Section 1 Supraventricular rhythms

Normal sinus rhythm

Normal sinus rhythm with a normal U wave

Sinus arrhythmia (irregular sinus rhythm)

Sinus tachycardia

Sinus bradycardia

Atrial bigeminy

Atrial trigeminy

Ectopic atrial rhythm

Multifocal atrial tachycardia

Atrial fibrillation

Atrial fibrillation with rapid ventricular response

Atrial fibrillation and bundle branch block

Atrial flutter

Atrial flutter with 2:1 AV block

Atrial flutter with variable AV conduction

Accelerated junctional rhythm

Junctional bradycardia

Paroxysmal SVT – AV nodal re-entry tachycardia

Paroxysmal SVT – AV reciprocating tachycardia (orthodromic)

AV reciprocating tachycardia (antidromic)

Wolff-Parkinson-White syndrome with atrial fibrillation

Supraventricular tachycardia with aberrant conduction

Sick sinus syndrome

Case 1 A 29-year-old healthy man

Normal sinus rhythm

• There are P waves.

• Each P wave is followed by a QRS complex.

• The rate is 60-100 b.p.m.

Features of this ECG

• Sinus rhythm, 66 b.p.m., normal QRS axis

• P waves followed by QRS complexes (Fig. 1.1).

• Baseline wander (Fig. 1.1):

– the isoelectric line is not flat

• Skeletal muscle interference (Fig. 1.2):

– high frequency irregular waves of muscular contractions

Fig. 1.1 Rhythm strip.

Fig. 1.2 Lead I.

Causes of poor ECG recordings

→ Baseline wander:

– poor electrode contact, movement, twisted cables

→ Skeletal muscle interference:

– anxious patient

→ Electrical interference:

– poor insulation, poor filtering

→ Poor print quality:

– problems with paper and ink

Case 2 A 35-year-old healthy female volunteer in a clinical trial

Normal sinus rhythm with a normal U wave

• A low amplitude, rounded, positive deflection following the T wave (< 25% amplitude of the preceding T wave, maximum of 1.5 mm).

Features of this ECG

• Sinus rhythm, 65 b.p.m., normal QRS axis (+30°)

• U wave seen in the right chest leads (Fig. 2.1)

Fig. 2.1 Lead V3.

Clinical Note

U waves are often so low in amplitude that they go unrecognised. U waves are usually easiest to see in the right sided precordial leads. The origin of the U wave is controversial but may represent repolarisation of the His-Purkinje system or of the papillary muscles.

Causes of abnormal U waves

→ Inverted U waves:

– ischaemic heart disease

– left ventricular volume overload

→ Prominent U waves:

– hypokalaemia

– hypercalcaemia

– digitalis

– class 1A and class 3 antiarrhythmic drugs

– thyrotoxicosis

– intracranial haemorrhage

– exercise

– congenital long QT syndrome

Case 3 A 25-year-old junior doctor

Sinus arrhythmia (irregular sinus rhythm)

• A variation in the P-P interval of more than 10%.

Types of sinus arrhythmia:

1. respiratory – alternating periods of gradually lengthening and shortening P-P intervals (shown here)

2. non-respiratory

3. ventriculo-phasic – seen in association with complete heart block.

Features of this ECG

• Sinus arrhythmia, mean rate 54 b.p.m., normal QRS axis

• There are short P-P intervals at the beginning of the rhythm strip (Fig. 3.1) and longer P-P intervals at the end of the rhythm strip (Fig. 3.2)

• Early repolarisation in leads II, III, V5 and V6

Fig. 3.1 Short cycles.

Fig. 3.2 Longer cycles.

Clinical Note

The cycle length is shorter (and the rate is faster) with inspiration.

Associations of sinus arrhythmia

→ Seen in normal individuals:

– especially the young or athletic

→ Accentuated by:

– rest

– digoxin

– carotid sinus massage

→ Abolished by:

– exercise

– atropine

Case 4 A 73-year-old man with pneumonia

Sinus tachycardia

• Sinus rhythm with a rate greater than 100 b.p.m.

Features of this ECG

• Sinus tachycardia, 126 b.p.m., left axis deviation (−50°)

• There is a rapid P wave rate (Fig. 4.1)

• Left atrial hypertrophy (Fig. 4.1):

– wide, notched P waves in lead II

• Left anterior hemiblock (Fig. 4.2):

– left axis deviation

– initial r waves in the inferior leads

Fig. 4.1 P-mitrale.

