DYSRHYTHMIA

DEFINITION: ABNORMAL
HEART RATE OR RHYTHM
 OUTLINE
DEFINITION
BASIC ECG
ECG RHYTMS
• ECG Rhythms
• This section is intended to give you an insight into some of the
ECG's you may come across while working in the prehospital
environment. (Note these are rhythm strips and not diagnostic 12
lead patterns)
• Normal Sinus Rhythm
• Looking at the ECG you'll see that:
• Rhythm - Regular
• Rate - (60-99 bpm)
• QRS Duration - Normal
• P Wave - Visible before each QRS complex
• P-R Interval - Normal (<5 small Squares. Anything above and this
would be 1st degree block)
• ^ What you want your patient ECG to look like
• · Sinus Bradycardia
• A heart rate less than 60 beats per minute (BPM). This in a healthy
athletic person may be 'normal', but other causes may be due to
increased vagal tone from drug abuse, hypoglycaemia and brain
injury with increase intracranial pressure (ICP) as examples
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - less than 60 beats per minute
• · QRS Duration - Normal
• · P Wave - Visible before each QRS complex
• · P-R Interval - Normal
• · Usually benign and often caused by patients on beta blockers
• · Sinus Tachycardia
• An excessive heart rate above 100 beats per minute (BPM) which
originates from the SA node. Causes include stress, fright, illness
and exercise. Not usually a surprise if it is triggered in response to
regulatory changes e.g. shock. But if their is no apparent trigger
then medications may be required to suppress the rhythm
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - More than 100 beats per minute
• · QRS Duration - Normal
• · P Wave - Visible before each QRS complex
• · P-R Interval - Normal
• · The impulse generating the heart beats are normal, but they are
occurring at a faster pace than normal. Seen during exercise
• · Supraventricular Tachycardia (SVT) Abnormal
• A narrow complex tachycardia or atrial tachycardia which
originates in the 'atria' but is not under direct control from
the SA node. SVT can occur in all age groups
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - 140-220 beats per minute
• · QRS Duration - Usually normal
• · P Wave - Often buried in preceding T wave
• · P-R Interval - Depends on site of supraventricular
pacemaker
• Impulses stimulating the heart are not being generated by
the sinus node, but instead are coming from a collection of
tissue around and involving the atrioventricular (AV) node
• · Atrial Fibrillation
•
• Many sites within the atria are generating their own electrical impulses,
leading to irregular conduction of impulses to the ventricles that
generate the heartbeat. This irregular rhythm can be felt when palpating
a pulse
• It may cause no symptoms, but it is often associated with palpitations,
fainting, chest pain, or congestive heart failure.
• Looking at the ECG you'll see that:
• · Rhythm - Irregularly irregular
• · Rate - usually 100-160 beats per minute but slower if on medication
• · QRS Duration - Usually normal
• · P Wave - Not distinguishable as the atria are firing off all over
• · P-R Interval - Not measurable
• · The atria fire electrical impulses in an irregular fashion causing
irregular heart rhythm
• · Atrial Flutter
•
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - Around 110 beats per minute
• · QRS Duration - Usually normal
• · P Wave - Replaced with multiple F (flutter) waves,
usually at a ratio of 2:1 (2F - 1QRS) but sometimes 3:1
• · P Wave rate - 300 beats per minute
• · P-R Interval - Not measurable
• · As with SVT the abnormal tissue generating the
rapid heart rate is also in the atria, however, the
atrioventricular node is not involved in this case.
• · 1st Degree AV Block
• 1st Degree AV block is caused by a conduction delay
through the AV node but all electrical signals reach the
ventricles. This rarely causes any problems by itself and
often trained athletes can be seen to have it. The normal P-
R interval is between 0.12s to 0.20s in length, or 3-5 small
squares on the ECG.
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - Normal
• · QRS Duration - Normal
• · P Wave - Ratio 1:1
• · P Wave rate - Normal
• · P-R Interval - Prolonged (>5 small squares)
• · 2nd Degree Block Type 1 (Wenckebach)
• Another condition whereby a conduction block of some,
but not all atrial beats getting through to the ventricles.
There is progressive lengthening of the PR interval and then
failure of conduction of an atrial beat, this is seen by a
dropped QRS complex.
• Looking at the ECG you'll see that:
• · Rhythm - Regularly irregular
• · Rate - Normal or Slow
• · QRS Duration - Normal
• · P Wave - Ratio 1:1 for 2,3 or 4 cycles then 1:0.
