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Med. Student
Ahmed Abbas
Educational Lecture
Summary of Medicine books
Lecture 8
Myocardial Ischaemia
Cardiovascular System

Lecure 8 (Myocardial Ischaemia)
‘Ischaemia’:
= Restraint of Blood (Ie. Insufficient Blood)
· Leads to Imbalance Between Oxygen Supply & Demand.
· Oxygen Supply – Increased By:
o ↑Coronary Blood Flow:
○ ↑Aortic, Diastolic Perfusion Pressure:
· Aortic Pressure During L-Ventricular Diastole
· If High  ↑Coronary Perfusion
· Influenced by:
o Hypotension
o Aortic Regurgitation
○ ↓Coronary Vascular Resistance:
· Resistance to Coronary Blood Flow
· Depends on Vascular Diameter...
· Influenced by:
o External Compression (eg. Oedema)
o Intrinsic Regulation (Dilation/Constriction).
○ Metabolites
○ Neural
o ↑O2-Carrying Capacity of Blood:
○ Influenced By:
· Hb Saturation
· Hb Levels (Anaemia)
· Blood pH
· CO Poisoning
· Lung Disease

· Oxygen Demand – Increased By:
o ↑Wall-Tension Force:
○ ↑Preload – (Degree of Stretch of Myocardium):
· The degree of Stretching of the Heart Muscle during Ventricular Diastole.
○ ↑Afterload – (Back Pressure Exerted by Arterial Blood):
· The tension needed by Ventricular Contraction to Open Semilunar Valve.
o ↑Heart Rate (Chronotropic State)
o ↑Force of Contraction (Inotropic State)

*Ischaemia Vs. Hypoxia Vs. Infarction:
· Ischaemia: A ‘FLOW’ Limitation, Typically due to Coronary Artery Stenosis (Narrowing)
· Hypoxia: An ‘O2’ Limitation,Typically due to High-Altitude/Respiratory Insufficiency/etc.
· Infarction: Irreversible Cell-DEATH, Typically due to sustained Ischaemia.
· NB: Ischaemia can lead to Hypoxia & Infarction.
Myocardial Ischaemia:
- Largest Cause of Deaths (50% of all deaths) in Western Society
- Mostly Attributed to ↓Coronary Blood Flow – Due to Plaque/Thrombosis.
- Regional Ischaemia:
o Ischaemia Confined to Specific Region of Heart.
o Due to Plaque/Thrombosis
- Global Ischaemia (Rare):
o Ischaemia of Entire Heart
o Due to Severe Hypotension/Aortic Aneurysm/Open-Heart-Surgery

What Happens During Myocardial Ischaemia:
- Myocardial Damage:
o Inner-Myocardium will become Ischaemic first, then progress Outwards.
o (Same with necrosis/infarction)
- Metabolic Changes – (Aerobic  Anaerobic):
o ↑Lactate (Anaerobic Metabolism), ↓pH
o ↓ATP, ↑ADP, ↑Pi
o ↓Glycogen
- Pain:
o Nociceptor (pain receptor) Activation  Angina Pain
- Acute Ischaemic Attack:
o SNS & PNS Stimulation  Tachycardia, Sweating, Nausea......
- Reversible Cell Injury:
o ↓Blood-Flow  ↓Myocardial Relaxation (diastolic)  Stiffening of L-Ventricle  ↑LVDP

- Reperfusion Injury:
o Cell Damage that occurs When Blood Supply is Restored (after being stopped)
o Due to inflammation and oxidative damage through the induction of oxidative stress.
- Pulmonary Congestion:
o Stiffening of L-Ventricle & ↑LVDP  ↑Pulmonary Vascular Pressure
○  Pulmonary Congestion
○  Shortness of Breath
- Ventricular Arrhythmias:
o Due to Myocyte Ion-Disturbances:
○ ↑ Extracellular K+
○ ↑ Intracellular Na+
○ ↑ Intracellular Ca+
(“Calcium-Loading”) – If Ischaemia is Prolonged  IrreversibleDamage
o  Alters Conduction Patterns of the Heart  Arrhythmias

