Related Subjects:
|ECG Basics
|ECG Axis
|ECG Analysis
|ECG LAD
|ECG RAD
|ECG Low voltage
|ECG Pathological Q waves
|ECG ST/T wave changes
|ECG LBBB
|ECG RBBB
|ECG short PR
|ECG Heart Block
|ECG Asystole and P wave asystole
|ECG QRS complex
|ECG ST segment
|ECG: QT interval
|ECG: LVH
|ECG RVH
|ECG: Bundle branch blocks
|ECG Dominant R wave in V1
|ECG Acute Coronary Syndrome
|ECG Crib sheets
In all cases look for causes and context
- Hypothyroidism, Acute MI
- Reduce/stop Beta blockers, Digoxin, Verapamil if symptoms
- If slow ventricular rate consider Atropine IV
- A pacemaker will treat all refractory bradycardias with compromise
1st Degree heart blocks
- Rate: First-degree heart block can be seen with both sinus bradycardia and sinus
tachycardia
- Rhythm: sinus, regular, both atria and ventricles
- PR: prolonged, >0.20 sec, but does not vary (fixed)
- P waves: size and shape normal; every P wave is followed by a QRS complex; every QRS
complex is preceded by a P wave
- QRS complex: narrow; =0.10 sec in absence of intraventricular conduction defect
- Usually not clinically significant with a few exceptions
- An aortic root abscess can cause progressive 1st degree HB
Mobitz type 1: Wenckebach
- Rate: atrial rate just slightly faster than ventricular (because of dropped beats); usually normal
range
- Rhythm: regular for atrial beats; irregular for ventricular (because of dropped beats); can
show regular P waves marching through irregular QRS
- PR: progressive lengthening of the PR interval occurs from cycle to cycle; then one P wave
is not followed by a QRS complex (the “dropped beat")
- P waves: size and shape remain normal; occasional P wave not followed by a QRS complex (the “dropped beat")
- QRS complex: =0.10 sec most often, but a QRS “drops out" periodically
- Also known as the Wenckebach phenomenon.
- Can be seen in healthy individuals. Does not need a pacemaker.
Mobitz type 2
- Atrial Rate: usually 60-100 beats/min
- Ventricular rate: by definition (due to the blocked impulses) slower than atrial rate
- Rhythm: atrial = regular; ventricular = irregular (because of blocked impulses)
- PR: constant and set; no progressive prolongation as with type I—a distinguishing characteristic.
- P waves: typical in size and shape; by definition some P waves will not be followed by a
QRS complex
- QRS complex: narrow (=0.10 sec) implies high block relative to the AV node; wide(>0.12 sec) implies low block relative to the AV node
- More serious than Mobitz Type 1. Can precede Complete heart block.
- Management usually involves a pacemaker unless the readily reversible cause
Third Degree
- Atrial rate: usually 60-100 beats/min; impulses completely independent (“dissociated")
from ventricular rate
- Ventricular rate: depends on rate of the ventricular escape beats that arise:
- Ventricular escape beat rate slower than atrial rate = third-degree heart block (20-40
beats/min)
- Ventricular escape beat rate faster than atrial rate = AV dissociation (40-55 beats/min)
- Rhythm: both atrial rhythm and ventricular rhythm are regular but independent (“dissociated")
- PR: by definition there is no relationship between P wave and R wave
- P waves: typical in size and shape
- QRS complex: narrow (=0.10 sec) implies high block relative to the AV node; wide(>0.12 sec) implies low block relative to the AV node
- This may be an acute and potentially spontaneously reversible complication of, for example, STEMI - reperfusion therapies and pacing
- Management usually involves a pacemaker unless readily reversible cause
