The document summarizes key aspects of cardiac physiology including the cardiac cycle, myocardial action potential, coronary circulation, and jugular venous pulse (JVP). It describes the electrical and mechanical events of the heart during one cardiac cycle as represented by an electrocardiogram (ECG) and pressures. It also discusses the anatomy and regulation of coronary blood flow to meet metabolic demand of the myocardium.

1. Moderator: Dr Shaila S. Kamath
Presenter :Samiksha Khanooja

2.  Cardiac cycle
 JVP
 Myocardial action potential
 Coronary circulation

3.  Modern concept of circulation & heart as generator of
circulation was advanced by Harvey in 1628.
 Field of cardiac physiology has developed to include
• physiology of heart as pump
• cellular & molecular biology of cardiomyocyte, &
• regulation of cardiac function by neural & humoral
factors

4.  Basic anatomy of heart consists of 2 atria & 2 ventricles -
provide 2 separate circulations in series.
 Pulmonary circulation, low-resistance & high-
capacitance vascular bed, receives output from right side
heart, chief function - bidirectional gas exchange.
 Systemic circulation, high resistance, receives output from
left side heart & provides output for systemic circulation,
delivers O2, nutrients & removes CO2 & metabolites from
tissue beds.

5. CARDIAC CYCLE
 Sequence of electrical & mechanical events during
course of single heart beat.
1. Electrical events represented by ECG
2. Mechanical events represented by left atrial & left
ventricular pressure pulses correlated in time with
aortic flow & ventricular volume

6.  Electrical events of pacemaker & specialized
conduction system are represented by ECG at body
surface & is result of differences in electrical potential
generated by heart at sites of surface recording.

7.  P wave action potential initiated at SA node is
propagated to both atria by specialized conduction
tissue, it leads to atrial systole (contraction) & P wave
of ECG
 P-R interval.. PR interval can be used to measure
delay between atrial & ventricular contraction at
level of AV node

8.  From distal His bundle, electrical impulse
propagated through left & right bundle branches
finally to Purkinje system fibers
 Electrical signals are transmitted from Purkinje
system to individual ventricular cardiomyocytes.

9.  Spread of depolarization to ventricular myocardium
is manifested as QRS complex on ECG.
 Depolarization is followed by ventricular
repolarization and appearance of T wave on ECG.

11. LATE DIASTOLE
 Mitral & tricuspid valves - open, aortic & pulmonary
valves -closed
 Blood flows into heart throughout diastole
 Rate of filling declines as ventricles become
distended, —especially when heart rate is low—
cusps of AV valves drift toward closed position
 Pressure in ventricles remains low

12. Atrial Systole
 It pumps additional blood into ventricles, but about
70% of ventricular filling occurs passively during
diastole
 Contraction of atrial muscle that surrounds the
orifices of SVC,IVC & pulmonary veins narrows
their orifices; however, there is some regurgitation of
blood into veins during atrial systole

13. Ventricular Systole
 Mitral & tricuspid valves close
 Intraventricular pressure rises sharply as myocardium
presses on blood in ventricle .

14.  This isovolumetric (isovolumic, isometric)
ventricular contraction lasts about 0.05 s, until
pressures in left & right ventricles exceed pressures
in aorta (80 mm Hg ) & pulmonary artery (10 mm
Hg) & aortic & pulmonary valves open
 AV valves bulge into atria, causing a sharp rise in
atrial pressure

15.  When aortic pulmonary valves open, phase of
ventricular ejection begins
 Rapid at first, slowing down as systole progresses.
 Intraventricular pressure rises to a maximum ,then
declines before ventricular systole ends
 Peak left ventricular pressure is about 120 mm Hg, &
peak right ventricular pressure is 25 mm Hg or less

16.  Late in systole, the aortic pressure actually exceeds
the ventricular, but for a short period momentum
keeps the blood moving forward
 The AV valves are pulled down by the contractions of
the ventricular muscle, and atrial pressure drops

17.  Amount of blood ejected by each ventricle per stroke
at rest is 70–90 mL.
 End-diastolic ventricular volume is about 130 mL.
 Thus, about 50 mL of blood remains in each
ventricle at end of systole (end-systolic ventricular
volume), the ejection fraction, percent of EDVV-
that is ejected with each stroke, is about 65%.
 Ejection fraction is a valuable index of ventricular
function.

