CVPR 03-31-14 11am-Noon Arrhythmias slides - Horwitz Flashcards
Normal conduction pathway & waves generated
SA node generates an electrical impulse which cannot be seen on the ECG —> electrical current travels through Rt. & Lt. atrial muscles and atrial depolarization is visible as the P wave —> electrical impulse then arrives at AV node, which conducts electricity at a slower pace, creating a pause (PR interval) before the ventricles are stimulated [pause allows blood to be emptied into ventricles from atria prior to ventricular contraction] —> QRS is due to ventricular depolarization —> T-wave is due to repolarization
Sinus rhythm
Ever QRS is triggered by a P wave (P before QRS)
Normal sinus rate in adults
60-100 beats/min
Normal PR interval in adults
0.12-0.20 seconds
Normal QRS in adults
Whereas the QRS is normally narrow, if there is widening of the QRS (as occurs w/bundle branch blocks) but there is a P wave preceding each QRS by a normal PR interval, the rhythm is still sinus…… If the rate is 60-100, the QRS is regular, or only varies slightly due to respiration, and each QRS is preceded by a normal P wave with a normal PR interval, it is normal sinus rhythm.
Sinus Tachycardia - causes
Commonly occurs during exercise or emotional stress, with no treatment generally needed (appropriate compensatory increase in HR)….. In pts w/coronary artery disease as well as in hyperthyroidism, the increased cardiac oxygen demand may precipitate angina …… May also be caused by hypotension, acute lung/abdominal pathology, Thyrotoxicosis
Sinus Tachycardia – typical rates & ECG findings
Regular, fast …..Typical rates are 101-150…..Normal P & QRS
Sinus Tachycardia – treatment
Usually none is needed, but would want to look for underlying disease if it occurs at rest….. If treatment needed (as in thyrotoxicosis), beta blockade is usually effective
Sinus Bradycardia - causes
Common in normal individuals, especially athletes; Vagotonic states (faint; sick sinus syndrome; small inferior infarctions which increase vagal tone)
Sinus Bradycardia – symptoms
Can cause syncope, lightheadedness or fatique in elderly patients w/age-related dysfunction - the ‘sick sinus syndrome’
Sinus Bradycardia – typical rates & ECG findings
Regular, slow HR (<60bpm)….. P waves precede QRS, as normal
Sinus Bradycardia - treatment
Often requires no treatment; However, it may produce syncope during intense vagal activation as in fainting (‘Vaso-Vagal event’), for which atropine is effective. Treatment of sick sinus syndrome may require placement of an electronic pacemaker.
First-degree AV block – ECG findings
PR interval prolonged (>0.2 s, or more than one large block) = increased junctional delay
First-degree AV block – causes
Most commonly drug-induced (beta-blockers, some Ca2+ blockers [diltiazim, verapimil], digitalis. Also, conduction system disease
First-degree AV block – severity of the problem
Benign condition, but can proceed to more serious type of block
Second-degree AV block - causes
Some P waves conduct normally to the ventricles, but some do not (patterns vary…. Some P waves not followed by QRS; may or may be change in PR interval in normal P/QRS)….. May reflect conduction system disease, high vagal tone, or excessive effects of drugs
Second-degree AV block – symptoms
If rate is too slow to support cardiac output adequately, syncope or confusion may occur, requiring a pacemaker
Second-degree AV block - Mobitz type 1 vs. type 2
Mobitz 1 type: PR gets longer & longer until a P does not conduct (no QRS) = usually less severe….. Mobitz 2 type: no change in PR, just P waves sometimes not followed by a QRS (generally more sever & worry about transition to 3rd degree AV block)
Third-degree AV block – causes
Due to AV node or “junctional” failure with aging, infarct, severe conduction system disorders or disruption during cardiac surgery; Rarely drug-induced
Third-degree AV block – On ECG + symptoms/outcomes
Complete Heart Block…. Both Ps & QRSs show regular rhythm, but they are at different rates, with P rate > QRS rate…. No relationship between P and QRS waves (a pacemaker below the AV node has taken over)….. May cause syncope or sudden death
Third-degree AV block – treatment
Pacemaker if ventricular rate or BP are to low (probably a permanent pacemaker)
Premature atrial beat/contraction
Typically an abnormally-shaped P wave before a normal,narrow QRS, w/out widening of PR …. Usually benign
Premature ventricular beat/contraction
Typically QRS widens substantially and has no P wave in front of it….. Ectopic Ventricular Focus – conducted by slow myocardium (no Purkinje)….. Short path length blocks Re-entry …..Usually benign
Premature Atrial/Ventricular Contractions
Both are common in healthy persons and are experienced as single-beat palpitations….. Most commonly noticed at rest when low HR permit occurrence of premature ‘skipped beats’ and when distractions are reduced allowing awareness.