Clinical Presentations of Myocardial Ischaemia:
- Ischaemic Heart Failure:
o Weakness of Heart Muscle  Difficulty Breathing + Peripheral Oedema
- Angina Pectoris:
o Substernal/Precordial Chest Pain – Due to Myocardial Ischaemia  No Cell Necrosis
o Pain Usually lasts up to 15min.
o 3 Subtypes:
○ Stable Angina (Typical):
· Angina-Pain During Exertion/Stress
· No Permanent Injury
· ST-Depression (Indicates Subendocardial Ischaemia)
· Treated with Vasodilators
○ Variant Angina (Prinzmetal):
· Angina-Pain Unrelated to Activity
· Due to Coronary Vascular Spasm
· ST-Elevation (Indicates Transmural Ischaemia)
○ Unstable Angina (Dangerous):
· Occurs @ Rest – Prolonged Pain
· Increasing Frequency & Duration of Angina-Pain
· Due to unstable Atherosclerotic Plaque
· Can Lead to Myocardial Infarction (if untreated)
- Silent Ischaemia:
o No Pain
o Abnormal ECG (ST-Elevation)

Prolonged Ischaemic  Irreversible Damage  Leads to:
- Ca+
Loading Within Cell:
o Ca+
Recycling Cycle (between Sarcoplasmic Reticulum, Sarcoplasm & Actin) Changes.
o Marks the transition between Reversible & Irreversible Damage.
- Heart Failure – Due to:
o Lethal Arrhythmias
o ↑LVDP  Pulmonary Congestion  R-Heart Failure.
- Infarction (Necrosis):
o Irreversible Cell Death – Due to Ischaemia/Acute Thrombus
o Myocyte Membrane damage  Cell Enzymes/Proteins into Blood  Used as bloodMarkers:
○ Troponin I (Preferred)
○ Creatinine Kinase
ECG Changes Due to Ischaemia:
- Normally:
o QRS = Ventricular Depolarisiation
o T-Wave = Ventricular Repolarisation
○ NB: Ven.Repol – Very sensitive to myocardial perfusion. (ie. Lack of blood supply alters
Ven.Relaxation)

- Subendocardial Ischaemia:
o Poor Perfusion  Altered Ven.Repolarisation 
○ ST-Depression
○ T-Wave Inversion
- Transmural Ischaemia:
o Full-thickness of the heart wall is damaged  Altered Ven.Repolarisation 
○ ST-Elevation

Myocardial Infarction (Heart Attack):
- *90% Infarcts due to Thrombosis from Ruptured Atherosclerotic Plaque.
- Diagnosis Requires 2 of the Following:
o History of Ischaemic-Related Chest Pain:
○ Eg. Angina
o Changes on Sequential ECGs:
○ ST-Segment Elevation  Indicates Transmural Ischaemia:
· Where the full-thickness of the heart wall is damaged.
· NB: ST-Elevation isn’t always due to MI.
o Rise/Fall in Serum Cardiac Markers:
○ Spilt contents of dead cells  Blood
○ Eg. Cardiac Troponin & Creatinine Kinase
- Ensuing Inflammatory Response:
o When Cells Die  Neutrophils Infiltrate Area  Attack/Decompose/Phagocytose DeadCells
o After Inflammatory Response  Fibrosed Scar Tissue (Such Tissue in Heart is Non-Contractile*)

My advice to you on this subject is important for study
When reading the curriculum, make sure you never go beyond a word you don't fully understand. The only reason that a person abandons school,
becomes confused or becomes unable to learn, is because he or she has passed an incomprehensible word.
Confusion or inability to absorb or learn comes after passing through an unknown and incomprehensible word. (Even if understood on a previous
context) it's not just the new and unusual words you should be looking for. But some commonly used words can often be misdefined and lead to
confusion.
This is. Information about not exceeding the word "unknown" represents the most important fact in the subject of the study. Every topic you
addressed and then abandoned was the reason for which words failed to reach a definition. (This is routine and if you don't feel it, it's up to the
subconscious.)
Therefore, when studying this year and the future, make sure that you never exceed a word that you do not fully understand. If the subject
becomes confusing or you can't understand it, it will be a word that you've been through before and you don't understand it. Then, don't go any
further, but go back to before you face the difficulty, and come up with the word incomprehensible and clarify it.
In conclusion, I ask the God that it will be done with great success in the day and the future.
With regards
Ahmed Abbas
Berlin, 19.Jan.2021
Thank You
That’s the end of the Lecture 8 in Cardiovascular System

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