The criteria for a Normal Sinus Rhythm is:
• P-wave before each QRS with an interval of 0.12 to 0.20 seconds in duration.
• A QRS width of 0.04 to 0.12 seconds
• Q-T interval of less the 0.40 seconds.
• The rate for a normal sinus rhythm is 60 to 100 beats a minute.
Normal Sinus Rhythm
P-R interval 0.12 to 0.20 seconds
QRS duration 0.04 to 0.12 seconds
Rate 60 to 100 beats a minute
________________________________________
If the rate is below 60 beats a minute but the rest is the same it is a Sinus Bradycardia.
Brady- means slow.. Like your brain after you watch the Brady Bunch!
Sinus Bradycardia
P-R interval 0.12 to 0.20 seconds
QRS duration 0.04 to 0.12 seconds
Rate less than 60 beats a minute
Yes... the QRS complexes look completely different... That's okay. I already said that we're all different. Relax.
________________________________________
If the rate is between 100 to 150 beats a minute with the same intervals it is a Sinus Tachycardia.
Tachy- means fast. (Think of what happens to your heart rate when you sit on a tack)
Sinus Tachycardia
P-R interval 0.12 to 0.20 seconds
QRS duration 0.04 to 0.12 seconds
Rate 100 to 150 beats a minute
________________________________________
When the pattern becomes irregular with normal intervals it is a Sinus Arrhythmia
Sinus Arrhythmia
P-R interval 0.12 to 0.20 seconds
QRS duration 0.04 to 0.12 seconds
Rate 60 to 100 beats a minute, regular rhythm with periodic irregularity

Atrial Fibrillation describes a condition in which the atrial tissue randomly generates action potentials from many different regions. Physically, the atrial muscle appears to quiver (it looks like Jell-o). There are no noticable p-waves, and the overall rhythm is irregularly irregular.
The reason you cannot see P-waves is that the atrial activity is about as scrambled as a breakfast omelette. The key to recognizing A-fib are the narrow QRS's and the irregularly irregular rhythm.
________________________________________
Atrial Flutter is recognized by the distinct "saw tooth" pattern of P-waves.
The QRS complexes can appear at different intervals and frequencies. Naming conventions for A-flutter depend on these relations.

Atrial Flutter, 2:1 Block
The 2:1 block indicates there are 2 P-waves followed by 1 QRS.

Atrial Flutter, Variable Block
This is extremely common among A-flutter patients. There can be as few as a single P-wave or as many as 6 or more P-waves between each QRS complex.

________________________________________
1st Degree Heart Block
1st degree blocks are generally benign. They are characterized by a constant PR interval greater than 0.2 seconds. The rhythm is otherwise normal. Rates may range from bradycardias to tachycardias with a full degree of variation in between. Ordinarily, there will be no symptoms associated with a 1st degree block.

________________________________________
2nd Degree Heart Block
2nd degree blocks are subdivided into two types:
• 2nd Degree - Type I
(Wenkebach)
This rhythm is distinguished by a repeating cycle of increasing PR intervals. As the interval get longer, a P-wave is either not conducted (ie; there is no QRS) or the P-wave is simply dropped. The cycle then repeats again. Typically, RR intervals become shorter until the dropped beat.
Type I blocks are generally not dangerous. The patient may complain of palpitations, or skipped beats.
• 2nd Degree - Type II
(Mobitz)
This rhythm can be recognized by a consistent PR interval and frequently non-conductive P waves. QRS complexes may appear widened depending on the location of the block. Wide QRS complexes indicate that the ventricles are depolarizing from an action potention in the ventricular tissue, rather than from or above the AV junction.
Generally speaking, Type II blocks are not a good sign. They have a tendency to worsen, leading to 3rd degree blocks. ________________________________________
3rd Degree Heart Block
The 3rd degree block is by far the most dangerous. There is absolutely no conduction through the AV node. Due to the automaticity of each region of the heart, the atria beat at there intrinsic rate (60-80 bpm) and the ventricles, which are completely isolated from the atria beat at their slower rate of 20-40 bpm.
The QRS complexes will often be wide, but depending on the origin the ventricular action potential, they may remain narrow.
The P-P interval and R-R interval will each be regular and consistent. The P-P interval will be faster than the R-R and there will be no relation between the two.
A 3rd degree block is also called Atrioventricular dissociation.
The danger of these high-degree blocks should be obvious. Ventricular contraction will not always be preceeded by an atrial contraction. Hence, the ventricles are not guaranteed to contain enough blood for a detectable contraction.
________________________________________
Clinical treatment for high degree heart blocks can be pharmacological, or invasive. Autonomic drugs, such as Atropine, can be used to inhibit vagal stimulation and increase the bradycardic rates typically associated with heart blocks. If conduction is not improved with medication, artificial pacemakers can be installed to stimulate either the atria, ventricles, or both, in a synchronized rhythm.
Premature Ventricular Contractions
On occasion, a ventricular cell may initiate an impulse and cause a contraction. A single occurrence probably won't cause any serious problems. PVCs can be caused by a variety of conditions including respiratory problems and stress (and taxes).
Ordinarily, there will be a compensatory pulse with a PVC. If there is no pulse, we say the PVC is interpolated. If you have a patient with PVCs, be sure to check for a corresponding pulse. This has a large part in deciding whether the PVCs are dangerous or not.
PVCs are classified on the basis of their origin
• Unifocal PVCs originate from the same focus.
They all have the same shape, or morphology.
• Multifocal PVCs arise from multiple focii.
Each focus has a unique morphology. Often, there will be a repeating sequence, indicating several specific focii. Make an effort to note the number and sequence of focii.
PVCs are also classified by their frequency
• Bigeminy, trigeminy, etc...
If each normal contraction is followed by a single PVC, we call this bigeminy. If two normal contractions are followed by a single PVC, we have trigeminy. Be smart... what do you think quadrigeminy is?
Notice in this example, that the PVCs are unifocal... bigeminy tends to arise from a single focus.
• Couplets
Exactly two PVCs in a row is called a couplet.
________________________________________
R on T Phenomena
We discussed R on T when we spoke about the refractory periods. R on T can lead to a fatal dysrhytmia called ventricular tachycardia. Obviously, we'd like to avod this. R on T can occur with very fast rates, but also with ectopic beats like PACs, PJCs, and PVCs.
Ventricular Tachycardia
V-Tach is a rapid dysrhytmia in which the ventricles depolarize very quickly and without regard for the atria.V-Tach is actually said to happen whenever three or more PVS occur in a row (which is why we don't name anything beyond a couplet). Regarding pulses, any of the following could happen:
• pulse for every complex - the pulses will be weak and cardiac output low.
• pulse for some beats - this is ominous
• no pulse - there may or may not be any contraction at all, but if there's no pulse, you're patient is in bad shape.
We'll discuss the treatment for this a little later.
Ventricular Fibrillation
V-fib is the most common fatal dysrhytmia in adult patients. You see it "E.R." every week. V-fib represents a chaotic depolarization of random ventricular cells. A heart in V-fib literally looks like jiggling Jell-o. There is no pulse associated with this rhythm. CPR won't do much good either, nor will most drugs. You'd better hope the defibrillator works!
V-Fib is usually described as coarse (above) or fine (below). Generally, as the tissue dies, the voltage decreases. Hence, coarse is a little better than fine V-Fib.