The Electrocardiogram - Part VII

Sinus Rhythms

Sinus rhythms are characterized by electrical flow through the normal conduction pathways of the heart. The natural pacemaker, the SA node, is represented by a P wave with a normal PR-interval.

Normal Sinus Rhythm

ECG Characteristics:

Rate 60 to 100 bpm

Rhythm Regularly Regular
P wave Upright & Rounded, a P wave exists for every QRS complex
PR-Interval 0.12 to 0.20 seconds (120 - 200 ms)
QRS Complex 0.06 to 0.12 seconds (60 - 120 ms)
T wave Upright & Rounded
QT-Interval 0.36 to 0.44 seconds (360 - 440 ms) may be longer for females

Sinus Bradycardia

ECG Characteristics:

Rate less than 60 bpm

Rhythm Regularly Regular
P wave Upright & Rounded, a P wave exists for every QRS complex
PR-Interval 0.12 to 0.20 seconds (120 - 200 ms)
QRS Complex 0.06 to 0.12 seconds (60 - 120 ms)

T wave Upright & Rounded

QT-Interval 0.36 to 0.44 seconds (360 - 440 ms) may be longer for females

Sinus Tachycardia

ECG Characteristics:

Rate greater than 100 bpm (usually between 100 - 160 bpm)

Rhythm Regularly Regular

P wave Upright & Rounded, a P wave exists for every QRS complex

PR-Interval 0.12 to 0.20 seconds (120 - 200 ms)

QRS Complex 0.06 to 0.12 seconds (60 - 120 ms)

T wave Upright & Rounded
QT-Interval 0.36 to 0.44 seconds (360 - 440 ms) may be shortened

Sinus Arrhythmia

ECG Characteristics:

Rate 60 to 100 bpm, varies with respiration (faster with inspiration, slower with expiration)

Rhythm Irregularly Irregular, the R-R interval is shorter during inspiration and longer with expiration.
P wave Upright & Rounded, a P wave exists for every QRS complex
PR-Interval May vary slightly within normal limits
QRS Complex 0.06 to 0.12 seconds (60 - 120 ms)
T wave Upright & Rounded
QT-Interval Usually within normal limits

Possible Causes:

• Reflex vagal tone inhibition related to the normal respiratory cycle.
• Underlying conditions that increase vagal tone, digitalis toxicity, increased ICP, and inferior wall MI

Sinus Arrest

ECG Characteristics:

Rate 60 to 100 bpm, varies with the pause

Rhythm Regularly Regular, except where there is dropped beats
P wave Exists for every QRS complex, absent during pause
PR-Interval Within normal limits when present
QRS Complex 0.06 to 0.12 seconds (60 - 120 ms), absent during pause
T wave Upright & Rounded, absent during pause
QT-Interval Within normal limits when present

Possible Causes:

• Acute infection
• Inferior wall AMI
• Digitalis, quinidine, salicylate toxicity
• Carotid sinus massage
• Contrast dye
• Coronary artery disease
• Vagal stimulation
• Pesticide poisoning
• Degenerative heart disease

The tutorial:

• Basic Cardiology I
• Basic Cardiology II
• The ECG I
• The ECG II
• The ECG III
• The ECG IV
• The ECG V
• The ECG VI
• The ECG VII