ECG wave discrimination: Normal, LBBB, RBBB, PVC

[Huabin]

Hi everyone.

    I'm a student with just a little ECG knowladeg. I am now working on ECG wave automatic identification, exactly, discrimination of the following 4 kinds of waves: Normal, LBBB, RBBB, PVC. I am so confused because sometimes I found some of them look the same, such as the PVC and Normal wave showed in the attached picture.( The waves are extracted from the MIT-BIH arrythmia database. And they are labeled with Normal or PVC or others by cardiologists.)

    So I come here to ask for your help on how to discriminate them. Could you tell me what's the fundamental character of each wave, or any suggestions about my work. Thanks very much!

[Huabin]

Dear kenkeith,

    Would you please send me a mail, so we can chat by email, which is easy to attach pictures. My email: Huabin.***@****. Note there is a dot between Huabin and Zheng.

[kenkeith]

The PR interval is defined as the period that extends from the onset of atrial depolarization (contraction is beginning of the P wave) until the onset of ventricular depolarization (contraction is beginning of the QRS complex).

The best lead to use for MEASURING the PR interval is lead II.  In adults, if the P wave is upright in lead II,  the PR interval is considered normal if between .12 and .20 second. The PR is short if it is less than .12 second in lead II (as may occur with WPW when the AV node is bypassed ) The PR is long if more than .20 second.

Precise determination of a PR interval that falls within the normal range is not necessary.  Clinically, in this situation it suffices to say that the PR interval is "normal".

PR interval does not include "R" of the QRS complex although complete contractions of the atruim does extend about midway between QR as intra ventricular pressure increases,  chamber fills and closes the valve.

[Huabin]

I am back again :)

The PR interval is specified as the interval between the start of P wave and QRS complex. But it's obvious the P wave top and R peak are much easier to determine in the EKG wave. So can I redefine the PR interval as the interval between top of P wave and R peak? I know it's not reasonable looked from the professional aspects. I mean if it's possible to discriminate the abnormality based on the redefined PR interval. In other words, if the redefined PR interval share the same characteristic with the professional PR interval.

[kenkeith]

You're must welcome.  If you have the time, you may want to participate in answering EKG questions by members.  Good luck with your education, etc.

[Huabin]

I appreciate your informative and enlightening post very much.

[kenkeith]

Normal sinus rhythm (NSR): indicates that the rate is between 60 and 100, inclusive, and that the P waves are identifiable and are of the same morphology throughout. If not seen that may indicate an abnormal condition.  The EKG recording output strip should be calibrated to 25 mV/s which results in and I believe the calibration is standard so the measurementswould be as follows:

1 mm = 0.04 sec (or each individual block)
5 mm = 0.2 sec (or between 2 dark vertical lines)
Distance between  Tick marks = 3 seconds (in the rhythm strip)
The voltage recorded from the leads is also standardized on the paper where 1 mm = 1 mV (or between each individual block vertically) This results in:

1 mm = 0.1 mV
5 mm = 0.5 mV (or between 2 dark horizontal lines)
10 mm = 1.0 mV

We know the P wave represents discharge of SA node and depolarization of both atria and preceeds QRS complex (ventricular activation) and is always present unless there is arrhythmia, etc.

The best lead to look at the P wave is V1 and it is upright and rounded.  The duration, generally, should not be more than 1 box wide and not more than 1 box tall...If  P wave exceeds the normal range for duration or voltage, it generally means that either or both atria is enlarged (hypertrophied).

For atrial enlargement: Peaking of P wave (Voltage increase) suggests right atrial hypertrophy.Broad slurred (increased duration)  suggests Left atrial hypertrophy
When biphasic the initial positive wave is prominent with RA hypertrophy and the negative deflection is prominent with LA hypertrophy The electrocardiographic representation of atrial depolarization is the P wave. Right atrial depolarization forms the initial portion of the P wave, and left atrial depolarization forms the terminal portion of the P wave. If the P wave contour changes between beats it could mean that there is an ectopic atrial focus.

Normal T waves in general are in the same direction as the largest deflection of the QRS (normally the R wave). It should be negative in AVR. Inverted T waves in precordial leads V1, V2, V3 can be seen in normal, young athletes. Low T voltage changes may occur in the absence of any heart disease at all. Inverted T waves: Inverted T waves that are symmetrical, "round-shouldered" can be caused by coronary ischemia. especially when it occurs in a pattern as previously described for ST segment changes. Abnormal: T wave changes can be primary or secondary. Primary T wave change refer to abnormal repolarization. Secondary T wave changes are caused by QRS changes.  T wave changes caused by bundle branch block or ventricular hypertrophy are secondary.

Tall peaked T waves. can be electrolyte imbalance =  Hyperkalemia causes tall peaked T waves.  There is an overall maximum of 15 mV but this is not sensitive.  T wave looks like an isosceles triangle.

Hypokalemia causes low voltage T waves and prominent U waves.  T waves less than 1mV in the limb leads and less than 2mV in the precordial leads.  There can be low T voltage and sagging or flattened ST segments and these changes may occur in the absence of any heart disease at all.

[Huabin]

Thanks for your illumilation very much.
but still, I find it very difficult to analyze the duration. Let's take the P wave duration as an  example. how do you determine where the wave's onset and offset are? The real ECG waveforms are not as clear as that showed in the book. Are there any criterion to determine the onset, such as the wave's slope?

in addition, there may be no P wave or T wave or both in normal ECG wave, right?
so, I am confused very much. I wonder whether there are some solid characters, that the type of wave can be classified reliably.

[kenkeith]

Wave forms are analyzed by duration, amplitude and frequency.  Amplitude is measured by the vertical axis in mvolts and time is on the horizontal axis is msecs.  Whether the signal is upright or downward depends on the transducer to the lead location distinquishing the direction of blood flow..

The wave output is calibrated to each small box on the horizontal line represents 0.04 seconds. Each large box on the horizontal line represents 0.20 seconds. There are five small boxes in one large box. Each small box on the vertical line equals 0.1 millivolts. 10 small boxes = 10 mm tall.

You can cross reference which lead, what amplitude and duration for each condition you are interested in diagnosing.