• · P Wave rate - Normal but faster than QRS rate
• · P-R Interval - Progressive lengthening of P-R interval until
a QRS complex is dropped
• · 2nd Degree Block Type 2
• When electrical excitation sometimes fails to pass through
the A-V node or bundle of His, this intermittent occurance
is said to be called second degree heart block. Electrical
conduction usually has a constant P-R interval, in the case
of type 2 block atrial contractions are not regularly followed
by ventricular contraction
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - Normal or Slow
• · QRS Duration - Prolonged
• · P Wave - Ratio 2:1, 3:1
• · P Wave rate - Normal but faster than QRS rate
• · P-R Interval - Normal or prolonged but constant
• · 3rd Degree Block
• 3rd degree block or complete heart block occurs when atrial
contractions are 'normal' but no electrical conduction is conveyed to
the ventricles. The ventricles then generate their own signal through
an 'escape mechanism' from a focus somewhere within the
ventricle. The ventricular escape beats are usually 'slow'
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - Slow
• · QRS Duration - Prolonged
• · P Wave - Unrelated
• · P Wave rate - Normal but faster than QRS rate
• · P-R Interval - Variation
• · Complete AV block. No atrial impulses pass through the
atrioventricular node and the ventricles generate their own rhythm
• · Bundle Branch Block
• Abnormal conduction through the bundle branches will cause a depolarization delay through the ventricular
muscle, this delay shows as a widening of the QRS complex. Right Bundle Branch Block (RBBB) indicates
problems in the right side of the heart. Whereas Left Bundle Branch Block (LBBB) is an indication of heart
disease. If LBBB is present then further interpretation of the ECG cannot be carried out.
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - Normal
• · QRS Duration - Prolonged
• · P Wave - Ratio 1:1
• · P Wave rate - Normal and same as QRS rate
• · P-R Interval - Normal
• · Bundle Branch Block
• Abnormal conduction through the bundle branches will cause a depolarization delay through the ventricular
muscle, this delay shows as a widening of the QRS complex. Right Bundle Branch Block (RBBB) indicates
problems in the right side of the heart. Whereas Left Bundle Branch Block (LBBB) is an indication of heart
disease. If LBBB is present then further interpretation of the ECG cannot be carried out.
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - Normal
• · QRS Duration - Prolonged
• · P Wave - Ratio 1:1
• · P Wave rate - Normal and same as QRS rate
• · P-R Interval - Normal
• · Premature Ventricular Complexes
• Due to a part of the heart depolarizing earlier than it should
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - Normal
• · QRS Duration - Normal
• · P Wave - Ratio 1:1
• · P Wave rate - Normal and same as QRS rate
• · P-R Interval - Normal
• · Also you'll see 2 odd waveforms, these are the ventricles
depolarising prematurely in response to a signal within the
ventricles.(Above - unifocal PVC's as they look alike if they
differed in appearance they would be called multifocal PVC's,
as below)
•
• Junctional Rhythms
• In junctional rhythm the sinoatrial node does not control the
heart's rhythm - this can happen in the case of a block in
conduction somewhere along the pathway. When this happens,
the heart's atrioventricular node takes over as the pacemaker.
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - 40-60 Beats per minute
• · QRS Duration - Normal
• · P Wave - Ratio 1:1 if visible. Inverted in lead II
• · P Wave rate - Same as QRS rate
• · P-R Interval - Variable
• · Below - Accelerated Junctional Rhythm
•
• Ventricular Tachycardia (VT) Abnormal
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - 180-190 Beats per minute
• · QRS Duration - Prolonged
• · P Wave - Not seen
• · Results from abnormal tissues in the ventricles
generating a rapid and irregular heart rhythm. Poor cardiac
output is usually associated with this rhythm thus causing
the pt to go into cardiac arrest. Shock this rhythm if the
patient is unconscious and without a pulse
• · Ventricular Fibrillation (VF) Abnormal
• Disorganised electrical signals cause the ventricles to
quiver instead of contract in a rhythmic fashion. A
patient will be unconscious as blood is not pumped to
the brain. Immediate treatment by defibrillation is
indicated. This condition may occur during or after a
myocardial infarct.
• Looking at the ECG you'll see that:
• · Rhythm - Irregular
• · Rate - 300+, disorganised
• · QRS Duration - Not recognisable
• · P Wave - Not seen
• · This patient needs to be defibrillated!! QUICKLY
• · Asystole - Abnormal
• A state of no cardiac electrical activity, as such no
contractions of the myocardium and no cardiac
output or blood flow are present.
• Looking at the ECG you'll see that:
• · Rhythm - Flat
• · Rate - 0 Beats per minute
• · QRS Duration - None
• · P Wave - None
• · Carry out CPR!!
• · Myocardial Infarct (MI)
• Looking at the ECG you'll see that:
• · Rhythm - Regular
• · Rate - 80 Beats per minute
• · QRS Duration - Normal
• · P Wave - Normal
• · S-T Element does not go isoelectric which could
indicate infarction. However this is NOT
diagnostic unless associated with a 12 lead ECG