Cardiac lecture IIA Flashcards
Cardiac biomarkers. (2)
NT-proBNP
(N-terminal pro B-type natriuretic peptide) which is a myocardial stretch biomarker
cTnI (“i”)
(cardiac troponin I) which is a myocyte damage biomarker
Physiological function of NT-proBNP.
It’s a natural diuretic, it naturally opposed RAAS’ effects.
RAAS holds onto water to increase plasma volume.
NT-proBNP in different species
There are significant structural differences in the molecule between species.
Thus you must use canine/feline specific assays.
- Quantitative assay (Cardiopet proBNP)
- Point-of-care (Snap Feline proBNP, Bionote
Vcheck Canine NT/proBNP)
NT-proBNP is good to use to find
Occult heart disease aka subclinical heart disease, “catch it early”.
Hypertrophic (HCM) and restrictive cardiomyopthies (RCM) are common in cats and may have long pre-clinical phases. proBNP may begin to rise before the occurance of clinical signs.
Or alternatively, if you notice cardiomegaly indicdentally on radiograph, test proBNP.
Elevation in cats with gallop, arrhythmias, cardiomegaly suggests cardiac disease: further investigations warranted.
Sensitivity and specificity of NT-proBNP.
You can do a quantitative test as well as POC snaptest.
The QUANTITATIVE TEST is:
A Good rule IN test.
* >100 pmol/L indicates heart disease likely
It’s Less good for ruling OUT heart disease.
* <100 pmol/L heart disease still technically possible, its just not a blatant positive.
The SNAP test is:
* Less accurate rule IN test
* Similar rule OUT test though
Why use NT-proBNP in Respiratory distress cases?
If you have a Dyspnoea, tachypnoea, coughing case.
You can do
* QUANTITATIVE measurement (cut-off 220-265 pmol/L)
or
* SNAP test: good rule OUT
to differentiate overt CHF vs non-cardiac causes.
Normal biomarker levels - > primary respiratory disease more likely.
cardiac troponin i can also be utilized to differentiate CHF vs non-cardiac
Why use NT-proBNP in Mitral valve disease?
Can be used for:
- Prediction of CHF in next 6-12 mths
If NT-proBNP >1500 pmol/L. - Longitudinal monitoring of disease progression
- Biomarker guided therapy?
Why use NT-proBNP in Dilated cardiomyopathy cases?
- Not useful for screening because asymptomatic.
Can be Useful for
* Prediction of mortality (900 pmol/L)
Describe Cardiac troponin I (cTn”i”)
Is an intracellular protein released in cell damage such as Ischemia, inflammation, trauma (famously, cardiac infarcts)
- Has a Short half-life (~2h)
- Different troponin assays have different cut-off
values so they Cannot necessarily be used interchangeably.
Describe cTnI for Occult heart disease.
Sensitivity 85% - those that test positive are truly positive.
Specificity 97% - those that test negative are truly negative.
So, its a good rule IN test. Recommend echo, if positive.
- Stratus CS analyzer uses Cut-off of 0.157 ng/ml
A good rule-in test should have high specificity, which minimizes false positives.
A good rule-in test should have
high specificity, which minimizes false positives.
Specificity is the key factor for a rule-in test because a highly specific test (close to 100%) ensures that a positive result strongly indicates the presence of disease (low false positives).
A good rule-out test should have…?
high sensitivity.
High sensitivity means the test correctly identifies most that have the disease (low false negatives).
If a test is highly sensitive and the result is negative, you can be confident that the person does not have the disease (SnNout: SeNsitivity rules OUT vs SpPin: SPecificity rules IN).
Example:
If a test has 99% sensitivity, it will correctly detect 99 out of 100 true positives. If someone gets a negative result, there’s a very low chance they actually have the disease.
So, for a good rule-out test, you need high sensitivity (≥95-99%).
How does cardiac troponin i relate to mitral valve disease?
- Can be used for Prediction of all cause mortality
- When Cut-off 0.025ng/mL, Risk of death increased by 91%
Perhaps Longitudinal monitoring of disease progression too?
Cardiac biomarker results may be affected by: (4)
- Azotemia
- Hyperthyroidism
- Severe hypertension (BNP)
- Anemia (cTnI)
Main 3 types of cardiac specific imaging.
Two-dimensional (2D) echo
M-mode
Doppler echocardiography
- Spectral Doppler – pulsed wave, continuous wave
- Colour Doppler
- Tissue Doppler
Examples of usage
* Chamber dimensions
* Wall thickness
* Left ventricular function
* Stenotic lesions
* Congenital defects
Describe M-mode for echocardiography.
The earliest form of echocardiographic imaging, M-mode echocardiography, displays fine detail of cardiac structure along a time-distance graph.
- Time-dependent measurements
Examples of usage
* Chamber dimensions
* Wall thickness
* Left ventricular function
* Stenotic lesions
* Congenital defects
Describe cardiac doppler-imaging?
