Cardiologia y electrocardiograma

VetGo Cardiology

January 10, 2005

CLINICAL CARDIOLOGY CONCEPTS for the dog and cat
Michael R. O'Grady, DVM, MSc, Diplomate ACVIM (Cardiology) M. Lynne O'Sullivan, DVM, DVSc, Diplomate ACVIM (Cardiology)

Contents

Electrocardiology General 1 What is a P wave; what electrocardiographic event does this represent?

P amp = amplitude of the P wave; P dur = duration of the P wave; PR int= PR interval; R amp = amplitude of the R wave; QRS dur = duration of the QRS complex; QT int = QT interval; T amp = amplitude of the T wave. The P wave is the electrocardiographic representation of electrical activation of the atrial myocardium. The amplitude measurement of the P wave depends on the calibration pulse (how many mm = 1 mv). The duration measurement of the P wave depends on thepaper speed (how many msec = 1 mm). top Electrocardiology: General

2 What is the PR interval; what is the significance of the PR interval?

P dur = duration of the P wave; PR int = PR interval; QRS dur = duration of the QRS complex; QT int = QT interval. The PR interval is the electrocardiographic representation of the delay in electrical activation of the ventricles after sino-atrial nodaldischarge. This interval is mainly a result of slow conduction through the atrio-ventricular node.

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The duration measurement of the PR interval depends on the paper speed (how many msec = 1 mm). top Electrocardiology: General

3 How are a Q, R, S, and QSdifferent?

For a wave to be defined as a Q wave it must fullfil the following criteria: a. It must be a negative deflection. b. It must be the first deflection of the QRS complex. c. It must be followed by a R wave. Thus there can be only one Q wave per QRS complex. For a wave to be defined as a R wave it must fullfil the following criteria: a. It must be a positive deflection. All positivedeflections are R waves and only R waves. There can be several R waves per QRS complex. For a wave to be defined as a S wave it must fulfil the following criteria: a. It must be a negative deflection. b. It must follow a R wave. There can be several S waves per QRS complex. For a wave to be defined as a QS wave it must fulfil the following criteria: a. It must be a negative deflection. b. There must be noR wave in the QRS complex. Therefore it describes a QRS complex with only one deflection and this deflection is negative. Comment: It should be noted that a QRS complex may thus consist of only an R wave, or only of RS waves, or only of QR waves, etc. top Electrocardiology: General

4 What is the significance of the QRS complex?
The QRS complex is the electrocardiographic expression of theelectrical activation of the ventricular myocardium. 5. What is a T wave; what is the significance of a T wave?

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P amp = amplitude of the P wave; R amp = amplitude of the R wave; T amp = amplitude of the T wave. The T wave is the electrocardiographicexpression of repolarization of the ventricular myocardium. In domestic animals patient cooperation is usually poor and therefore movement artifact is frequently encountered on the electrocardiogram. These deflections can usually be diagnosed as artifact as opposed to a QRS complex because of the absence of a T wave. Therefore for any deflection on an electrocardiogram to be considered as a "beat" it musthave a repolarization wave (T wave). top Electrocardiology: General

5 What is the significance of a positive deflection in a lead; of a negative deflection in a lead?

An electrical lead used to examine the heart on the EKG can be described in terms of a negative pole and a positive pole. As a wave of electrical depolarization moves parallel to the direction of a lead, if it moves towards...