Conduction Disorders Part One Flashcards
Diagnostic Characteristics of Normal Sinus Rhythm
Normal: rate 60-100 Sinus Rhythm: p waves are regular with normal upright configuration, PR interval is normal, QRS is regular and normal width, P to QRS relationship is 1:1
Diagnostic Characteristics of Sinus Bradycardia
slowing of discharge rate s, normal PR, 1:1 AV conduction
Cause of Sinus Bradycardia
Physiologic: well conditioned athlete, sleep, vagal stimulation Pharmacologic: digoxin, beta-blockers, calcium channel blockers Pathologic: inferior MI, increased intracranial pressure, hypothyroidism
Clinical Significance of Sinus Bradycardia
depends on cause; most causes are benign
Diagnostic Characteristics of Sinus Tachycardia
Acceleration of sinus discharge rate (usually 100 - 160) Normal sinus P’s, normal PR, 1:1 AV conduction
Cause of Sinus Tachycardia
Acceleration of sinus rate may be: Physiologic: infants/children, exertion, anxiety Pharmacologic: atropine, epinephrine, nicotine, caffeine, cocaine Pathologic: fever, hypoxia, anemia, pulmonary embolus
Clinical Significance of Sinus Tachycardia
depends on cause; most causes are benign
Diagnostic Characteristics of Sinus Arrhythmia
Variation in sinus node discharge rate Normal P waves, normal PR interval, 1:1 AV conduction
Cause of Sinus Arrhythmia
Most common in children, young adults Usually results from change in vagal tone during respiration
Clinical Significance of Sinus Arrhythmia
Benign, usually asymptomatic
Describe the characteristics of first degree AV block.
Characteristics: Delay in AV conduction; each impulse is conducted to the ventricles but slower than normal; PR interval > 0.2 seconds
Describe the causes of first degree AV block.
Cause: increased vagal tone, Digoxin or Digitalis toxicity, inferior MI, myocarditis
Describe the clinical significance of first degree AV block.
Clinical Significance: The delay is typically at the level of the AV node; usually benign.
Describe the characteristics of second degree AV block, type I (Wenckebach or Mobitz Type I).
Characteristics: progressive prolongation of PR interval until a P wave is blocked or not conducted; cycle usually repeats itself; conduction ratio describes the number of atrial depolarizations to ventricular depolarizations.
Describe the causes of second degree AV block, type I (Wenckebach or Mobitz Type I).
Cause: acute inferior MI, Digoxin or Digitalis toxicity, myocarditis, cardiac surgery, rheumatic heart disease, increased parasympathetic tone
Describe the clinical significance of second degree AV block, type I (Wenckebach or Mobitz Type I).
Clinical Significance: Occurs at the level of the AV node; may be due to progressive prolongation of AV node refractory period until the AV node is blocked; then the AV node resets itself; generally does not progress to complete heart block.
Describe the characteristics of second degree AV block, type II (Mobitz Type II).
Characteristics: constant PR interval, then non-conducted P wave; QRS complexes may be narrow or wide, depending on whether a bundle branch block is present.
Describe the causes of second degree AV block, type II (Mobitz Type II).
Cause: acute anteroseptal MI, cardiomyopathy
Describe the clinical significance of second degree AV block, type II (Mobitz Type II).
Clinical Significance: block usually occurs in infranodal conduction system; prognosis worse than Mobitz Type I; usually permanent and may progress to complete heart block; pacemaker is likely needed.
Describe the characteristics of third degree AV block (complete).
Characteristics: atrial and ventricular depolarizations are independent of each other; P waves and QRS complexes have no consistent relation to each other; PR interval varies; QRS may be either narrow or wide.
Describe the causes of third degree AV block (complete).
Cause: usually acute MI; drug effect (digoxin, beta-blocker); may be transient or permanent.
Describe the clinical significance of third degree AV block (complete).
Clinical Significance: no atrioventricular conduction; for a nodal block, the ventricular pacemaker is above the bundle of His and produces narrow QRS complexes; for an infranodal block, the ventricular pacemaker is at or below the bundle of His and produces a wide QRS complex (more unstable); pacemaker is required.
What are the diagnostic characteristics of PAC’s?
Ectopic P-wave occurs sooner than expected
Ectopic P-wave has a different shape than other P’s
Ectopic P-wave may or may not be conducted through AV node
What are common causes of PAC’s
Common in all ages - even without heart disease
Possibly precipitated by stress, fatigue, alcohol, tobacco, caffeine, sympathomimetics
Frequent PAC’s may be seen in chronic lung disease heart disease, or digoxin toxicity