Representation of flow direction
Assessment of flow pattern and velocity measurement
Different types
- Pulsed wave
- Continuous wave
- Colour Doppler
Electrocardiography - indications (8)
- Arrhythmia on PE
- Hx of collapse or exercise intolerance
- Part of investigation for heart disease
- (cardiac chamber enlargement)
- Suspected electrolyte abnormalities (K+;Ca++)
- Pericardial disease/effusion
- Drug toxicity (e.g. digoxin)
- Anaesthesia monitoring
ECG ACQUISITION
- Right lateral recumbency
- Sternal/standing,
If patient unstable
If only interested in rhythm
red-yellow-green starting right fore-left fore-left hind
ECG interpretation steps (7)
- RATE - calculate heart rate
- Rhythm - is the rhythm regular, irregular or chaotic?
- P-s and QRS-s
- Are there P waves for every QRS?
- Is there a QRS for every P?
- Are the PR-intervals consistent
Four. QRS morphology “nice and narrow” or “wide and bizarre”
Five. Measure all the intervals and amplitudes.
- Durations: P; PR; QRS; QT;
- Amplitudes: P; QRS; T
Six. Calculate Mean Electrical Axis (MEA)
Seven. Formulate rhythm diagnosis
* !!! Consider the history, physical exam and other diagnostic test results
ECG interpretation steps 3 & 4
Three. P-s and QRS-s
- Are there P waves for every QRS?
- Is there a QRS for every P?
- Are the PR-intervals consistent
Four. QRS morphology “nice and narrow” or “wide and bizarre”
ECG interpretation steps 5, 6 & 7.
Five. Measure all the intervals and amplitudes
* Durations: P; PR; QRS; QT;
* Amplitudes: P; QRS; T
Six. Calculate Mean Electrical Axis (MEA)
Seven. Formulate rhythm diagnosis
What is the Mean Electrical Axis (MEA) on ecg and how do you calculate it and what for?
The Mean Electrical Axis (MEA) represents the average direction of the heart’s electrical activity during ventricular depolarization. It is determined from the QRS complex in the frontal plane leads (limb leads) of an ECG.
MEA is primarily used to assess cardiac orientation, hypertrophy, and conduction abnormalities.
sick sinus syndrome is
a disorder of the heart’s natural pacemaker, the sinus node, which leads to abnormal heart rhythms (arrhythmias). It causes the heart to beat too slowly (bradycardia), too fast (tachycardia), or alternate between both.
the bradycardia can cause escape beats meaning ventricular polarization stimulus originates elsewhere in the conduction system, not at the SA node (cause its sick)
Treatment:
Pacemaker implantation (for bradycardia)
Medications (for tachycardia)
Describe 1st-Degree Heart Block (Mildest)
🔹 Abnormally slow electrical signals in the AVN move through the heart slower than normal - “incomplete heart block”.
🔹 Usually no symptoms and often found by accident on an ECG - results in an extended PR-interval.
🔹 No treatment needed in most cases.
Describe 2nd-Degree Heart Block (Moderate)
2nd degree occurs when a fraction of impulses are conducted.
Two types:
- Mobitz Type I (Wenckebach) – the PR interval progressively lengthens until no transmission from tria to ventricles and a QRS complex is missed.
- Mobitz Type II – when ventricular contraction is only initiated every 2nd or 3rd atrial contraction (2:1, 3:1 blocks).
Symptoms: Dizziness, fainting, fatigue.
May need a pacemaker if severe.
Describe 3rd-Degree Heart Block (Severe)
“Complete heartblock”, no conduction between atria and ventricles.
In the abcsnce of a signal from the SA node, the AVN and bundle of His can generate a heart rate of approx. 40 bpm.
Symptoms: Extreme fatigue, dizziness, fainting, chest pain.
Treatment: Pacemaker is required to keep the heart beating properly.
Describe a bundle branch block.
When one branch of the bundle of His doesn’t conduct. That part of the ventricle will instead get stimulation from myocardium that isn’t affected.
Because this form of conduction is slower, the QRS complex broadens.
Name the valves between veins and atria.
There are no valves between the veins and atria so its normally that some blood regurgitates into the veins during atrial systole.
from body to right atrium, from lungs to left atrium
During the initial phase of ventricular contraction pressure is less than that in the pulmonary artery and aorta, so the outflow valves remain close. This is termed…
isovolumetric contraction.
What is the dicrotic notch?
Ventricular contraction involves a rapid ejection phase and a reduced ejection phase. Ventricular pressure during the reduced ejection phase is slightly less than that in the artery, but blood continues to flow out of the ventricle due to momentum.
Even tually the flow briefly reverses, causing closure of the outflow valve and a small increase in aortic pressure.
The ejection fraction is the
portion of EDV that is actually ejected because a portion of blood will remain in the ventricle at the end of systole.
Isovolumetric relaxation is when
The ventricles are relaxing following closure of the outflow valves. Ventricular pressure is still greater than atrial pressure so the AV valves remain close and the blood volume in the ventricle is not changing (for a moment).
