27.8.2013(AV block) Flashcards
Causes of first degree AV block
Drugs Beta blockers CCB digitalis Hypothyroidism Rheumatic fever Enhanced Vagal tone Disease of conduction system
First degree AV block
PR Interval more than 0.20s
When does first degree AV block become symptomatic?
When p wave falls within QT interval of previous cycle
Synchronous contraction of both atria and ventricles,reduced cardiac output
S1 in first degree AV block
Intensity is diminished
Types of second degree AV block
Mobitz type 1 or wenkebach
Mobitz type 2
High degree AV block
Advanced second degree AV block
When two or more p waves are not followed by QRS complexes
How to diagnose type 1 second degree AV block
PR interval after pause is shortest and before pause is longest
ECG findings in type 1 Second degree AV block
Two or more consecutive p waves are conducted
Only single p waves are blocked
There is gradual prolongation of PR interval before a ventricular complex is dropped
PR intervals always shorten immediately after pause
QRS complexes are usually narrow
Group beating is present
RR intervals are variable
AV block and MI
Inferior MI- nodal AV block
Anterior MI- infra nodal block
Physiological causes of type 1 AV block
Sleep,due to increased Vagal tone
Causes of type I AV block
Sleep Intense Vagal stimulation due to cough or vomiting Drugs Myocarditis Acute Rheumatic fever Lyme disease
Cause of infra nodal AV block
Structural heart disease
Infra-nodal AV block is almost always associated with
Bundle branch block
Rx of first degree heart block
Permanent pacing is indicated only if PR interval is more than 0.30s and ventricular filling is impaired
Indications for pacemaker implantation in type 1 second degree AV block
Symptomatic patients with LV systolic dysfunction
Asymptomatic pts with infra nodal AV block
Asymptomatic pts with any level of AV block but with third degree block developing during exercise without myocardial ischemia and pts with myotonic dystrophy,erbs dystrophy,Peroneal muscular dystrophy
ECG findings in type 2 second degree AV block
Two or more consecutive p waves are conducted
Only single p waves are blocked
PR intervals are fixed and do not vary
QRS complexes are wide due to presence of bundle branch block
RR intervals are fixed
Finding that is a must for diagnosis of type 2 second degree AV block
Presence of RBBB or LBBB with or without fascicular block
Cause of type 2 second degree AV nodal block
One bundle has fixed block
Other bundle has intermittent block
Acute infarct with type 2 second degree AV block,the mortality is higher because
It is usually due to extensive anterior wall infarct
Etiologies of type 2 block
Sclerosis and calcification due to ageing
Infarct
Sarcoidosis
Amyloid
Neuromuscular dystrophy
After cardiac surgery or ablation procedures
Autonomic nervous system and conduction system of heart
Sinus node and AV node are under the influence of both sympathetic and parasympathetic nervous system
Intra ventricular conduction system below AV node is influenced mainly by sympathetic nervous system
Diff btw type 1 and type 2 second degree block,autonomic manoeuvres
Sympathetic stimulation improves type 1 block and worsens type 2 block
Parasympathetic stimulation improves type 2 block
Ventriculophasic sinus arrythmia in 2:1 AV block
PP interval with QRS is shorter than PP without QRS
Atropine is not effective if the AV block is
Infra nodal
normal AH interval
60-125 msec
Normal HV interval
35-55 msec
Regular RR interval in AF
Complete heart block
non respiratory cause of sinus arrythmia
digitalis
Drug that can be given in place of pacemaker in sick sinus syndrome
theophylline 200-400mg/day
Manoeuvre that can terminate a sinus arrest
forceful coughing
