ATRIOVENTRICULAR CONDUCTION SYSTEM

•  1st-degree AV block—PR interval increased >0.2 sec

•  2nd-degree AV block

• Mobitz type I (Wenckebach)—AV delay (PR interval) increases with each beat, until QRS is dropped after P wave

• Treatment—only if symptomatic: Atropine, isoproterenol, permanent pace

• Mobitz type II—sudden unpredictable dropped QRS not associated with progressive PR interval prolongation

• Caution: May progress to 3rd-degree heart block

• Treatment—permanent pacemaker

•  3rd-degree AV block (complete heart block)

• No relationship between P wave & QRS—“AV dissociation”

• Treatment—permanent pacemaker

•  Bundle branch block

• Right bundle branch block (RBBB)

• Examine QRS in V1 & V2

• Right ventricular depolarization delayed

• LBBB makes it difficult to determine infarction on ECG

• Left bundle branch block (LBBB)

• Examine QRS in V5 or V6

• Left ventricular depolarization delayed

• Difficult to determine infarction on ECG

• Atrial flutter

• Regular atrial activity; 180–350 bpm; ventricular rate 150 bpm (2:1 AV block)

• ECG: “F waves,” “sawtooth” pattern, flutter waves

• Treatment

• Unstable → immediate electrical cardioversion

• Burst pacing (temporary or permanent pacemaker)

• Medical therapy (β-blockers, Ca²⁺-channel blockers)

• Radiofrequency catheter ablation (RFA)

• Atrial fibrillation

• Irregular atrial activity at 350–600 bpm, ventricular rate 160

• ECG: Wavy baseline, absent P waves

• Treatment

• Unstable → immediate electrical cardioversion

• Chemical cardioversion (Class IA, IV, III antiarrhythmics)

• Antiarrhythmic drugs

• Anticoagulation

• Rate control: β- or Ca²⁺-channel blockers, digoxin

• Maze procedure

• Paroxysmal SVT

• Ventricular rate 140–250 bpm

• ECG: Narrow complex, P waves hidden in QRS complexes (QRS may be slightly widened, not more than 0.14 sec)

• Treatment: Vagal maneuvers, β- or Ca²⁺-channel blockers, radiofrequency ablation

•  AV reentrant tachycardia

• Wolff–Parkinson–White

• PR interval shortened, delta wave, wide QRS

• Treatment: β- or Ca²⁺-channel blockers, radiofrequency ablation

VENTRICULAR ARRHYTHMIAS

•  Premature ventricular beats

• Widened QRS

• Couplet—two in a row; Bigeminy—every other beat is PVC

•  Ventricular tachycardia—3 or more PVCs in a row, 100–200 bpm

• Nonsustained VT (NSVT)—persists for <30 sec

• Sustained VT—persists for ≥30 sec

• Treatment

• Symptomatic: Electrical cardioversion followed by antiarrhythmic drugs; follow ACLS protocol

• Asymptomatic NONSUSTAINED VT: β-blockers, implantable cardioverter-defibrillator (ICD) in pts at high risk

• Unstable: Defibrillation as if ventricular fibrillation

•  Torsades de pointes

• Polymorphic VT with varying amplitudes of QRS twisting about the baseline

• Treatment: Magnesium 1–2 g IV followed by infusion

•  Ventricular fibrillation

• Chaotic irregular appearance without discrete QRS waveforms

• Treatment: See ACLS protocol; ICD if arrhythmia not associated with acute MI

OTHER ECG ABNORMALITIES

Hypertrophy

•  Right atrial hypertrophy

• Large, biphasic P wave with tall initial component

•  ●Left atrial hypertrophy

• Large, biphasic P wave with wide terminal component

• Ventricular hypertrophy

• Right ventricular hypertrophy

• R wave >S in V1 (R wave becomes progressively smaller from V1 to V6)

• S wave persists in V5 & V6

• Right axis deviation with slightly widened QRS

• Rightward rotation in horizontal plane

• Left ventricular hypertrophy

• S wave in V1 + R wave in V5 >35 mm

• Left axis deviation with slightly widened QRS

• Leftward rotation in horizontal plane

• Inverted T wave that slants downward gradually but upward quickly

Electrolyte Imbalances

•  Hypokalemia

• Flattened T wave

• U waves

•  Hyperkalemia

• Peaked T waves

• Wide or flat P wave

• Wide QRS

•  Hyper-/hypocalcemia

• Hypercalcemia—shortened QT

• Hypocalcemia—prolonged QT

Drug Effects

•  Digitalis toxicity

• Inverted or flattened T waves

• Shortened QT interval

Pulmonary Embolism

•  Right axis deviation

•  Acute RBBB

•  Inverted T waves in V1 to V4 from right ventricular overload

•  Wide S in I large Q; and inverted T in III

Pericarditis

• Diffuse ST-segment elevation (looks similar to acute MI, usually more universal in nature)

•  May see subsequent inverted T waves (similar to acute MI)

Hypothermia

•  J wave or Osborne wave—J POINT ELEVATION WITH T WAVE INVERSION, ESPECIALLY IN THE SETTING OF SLOWED CONDUCTION

Biventricular Pacemaker

•  Cardiac resynchronization therapy-–used to synchronize contraction of right and left ventricles to increase cardiac output in patients with heart failure.

Cardiac Transplantation

•  2 sets of P waves

•  Increased SA node refractory period

•  Prolonged atrial conduction

•  1st-degree AV block common