Cardiac Rehabilitation Flashcards
What is the definition of health?
“A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity” (p 1. W.H.O., 1947)
What did Bouchard et al. (2007) show?
That there is a complex interaction between health, physical activity and physical fitness. There are important determinants from heredity, lifestyle and environment.
Which key studies give evidence of lower mortality in more physically active and / or higher fit people?
• Harvard Alumni Health Study 1986: (Paffenbarger et al., NEJM, 315) + Harvard Alumni Health Study 1995: (Lee et al., JAMA, 273) • Blair et al. 1989: aerobic centre longitudinal study • Framingham study • Baugerleuser study • Zutphen elderly study & Finnish Twin Cohort
What did the Harvard Alumni Health Study 1986: (Paffenbarger et al., NEJM, 315) study show?
Mortality ↓ with ↑ physical activity 27% less risk of mortality from expending >2000kcal per week
What did the Harvard Alumni Health Study 1995: (Lee et al., JAMA, 273) show?
Mortality ↓ with ↑ physical activity (Confirmed the 1986 HAHS results; that less risk of mortality from expending >2000kcal per week)
How would you expend >2000kcal per week?
Walking at 4mph = 400Kcal ph, thus 5hrs walking per week for 2000Kcal
What did the results of the Harvard Alumni Health Studies recommend?
less risk of mortality from expending >2000kcal per week (Walking at 4mph = 400Kcal ph, thus 5hrs walking per week for 2000Kca)
What did the Aerobic centre longitudinal study 1989: (Blair et al., JAMA, 262) show?
- Biggest drop in mortality moving from lowest fit (Q1) to below average fitness (Q2) 2. Low fit men have 3.3 and low fit women 4.7 X more mortality than high fit (Q5)
The combination of results from the Zutphen elderly study & Finnish Twin Cohort study + British regional heart study, • Harvard Alumni Health Study, aerobic centre longitudinal study and the study of osteoporotic fractures shows what?
That it is never too late for previously inactive patients to become more active as it has been shown to have an impact on their mortality risk ratio. Also that those with the lowest activity/fitness have the most to gain in terms of mortality risk when commencing PA.
What does the ACSM, 2010 evidence show?
A) Occupational and leisure activity: 2 X more CHD death for sedentary vs. active occupations. 2 X more CHD death for low vs. high non- occupational physical activity. B) Fitness Every 1 MET increase in aerobic fitness = 12% more survival Below 5 METs = worse prognosis
Below which MET level do you have a worse prognosis?
Below 5 METs
Increasing your MET by 1 improves your survival by what percentage?
Every 1 MET increase in aerobic fitness = 12% more survival
What is the best recommendation for occupation & leisure activity in terms of CHD death risk?
Active occupation + high PA outside occupation [2 X more CHD death for sedentary vs. active occupations. 2 X more CHD death for low vs. high non- occupational physical activity.]
What are the axis on the dose-response curve?
Y - health benefits X - activity status
What are the consequences of the dose-response curve?
The greatest health benefits are achieved when increasing physical activity levels from sedentary to moderately active + The more physical activity you do, the greater the health benefits – Each 10 minutes of MVPA results in 10% mortality risk reduction (RR) – Achieve 150 mins MVPA then 30-40% less RR – 750 mins MVPA (3 X recs) only increases RR to 50%
What does the dose-response curve tell us about mortality risk reduction (RR)?
– Each 10 minutes of MVPA results in 10% mortality risk reduction (RR) – Achieve 150 mins MVPA then 30-40% less RR – 750 mins MVPA (3 X recs) only increases RR to 50%
Is there truly a steeper relationship between fitness and relative risk than PA? And what are the consequences for public health initiatives?
–Likely due to measurement error in physical activity studies (Easier to objectively measure physical fitness) –Public health initiatives should target physical activity because that will increase fitness levels
What did Clarke et al, BMJ 2012 show about Olympians?
Olympians live 2.8 years longer on average. Thought to be due to genetics, wealth and PA throughout life. Endurance athletes had greatest benefit, but even resistance athletes benefitted.
Should you exercise even if unwell? What is the evidence?
Yes: Physically fit men with existing chronic conditions (e.g., CVD, HTN, DM) have a lower risk of mortality compared with men who are unfit. Hypertension High fit without HTN had 0.5 mortality risk reduction (RR) of low fit High fit with incidental (white coat) HTN had 0.4 RR of low fit High fit with history of HTN had 0.4 RR of low fit Diabetes High fit with DM had 0.5 RR of low fit without DM
For which clinical health conditions is there good evidence to suggest that being active / fit helps prevent or treat?
