Exclusive for my Gen Phy BS BIO students

1. Matters of the Heart
Doc Bien Nillos, MD

2. The Heart
• The heart itself is made up of 4 chambers, 2 atria and 2
ventricles. De-oxygenated blood returns to the right
side of the heart via the venous circulation. It is
pumped into the right ventricle and then to the lungs
where carbon dioxide is released and oxygen is
absorbed. The oxygenated blood then travels back to
the left side of the heart into the left atria, then into the
left ventricle from where it is pumped into the aorta
and arterial circulation.

4. BP = 130/90, BP= 90/120 BP =3/4
• The pressure created in the arteries by the contraction
of the left ventricle is the systolic blood pressure.
Once the left ventricle has fully contracted it begins to
relax and refill with blood from the left atria. The
pressure in the arteries falls whilst the ventricle
refills. This is the diastolic blood pressure.

5. Electricals of the heart
This pathway is made up of 5 elements:
1.The sino-atrial (SA) node
2.The atrio-ventricular (AV) node
3.The bundle of His
4.The left and right bundle branches
5.The Purkinje fibres

6. • The SA node is the natural
pacemaker of the heart.
• The electrical stimulus from the
SA node eventually reaches the
AV node and is delayed briefly
so that the contracting atria
have enough time to pump all
the blood into the ventricles.
• electrical stimulus passes
through the AV node and
Bundle of His into the Bundle
branches and Purkinje fibers.
• The SA node and AV node contain
only one stimulus. Therefore every
time the nodes release a stimulus
they must recharge before they
can do it again.
In the case of the heart, the SA node recharges while the atria
are refilling, and the AV node recharges when the ventricles are
refilling. In this way there is no need for a pause in heart
function. Again, this process takes less than one third of a
second.

7. Cardiac Cycle
• A single cycle of cardiac activity can be divided into two basic
phases - diastole and systole.

8. • The cardiac cycle diagram
shown to the right depicts
changes in aortic pressure
(AP), left ventricular pressure
(LVP), left atrial pressure
(LAP), left ventricular volume
(LV Vol), and heart sounds
during a single cycle of cardiac
contraction and relaxation.
These changes are related in
time to the electrocardiogram.

11. Let’s recall action potentials
Sodium
Sodium
Sodium
K
K
K
K

13. Events during systole
• Isovolumetric ventricular contraction
• The beginning of this phase corresponds with the peak of the R wave
• This corresponds to Phase 0 (rapid sodium influx) of the ventricular
myocyte action potential
• The ventricles begin to contract during this period
• This contraction increases the ventricular chamber pressure and closes
the mitral and tricuspid valves.
• As a result, there is a fixed ventricular volume during this contraction

14. • Early ejection
• The contracting ventricles achieve a pressure high enough to open the
aortic and pulmonic valves, and rapidly empty into the systemic and
pulmonary circulations.
• This period corresponds to Phase 2 (plateau, rapid calcium influx) of
the cardiac myocyte action potential
• On the surface ECG, the end of this phase corresponds to the
beginning of the T wave

15. • Late ejection
• This period begins when ventricular pressure starts to drop, and ends
with the closure of the aortic and pulmonic valves
• The end of this period corresponds to the peak of the T wave on the
surface ECG
• This corresponds to Phase 3 (repolarization) of the cardiac myocyte
action potential

16. Events during diastole:
Isovolumetric relaxation
• The ventricles relax without any change in volume
• The pressure drops until the tricuspid and mitral valves open
• This period corresponds to the end of the T wave on the surface
ECG, and the end of Phase 3 of the action potential

17. • Early rapid diastolic filling
• During this period the relaxing ventricles have pressure lower than
atrial pressure, and they fill rapidly
• 80% of the ventricular end-diastolic volume is achieved during this
phase
• Coronary blood flow is maximal during this phase

18. • Late slow diastolic filling
• Ventricular and atrial pressures equilibrate and the atria act as passive
conduits for ventricular filling
• The end of this phase corresponds to the end of the P-wave on the
surface ECG

19. • Atrial systole
• The atria contract (right first, then left shortly after)
• This increases the pressure in the ventricles up to the end-diastolic
pressure, and adds about 20ml of extra volume to the end-diastolic
volume
• These events start at the end of the P-wave on the surface ECG, and
finish during the PR interval.
• The end of this phase corresponds to the peak of the R wave, or the
Phase 0 (rapid sodium influx) of the ventricular myocyte action potential

20. Atrial Contraction (Phase 1)
• This is the first phase of the cardiac cycle. It is initiated by the P wave
of the electrocardiogram (ECG), which represents electrical
depolarization of the atria. Atrial depolarization initiates contraction of
the atrial musculature. As the atria contract, the pressure within the
atrial chambers increases, which forces more blood flow across the
open atrioventricular (AV) valves, leading to a rapid flow of blood into
the ventricles. Blood does not flow back into the vena cava because
of inertial effects of the venous return and because the wave of
contraction through the atria moves toward the AV valve thereby
having a "milking effect."

