EKG Strip Interpretation Jennifer Kean MSN,RN,CCRN

Electrical Conduction System of the Heart The heart is supplied with its own electrical conduction system Conducts impulses along specialized pathways to the atria and ventricles, causing them to contract, called automaticity Has highest rate of automaticity System consists of the SA node, the intermodal tract (The AV node),, the bundle of His, the right and left bundle branches, and the Purkinje fibers

The SA node Located in the wall of the upper right atrium Consists of specialized electrical cells, called pacemaker cells Discharges impulses at a rate of 60-100 beats per minute in a rhythmic fashion

The AV (atrioventricular) Node Located in the tissue that divides the right atrium and right ventricle (near tricuspid valve) Can function as a secondary pacemaker at a rate of 40-60 beats per minute Relays the electrical impulses from the atria to the ventricles Has 3 main functions: To slow conduction time, allowing the atria to fill To serve as a backup pacemaker if the AV node fails To block some impulses from reaching the ventricles if the rate is too rapid

The Bundle of His, the bundle branches and the Purkinje fibers After the delay in the AV node, the impulse moves rapidly through the bundle of His The Bundle of His divides into two important conduction pathways: The right bundle branch The left bundle branch The right bundle branch conducts the electrical impulse to the right ventricle The left bundle branch conducts the electrical impulse to the left ventricle Both bundle branches terminate in a network of conduction fibers called the Purkinje fibers, which carry the electrical impulses directly to the contractile cells of the ventricles

The cardiac cycle Consists of one heartbeat Represented on EKG strip as one PQRST sequence Represents one atrial contraction followed by a ventricular contraction

The PQRST

The PR interval The distance between the P and the peak of the R represents an atrial contraction

The QRS complex The QRS complex represents a ventricular contraction

The S-T segment Segment on strip between the “S” and the end of the “T” Represents the refractory phase (the resting phase; the heart is unable to contract at this time)

EKG graph paper The PQRST is recorded on special graph paper that is made up of horizontal and vertical lines The horizontal lines measure the duration of the waveforms in seconds of time Each small square measured horizontally represents 0.04 second in time; 5 boxes equal 1 second The vertical lines measure the voltage or amplitude of the waveform in millimeters (mm)

Cardiac dysrhythmias- atrial fibrillation The atria are not beating regularly- they are quivering Described as and appears as “irregularly irregular”; P-R is wavy, not defined Very rapid conduction of atrial impulses: rates of 350-600 bpm Ventricular rate may be up to 100

Premature ventricular contractions (PVCs) Abnormal beats arising from the ventricles The QRS complex is very wide and bizarre-looking May originate from electrolyte imbalances- if they keep occurring, test electrolytes and replace if necessary (Potassium {K} or magnesium {Mg})

Cardiac dysrhythmias- ventricular tachycardia Three or more successive PVCs Large wavy QRS complexes Pt. may be awake, or may be unconscious Treated with antiarrythmics: amiodarone, lidocaine, adenosine Usually occurs in pts. with underlying heart disease

Cardiac dysrhythmias: ventricular fibrillation Ventricles are quivering; not beating; represented on strip as wavy, unorganized line Blood not being pumped Pt. is clinically dead Treat with CPR, call 911/code blue, meds: epinephrine, vasopressin, sodium bicarbonate

Cardiac dysrhythmias- asystole Heart has ceased to beat- appears on strip as “flatline”- :”code blue!” Pt. is clinically dead Treated with CPR and same meds as for v-fib Does not get “shocked”- not a shockable rhythm

Myocardial Infarction (MI) Appears on strip as elevated S-T segment Often looks like a “fireman’s hat”