Fig. 4.2 Lead aVF.

Causes of sinus tachycardia

→ Exercise

→ Anxiety

→ Fever

→ Hypotension

→ Cardiac failure

→ Anaemia

→ Pregnancy

→ Thyrotoxicosis

→ Pulmonary embolus

→ Acute pericarditis

→ Sinus node dysfunction

Case 5 A 60-year-old man with hypertension and angina

Sinus bradycardia

• Sinus rhythm with a rate less than 60 b.p.m.

Features of this ECG

• Sinus bradycardia, 40 b.p.m., normal axis

• There is a slow P wave rate (Fig. 5.1)

• Incomplete right bundle branch block (Fig. 5.2):

– an rSr′ pattern in V1

• Features suggesting left ventricular hypertrophy:

– left atrial abnormality (Fig. 5.2)

– non-specific lateral ST-T abnormalities

• A normal Q wave in lead III (Fig. 5.3):

– although wide > 40 ms (1 small square), there is no q in aVF > 20 ms or q in lead II

– normal Q waves in lead III disappear with deep inspiration

• Beats 2 and 5 of the rhythm strip are atrial premature beats:

– occur earlier than expected

– preceded by an abnormal P wave

Fig. 5.1 Rhythm strip.

Fig. 5.2 Lead V1.

Fig. 5.3 Lead III.

Clinical Note

This man was on a beta blocker.

Causes of sinus bradycardia

→ Normal finding in athletes

→ Sleep

→ Drugs:

– beta blockers, amiodarone

– digoxin

– calcium channel blockers

→ Vasovagal syncope

→ Sinus node dysfunction

→ Hypothyroidism

→ Obstructive jaundice

→ Uraemia

→ Increased intracranial pressure

→ Glaucoma

Case 6 A 60-year-old man noted to have a regularly irregular pulse

Atrial bigeminy

• An atrial premature beat (APB) following every sinus beat.

Features of this ECG

• Atrial bigeminy, 66 b.p.m., normal QRS axis (+45°)

• The 9th complex is the only sinus beat not followed by an APB (Fig. 6.1)

• Sinus rate is 50 b.p.m (Fig. 6.1)

• Features of atrial bigeminy (Fig. 6.2):

– after each sinus beat there is a premature and abnormal-appearing P wave associated with a QRS complex of the same morphology as the sinus beats

– the pause after the ectopic beat is not a full compensatory pause

Fig. 6.1 Lead V4.

Fig. 6.2 Rhythm strip.

Clinical Note

If an APB occurs early in the cardiac cycle (in the refractory period of the AV node) it may be conducted aberrantly and as a result the APB QRS complex will have a RBBB (most common) or LBBB morphology.

The pause after a VPB is not usually a full compensatory one as the APB depolarises the SA node, resetting it.

Case 7 A 70-year-old man with hypertension and a regularly irregular pulse

Atrial trigeminy

• An atrial premature beat (APB) following every second sinus beat.

Features of this ECG

• Atrial trigeminy, 84 b.p.m., normal QRS axis (+20°)

• Features of atrial trigeminy (Fig. 7.1):

– after every second sinus beat there is a premature and abnormal-appearing P wave associated with a QRS complex of the same morphology as the sinus beats

– the pause after the ectopic beat is not a full compensatory pause

• Features of left ventricular hypertrophy:

− voltage criteria for LVH in the chest leads, SV1 + RV6 > 35 mm (Fig. 7.2)

− widespread ST depression and T wave inversion, LV strain pattern

Fig. 7.1 Rhythm strip. The arrow indicates where the next QRS complex would have occurred with a full compensatory pause.

Fig. 7.2 Voltage criteria for LVH.

Case 8 A 50-year-old man with palpitations

Ectopic atrial rhythm

An atrial pacemaker outside the sinoatrial node.

• A sequence of three or more atrial premature beats.

• Abnormal P waves.

Features of this ECG

• Two rhythms are present:

– beats 1-5 and 11, ectopic atrial rhythm, 95 b.p.m.

– beats 6-10, sinus bradycardia, 55 b.p.m.

• Leftward QRS axis

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