Credit 3 Flashcards
Describe sinus tachycardia
(2 causes, ECG changes, characteristics) *
Characterized by increased heart-rate frequency.
Impulses are generated at the SA node, but at a faster than normal frequency.
It is associated with decreased vagal tone or an increased sympathetic
tone.
Pathologic responses that cause sinus tachycardia include: - fever - shock, - hypotension - anemia - congestive heart failure - hyperthyroidism and infections.
A large number of drugs can cause sinus tachycardia, either as a
desirable response or as a side-effect and include sympathomimetics,
parasympatholythics, and vasodilators.
Changes on the ECG include:
- the T-P interval shorters
- the P waves may be partially or completely fused with the preceding T waves.
For example:
Often associated with an increased temperature. The heart rate can then be 250 beats/min and at this speed the P waves are buried in the T waves of the preceding beats.
P waves are not distinguisable cause of the high temperature!
Cold water bath can help the patients temperature to decrease and P waves will be visible
Describe sinus bradycardia. Characteristics, cause and changes on ECG tracings *
Sinus bradycardia is a regular rhythm that originates from the sinus node but a rate is too slow.
Sinus bradycardia is observed in normal large-breed and well- conditioned dogs at rest and sleeping. Causes can also be result from: - increased in vagal tone - increases in cerebrospinal fluid pressure, gastrointestinal and respiratory disorders - hypothermia - hypothyroidism, - intoxicants - central nervous system lesion.
Changes on the ECG include T-P interval prolongation.
Example
In sleeping dog with sinus bradycardia wiyh 35 beats/min.
Everything is usually well visible of ECG but number of complexes / min are lower.
The heart rate frequency are too low but AV node generates impulses but at a lower frequency than normal
Describe sinus arrest
= Sinus rythm
Sinus node fails to fire impulse for the duration of 2 P-P intervals or longer, causing a pause and absence of P intervals
Causes: Sick sinus syndrome, drugs or electrolyte disturbances
Describe atrial flutter *
Characteristics:
- There are extremely rapid (more than 300 beats/min in dog) P or flutter waves, which give the baseline a sawtooth appearance.
- Physiologic block of some of the flutter waves in the AV node is common and results in a ventricular rate that is slower than the atrial rate.
- Conduction through the AV node to the ventricle may follow a
pattern expressed as 2:1 or 3:1 AV conduction, producing a regular ventricular rhythm, whereas at other times the conduction pattern
appears random, resulting in a very irregular ventricular rhythm that can mimic atrial fibrillation.
- QRS configuration are normal!
Atrial flutter is an uncommon rhythm disturbance in veterinary patients and is associated with:
- mitral stenosis
- myocarditis
- hyperthyroidism.
Describe Atrial fibrillation *
Due to a high number of disorganized atrial impulses bombarding the AV node
- Many of them approach the AV node in a refractory period and are NOT conducted to ventricles.
- The atrial depolarization rate are very rapid: From 400 - 600 beats/min
- The P waves are replaced by fibrillation waves, f waves which represents chaotic atrial activity.
QRS complexes are usually normal, the ventricular rate is rapid: 200 - 280 beats/min
Often associated with
- Cardiomyopathy
- Severe ischaemia
- Shock
- Electrolyte disturbances
Desribe the atrioventricular junctional rhythm *
- Escape rhythm (atrioventricular junctional rhythm).
- An escape rhythm can occur only when the normal cardiac pacemaker
(the SA node) stops or slows to a rate less than that of a subsidiary
automatic pacemaker. - The subsidiary pacemakers (AV nodal or junctional tissue and the Purkinje fibers in the ventricle) function as a rescue mechanism during
severe bradycardia. - Depolarizations that occur after a pause are called escape rhythms. An escape rhythm = A run of 3 or more complexes.
- Escape rhythms originate either from the AV junctional region (junctional) or from Purkinje fibers (ventricular).
- The heart rate of the junction is always lower. Usually less than 6 beats/min
An escape complex (beat) = A single spontaneous impulse from a lower pacemaker
There will be a negative P wave! Either before, after or masked by the QRS-complex
Describe premature ventricular depolarizations, characteristics ECG *
A type of ventricular arrythmia.
Result from the spontaneous depolarization of the distal to
the bifurcation of the bundle of His.
Since it starts the depolarization within the bundle branch the depolarization are not able to use the conduction system in the ventricles but instead must occur from myocardial -> myocardial cell which is a longer process.
Resulting in a
- QRS complex that is wider than normal.
- Large, bizzare T wave
= Premature QRS complex followed by the bizarre T wave with an opposite polarity
It can appear in two patterns
- Ventricular bigeminy = Each sinus beat is followed by a VPD for a period
- Ventricular trigeminy = Every 3rd depolarization is a VPD
1st degree AV block *
First-degree AV block is simply a delay in conduction across the AV
node.
