EKG Basics

heart beart

There are three basic parts to an EKG:

  1. P wave: this is the wave that shows what is going on in the atria of the heart aka atrial contraction
  2. QRS: think ventricles, if there’s an abnormal QRS the problem is almost always in the ventricles
    1. If the QRS is narrow: the problem is above the ventricles (think atria)
    2. If the QRS is wide: the problem is ventricular
  3. T wave: the heart is resetting to beat again aka ventricular repolarization

5 things to look at:

  1. Heart rate: To calculate heart rate: count the number of R waves in 6 seconds (six large blocks) and multiply by 10. Normal is 60-100 beats per minute (bpm)
  2. rhythm: is it regular or not?
  3. Is there a P wave before each QRS?
  4. What is the PR interval? normal is 0.12-0.2 seconds (or 3-5 little boxes, each little box is 0.04 seconds, there are 5 little boxes per big box)
  5. Is the QRS narrow? normal is 0.06-0.12 seconds (or 1.5-3 little boxes)

If the heart rate is 60-100 bpms, the rhythm is regular (happens at an even interval), there’s a P wave before each QRS, the PR interval is normal and the QRS is normal than it’s Normal Sinus Rhythm.

sinus brady


This means the heart is beating <60 bpm AND The rhythm is regular.There’s a P wave before each QRS.The PR interval is normal. The QRS is narrow.

  • Tx: ABC: Atropine treats BradyCardia…
  • usually you only treat if the patient is symptomatic or drops below a specific bpm (the doctor will determine the parameters)

sinus tach

Sinus Tachycardia:

This is when the heart is beating >100 bpm AND The rhythm is regular.There’s a P wave before each QRS.The PR interval is normal. The QRS is narrow.

  • Tx: Calcium Channel Blockers: usually cardizem
  • what to look for: chest pain (priority), decreased BP, check pulse

Abnormal rhythms:

a fib

Atrial Fibrillation:

if there are no P waves and the QRS is narrow, think a. fib.

  • what’s happening: the atria is basically quivering, this means blood isn’t being pumped effectively from the atria into the ventricles. This causes blood to pool in the atria which means clots can form. A patient will be started on an anticoagulant to help prevent clots from forming. If a clot is thrown, it could go bad very fast.
  • Treatment: The patient will probably first be started on medication to try to convert them out of a. fib into a normal sinus rhythm (NSR). If this doesn’t work the next course of action is to cardiovert the patient. The last resort is an ablation. Some patient’s never convert and are controlled with a PO medication as well as an anticoagulant at home
  • if >100 bpm, considered uncontrolled

a flutter

Atrial flutter:

“saw toothed” p waves

  • priorities: check BP, assess level of consciousness and mental status
  • what’s happening: ineffective atrial contractions
  • tx: cardioversion


PVC (preventricular contraction):

wide and bizarre QRS (>0.12 seconds)

  • usually benign
  • causes: hypoxia, low K+, caffeine, stress, etc
  • what to look for: check O2 saturation then K+, low BP, low HR, decreased LOC
nonsustained vtach
Nonsustained V Tach
sustained vtach
Sustained V Tach

Ventricular tachycardia:

if the QRS is wide and fast, think V tach (looks like 4 or more PVCs in a row)

  • sustained: v. tach is continuing without converting back to NSR by itself
  • nonsustained: this is bursts of v tach where the patient converts back to a different rhythm without any interventions
  • why you should be concerned? v tach can quickly turn into v fib or worse. This is a critical rhythm that needs attention right away
  • treatment:
    • V tach and awake, meds he must take (patient has a pulse)
      • 1st try vagal maneuvers, this sometimes can convert a patient without any medications
      • give meds: usually amiodarone
    • V tach and nap, ZAP ZAP ZAP  (patient is passed out and/or pulseless)
      • the patient will be cardioverted

v fib

V. fib:

if no P’s and no QRS’s, think V fib

  • Tx: V fib, you defib … go get the defibrillator, crank it up and zap that rhythm back to normal
    • Remember to check for a pulse!



this is when the patient flatlines.

  • tx: epinephrine and a pacemaker, defibrillation will not work. Start CPR immediately.

Pacemaker Spikes: if the patient has pacemaker, you will see a pacemaker spike (it literally looks like a spike). Where the spike occurs depends on the type of pacemaker.

A Paced

Atrial Paced ( A paced):

The pacer spike occurs in place of the p wave. This is taking place of the SA nodes action of firing. If there is no QRS after the spike, this means there is failure to capture

V paced 2

Ventricular Paced (V Paced):

The pacer spike occurs directly in front of the QRS causing a wide QRS. Again, if there is no QRS after the spike, it has failed to capture.

AV paced

Atrial Ventricular Paced (AV Paced):

A spike occurs before the P wave and again in front the QRS. This is considered AV paced.

heart block

Heart Blocks

I’m a big fan of the heart block poem, it comes in handy whenever I’m trying to figure out what type of block a patient has!

If R is far from P, you have a first degree.

Longer, longer, drop! You have a Wenkebach!

If some P’s don’t get through, then you have a Mobitz II.

If Ps and Qs don’t agree, then you have third degree.

1st degree
First Degree Block

First degree: the PR interval is >0.20 (usually benign, monitor for possible new arrhythmias)… Remember to measure those PR intervals!

2nd Degree:

There are two types: type 1 aka Wenckebach or Mobitz I and type 2 or Mobitz II

weinkebach best


Wenckebach (Mobitz I): the PR interval increases more and more with each beat until there’s a P wave without a QRS (aka the PR interval gets longer and longer and then there’s a drop). This  usually occurs in a pattern. Tx is usually atropine first followed by a pacemaker

type II block mobitz iiMobitz II: P waves continue to march out as usual and then all of a sudden you’ll have a dropped QRS. (Measure the distance between the P waves to see if they are occurring regularly). This can happen in a pattern either a 2:1 or 3:1. A 2:1 is there are 2 P waves for every QRS. A 3:1 is when there are 3 Ps per QRS. Tx is a pacemaker

third degree

3rd degree: This is very bad and considered a complete heart block. There is basically no communication between the atria and the ventricles. There are more P waves than QRS waves and the P waves are inconsistent. Tx begins usually with a dopamine drip followed by a pacemaker.

AND there you have it! The nitty gritty need to know basics for EKG interpretation. Now that you’re ready, go practice your new skills! A great website to use is http://www.skillstat.com. If you have any questions, spot any errors or see any rhythms I left out, please let me know and GOOD LUCK!


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