Voluntary ECG stuff Flashcards
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The vertical axis of the ECG trace shows?
Whats the default setting?
voltage, generally measured in millivolts, and 10mm/mV is the default setting.
Adjusting your trace sensitivity (or gain) settings will have an effect on your vertical axis.
The magnitude of the signal is the height of the wave (amplitude) and, in the context of an ECG, is measured in millivolts.
For example, 5mm/mV may be useful if the R wave amplitude is high to avoid superimposition of multiple leads; conversely, 20mm/mV may be useful for ECGs with low amplitudes, as
often seen in cats.
At the start of a recording, many ECG machines will insert a
calibration spike (Figure4.6). The purpose of this
spike is to show that the data conform to a standard format.
Interpretation oftheECG
Step 1)
1) Calculate heart rate. First focus on the horizontal axis.
Most ECG machines produce traces at 25mm/s or 50mm/s, and some slower.
The grid on the ECG paper is divided into small squares, each measuring 1×1mm, usually with a
slightly thicker line every 5mm.
Therefore, at 25mm/s, each 1mm box= 1/25s = 0.04s = 40ms.
At 50mm/s, each 1mm box= 1/50s = 0.02s = 20ms.
An ECG ruler can be used to measure instantaneous heart rate more easily. The key is to ensure that the scale used on the ruler (25 mm/s or 50 mm/s) corresponds to the scale on the ECG.
The arrow on the ruler is placed against an R wave, and
the position of the following R wave on the scale will show the instantaneous heart rate.
Interpretation oftheECG
Step 2)
2) Assess whether the heart rhythm is regular or irregular.
Callipers or a ruler can be useful to determine whether the rhythm is regular or irregular.
Premature beats are beats that occur earlier than the
normal R‐R interval, and these can occur singly or as multiple consecutive beats.
If these beats have a QRS complex similar to the sinus beats, they are likely to originate above the atrioventricular node.
If these beats have a wide QRS that appears different from the sinus beats, then they are more likely to be either ventricular in origin or supraventricular with aberrant conduction.
Escape beats are beats originating outside the sinoatrial node after a longer than normal R‐R.
1) Calculate heart rate.
Interpretation oftheECG
Step 3)
3) Assess the relationship (synchrony) between P waves and QRS complexes – is there consistent coupling between the P waves and the ensuing QRS
complexes?
If there is baseline artefact, it may be difficult to see every P wave, so efforts should be made to keep the patient as still.
With supraventricular premature beats, a P wave may or may not be visible prior to the premature QRS.
With ventricular ectopy, a P wave may be seen but is not coupled to the ectopic QRS complex.
1) Calculate heart rate.
2) Assess whether the heart rhythm is regular or
irregular.
Interpretation oftheECG
Step 4)
4) Evaluate the QRS complexes – are they upright in
lead II and narrow, or are they wide and bizarre?
There are several potential mechanisms by which a QRS complex can have a wide, bizarre morphology, contrasting with the sinus beats.
Examples would include:
● Ventricular ectopic beats
● Intraventricular conduction disturbances, for example bundle branch block
● Notched QRS, for example in tricuspid dysplasia
● Accessory pathway with antegrade conduction from
atria to ventricles
1) Calculate heart rate.
2) Assess whether the heart rhythm is regular or
irregular.
3) Assess the relationship (synchrony) between P waves
and QRS complexes.
Interpretation oftheECG
Step 5)
5) Take P‐QRS‐T measurements, and know how to interpret them.
Measurements of the ECG complex are usually made
from lead II, with the paper speed set at 50mm/s.
The increase in the availability of echocardiography means that cardiologists of this generation will use the ECG primarily for assessing heart rate and rhythm rather than for assessing heart size, which is done with echos.
3) Assess the relationship (synchrony) between P waves
and QRS complexes.
4) Evaluate the QRS complexes – are they upright in
lead II and narrow, or are they wide and bizarre?
The amplitude of the P wave is directly
proportional to the
atrial mass. An increase in amplitude suggests atrial enlargement, particularly affecting the right atrium.
This change is sometimes known as P pulmonale.
Associated conditions include respiratory disease
and also congenital cardiac defects, resulting in right
atrial enlargement such as tricuspid dysplasia.
Interpretation oftheECG
Step 6)
6) Calculate the MEA, and know how to interpret it.
3) Assess the relationship (synchrony) between P waves
and QRS complexes.
4) Evaluate the QRS complexes – are they upright in
lead II and narrow, or are they wide and bizarre?
5) Measurements.
Interpretation oftheECG
Step 7)
7) Formulate a rhythm diagnosis.
4) Evaluate the QRS complexes – are they upright in
lead II and narrow, or are they wide and bizarre?
5) Measurements.
6) Calculate the MEA.
Interpretation oftheECG
Step 8)
8) Most importantly, interpret the ECG findings in light of patient history, clinical findings and the results of other tests.
5) Measurements.
6) Calculate the MEA.
7) 7) Formulate a rhythm diagnosis.
What is P pulmonale?
An increase in P wave amplitude due to right atrial enlargement.
