PBL 2 Flashcards
1
Q
What factors determine the amount of blood pumped out of the heart?
A
- CO=HRxSV
- CO is determined by filling pressure/central venous pressure, peripheral venous pressure.
- must be a change in pressure for flow to occur.
- Starling’s law: “the heart pumps what it receives”
2
Q
What factors determine the amount of blood pumped through a given tissue?
A
- Q=ΔP/R
- Arteriole constriction is the most important factor in tissue resistance.
3
Q
What are the components of a normal electrocardiogram (ECG)?
How does each component of the ECG relate to the mechanical events of the cardiac cycle?
A
- P wave = Atrial Depolarization (contraction)
- PRI = impulse traveling from SA to AV Node
- QRS Complex = Ventricular Depolarization
- ST segment = Plateau phase of Myocardial AP
- T wave = Ventricular repolarization
4
Q
What makes the heart beat in a regular fashion?
A
- Pacemaker cells
- have the funny channels which allow in Na+, but allow out K+ (Overall net increase of Na+ in, and thus slow depolarization).
- Transient Ca+2 channels allow calcium in to reach threshold for full depolarization
- Transient channels then close
- Slow channels of Ca+2 allow for sustained entry of calcium and for the cell to remain in a depolarized state until contraction, and influx of K+ hyperpolarize the cell again.
5
Q
What alterations in pacemaker cell structure and function can lead to an irregular heartbeat?
A
- Disturbance of either impulse FORMATION or impulse CONDUCTION = arrhythmia
- Irregular heartbeats can happen in times of sympathetic innervation.
- NE acts on alpha 1 receptors to increase Na+ permeability and decrease K+ permeability
- PVC/PACs
- NE acts on alpha 1 receptors to increase Na+ permeability and decrease K+ permeability
- When there is damage to parts of the heart, like the AV node, it can have conduction re-entry block (A-fib, A-flutter, or 2° blocks)
6
Q
How do you explain the pain associated with myocardial infarction?
A
- Viscerosomatic Convergence
- Heart → innervated by the Vagus (CNX) Nerve (parasympathetic), Cervical & Thoracic Sympathetic Trunk.
- central nervous system (CNS) perceives pain from the heart as coming from the somatic portion of the body supplied by the thoracic spinal cord segments T1-4(5) because the dermatomes of this region of the body wall and upper limb have their neuronal cell bodies in the same dorsal root ganglia (T1-5) and synapse on the same second order neurons in the spinal cord segments (T1-5) as the general visceral sensory fibers from the heart.
7
Q
What is the classic presentation of a myocardial infarction?
A
- Chest pain described as sensation of tightness, pressure, or squeezing
- Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and upper abdomen, where it may mimic heartburn
- Dyspnea, diaphoresis, weakness, light-headedness, nausea, vomiting, and palpitations
8
Q
How does MI presentation differ in women?
A
- Women are more likely than men to experience some of the other uncommon symptoms, such as jaw or back pain, shortness of breath, and nausea or vomiting.
9
Q
What biochemical markers can be measured to assess the likelihood of a myocardial infarction?
A
- Troponin
- highly sensitive and specific for damage to the myocardium
- NTproBNP
- detects heart failure, indicative of excess ventricular stretching
- D-dimer
- rule out PE, DVT, DIC
- CK
- measure of reinfarction
10
Q
What is the basic biochemistry and physiology of NTproBNP?
A
- N-terminal pro B-type Natriuretic Peptide, or BNP
- pro form gets cleaved by an enzyme → Brain Natriuretic Protein aka Ventricular Natriuretic Protein
- which is secreted by the ventricles in response to excessive stretching in the cardiac tissue.
- The half-life of these proteins are 10x longer than that of ANP (atrial natriuretic protein) so it helps to interpret the pathophysiology.
11
Q
What is the basic biochemistry and physiology of Troponin?
A
- Troponin is a protein made of three smaller proteins: c, i, and t
- found in striated muscles.
- Gets released into circulation as a result of myocardial death/damage → loss of membrane stability → leak contents of the cell
- Troponins i and t are highly sensitive and specific for damage to the myocardium, and most notably myocardial infarctions.
- can remain high up to two weeks
- can also be high due to other strains on the heart e.g. SVT
-
Troponin I = most sensitive and specific marker
- rises 2-4 hours after infarction
- peaks at 24 hours
- returns to normal by 7-10 days
12
Q
What is the basic biochemistry and physiology of Creatine Kinase?
A
- A measure of reinfarction.
- Because Troponin remains elevated 7-10 days post MI and CK normalized 48-72 hours post-infarct
- CK can be used to rule in a reinfarction before Troponin normalizes.
- Rises 4-6 hours after infarction
- Peaks at 24 hours
- Returns to normal in 48-72 hours
13
Q
What is the basic biochemistry and physiology of D-dimer?
A
- Plasmin breaks cross-linked Fibrin into D-dimers
- They are not normally in circulation unless there has been some kind of coagulation event.
- When there is an abnormal level it is indicative of:
- Pulmonary Embolism
- Deep Vein Thrombosis
- DIC
- IF NEGATIVE, RULE OUT.
- IF POSITIVE… You don’t know shit.
14
Q
What is the epidemiology (deaths/yr, incidence, prevalence) of coronary artery disease and MI in the US?
A
- Epidemiology: Heart disease=~600,000 Deaths/year.
- NUMBER 1 KILLER IN THE US
- Incidence: 735,000 people will have an MI each year.
- 525,000 will have their first
- 210,000 will have their second
- Prevalence: 6.2% in persons ≥ 20 years old
15
Q
What is a coronary angiogram?
A
- X-ray with radiocontrast in the coronary arteries
- Fluorescent dye is injected into coronary vessels via catheterization and X-Rays are taken
- Used to determine which coronary arteries are blocked and the extent of the blockage, and what treatment is best.