The P-R interval is prolonged with the normal P wave and QRS
complexes, at a 1:1 ratio
Occur due to
- drug administration
- hyperkalaemia
- increased vagal tone
2nd degree AV block *
Second-degree AV block results when not all of the sinus impulses are
conducted to the ventricles.
This produces an abnormal heart rhythm and is also a cause of cardiac
arrhythmia.
It can range in severity from only an occasional P wave not followed by
a QRS complex on the ECG to most P waves being blocked.
However most often:
- P wave is present without QRS complex
- More P waves than QRS complexes
Second-degree AV block is classified as either type I or type II.
3rd degree AV block *
Can be a complete heart block.
- There is no conduction between the sinus node and the ventricles. All of the impulses generated by the sinus node are blocked at the AV node or bundle brances.
The sinus node depolarizes at its own inherent rate, depolarizing the atria and producing P waves, whereas the ventricles are depolarized by a subsidiary pacemaker (either the AV node or Purkinje fibers) that depolarizes at a slower rate, depolarizing the ventricles and producing QRS complexes.
Changes on the ECG:
There is no relationship between the P waves and QRS complexes, resulting in varying P-R interval from beat to beat.
Atrial rate is faster than the ventricular rate.
- The ventricles function as a rescue mechanism
- Atria contracts faster than ventricles cause they are controlled by different pacemakers
Define myopathy *
Non inflammatory degeneration of skeletal and cardiac muscle
• Characterized by
- Muscle weakness
- Myoglobinuria
- Increased activity of several enzymes like CPK, LD, AST
- Often myoglobinuria
In the affected muscle occurs
- Atrophy, Necrosis or degeneration
Degeneration = Loss of specialized function of muscle cells e.g. Ca salts, fat or fibrous tissue may be deposited in the affected muscle
Necrosis = Death of muscle cells in demarcated area.
Necrosis can also cause a different morphological forms
- Focal = Small areas of necrosis
- Coagulation = Caused by agents that rapidly abolish vital processes
- Zenker’s = Death of striated muscle cells -> Coagulation of the proteins contained in these cells.
Nutritional myopathy, in piglets *
Young rapidly growing pigs/animals fed high energy, low vitamin E and selenium diet or diet rich in unsaturated fatty acids.
Deficiency of vitamin E and selenium cause - lipoperoxidation of the tissue
- hepatic necrosis
- fibrin presence of the myocardium also known as Mulberry disease
Name the 7 types of myopathies. *
a) Nutritional myopathies
b) Non-nutritional myopathies
c) Exercise-related myopathies
d) Metabolic and hormonal myopathies
e) Ischemic myopathies
f) Inherited myopathies
g) Myopathies caused by plant
Mechanism of development of myopathies caused by selenium and vitamin E deficiency *
Nutritional myopathy and Nutritional muscular dystrophy; also called white muscle disease
Selenium is a component of the enzyme glutathione peroxidase acting in the breakdown of hydrogen peroxidase into catalase -> Responsible for protecting the body from oxidative damage
Deficiency can be from
- legume feed
- prolonged transport
• Vitamin E maintains the integrity of cellular membrane
• In conjugation both selenium and vitamin E protect the cell membrane and lipid
containing organelles such mitochondria and endoplasmic reticulum
• In lambs, calves and foals fed a diet with deficiency in vitamin E and selenium cause Lipo-peroxidation of the tissue ( skeletal and myocardial) leading to degeneration of muscle causing
- acute heart arrest
- necrosis of muscle cells
- retention of Calcium in muscle fibers also known as calcification
- release of enzymes such as LD, CPK, ALT
Clinical signs: inability to stand, stiffness, trembling and weakness
• In young, rapidly growing pigs fed a diet with deficiency in vitamin E and selenium cause Lipo-peroxidation of the tissue,
hepatic necrosis and fibrin presence of the myocardium also known as Mulberry disease in pigs
Mechanism of development of non-nutritional myopathy in piglets. *
Myodegeneration induced by iron of piglets.
- An acute poisoning and seen in piglets if deficient in Se or vit E and will be administered with exogenous Iron to prevent iron deficiency - for anemia for example.
Piglets born from sows deficient in vitamin E and Se, and by addition of Iron will damage muscle cell membrane leading to an leakage of K+ from muscle cells to plasma, causing Hyperkaliemia which has a toxic effect on cardiac activity since very young piglets are unable to excrete administered K+
Can lead to cardiac arrest and sudden death.
On ECG;
- Tall and peaked T waves
- Prolonged P wave and QRS duration
- Later decreased and disappeared P wave