18. Early Diastole
 Once ventricular muscle is fully contracted,already
falling ventricular pressures drop more rapidly
 This is the period of protodiastole ,lasts about 0.04sec,
ends when aortic & pulmonary valves close
 After the valves close, pressure continues to drop rapidly
during isovolumetric ventricular relaxation

19.  Isovolumetric relaxation ends when ventricular
pressure falls below atrial pressure & AV valves
open, permitting ventricles to fill
 Filling -rapid at first, then slows as next cardiac
contraction approaches
 Atrial pressure continues to rise after the end of
ventricular systole until AV valves open, then drops
and slowly rises again until next atrial systole

20. Length of Systole & Diastole
 Cardiac muscle has unique property of contracting &
repolarizing faster when heart rate is high
 Duration of systole decreases from 0.27 s at a heart
rate of 65 to 0.16 s, diastole from 0.62sec to 0.14 sec
at a rate of 200 beats/min
 THUS, duration of systole is much more fixed than
diastole, & when heart rate is increased, diastole is
shortened to much greater degree

21.  This fact has important physiologic and clinical
implications
 It is during diastole that heart muscle rests, and
coronary blood flow to the subendocardial portions of
the left ventricle and most of the ventricular filling
occurs

22.  At heart rates up to about 180, filling is adequate as
long as there is ample venous return, and cardiac
output per minute is increased by an increase in rate
 At very high heart rates, filling may be compromised
such that cardiac output per minute falls and
symptoms of heart failure develop

24.  JVP is a vertical height from sternal angle to zone of
transition of distended & collapsed IJV’s
 Patient reclining at 45 degree,it is normally 4-5cm
 It is an indicator of right mean atrial pressure.
 It is the reflection of phasic pressure changes in right
atrium
 Consists of three positive waves (a,c,v) and two
negative troughs(x,y)

26.  a wave depicts atrial contraction(atrial systole)
 c wave depicts bulging of tricuspid valve into the atria
(isovolumetric contraction)
 x descent shows atrial relaxation(ventricular systole)
 v wave venous filling,(isovolumetric relaxation)
 y descent indicates atrial emptying(ventricular filling)

28. The types of action potential in the heart can be separated
into two categories:
 fast-response action potentials, which are found in the
His-Purkinje system and atrial or ventricular
cardiomyocytes,
and
 Slow response action potentials, which are found in the
pacemaker cells in the SA and AV nodes

30.  Phase 0 – Depolarization ( Na influx)
 Phase 1 -Transient repolarization(activation of
transient outward K+ current)
 Phase 2 -Plateau phase(net influx of Ca2+ through L-
type calcium channels efflux of K+ through K+
channels
 Phase 3 -Repolarization(when efflux of K+ from 3
outward K+ currents exceeds the influx of Ca2+)
 Phase 4 -Diastole(little ionic changes)

31.  Action potentials in SA & AV nodes are largely due
to Ca+, with little contribution by Na influx
 So there is no sharp rapid depolarization spike before
plateau,as in other parts of conduction system
 When compared with fast-response action potential,
phase 0 is much less steep, phase 1 is absent, phase
2 is indistinct from phase 3

33. ANATOMY
 RCA and LCA
 RCA - rt atrium, most of rt ventricle & inferior wall
of left ventricle
 In 85% cases,RCA gives rise to posterior descending
artery(superior posterior IVS & inferior wall)-Rt
Dominant Circulation

34.  LCA –left atrium, most of interventricular septum,
left ventricle
 Bifurcates into left anterior descending(septum
&anterior wall) and circumflex artery(lateral wall)
 SA node-RCA(60%), LAD(40%)
 AV node-RCA(85%),circumflex(15%)
 Bundle of His-PDA,LAD

35.  Difference between aortic & ventricular pressure
 CPP= arterial diastolic pressure – LVEDP
 Decrease in aortic pressure ,increase in VEDP
reduces CPP
 Increase in heart rate also decrease CPP(because of
reduction in diastolic time)
 Endocardium-most vulnerable to ischemia

36.  Parallels myocardial metabolic demand
 Approx 250ml/min at rest
 Myocardium regulates its own blood flow between
perfusion pressures 50 &120mm Hg
 Changes in blood flow mainly due to coronary
arterial tone
 Hypoxia cause vasodilation(directly or by adenosine
release)
 Sympathetic stimulation increases myocardial blood
flow

37.  Most important determinant of myocardial blood
flow
 Myocardium extracts 65% of oxygen in arterial
blood, compared with 25% in other tissues
 Coronary sinus saturation -30%
 Myocardium cannot compensate for blood flow
reductions by extracting more O2 from Hb
 Increase in demand must be met by increase in CBF