Cardiovascular L4.1 Flashcards
Electrical system of heart
Atrial muscle conducts relatively fast (0.5m/sec)
➢ The AVN has a slower conduction velocity (0.05m/sec)
➢ Branches of the bundle of His conduction velocity (2m/sec).
➢ Purkinje fibers conduction velocity (4m/sec).
1) What occurs during atrial depolarization?
2) What phase are ventricular myocytes in during atrial depolarization?
3)What is the role of the Na⁺/K⁺ pump during Phase 4 in ventricular myocytes?
4) Why is the Na⁺/K⁺ pump important during Phase 4 of the ventricular action potential?
5)How is atrial depolarization related to ventricular depolarization?
1) - electrical activation of atria, causes them to contract, pump blood into ventricles
- P wave on ECG
2) -During atrial depolarisation, VENTRICULAR MYOCYTES in PHASE 4 of DEPOLARISATION/REPOLARISATION cycle (Phase 4 = resting phase/diastolic phase for ventricles)
3) RESTORES IONIC BALANCE Na+/K+ATPase
(pump actively transports 3 Na+ out of cell, 2K+ into cell). This maintains resting membrane potential + prepares ventricular cells for next depolarisation
4) Na+/K+/ATPase pump maintains ion gradients necessary for generating next action potential, ensures cells ready for next depolarisation phase
5) Atrial depolarization initiates the contraction of the atria, while ventricular myocytes restore ionic gradients during Phase 4, preparing for the next ventricular depolarization (QRS complex).
1) What is the role of AV node?
2) What is the importance of AV node delay?
3) Describe conduction after the AV node
1) Slow down electrical impulse from atria before it is transmitted to ventricles.
Electrical impulse causing heart to originates in SAN, travels through atria, causinf atrial depolarisation. As impulse reaches AV node, BRIEF DELAY before transmitted to ventricles.
2) Allows atria to complete contraction, ensuring all blood is pumped to ventricles before ventricles contract
Allows ventricles enough time to fill with blood from the atria before they depolarise + contract. Without delay, may conract too early, leading to incomplete filling, therefore, reduced cardiac output.
3) After delay, electrical impulse continues from AV node inti Bundle of His, then into right and left bundle branches, and finally through purkinje fibers to trigger ventricular depolarisation (QRS COMPLEX ECG)
1) What is ventricular depolarisation ?
2) What is phase 0 of ventricular action potential?
3) Describe influx of Na+ via fast sodium channels
(2,3 same answer)
1) Ventricular myocytes eletrcially activated = ventricular contraction (QRS COMPLEX ECG)
2) Depolarisation phase of ventricular action potential where membrane potential of myocytes rapidly become positive. Triggered by rapid influx of Na+ through fast sodium channels
3) Fast Na+ channels open when ventricular myocytes reach threshold potential. When open, rapid influx of Na+ ions into cell, drives membrane potential from +30 to +40 mV, initiating the depolarization phase.
1) Describe Phase 1 - early rapid repolarisation
2) Describe Phase 2 - Plateu Phase (slow repolarisaion)
3) What is the significance of the plateu phase?
1) Phase 1 - initial rapid repolarisation, Happens so quickly, we do not see it on ECG
Fast Na+ channels close after rapid depolarisation of phase 0, preventing further Na+ influx
Brief efflux of K+ ions, causing membrane potential to start becoming more negative
2) Balance between:
Efflux of K⁺ (potassium leaves the cell).
Influx of Ca²⁺ (calcium enters the cell).
Balance creates plateau in membrane potential, where voltage remains stable for period of time
3) Prolongs action potential in ventricular mypcytes - sustained contraction of ventricles, allowing efficient ejection of blood from heart
1) Describe Phase 3 rapid repolarisation
2) Describe ion movement during phase 3
3) When does phase 3 end?
4) Why is phase 3 important?
1) Final phase of repolarisation (in ventricular myocytes)
Rapid return of membrane potential to resting state
2) Continuation of K+ efflux out of cell
Makes inside of cell more -ve, back towards resting potential
As K+ efflux continues and calcium influx stops, membrane potential becoems more negative, appraoching resting membrane potential (-90mv)
3) When cell has fully repolarised and ready to begiin next action potential cycle with phase 4 (resting potential)
4) Ensuring ventricular myocytes fully repolarised. Preparing ventricular myocytes for next cycle of depolarisaion and contraction
What happened to Atrial
Repolarisation on an ECG?
What happened to Atrial
Repolarisation??
Atrial repolarization wave (Ta wave) is usually not evident on
the ECG as it has a low amplitude of hundred to two hundred
microvolts and is usually hidden in the QRS complex.
Diagram showing coronary arteries
1) What are ECG leads?
2) How many electrodes are placed on the patient?