CHD, stroke, HTN, cancer, diabetes, falls, depression, dyslipidaemia. (2008 physical activity guidelines for Americans: US Dept Health and Human Services)
What are the key new points from the 2008 physical activity guidelines for Americans?
• VPA and MPA can be mixed up. VPA>MPA? • Fq: can spread over week/weekend warriors (but fq bouts better for DM, HTN, depression, hyperlipidaemia etc.) • Duration: 10min bouts currently recommended; but <10min still beneficial as avoids sedentary behaviours
What are the 2008 PA guidelines for American Adults?
- Inactivity should be avoided. Some is better than none, especially in low active groups. 2. 75min VPA/week 3. Or 150 MPA/week 4. Or equivalent blend 5. At least in episodes of 10min 6. Preferably spread throughout the week 7. For extensive health benefits, 5h/week MPA 8. Or 150VPA/week 9. Or equivalent combination of MPA and VPA 10. 2x strength training moderate/high intensity per week for bone density health
What are the 2008 PA guidelines for Children?
- Generally 1h/day MPA-VPA. 2. VPA at least 3d/wk. 3. Muscle strengthening at least 3d/wk. 4. Bone strengthening at least 3d/wk.
What is preload?
Preload–theamountof blood in the ventricles before contraction ♥ End diastolic volume About 100mL
What is afterload?
Afterload=the amount of blood left in the ventricles after contraction ♥ End systolic volume About 40mL
What is the ejection fraction?
SV/EDV x 100 = ((EDV-ESV) / EDV)) x 100 Approx at rest 70%
What is Q?
Cardiac output = HR (bpm) x SV
What is SV?
Stroke volume End Diastolic Volume – End Systolic volume Preload - afterload
What is shortening fraction?
((EDD - ESD) / EDD) x 100 Approx at rest 35%
What triggers the cardiovascular response?
Efferent signals: Balance between (PNS/vagus and SNS/cardiac) autonomic branches to control myocardial contraction.
Describe the sympathetic innervation of the myocardium.
• Sympathetic (CARDIAC) nerves innervate atria, SAN, AVN, myocardial muscle of ventricle. Release noradrenaline. [Also a direct link to adrenal gland leading to adrenaline response which acts on heart but is obviously slower.] • SNS exerts a chronotropic effect to increase HR and an ionotropic effect to increase strength of contraction.
What type of effect does the SNS have on the myocardium?
• SNS exerts a chronotropic effect to increase HR and an ionotropic effect to increase strength of contraction.
Describe the parasympathetic innervation of the myocardium.
Parasympathetic nerves (VAGUS NERVE) innervates the SAN and AVN and atria. PNS only exerts a chronotropic effect to decrease HR.
Which branch of the autonomic nervous system innervates the SAN, AVN and atria?
Parasympathetic nerves (VAGUS NERVE)
Which branch of the autonomic nervous system innervates the SAN, AVN and ventricles?
Sympathetic (CARDIAC) nerves
What effect does the PNS have on HR?
PNS =↓ HR
What effect does the SNS have on HR and contraction?
SNS = ↑ HR and strength of contraction
What bpm would a denervated heart have?
~100bpm (=intrinsic heart rate)
What is a normal HR (bpm)? Which autonomic branch dominates?
Normal HR ~72bpm; dominated by PNS
By what percentage could SNS increase HR in theory?
SNS could in theory increase HR by 300%
By what percentage could PNS increase HR in theory?
By 100%, to 0bpm = cardiac arrest
What happens to autonomic innervation of the heart during exercise?
At onset of exercise, PNS activity decreases before sympathetic activity increases. = massive flexibility for HR to vary during different activities +increased SNS will increase contractility. ::Therefore enhanced SV from SNS contribution.
What are the following abbreviations? PWT SWT LVEDD
PWT=posterior wall thickness; SWT=septal wall thickness; LVEDD=Left ventricular end diastolic diameter
If left ventricular size increases, what also increases?
Stroke volume. eg. in athletes
What is the limiting factor to myocardial stretch?
The pericardium –Pericardectomy allows SV to increase and hence Q
What is the Frank-Starling law?
