ECG: Type II Second degree SA Block

1. Prof.S.SUNDAR’s unit
Dr.G.Rengaraj.PG
ECG OF THE WEEK

2. History & Exam.
A 58 yr. female came with
 c/o chest pain – 1 hr
 no h/o breathelessness, sweating,
palpitations,syncope,leg swelling
Not a known DM/SHT
O/E pulse- 80/min, BP- 120/80
 GC fair
 CVS & RS – Normal
 p/a – soft , CNS -NFND

4. Rhythm strip

6. IN THIS ECG
 Rate – 74/min
 Rhythm - SINUS rhythm with absent P-QRS-T every 5
th
wave
Axis- LAD
PR interval – 0.14 s
 P, QRS & T wave morphology – Normal
 The relatively short P-P intervals of 0.68 sec alternate with
intervals of 1.36 sec – twice the cycle length of the shorter
interval

7. Ecg
This indicates that the long interval is due to the omission of
a complete P-QRS-T complex
Every 5
th
impulse is blocked at the SA junction resulting in
5:4 SA block
Type 2 second-degree SA exit block

8. Sino-atrial block
The sinus impulse is blocked within the SA junction(between
SA node–atrial myocardium)
A complete cardiac cycle ( P-QRS-T ) drops out
This is a form of exit block, since the impulse cannot exit
from its pacemaker site
There are three types of SA block:
 1. First-degree
 2. second-degree- type 1(wenkebach)
 type 2
 3. third-degree

9. SA block
First-degree – the SA node impulse is merely slowed. It cannot be
recognised on the ECG because SA nodal discharge is not
recorded
Second-degree-
 1. type 1(wenkebach) – the P-R interval progressively lengthens,
P-P interval progressively shortens prior to the pause, and the
duration of the pause is less than two P-P cycles
 2.type 2 –no change in P-R interval before the pause, an interval
without P waves that equals approx. two,three or four times the
normal P-P cycle
Third-degree – complete absence of P waves . Difficult to
diagnose without sinus node electrograms

10. SA node disease
SA node dysfunction manifest in ECG as:
1. sinus bradycardia
2. sinus pauses
3. sinus arrest
4. sinus exit block
5. chronotropic incompetence

11. SA Node dysfunction
It can be classified as intrinsic or extrinsic
The distinction is important because extrinsic dysfunction is
often reversible and should generally be corrected before
considering pacemaker therapy
The most common causes of extrinsic SA node dysfunction
are drugs & ANS influences that suppress automaticity
and/or compromise conduction
Intrinsic sinus node dysfunction is degenerative and often
characterised by fibrous replacement of the SA node or its
connections to the atrium

12. Extrinsic causes
Autonomic : carotid sinus hypersensitivity
 vasovagal stimulation
Drugs : beta-blockers, CCB
 digoxin
 anti-arrhythmics( class 1 & 3)
 lithium,amitryptiline
Hypothyroidism
Sleep apnea
Increased ICP

13. Intrinsic
SSS
CAD ( chronic & acute MI )
Inflammatory – pericarditis
 myocarditis
 RHD
Senile amyloidosis
Chest trauma
Iatrogenic- radiation therapy

14. Diagnosis
SA node dysfunction is most commonly a clinical or ECG
diagnosis
Pacemaker implantation is the primary therapeutic
intervention in pts with symptomatic SA node dysfuction
A number of drugs including Beta-blockers & CCB modulate
SA node function and such agents should be discontinued
prior to making diseases regarding the need for permanent
pacing

15. THANK YOU