Cardiac Cycle and its various phases shown

Cardiac cycle

1. Cardiac cycle

2. Cardiac cycle : Sequence of electrical and mechanical events in heart chambers in between two subsequent heart beats Normal duration  0.8 sec. @ HR  75/min Cardiac cycle time – time required to complete one cycle = 60 / HR = 60 / 75 = 0.8 sec.

3. Electrical events are recorded with ECG Mechanical events are : Changes in the pressure volume, and flow in different chambers . The pressure changes results in production of heart sounds (Recorded as phonocardiogram ) and “Juglar Venous Pulse” tracing ( JVP).

4. Mechanical Events of the Cardiac Cycle Each cardiac cycle consist of 2 major cycles: Atrial and Ventricular Systole (contraction and blood ejection) Diastole (relaxation and blood filling)

5. Different Phases of cardiac cycle Atrial Systole : 0.1 s Atrial Diastole : 0.7 s Ventricular Systole : 0.30 s Isovolumic Contraction phase: 0.05 s Rapid (Maximal) ejection phase : 0.10 s Slow (Reduced) ejection phase: 0.15 s

6. Ventricular Diastole : 0.50 s Protodiastole : 0.04 s Isovolumic Relaxation phase: 0.06 s Early Rapid Filling phase :0.1 s Slow Filling phase ( or Diastasis) : 0.2 s Late Rapid Filling phase :0.1 s

7. List of the features to be noted and remembered during each phase: Name of the phase Duration Position of valves Left ventricular pressure changes Left ventricular volume changes Aortic pressure changes ECG Heart sounds Blood flow Note : Illustration of these coordinated events is by “ Wiggers diagram”.

8. Wiggers diagram The X axis is used to plot time, The Y axis contains all of the following on a single grid: Aortic pressure Ventricular pressure Atrial pressure Ventricular volume Electrocardiogram Heart sounds JVP Arterial flow (optional)

9. Atrial systole (0.1sec.): contraction of atria  propels some additional blood (30%)  ventricle Rt atrial pressure:  4-6 mmHg  a-wave Lt a trial pressure  7-8 mmHg with ventricular pressure following it Narrowing of IVC ,SVC orifices some regurgitation of blood into veins A-V valves open Semilunar Valves Closed

10. Ventricular systole[0.3sec.] at start  v entricular P  than atrial P rapid  in P  MV & TV  close  1 st heart sound Ventricle as  closed cavity Ventricular muscle initially shortens  shape change but length remains same   intra v entricular pressure  myocardium presses on blood in ventricle  Isovolumetric ventricular contraction  0.05sec As Lt & Rt ventricle pressure exceed aortic [80mmHg] & pul . artery [10mmHg] pressure  aortic & pul . valve opening during isovolumetric contraction  AV valve bulge in atria    small but sharp atrial pressure  c-wave

11. 2. Ventricular systole proper (0.25 Sec.) On opening aortic & pul . valve  ventricular ejection begin Is Divided into

12. a. Rapid ejection phase [0.1sec]  intraventricular pressure to maximum [ peak lt ventricle 120mmHg & rt ventricle 25 mmHg ]  Rapid  output  ventricles 2/3 rd of SV  ejected in this phase  arterial P  blood enters vessels faster than it can escape via peripheral arteriolar branches Opening  SV  causes AV valve to come to their position  causes  sharp  in atrial P  x-descen t

13. b. slow ejection phase: 0.15sec. late in systole  ventricular P   So aortic pressure exceeds for short period than ventricular But momentum keeps blood moving forward AV valve pulls down by contraction  ventricular muscle   atrial pressure   x-descen t

14. 70-90 ml blood ejected each ventricle/stroke (beat) EDV 130 ml  50 ml blood in each ventricle after systole  ESV 50 ml Ejection fraction  % of EDV ejected Stroke volume at rest  70-90ml ( Avg. 80 ml) E.F= SV x 100/EDV Value of E. F is 60-65% Valuable index for Myocardial function