21. Isovolumetric Contraction (Phase 2)
• This phase of the cardiac cycle begins with the appearance of the QRS
complex of the ECG, which represents ventricular depolarization. This
triggers excitation-contraction coupling, myocyte contraction and a
rapid increase in intraventricular pressure. Early in this phase, the rate
of pressure development becomes maximal. This is referred to
as maximal dP/dt.
• The AV valves close when intraventricular pressure exceeds atrial
pressure. Ventricular contraction also triggers contraction of the
papillary muscles with their chordae tendineae that are attached to the
valve leaflets. This tension on the the AV valve leaflets prevent them
from bulging back into the atria and becoming incompetent (i.e.,
“leaky”). Closure of the AV valves results in the first heart sound (S1).
This sound is normally split (~0.04 sec) because mitral valve closure
precedes tricuspid closure.

22. Rapid Ejection (Phase 3)
• This phase represents initial, rapid ejection of blood into the
aorta and pulmonary arteries from the left and right ventricles,
respectively. Ejection begins when the intraventricular
pressures exceed the pressures within the aorta and pulmonary
artery, which causes the aortic and pulmonic valves to open.
• During this phase, ventricular pressure normally exceeds
outflow tract pressure by a few mmHg. This pressure gradient
across the valve is ordinarily low because of the relatively large
valve opening (i.e., low resistance). Maximal outflow velocity is
reached early in the ejection phase, and maximal (systolic)
aortic and pulmonary artery pressures are achieved.

23. Reduced Ejection (Phase 4)
• Approximately 200 msec after the QRS and the beginning of
ventricular contraction, ventricular repolarization occurs as
shown by the T-wave of the electrocardiogram. Repolarization
leads to a decline in ventricular active tension and pressure
generation; therefore, the rate of ejection (ventricular emptying)
falls. Ventricular pressure falls slightly below outflow tract
pressure; however, outward flow still occurs due to kinetic (or
inertial) energy of the blood.
• Left atrial and right atrial pressures gradually rise due to
continued venous return from the lungs and from the systemic
circulation, respectively.

24. Isovolumetric Relaxation (Phase 5)
• When the intraventricular pressures fall sufficiently at the end of
phase 4, the aortic and pulmonic valves abruptly close (aortic
precedes pulmonic) causing the second heart sound (S2) and
the beginning of isovolumetric relaxation. Valve closure is
associated with a small backflow of blood into the ventricles and
a characteristic notch (incisura or dicrotic notch) in the aortic
and pulmonary artery pressure tracings.
• After valve closure, the aortic and pulmonary artery pressures
rise slightly (dicrotic wave) following by a slow decline in
pressure.

25. Rapid Filling (Phase 6)
• As the ventricles continue to relax at the end of phase 5, the
intraventricular pressures will at some point fall below their
respective atrial pressures. When this occurs, the AV valves
rapidly open and passive ventricular filling begins. Despite the
inflow of blood from the atria, intraventricular pressure
continues to briefly fall because the ventricles are still
undergoing relaxation. Once the ventricles are completely
relaxed, their pressures will slowly rise as they fill with blood
from the atria.

26. Reduced Filling (Phase 7)
• As the ventricles continue to fill with blood and expand, they
become less compliant and the intraventricular pressures rise.
The increase in intraventricular pressure reduces the pressure
gradient across the AV valves so that the rate of filling falls late
in diastole.
• In normal, resting hearts, the ventricle is about 90% filled by the
end of this phase. In other words, about 90% of ventricular
filling occurs before atrial contraction (phase 1) and therefore is
passive.
• Aortic and pulmonary arterial pressures continue to fall during
this period.

28. POST LECTURE
• To submit via email a video presentation of you doing a proper
auscultation of the heart in an adult human being.