Updated: 8/26/2019

Cardiac Cycle

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Snapshot
  • A 15-year-old boy presents to the emergency room after collapsing on the basketball court. His mom reports that he has been pushing himself physically to do well in basketball. She states that he has had several episodes of syncope while playing basketball. There is also a family history of sudden cardiac death in several relatives. On physical exam, the boy has an S4 heart sound and a systolic murmur. (Hypertrophic cardiomyopathy)
Introduction
  • The cardiac cycle is divided into 7 components
  • Atrial systole (1) 
    • atria contract
      • this is the final phase of ventricular filling
      • electrocardiogram (ECG) finding
        • P wave
    • final phase of ventricular filling
      • ECG finding
        • PR interval
  • Isovolumetric contraction (2)
    • period from between mitral valve closure to aortic valve opening
    • ventricles contract and pressure increases
      • ECG finding
        • QRS complex
    • pressure is constant, as all the valves are closed
    • period of highest O2 consumption
  • Systolic ejection
    • period from aortic valve opening to aortic valve closing
    • two phases
      • rapid ejection (3)
        • ventricles contracts and pumps blood into arteries
        • ventricular pressure reaches maximum
        • ECG finding
          • ST segment
      • reduced ejection (4)
        • ventricles pump blood at a slower rate
        • ventricular volume is at its minimum
        • ECG finding
          • T wave
  • Isovolumetric relaxation (5)
    • period from aortic valve closure to mitral valve opening
    • ventricles relax with no filling
  • Rapid ventricular filling (6)
    • period right after mitral valve opens
  • Reduced ventricular filling, or diastasis (7)
    • period right before mitral valve closes
Heart Sounds
  • S1
    • closure of the mitral and tricuspid valves
    • loudest at mitral area
  • S2
    • closure of aortic and pulmonary valves
    • loudest at left upper sternal border
  • S3 
    • early diastole
    • associated with ↑ filling pressures
      • mitral regurgitation
      • congestive heart failure
      • dilated ventricles
    • normal in children and pregnancy
  • S4
    • late diastole
    • also referred to as “atrial kick”
    • loudest at apex with the patient in left lateral decubitus position
    • associated with ↑ atrial pressure and ventricular hypertrophy
      • left atrium pushes against a stiff and noncompliant left ventricular wall
    • always abnormal
Jugular Venous Pulse (JVP)
  • a wave
    • atrial contraction
    • absent in
      • atrial fibrillation
  • c wave
    • right ventricular contraction
    • tricuspid valve is closed and bulges into atrium
  • x descent
    • tricuspid valve is closed and is displaced downward during rapid ejection phase
    • reduced or absent in
      • tricuspid regurgitation
      • right heart failure
  • v wave
    • ↑ right atrial filling pressures against closed tricuspid valve
  • y descent
    • right atrium empties into right ventricle
    • increased in
      • constrictive pericarditis
    • absent in
      • cardiac tamponade

 

 

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(M1.CV.15.75) A 69-year-old male with a history of well-controlled hypertension, diabetes, and depression presents to his primary care physician for a routine visit. He has no present complaints at this time and states that he has been compliant on all his medications. On exam, the physician appreciates a IV/VI crescendo-decrescendo systolic ejection murmur that is immediately preceded by a click and radiates into the carotids. Which of the following pressure-volume loops corresponds to this patient's condition? Tested Concept

QID: 106831
FIGURES:
1

Figure A

8%

(14/177)

2

Figure B

68%

(120/177)

3

Figure C

12%

(21/177)

4

Figure D

8%

(15/177)

5

Figure E

0%

(0/177)

M 1 A

Select Answer to see Preferred Response

(M1.CV.13.42) Figure A shows a pressure-volume loop for the left ventricle. Which of the following changes on the pressure-volume loop best corresponds to stroke volume? Tested Concept

QID: 100558
FIGURES:
1

4 => 1

2%

(2/93)

2

1 => 2

24%

(22/93)

3

3 => 4

42%

(39/93)

4

2 => 3

20%

(19/93)

5

Stroke volume can not be calculated from this diagram

9%

(8/93)

M 1 E

Select Answer to see Preferred Response

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