15. Diastole [0.5sec. ]  at the end of ventricle systole 1.[Early Diastole] 0.04 sec. V entricular pressure rapidly   period of protodiastole during this  arterial P is better sustained due to elastic recoil of BV wall & immediately arterial P exceeds that in ventricles  closure  of Aortic & Pulmonary valves  sharp 2 nd heart sound 2. Isovolumetric ventricular relaxation(0.08sec.) begins after semilunar valves closure intra ventricular P continue to  rapidly & ventricular muscle relax with out change in blood volume it ends when ventricular P  practically zero resulting  opening  AV valves

16. Isovolumetric Relaxation

17. 3. Ventricular Diastole proper 70% v entricular filling occur passively a. Early rapid filling ( 0.1-0.12sec. ) b . slow filling of ventricles  Diastasis  0.18-0.20 s due to continuous venous return filling both atrium & ventricle 4. Late Rapid filling ( 0.1s)  atrial systole Atrial diastole  0.7sec.  atrial muscle relax & atrial P gradually due to continuous venous return to drop to almost 0 mmHg with opening of AV valves atrial P again  in phase of Diastasis & follows the ventricular P

18. Atrial pressure changes depicted as Jugular Venous Pulse No valves in great veins  pressure changes  rt atrial  transmitted  great veins  3 characteristic waves  Jugular pulse waves ‘a’ (Atrial Wave)  atrial systole  some blood regurgitates into great veins ‘c’ (Carotid or Ventricular wave)   atrial P due to bulging of TV in atria during IVC ‘v’ (venous stasis wave)   atrial P before opening of TV during diastole

19. Heart sounds Duration frequency Nature cause First 0.15sec. 25-45 Hz soft @ low HR closure-MV & TV ‘ lub ’ Second 0.12sec. 5 Hz loud & sharp closure of semi.V ‘dup’ Murmurs /bruits

20. (1): S tart of isovolumetric systole, C losure of AVV and HS 1 (1–2): isovolumetric systole (0.05 s), (2): Opening of SL valves (2–3): maximum ejection (0.1s) (3–4): reduced ejection (0.15s) (4–5): protodiastole (0.05s) Closure of SL valves, HS 2 (5–6): isovolumetric relaxation (0.1 s); ( 6): Opening of AVV (1–8): atrial diastole(0.7 s) (1–4): ventricular systole (0.3 s), (4–1): ventricular diastole (0.5 s)

21. Events of rt & lt side of heart : similar but somewhat asynchronous Rt. atrial systole precedes left atrial systole Contraction of rt. ventricle starts after lt. ventricle Pulmonary arterial pressure is lower than aortic  Rt. ventricle ejection begins before Lt. ventricle During expiration  Pul . & aortic valve close at same time During inspiration  aortic valve close slightly before pulmonary valve slower closure of Pulmonary valve  due to lower impedance of pulmonary vascular tree When output from 2 ventricles measured over a period of minutes  equal. Transient differences during respiratory cycle  do occur

22. Length of Systole and Diastole Cardiac muscle contract & repolarize faster when HR   duration of systole  0.27 at 65 HR   to 0.16 at 200 HR this shortening due to  systolic ejection duration duration of diastole 0.62 at 65 HR   0.14 at 200 HR during diastole  heart muscle  rest  CBF to subendocardial part of lt ventricle & most of ventricular filling at HR 180 adequate filling as long as ample venous return &  CO/min by an  HR at very high HR  filling may be compromised &  CO  symptoms of heart failure  develops ventricular rate more than 230/min  paroxysmal ventricular tachycardia

23. HR-75/min HR-200/min Duration of CC 0.80sec. 0.30sec. Duration of systole 0.27 0.16 Duration of AP 0.25 0.15 Duration of ARP 0.20 0.13 Duration of RRP 0.05 0.02 Duration of diastole 0.53 0.14 During diastole  heart muscle rest CBF  subendocardial portion  left ventricle most of ventricular filling HR @ 180 /min filling  adequate on ample venous return & CO  HR   CO higher HR  filling may be compromised   CO  heart failure