3) How does the direction of depolarisation affect how it appears on ECG?
1) used to view hearts electrical activity from different angles
2) 10 physical electrodes but 12 leads generated
3) If depolarisation moves towards lead, produces upwaird (positive) deflection. If depolarisation moves away from lead, produces downward (negative) deflection
Describe the components of the ECG
P wave: atrial depolarisation, triggers atrial contraction
Q wave: septral depolarisaion. Electrical impulse spreads from septum to ventricles
R wave: main ventricular depolarsiaion. Causes their contraction
S wave: end of ventricular depolarisaion.
T wave: ventricular repolarisation
The paper used to record ECGs is standardised across all hospitals + has following characteristics
STANDARD ECG
P wave: Atrial depolarisation
PR interval: onset of P wave and beginning of QRS Complex (represents time taken from eletrical impulse to travel from atria through AV node into ventricles)
PR Segment: AV Node delay
Q wave: Initial depolarisation of ventricular septum (first negative deflection in QRS)
R wave: main positive deflection in QRS, bulk of ventricualr depolarisaiton
S wave: final negative deflextion in QR, represents end of ventricular depolarisation
ST segemnt: Represents period when ventricles are fully depolarised before they start repolarising
T wave: Ventricular repolarisation
QT interval: Time for both ventricular depolarization and repolarization.
OSCE Question.
Before beginning ECG interpretation, you
should check the following details
Confirm the name and date of birth of the patient matches the details
on the ECG.
✓Check the date and time that the ECG was performed.
✓Check the calibration of the ECG (usually 25mm/s and 10mm/1mV)
How do we interpretate ECGs?
- Rythm
check is p wave before every QRS complex. In sinus rhythm, the P wave should be upright in leads I, II, and aVF. If P wave is inverted, it is not a sinus rythm and this suggests depolarisation is not originating from SA node (could be coming from abnormal location in atria, AV node (that would be ectopic rythm) - Rate:
Normal heart rate: 50–100 beats per minute (bpm).
Tachycardia: Heart rate >100 bpm.
Bradycardia: Heart rate <50 bpm.Estimate rate by counting the number of large squares between R waves:
300 / Number of large squares between R waves. - PR Interval:
Normal duration: 0.12–0.20 seconds (3–5 small squares).
Is conduction 1:1? There should be one P wave for each QRS complex.Prolonged PR interval (>0.20 seconds) may indicate first-degree heart block.
Shortened PR interval may suggest pre-excitation syndromes (e.g., Wolff-Parkinson-White syndrome). - Axis:Normal axis: The QRS complex should be positive in leads I and aVF.
Left axis deviation: Positive in lead I, negative in aVF.
Right axis deviation: Negative in lead I, positive in aVF. - QRS Complex:Width:
Narrow QRS: Less than 0.12 seconds (normal).
Broad QRS: Greater than 0.12 seconds, which can indicate bundle branch blocks or ventricular origin of the rhythm.
Shape: Look for abnormal morphologies, such as notches or slurring.
Height:
Increased QRS amplitude can suggest left ventricular hypertrophy (LVH).
Decreased amplitude may indicate pericardial effusion or obesity - QT Interval:Normal duration: Varies by heart rate, but generally <0.44 seconds.
Prolonged QT interval can be a risk for ventricular arrhythmias (e.g., torsades de pointes).
Shortened QT interval may be seen in conditions like hypercalcemia - ST Segment:Isoelectric: The ST segment should be on the baseline (flat).
ST elevation: May indicate acute myocardial infarction (MI).
ST depression: Suggests myocardial ischemia or subendocardial infarction. - T wave:
Inverted T wave: ischemia, myocardial infarction, left ventricular hypertrophy
Peaked T wave: hyperalkemia
1) What shape should the P wave have in Lead II?
2) What shape should P wave have in lead V1?
3) What is the normal P wave duration?
4) What canit suggest if P wave is longer than 0.12 seconds?
5) What should the amplitude be n a normal P wave?
1) Monophasic (single upward deflection)
2) Biphasic (having both an upward and downward component)
Upward portion: right atrial depolarisation
Downward portion: left atrial depolarisation
3) Normal P Wave Duration: < 0.12 seconds (less than 3 small squares on ECG)
4) Atria enlargement
5) Amplitude in Limb Leads: < 2.5 mm.
Amplitude in Precordial Leads: < 1.5 mm.(P wave height
1) What does QT interval represent?
2) What is the relationship between QT interval and heart rate?
3) What is QTc?
1) Time taken for ventricular depolarisaion and repolarisation
2) Inversely proportional. The QT interval shortens at faster heart rates
* The QT interval lengthens at slower heart rates
3) corrected QT interval. Adjusts QT interval to a standard heart rate of 60 bpm.
