6.5 Coronary Circulation Flashcards
What symptoms would a patient have with a blocked left coronary artery?
Acute coronary syndrome is the term used to describe the
spectrum of clinical presentation attributed
to occlusion of coronary arteries.
The symptoms and signs depend on extent and duration of the
obstruction, volume of the affected myocardium and its complications.
They can be very varied and generally include
ACS symptoms
- Chest pain—
squeezing or burning,
often radiating to the left arm
or jaw - Nausea, vomiting, and sweating
due to vagal stimulation - Dyspnoea, mainly because of cardiac failure
- Sense of impending doom
- Arrhythmias
- Hypo or hypertension
- Signs and symptoms of complications:
ventricular aneurysm and rupture of interventricular septum,
papillary muscle or ventricular wall leading
to pulmonary oedema,
valvular incompetence
Describe the coronary arterial +supply in detail. see Figure 6.5.
The heart receives its blood supply from the right and left coronary arteries.
- The total coronary blood flow is about 250 mls/min,
which equates to 5% of the cardiac output.
he blood flow increases by 5 times in strenuous exercise.
- Right coronary artery:
- Left coronary artery:
Right coronary artery:
arises from the right aortic sinus,
runs between the right atrium and the pulmonary trunk
to descend in the right atrioventricular groove.
It winds around the inferior border to reach the diaphragmatic
surface of heart and runs backwards and left to reach posterior
interventricular groove.
It terminates by anastomosing with left coronary artery.
- Marginal branch
- Posterior interventricular artery (PIVA):
This anastomoses with the AIVA
in the posterior interventricular groove.
It is the PIVA that determines
the dominance of the arterial system.
In this case the right coronary is dominant.
Left coronary artery:
After originating from the left aortic sinus,
it passes forwards and to the left and
emerges between pulmonary trunk and the left atrium
gives off two main branches.
- Anterior interventricular artery (AIVA),
which runs downwards in anterior interventricular groove
and anastomose with the PIVA.
This is the major branch, as it supplies most of the muscle bulk.
- Circumflex branch, which runs to the left
in the left atrioventricular sulcus,
winds around the left border of heart
terminates by anastomosing with right coronary artery.
What are the structures supplied by the left and right coronary arteries?
Right
Musculature Rt atrium
Rt ventricle
Part of the IV septum
SA node 65%
AV node 80%
Rest of the conducting system 80%
Left
L Atrium
L + R Ventricle
IV septum
SA node 35%
AV node 20%
Rest of the conducting system 20%
What is the importance of knowing the coronary blood supply?
The ischaemic vessel can be identified from the clinical and ECG
presentation which would prevent delay in treatment.
Also, ischaemia/ infarction of the ventricle can lead to abnormal conduction.
Example: Right coronary artery involvement leads to inferior MI and is also
associated with bradycardia and heart block.
Rt coronary artery infarct
* Inferior MI (ECG leads II, III, aVF)
* Posterior MI (prominent R in V1, V2)
Anterior interventricular artery infarct
* Anteroseptal MI (V1, V2)
* Anterior MI (V2–V4)
* Anterolateral MI (I, aVL, V4–V6)
circumflex artery infarct
* Lateral MI (I, aVL, V5, V6)
What can you tell me about the venous drainage?
Two thirds of the venous drainage is by veins
that accompany the coronary arteries
open into the coronary sinus in the right atrium.
The remaining one third drains the endocardium
and inner myocardium directly into the cardiac cavity.
The coronary sinus lies in the right atrium between the superior and inferior
vena caval openings. The main veins draining into the coronary sinus are:
Great
Middle
Small
Oblique
Great
Middle
Small
Oblique
- Great cardiac vein, which accompanies the AIVA
- Middle cardiac vein,
which lies in the inferior interventricular groove near
the anastomosis of circumflex and right coronary arteries - Small cardiac vein,
which accompanies the marginal branch of the right coronary artery - Oblique vein,
which drains the posterior half of left atrium.
What drains anterior surface
Thebesian veins
The anterior cardiac vein drains most of the anterior surface of the heart and
opens into the right atrium directly.
The venae cordis minimae (Thebesian veins) drains the endocardium and
inner myocardium directly into the cardiac cavity and is an example of
physiological shunt as venous blood enters the left heart.
How does the coronary blood supply relate to cardiac cycle in right and left ventricles?
Left
Left ventricle
During systole,
intramuscular blood vessels are
compressed and twisted by the contracting heart muscle
and blood flow is at its lowest of only 10% to 30% of that during diastole.
The force is greatest in the subendocardial layers
where it approximates to intramyocardial pressure.
It is important to note that the layers of the heart,
excluding the subendocardium,
receive blood supply even in systole.
In diastole,
the heart musculature is relaxed and
cardiac muscle effects
do not impede blood flow to the heart.
How does the coronary blood supply relate to cardiac cycle in right and left ventricles?
Right ventricle:
The compression effect of systole on blood flow is minimal
as a result of the lower pressures developed by that chamber.
The heart is perfused from the epicardial (outside) to the endocardial (inside) surface.
The mechanical compression of systole
has a more negative effect on the blood flow
through the endocardial layers,
where compressive forces are higher and microvascular pressures are lower.
Therefore, subendocardial layers of the heart suffer more
impairment and ischemia than do the epicardial layers
What are the ECG changes associated with myocardial infarction in increasing chronology?
Hyperacute changes (within minutes)
° Tall T waves and progressive ST elevation
- Acute changes (minutes to hours)
° ST elevation and gradual loss of R wave - Early changes (hours to days)
° < 24 hours: inversion of T wave and the resolution of ST elevation
° Within days: pathological Q wave begins to form - Indeterminate changes (days to weeks)
° Q waves and persistent T wave inversion - Old changes (weeks to months)
° Persisting Q waves and normalised T waves
What are the determinants of coronary circulation?
- Factors inherent to the circulation
- Pressure or myogenic autoregulation
- Chemical/metabolic factors
- Neural factors
- Humoral factors
- Factors inherent to the circulation
- Coronary perfusion pressure (CoPP)
is the difference between aortic diastolic pressure (ADP)
and left ventricular end diastolic pressure (LVEDP).
- Coronary perfusion pressure (CoPP)
Any factor that increases the ADP and
decreases the LVEDP would increase the CoPP.
- Heart rate—
lower heart rate increases the diastole
thus the coronary filling time. - Cardiac output—
directly proportional to the coronary blood flow. - State of the cardiac cycle—
Coronary blood flow is the highest during the
isovolumetric relaxation phase.
