• Inversion in leads where the P is normally upright or the presence of an upright P wave in aVr. This change is often found in conditions where the impulse travels through the atria via an abnormal pathway, such as ectopic atrial or A-V nodal rhythms.
• Increased Amplitude usually indicates atrial hypertrophy and is found especially in A-V valvular disease, hypertension, cor-pulmonale, and congenital heart disease.
• Increased Width often indicates left atrial enlargement or diseased atrial muscle.
• Biphasity is a notable sign of left atrial enlargement when the second half of the P wave is significantly negative in leads III and V1.
• Notching In P-Mitrale the P often is wide and notched and is taller in lead I than in lead III. Notching is considered significant when the distance between peaks is greater than 0.04 seconds.
• Peaking indicates right atrial strain. These tall pointed P waves are often taller in lead III than in lead I. This is known as P-Pulmonale.
• Absence of P waves occurs in A-V nodal rhythms and S-A Block.

Return to Map

P-R Interval
The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. It reflects the time taken by the impulse to travel the entire distance from the SA Node to the ventricular muscle fibers. The normal duration for this is 0.12-0.20 seconds. Normally this interval varies with heart rate and is shorter at faster rates. Under certain circumstances, for instance if the conduction system is diseased or affected by Digitalis, the P-R interval may lengthen as the rate increases. Also if the atria are paced, the interval lengthens as the paced rate increases.
A prolonged interval, beyond normal limits (0.12-0.20 sec.), is considered evidence of AV block. An abnormally short P-R interval is cause for alarm as it is often seen in asociation with hypertension and paroxysms of tachycardia. The P-R interval is shortened when the impulse originates in the AV node rather than the SA node or when the passage of the impulse to the ventricle is accelerated as in Wolff-Parkinson-White syndrome (WPW).

Return to Map

QRS Complex
Probably the most important complex in the electrocardiogram is the QRS. It represents the spread of the electrical impulse through the ventricular muscle (depolarization).
The waves which make up this complex are labeled as follows:

The first deflection , if it is negative (downward), is labeled the Q wave.

The first positive (upright) delflection is labeled the R wave, whether it is predeceded by a Q wave or not.

A negative deflection following an R wave is labeled an S wave.

Any subsequent waveforms are labeled "primes". Positive being R', R'' etc.... Negative being S', S''.

There are a number of features which should be routinely examined in the interpretation of the QRS complex.

The duration (QRS interval) which is measured from the beginning of the QRS complex to it's end. The normal duration of this interval is 0.05 to 0.10 seconds. A measurement of 0.12 seconds or more indicates abnormal intraventricular conduction and often indicates a block of one of the bundle branches or a ventricular arrhythmia.

The amplitude ("voltage") has wide normal limits. An amplitude of 5 mm or less in all three standard leads is considered to be unhealthy. this is often seen coronary disease, cardiac failure, emphysema, and obesity to name a few.
The upper limit is variable from lead to lead, but generally is between 20 and 30 mm. Many factors can affect the amplitude besides the health of the heart, such as chest size, chest wall thickness, emphysema. These factors should always be taken into consideration before judging the voltage of any complex to be too high or too low.

This section is barely started, lots more info to come.

Return to Map

S-T Segment
The S-T segment follows the QRS complex. The point at which it begins is called the J (junction) point. There are two aspects that should always be examined:

Its level relative to the baseline (elevated or depressed and how much).

Its shape. Under normal circumstances the S-T segment is isoelectric or level with the T-P segment. It normally gently curves into the T wave.

Return to Map

T Wave
The T wave represents the period of recovery for the venticles (repolariztion). Generally we are concerned with three features: 1.) direction, 2.) shape, and 3.) height.

The direction of the normal adult T wave is upright in leads I, II and V3-V6. It is inverted in aVr. And it is inverted in leads III, aVl, aVf, V1 and V2.

The normal shape of the T wave is slightly rounded and slightly asymetrical. Sharply pointed or grossly notched T waves should cause suspicion, although either feature can occur as a normal variant of the precordial leads. Notching can be an indication of pericarditis, and sharply pointed symmetrical T waves should make one suspicious of myocardial infarction(MI).

The height of the T wave also has diagnostic importance. Normal height in the limb leads is not above 5 mm and is not above 10 mm in any precordial lead. Unusually tall T waves indicate MI, but can be seen in ischemia without infarction. Tall T waves are also seen in patients with hyperkalemia, CVAs, and sometimes in psychotic patients.

Return to Map

Q-T Interval

Return to Map

References
• Practical Electrocardiography
  Henry J. L. Marriott, M.D., F.A.C.P., F.A.C.C.
  Sixth Edition 1977
• Understanding Electrocardiography
  Mary B. Conover, R.N., B.S.N.Ed.
  Third Edition 1980
• Workshop in Electrocardiography
  Henry J. L. Marriott, M.D., F.A.C.P., F.A.C.C.
  Second Printing 1974
• Advanced Concepts is Arrhythmias
  Henry J. L. Marriott, M.D., F.A.C.P., F.A.C.C. / Mary B. Conover, R.N., B.S.N.Ed.
  First Edition 1983
• Advanced Concepts is Arrhythmias
  Henry J. L. Marriott, M.D., F.A.C.P., F.A.C.C. / Mary B. Conover, R.N., B.S.N.Ed.
  Third Edition 1998