Name the molecule that atrial myocytes release upon stretch in order to induce diuresis.
What else does this molecule do?
atrial natriuretic peptide (ANP) causes both diuresis and natriuresis by increasing
glomerular filtration rate
decreases renin and aldosterone secretion
reduces NA+ reabsorption throughout the nephron
also dilates arterioles and increases capillarity permeability
The PR interval represents
delayed conduction through the AV node.
sinus rhythm seen on 6 leads
determine your rhythm based on lead 2.
paper speed 50 mm/sec so using this you can count your heart rate
not regular
count QRSs
count Ts
count Ps
is there a P for every QRS?
is there a QRS for every P?
atrial or supraventricular premature contraction
can even be an incidental finding if patient otherwise fine and is a one off or just not too frequent.
Usually we would look at lead 2 but its not so nice looking in this example so we look at lead 1.
Irregular rhythm
Count QRSs, 8
Count T waves, 8
Count Ps, 9
There’s a “spare” P wave and no conduction to ventricles after it.
We call it an AV-block and we call it 2nd degree (Mobitz type I) because conduction was successful from the sinus node but not through the atrioventricular node.
Give atropine or pinch the patient because you want to decrease vagal tone (pinching increases sympathetic stimulation).
Mobitz I slow HR, Mobitz II fast HR
1st degree AV block is when the PR interval is abnormally long, continues to lengthen and eventually skips.
Name the cranial nerves I-XII.
Olfactory nerve (CN I),
optic nerve (CN II),
oculomotor nerve (CN III),
trochlear nerve (CN IV),
trigeminal nerve (CN V),
abducens nerve (CN VI),
facial nerve (CN VII),
vestibulocochlear nerve (CN VIII),
glossopharyngeal nerve (CN IX),
vagus nerve (CN X),
accessory nerve (CN XI), and
hypoglossal nerve (CN XII).
Rhythm is regular.
4 QRSs
4 T waves
15 P waves
There’s a P wave in front of every QRS.
There is not a QRS for every P wave.
Is the PR interval consistent in size? No.
The heart’s “lower” conduction systems must induce ventricular contraction intermittenly (escape rhythm), which they do in fact do very regularly, but the P waves are unable to induce ventricular contraction - they’re blocked.
3rd degree AV-block
Usually caused by AV nodal disease (e.g. fibrosis) or super high vagal tone caused by e.g. abdominal disease like pancreatitis.
You could do an atropine test to test if its caused by high vagal tone but it could be dangerous (cause heart could stop without the high vagal tone keeping the heart going).
Most animals with this condition would need a pace maker, or treat the condition that is causing the high vagal tone.
NB Cats can tolerate this ventricular escape rhythm surprisingly well.
12 QRSs
12 T waves
no discernible P waves but baseline undulation in all leads after lead I = atrial fibrillation
Atrial stretch (enlargement) can cause this via atrial myocardial hypoxia.
On auscultation it sounds like tennis shoes in a tumble dryer.
Can also be clinically asymptomatic.
Tx based on underlying cause. Digoxin or cardioversion etc. may be used in humans with atrial fib. Ablation of the atrial region causing the fibrillation is also done in people.
Irregular
Count QRSs
Count T waves
Count P waves
Is there a P for every QRS? Yes
Is there a QRS for every P wave? Yes
PR interval consistent? Yes
The wide bizarre QRS happens too early and there’s only one on the left so its a VPC. On the right we have 2 so we call it a couplet.
If you see 3 VPCs together, place an IVC and get your lidocaine doses ready because it may become ventricular fibrillation (2mg/kg for dogs, 0.5 mg/kg). Max 3 boluses 5-10 min apart.
Ventricular tachycardia is essentially when you have continuous VPCs. Ventricular fibrillation is not compatible with life.
Tx of ventricular tachycardia.
DOG: lidocaine 2 mg/kg slow IV bolus
Repeat maximum 3 boluses, 5-10 minutes apart.
Keep monitoring ECG. Give each new bolus if the rhythm does not convert to sinus rhythm. Give a 4th bolus if still no response cause otherwise its dead, but prepare for side effects. Can even consider a lido CRI or beta blocker like IV esmolol. Amiodarone is so slow onset so it may not help but if youre desperate you can try it (will give you side effects though).
CAT: 0.5 mg/kg
In cats, start with 0.25 mg/kg bolus and give more if needed.
SIDE EFFECTS:
* Neurological (obtundation, tremors, seizures)
* GIT (anorexia, nausea, vomiting, diarrhea)
Ventricular fibrillation is not compatible with life.
Ventricular tachycardia is essentially when you have continuous VPCs.
lidocaine drug class
anesthetic sodium channel blocker
Ambulatory ecg holter monitoring - indications: (5)
- Intermittent collapse or exercise intolerance
- Screening of breeds at risk of arrhythmias
- If arrhythmia detected or suspected
- Assessing severity of arrhythmia
- Antiarrhythmic treatment: need and monitoring
Continuous monitoring cause you can’t make a full diagnosis based on a few min ECG.
