Ventricular Rhythms

• Ventricular rhythms are the most lethal and should be taken seriously by health professionals
• They can result from escape or usurpation
• Heart rate can range from 0 to over 250 beats per minute.
• Many ventricular rhythms can cause decreased cardiac output, some can cause cardiac standstill
• Most ventricular rhythms are responsive to medications.
• Some ventricular rhythms can be caused by the medications used to treat them
• Some ventricular rhythms can be treated only by electric shock, while others are usually fatal, even with treatment
• Some ventricular rhythms have no QRS complexes, others have wide, bizarre QRS complexes
• Depending on the lead being monitored and the ventricle propagating the ventricular beats, the QRS may be positive or negative
• The best leads to use for identification of ventricular rhythms is V1 or MCL1 to determine the ventricle where the rhythm/beats originated
• Left ventricular premature ventricular complexes (PVCs) have an upward deflection in V1/MCL1
• Right ventricular PVCs have a downward deflection in V1/MCL1
• Criteria for identifying ventricular rhythms:
  • Wide QRS (>0.12 seconds) without a preceding P wave
  • No QRS at all
  • Premature, wide QRS beat without a preceding P wave, interrupting another rhythm

Premature Ventricular Complexes (PVCs)

• PVCs are premature beats that originate in irritable ventricular tissue before the next sinus beat
• Can occur at any rate
• Regularity is regular but interrupted
• P waves are usually not seen on PVCs
• PR interval is not applicable
• QRS interval >0.12 seconds; QRS is wide and bizarre in shape
• T wave slopes off in the opposite direction to the QRS
• The T wave will point downwards if the QRS points upwards
• Main causes are heart disease, hypokalemia (low blood potassium), and hypoxia
• Other causes: low blood magnesium, stimulants, caffeine, stress, anxiety
• These factors cause the ventricle to become irritable and fire early beats
• Occasional PVCs are of no concern
• Frequent PVCs (6 or more per minute) or PVCs close to or landing on the downstroke of the previous beat's T wave (R-on-T phenomenon) can progress to lethal arrhythmias like ventricular tachycardia/fibrillation
• PVCs with differing shapes are cause for concern since they mean multiple irritable areas

PVC Treatment

• Occasional PVCs don't require treatment, since they can occur in normal individuals
• For more frequent PVCs, treat the cause
• Examples: give supplemental potassium if potassium level is low
• Start oxygen
• Amiodarone can be used to treat both atrial and ventricular arrhythmias
• If PVCs happen during a slow bradycardia, treat with atropine, not antiarrhythmics
• Giving antiarrhythmics could further slow the heart rate
• Atropine speeds up the underlying rhythm and PVCs should go away
• Unifocal PVCs come from a single focus and look alike
• Multifocal PVCs come from different foci and look different
• Two consecutive PVCs are called a couplet, which can be either unifocal or multifocal
• If every other beat is a PVC, it's called ventricular bigeminy
• If every third beat is a PVC, it's called ventricular trigeminy
• If every fourth beat is a PVC, it's called ventricular quadrigeminy
• PVCs usually have a complete compensatory pause following them
• A complete compensatory pause measures two R-R cycles from the beat preceding the PVC to the beat following the PVC
• Fusion beats, happen when a sinus impulse arrives to depolarize the ventricle at the same time as a PVC
• Look like the sinus beat (just a little wider/taller/deeper), and others will look more like the PVC (but narrower)

Agonal Rhythm (Dying Heart)

• Irregular rhythm where the severely impaired heart is barely able to "cough out" an occasional beat from its only remaining pacemaker, the ventricle
• Higher pacemakers have failed
• Rate: <20, although an occasional beat might come in at a slightly higher rate
• Regularity is irregular
• P waves are none
• PR is not applicable
• QRS is interval >0.12 seconds; QRS is wide and bizarre
• T wave slopes off in the opposite direction to the QRS
• Usually happens because the patient is dying, usually from profound cardiac/other damage or hypoxia
• Adverse effects include profound shock, unconsciousness, and death
• Agonal rhythm usually doesn't provide a pulse; and if so, the cardiac output it produces won't sustain life
• Treatment is CPR, epinephrine and/or vasopressin, atropine, and oxygen

Idioventricular Rhythm (IVR)

• Rhythm originates in the ventricle at its inherent rate when higher pacemakers have failed
• Ventricle escapes to save the patient's life
• Rate is 20 to 40
• Regularity is regular
• P waves are none
• PR is not applicable
• QRS is interval >0.12 seconds; QRS is wide and bizarre
• T wave slopes off in the opposite direction to the QRS
• Cause is usually massive cardiac/other damage, or hypoxia
• Adverse effects include decreased cardiac output and cardiovascular collapse
• IVR may or may not result in a pulse
• Treatment: atropine, epinephrine, pacemaker, oxygen, dopamine
• If the patient is pulseless, do CPR

Accelerated Idioventricular Rhythm (AIVR)

• Rhythm originates in the ventricle, with a heart rate faster than the ventricle's normal rate
• Results from escape or usurpation
• Rate is 40 to 100
• Regularity is usually regular, but can be a little irregular at times
• P waves are usually not seen
• Intervals: No PR interval since no P waves
• QRS interval >0.12 seconds; QRS wide and bizarre
• T wave slopes off in the opposite direction to the QRS
• Common after an MI
• Can be caused by PVCs
• Common after administration of thrombolytic (clot-dissolving) medications
• Adverse effects are usually none
• Treatment: Atropine can be given if patient is symptomatic
• Consider starting oxygen
• Usually no treatment is necessary as AIVR tends to be a self-limiting rhythm

Ventricular Tachycardia (V-tach)

• Irritable ventricular focus has usurped the sinus node to become the pacemaker and is firing very rapidly
• Rate is >100
• Regularity is usually regular, but can be a little irregular at times
• P waves are usually none seen but dissociated from the QRS if present
• Intervals: Variable PR if present
• QRS >0.12 secs; QRS wide and bizarre
• T wave slopes off in the opposite direction to the QRS
• Cause is the same as PVCs
• Rhythm may be tolerated for short bursts, but prolonged runs of V-tach can cause profound shock, unconsciousness, and death if untreated
• Treatment is Amiodarone or lidocaine intravenously if the patient is stable
• Electric shock (cardioversion or defibrillation) if the patient is unstable or pulseless
• Treat the cause (low potassium, magnesium, or oxygen levels)
• CPR is indicated if the patient is pulseless

Ventricular Fibrillation (V-fib)

• Hundreds of impulses in the ventricle are firing, each depolarizing its own little piece of territory
• Ventricles wiggle instead of contract
• Heart's electrical system is in chaos, and the resultant rhythm looks like static
• Rate cannot be counted
• Regularity is none detectable
• P waves are none
• Intervals, no PR interval since no P waves
• no QRS interval since no QRS complexes—just a wavy or spiked baseline
• T wave is none
• Cause is the same as V-tach; also can be caused by drowning, drug overdoses, accidental electric shock
• Adverse effects: Profound cardiovascular collapse
• There is no cardiac output whatsoever
• There is no pulse, no breathing, and nothing
• Patient is functionally dead if not treated
• New onset V-fib has coarse fibrillatory waves
• These waves get progressively finer the longer it lasts
• Treatment is immediate defibrillation (electric shock to the heart), epinephrine, CPR, amiodarone, lidocaine, and oxygen
• Rhythm will not be converted with medications alone
• Defibrillation must be done
• Medications make the defibrillation more successful and can prevent recurrences of V-fib