Associated conditions include respiratory disease and also congenital cardiac defects, resulting in right atrial enlargement such as tricuspid dysplasia.
Sinus impulses traverse the atria from right to left;
therefore, left atrial enlargement may result in what ecg change?
prolongation of the P wave >40 ms in lead II in dogs orcats.
In dogs, conditions causing left atrial enlargement include myxomatous mitral valve disease, dilated cardiomyopathy and mitral valve dysplasia/stenosis.
What is a junctional rhythm?
A junctional rhythm is a heart rhythm that originates from the atrioventricular (AV) junction rather than the sinoatrial (SA) node.
It typically has a heart rate of 40–60 bpm, with absent or inverted P waves and a narrow QRS complex on ECG. It occurs when the SA node fails or conduction is blocked.
The diagnosis of atrial enlargement from an ECG is
unreliable and should always be supported by echocardiographic findings.
Biatrial enlargement may be seen in feline…? (3)
hypertrophic and restrictive cardiomyopathy and also
dilated cardiomyopathy in both dogs and cats.
● In dogs, biatrial enlargement is also commonly seen in dogs with advanced myxomatous atrioventricular
valve disease.
The PR interval reflects the
time taken for the depolarisation wave to be conducted through the atria, atrioventricular node and bundle of His.
The PR interval will naturally shorten as heart rate
increases.
The QRS complex is generated by
depolarisation of ventricular tissue.
It is normally upright and narrow in leads I, II, III and aVF; and negative in leads aVR and aVL.
Explain.
Variations in QRS morphology may occur as illustrated in Figure 4.20. If the deflection amplitude is >0.5mV, then it is designated with an uppercase letter (Q, R and S); and, if <0.5mV, then lowercase (q, r and s) is used for the respective components (Table4.5).
Tall QRS (>2.5 mV if <20kg and >3 mV if >20kg) can indicate:
LV enlargement; also seen normally in athletic, narrow‐chested breeds such as Greyhounds and
Whippets.
Low‐amplitude QRS complex may be seen in: (7)
● Effusions (pleural, pericardial)
● Intrathoracic mass
● Broad chest conformation
● Poor electrode contact
● Hyperkalemia
● Obesity
● Hypothyroidism
Wide QRS (>70ms in dogs, >40ms in cats) complexes may be seen in:
Ventricular beats and rhythms characterised by
a wide, bizarre QRS complex without an associated
P wave.
● Intraventricular conduction disturbance, such as
bundle branch block or ‘splintered QRS’ with tricuspid valve dysplasia
● Supraventricular ectopic/premature beats with
aberrant conduction result in a wide QRS.
● Hyperkalaemia.
The term electrical alternans is used when
P, QRS or T segments alter their configuration and/or magnitude in a rhythmic pattern, such as every other beat, or even every third or fourth complex.
In dogs with pericardial effusion, electrical alternans is likely to be due to the swinging movement of the heart within the fluid‐filled pericardial sac, and the phenomenon is also sometimes seen with movement.
In dogs with tachycardia, it may reflect varying refractory periods at high heart rates.
tetralogy of fallot
Tetralogy of Fallot (TOF) is a congenital heart defect consisting of four abnormalities: ventricular septal defect (VSD), pulmonary stenosis,
overriding aorta,
and right ventricular hypertrophy.
These defects cause reduced blood flow to the lungs and mixing of oxygen-poor and oxygen-rich blood, leading to cyanosis (bluish skin). Symptoms include “tet spells” (sudden cyanotic episodes), shortness of breath, and delayed growth.
TOF is diagnosed with echocardiography and treated with surgical repair, typically in infancy, to improve blood oxygenation and heart function.
Overriding aorta is a congenital heart defect where the aorta is positioned directly over the ventricular septal defect (VSD) instead of arising solely from the left ventricle. It is one of the four key features of Tetralogy of Fallot (TOF).
which way does the LV enlarge in response to pressure overload, and which way for volume overloas?
concentric hypertrophy (in response to pressure overload)
eccentric hypertrophy (in response to volume overload).
The ST Segment is measured from
the end of the QRS complex to the onset of the T wave and represents the time taken for ventricular contraction and then the early part of ventricular repolarisation.
It can be above or below the baseline but is considered abnormal if it is depressed by
0.2mV or elevated by 0.15mV
What is MEA?
Mean Electrical Axis (MEA) refers to the average direction of the heart’s electrical activity during ventricular depolarization, typically measured in the frontal plane using an electrocardiogram (ECG).
It is expressed in degrees and helps assess normal and abnormal conduction patterns.
A normal MEA in dogs ranges from +40° to +100°, while deviations can indicate conditions such as left axis deviation (LAD) (e.g., due to left ventricular hypertrophy) or right axis deviation (RAD) (e.g., due to right ventricular hypertrophy or pulmonary hypertension).
The QT interval is measured from the onset of the QRS to the end of the T wave. It represents
the time it takes for ventricular depolarisation and repolarisation to occur.
Review quick guide to making a rhythm diagnosis.
