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
What is/are the clinical significance of PAC’s
Usually benign
Occasionally PAC’s may trigger other atrial arrhythmias (i.e., a-fib/flutter)
What are the characteristics of SVT/atrial tachycardia?
Regular, rapid atrial rhythmn >160
May not see P waves
QRS are usually normal width
What are the common causes of SVT?
Fairly common in 2/1000
Can occur in an otherwise normal heart
No age or sex predisposition
Possibly in association with MI, Rheumatic Heart Disease, Pericarditis, Mitral Valve Prolapse
Due to reentry of depolarization
What is the clinical significance of SVT?
SVT is an abrupt onset of tachycardia caused by reentry of electrical impulse in the atria via closed loop of conducting tissue
Usually tolerated in young, healthy people
May cause palpitaitons, lightheadedness, dizziness, and shortness of breath
In elderly patients, or those with pre-existing heart disease, may cause syncope, pulmonary edema and myocardial ischemia
What are the characteristics of atrial flutter
Regular atrial rate 250-350 bpm
Sawtooth flutter waves
AV block (usually 2:1 and ventricular rate of 150)
What are the causes/clinical significance of Atrial Flutter?
Mostly (60%) due to underlying heart disease, ischemic heart disease, acute MI, hypertension
30% have no cause
Pulmonary embolus
Digoxin toxicity
May be a transitional arrhythmia between sinus rhythm and atrial fibrillation
May result in palpitations, fatigue, dyspnea
What are the characteristics of Atrial Fibrillation?
No organized P-waves - has a shimmering baseline
Irregular ventricular rhythm, usually rapid 160-180
Normal QRS complex width
What are the causes of Atrial Fibrillation?
**COMMON: **Rheumatic heart disease
Hypertension
Ischemic Heart Disease
Thyrotoxins
Other: COPD
Pulmonary Embolus
Pericarditis
ETOH
What is the clinical significance of Atrial Fibrillation?
Multiple areas of atria are continuously depolarizing
No uniform depolarization or contraction of atria - “quivering bag of worms”
Atrial depolarization rate >400 but the refractory period of AV node limits ventricular response
Loss of atrial contraction may lead to heart failure in patients with underlying left ventricular dysfunciton (due to loss of ‘atrial kick’)
Rapid ventricular response may lead to myocardial ischemia, hypotension and shock
Predisposes thrombus formation in atria = risk of stroke/CVA
