L19. ECG, Cardiac Cycle, and Control Flashcards
(20 cards)
Arrhythmias?
Are the uncoordinated atrial and ventricular contractions caused by a defect in the conduction system
- A fibrillation is rapid and irregular (usually out of phase) contraction where the SA node is no longer controlling heart rate
- Atrial fibrillation can cause clotting (stroke) and inefficient filling of the ventricles
- Warfarin is used to prevent stroke
Ventricular fibrillation?
More life threatening
- The ventricles pump without filling and if the rhythm is not rapidly reestablished then circulation stops and brain death occurs
Cardiac cycle?
The cardiac cycle is all the events involved with the blood flow through the heart during one heart beat
- Systole is the contraction phase
- Diastole is the relaxation phase
- Electrical events - spontaneous - ordered sequence
- Followed by mechanical events - coordinated - contraction (systole) and relaxation (diastole)
- Both sides of the heart contract at the same time
- Pressure changes close valves at appropriate times
- Together = cardiac cycle
*Heart spends more time relaxing (in diastole) than it does contracting (in systole)
Systole?
Begins with ventricular contraction and ends when ejection ceases
Diastole?
Begins when ejection ceases as ventricles relax and ventricular filling begins after sufficient relaxation occurs
Diastole 1 - isovolumetric relaxation?
- All valves are shut
- No blood flow, no change in blood volume in ventricle
- Minimal ventricular volume (end-systolic volume (ESV))
- Ventricles are relaxing
- Atrial pressure lower than ventricular, atrium fills with blood returning to the heart
- Atrial pressure rises above ventricular pressure
- AV valve opens passively, ventricular filling begins
Diastole 2 - Ventricular filling?
- AV valve opens passively, ventricular filling begins
- 80-90% ventricular filling occurs passively down pressure gradient
- Late diastole, atrial depolarisation (P wave on ECG)
- Atrial contraction, atrial pressure rises
- Last 10-20% blood ejected from atrium into ventricle “top up”
Systole 1 - Isovolumetric contraction?
- Ventricles are filled
- Ventricles depolarise (QRS complex on ECG)
- Ventricles contract, ventricular pressure rises
- AV valve closes (1st heart sound)
- All valves are shut, no blood flow, no blood volume change
- Isovolumetric contraction
Systole 2 - Ventricular ejection?
- When ventricular pressure exceeds aortic pressure aortic valve opens
- Blood ejected into aorta
- Arterial blood volume and arterial pressure increase
- LVP and AP rise in parallel
- 2/3 of blood ejection occurs in first 1/3 of ejection time, rapid ejection
- Late systole, both LVP and AP fall, slow ejection
- Repolarisation of ventricles, T wave in the ECG
- LVP falls below AP, semilunar valves close
- Closure of semilunar valves (2nd heart sound
- Cardiac cycle re-enters (isovolumetric relaxation)
Ventricular volume (Wiggers diagram)?
Diastole:
- Constant during isovolumetric relaxation
- Early rapid ventricular filling, late slow ventricular filling
- Top up after atrial contraction
- Maximum at end of diastole (EDV) after atrial systole
Systole:
- Constant during isovolumetric contraction
- Rapid fall during early ejection, slow fall during late ejection
- Minimum at end systole (ESV)
Ventricular pressure (Wiggers diagram)?
Diastole:
- Drops to minimum at beginning of diastole after isovolumetric relaxation
- Rises a little during ventricular filling and atrial contraction
Systole:
- Rises dramatically during isometric contraction
- Continues to rise to a maximum during ejection phase
- Falls during late-systole
Arterial pressure (Wiggers diagram)?
Diastole:
- Continues to fall during diastole to minimum
- Minimum at end of diastole/start of systole (diastolic blood pressure)
Systole:
- LVP > AP valves open, rises to a maximum (systolic blood pressure)
Heart sounds (Wiggers diagram)?
1st heart sound:
- Closure of AV valves
- Low, long sound (lubb)
2nd heart sound:
- Closure of semilunar valves
- Short, high pitch (dubb)
Excitation - ECG (Wiggers diagram)?
Electrocardiogram - PQRST
P wave: Atrial depolarisation precedes atrial contraction
QRS complex: Ventricular depolarisation precedes ventricular contraction
T wave: Ventricular repolarisation, ventricular relaxation
Intrinsic controls?
aka local controls
–> Controls that originate entirely from within a system
Extrinsic controls?
–> Controls that involve input from outside (in particular hormonal and nervous effects)
Both forms of intrinsic and extrinsic controls operate continuously to adjust the heart and vessels, so that both are always functioning appropriately
Lower pressure in the atrium than in the ventricle leads to opening of the AV valve BECAUSE at rest, the majority of ventricular filling happens before the atria contract
A. If both statements are true, and the second causes the first
B. If both statements are true, but the second does not cause the first
C. If the first is true and the second is false
D. If the first is false and the second is true
E. Both statements are false
D
During isovolumetric contraction:
A. All heart valves are open
B. All heart valves are closed
C. Only the AV valve are open
D. Only the semilunar valves are open
B
Pacemaker cells repolarise due to:
A. Movement of K+ out of the cell
B. Movement of K+ into the cell
C. Movement of Na+ out of the cell
D. Movement of Na+ into the cell
A
How can the cardiac cycle change?
Cardiac function needs to be adaptable –> e.g. posture, exercise, volume depletion
