaler
  • Presenter: Wen-Bin Luo
  • Link: https://www.amazon.com/Only-Book-Youll-Ever-Need/dp/1451119054

The Basics

QT interval

  • QTc is prolonged if > 440ms in men or > 460ms in women
  • QTc > 500 is associated with increased risk of torsades de pointes
  • QTc is abnormally short if < 350ms
  • A useful rule of thumb is that a normal QT is less than half the preceding RR interval

Hypertrophy and Enlargement of the Heart

Right atrial enlargement (RAE)

  • P waves with an amplitude exceeding 2.5 mm in the inferior leads
  • No change in the duration of the P wave
  • Possible right axis deviation of the P wave

Left atrial enlargement (LAE)

  • The amplitude of the terminal (negative) component of the P wave may be increased and must descend at least 1 mm below the isoelectric line in lead V1
  • The duration of the P wave is increased, and the terminal (negative) portion of the P wave must be at least 1 small block (0.04 second) in width
  • No significant axis deviation is seen because the left atrium is normally electrically dominant

Right ventricular hypertrophy (RVH)

  • Right axis deviation is present, with the QRS axis exceeding +100°
  • The R wave is larger than the S wave in V1, whereas the S wave is larger than the R wave in V6

Left ventricular hypertrophy (LVH)

  • The R wave in V5 or V6 plus the S wave in V1 or V2 exceeds 35 mm
  • The R wave in aVL exceeds 13 mm
  • Left axis deviation exceeding −15° is also present

Arrhythmias

Atrial tachycardia (AT)

  • Regular
  • Rate: 100-200 bpm
  • Characteristic warm-up period in the automatic form
  • Carotid massage: no effect, or only mild slowing

Multifocal atrial tachycardia (MAT)

  • Irregular
  • At least three different P wave morphologies
  • Rate: 100-200 bpm; sometimes less than 100 bpm
  • Carotid massage: no effect

Atrial flutter

  • Regular, saw-toothed
  • 2:1, 3:1, 4:1, etc., block
  • Atrial rate: 250-350 bpm
  • Ventricular rate: one-half, one-third, one-quarter, etc., of atrial rate
  • Carotid massage: increases block

Atrial fibrillation (AF)

  • Irregular
  • Undulating baseline
  • Atrial rate: 350-500 bpm
  • Ventricular rate: variable
  • Carotid massage: may slow ventricular rate

AV nodal reentrant tachycardia (AVNRT)

  • Regular
  • P waves are retrograde if visible
  • Rate: 150-250 bpm
  • Carotid massage: slows or terminates

Conduction Blocks

First degree AV block

  • The PR interval is greater than 0.2 seconds
  • All beats are conducted through to the ventricles

Second degree AV block: Mobitz type I (Wenckebach)

  • Second degree AV block: Mobitz type I (Wenckebach)

Second degree AV block: Mobitz type II

  • All-or-nothing conduction, in which QRS complexes are dropped without prolongation of the PR interval

Third degree AV block

  • No beats are conducted through to the ventricles
  • There is complete heart block with AV dissociation, in which the atria and ventricles are driven by independent pacemakers

Right bundle branch block (RBBB)

  • QRS complex widened to greater than 0.12 seconds
  • RSR′ in V1 and V2 (rabbit ears) with ST segment depression and T wave inversion
  • Reciprocal changes in V5, V6, I, and aVL

Left bundle branch block (LBBB)

  • QRS complex widened to greater than 0.12 seconds
  • Broad or notched R wave with prolonged upstroke in leads V5, V6, I, and aVL, with ST segment depression and T wave inversion
  • Reciprocal changes in V1 and V2
  • Left axis deviation may be present

Left anterior hemiblock (LAH)

  • Normal QRS duration and no ST segment or T wave changes
  • Left axis deviation between −30° and +90°
  • No other cause of left axis deviation is present

Left posterior hemiblock (LPH)

  • Normal QRS duration and no ST segment or T wave changes
  • Right axis deviation
  • No other cause of right axis deviation is present

Preexcitation Syndromes

Wolff-Parkinson-White (WPW) syndrome

  • PR interval less than 0.12 seconds
  • Wide QRS complexes
  • Delta wave seen in some leads

Lown-Ganong-Levine (LGL) syndrome

  • PR interval less than 0.12 seconds
  • Normal QRS width
  • No delta wave

Myocardial Ischemia and Infarction

Pathological Q wave

  • The Q wave must be greater than 0.04 seconds in duration
  • The depth of the Q wave must be at least one-third the height of the R wave in the same QRS complex

Non-Q wave myocardial infarction (NQMI)

  • T wave inversion
  • ST segment depression persisting for more than 48 hours in the appropriate setting

Finishing Touches

Hyperkalemia

  • Evolution of peaked T waves, PR prolongation and P wave flattening, and QRS widening
  • Ultimately, the QRS complexes and T waves merge to form a sine wave, and ventricular fibrillation may develop

Hypokalemia

  • ST depression
  • T wave flattening
  • U waves

Hypercalcemia

  • Shortened QT interval

Hypocalcemia

  • Prolonged QT interval

Hypothermia

  • Osborn waves
  • Prolonged intervals
  • Sinus bradycardia
  • Slow atrial fibrillation; beware of muscle tremor artifact

Digitalis

  • Therapeutic levels associated with ST segment and T wave changes in leads with tall R waves
  • Toxic levels associated with tachyarrhythmias and conduction blocks
  • PAT with block is most characteristic

Pericarditis

  • Diffuse ST segment and T wave changes
  • A large effusion can cause low voltage and electrical alternans

Hypertrophic cardiomyopathy (HCM)

  • Ventricular hypertrophy
  • Left axis deviation
  • Septal Q waves

Myocarditis

  • Conduction blocks

Chronic obstructive pulmonary disease (COPD)

  • Low voltage
  • Right axis deviation
  • Poor R wave progression
  • Chronic cor pulmonale can produce P pulmonale and right ventricular hypertrophy with repolarization abnormalities

Acute pulmonary embolism

  • Right ventricular hypertrophy with strain
  • right bundle branch block
  • S1Q3T3
  • Sinus tachycardia and atrial fibrillation are the most common arrhythmias

Central nervous system disease

  • Diffuse T wave inversion, with T waves typically wide and deep
  • U waves

Brugada syndrome

  • A pattern resembling right bundle branch block
  • ST segment elevation in leads V1, V2, and V3

Athletic heart syndrome (AHS)

  • Sinus bradycardia
  • Nonspecific ST segment and T wave changes
  • Left and right ventricular hypertrophy
  • Incomplete right bundle branch block
  • First-degree or Wenckebach AV block
  • Occasional supraventricular arrhythmia