= the ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return -aided by a health myocardium
↑ stretching of myocardial walls will ↑ strength of contraction… is part of what principle?
the Frank-Starling principle as stretching the ventricles increases the pressure they can generate
Does the heart ever stretch to the point of the ‘inaccessible region’ on a tension-sarcomere length graph?
No: There is no way to get a normal heart over the peak into the downslope of tension. The heart becomes very stiff above the optimal length, and the venous filling pressure never gets high enough.
What is a typical blood volume in adults?
5L
What happens to blood flow distribution around the body during exercise?
Blood flow distribution is altered during exercise; cardiac output can increase 5x and skeletal muscle receives the majority at about 25,000mL. Blood is shunted away from non-essential organs.
How is blood flow distribution controlled?
via vasoconstriction (mediated by NE) and vasodilation (mediated by NO) NB: dilation>constriction
How does NO cause vasodilation?
It relaxes smooth muscle in response to increased shear stress
What are 7 things that cause vasodilation of arterioles?
- bradykinin 2. prostaglandins 3. K+ 4. CO2 5. Lactate 6. local decrease in O2. 7. NO
What causes vasoconstriction?
NE, which acts on alpha receptors in smooth muscle to cause constriction
What percentage of blood resides in the venous system at rest?
70%
How does exercise effect venous capitance?
With exercise need to return more to central circulation to increase venous return • ↑ SNS activity with exercise leads to venoconstriction
What percentage of blood shunting occurs through venoconstriction?
20%
What is the main system that returns venous blood to the heart?
Muscular pump system in conjunction with venous valves.
What are the 5 methods that return blood to the heart?
- Muscular pump system 2. Venoconstriction 3. Low pressure of ventricle during diastole (creates vacuum) 4. Ventricular rotation during systole and recoil during diastole sucks blood back into myocardium 5. The abdomino-thoracic pump: ↑respiratory pressure in thorax during respiration ↑blood return to heart
Increasing the rate and depth of inspiration would have what effect on the heart?
↑venous return and enhanced CO
What effect does the Valsalva manoeuvre have on venous return?
forced expiration against a closed glottis (Valsalva maneuver) impedes and therefore reduces venous return and cardiac output
What is afterload?
how much blood is left in the heart at the end of contraction (End systolic volume)
What 6 factors affect afterload?
- Volume of blood in the arterial circulation 2. Pressure in aorta at onset of ejection (DAP) 3. Compliance of aorta 4. Inertial component of the ejecting blood column 5. Systemic vascular resistance 6. Size of pulmonary / aorta lumen
What are the 3 main effects of increased afterload?
- Stroke volume will be reduced in the acute phase ::Preload will increase (which is a compensation mechanism to restore SV by Frank-Starling mechanism) 2. Reduced velocity of contraction and ejection in acute phase 3. Marked increase in myocardial O2 consumption
What level of arterial BP will have a contribution to afterload?
>200mmHg has direct impact on reducing cardiac output
What 5 receptors effect the cardiovascular response?
- Mechanoreceptors 2. Baroreceptors 3. Chemoreceptors 4. Metaboreceptors 5. Bainbridge reflex
What is a mechanoreceptor and what do they do?
Type III (lightly myelinated) afferent receptors a. Receptors that detect stretch and muscle contraction send afferent signals to brain to increase SNS activity
What is a metaboreceptor and what do they do?
Type IV (unmyelinated) afferent receptors a. Sensitive to >lactate, phosphate, PGs,
What is a baroreceptor and how do they work?
a. In walls of carotid sinus and aortic arch b. Sense arterial pressure; are stretch activated c. Afferent nerves IX (carotid) and X (aortic arch) to brain d. Triggers brain to decrease SNS and increase PNS i. via increased peripheral dilation and reduced HR and Q :: reduced BP ii. = INHIBITION of vasometer and cardioacceleratory centres iii. = STIMULATION of cardio inhibitory centres
What nerves are affected by baroreceptors?
Afferent nerves IX (carotid) and X (aortic arch) to brain
What is the baroreceptor paradox?
It is the question of how the body gets round increased BP during exercise (which you would think leads to decreased HR?) i. The baroreflex is reset to a higher operating pressure with exercise ii. Won’t kick in until a higher arterial reassure is reached iii. Thus HR and Q can increase with exercise
What is a chemoreceptor and how do they work?
a. In walls of carotid sinus and aortic arch – sense >SpCO2 b. Triggers brain to >SNS and HR
What is a the bainbridge reflex?
a. Increased cardiac filling elicits tachycardia b. ↑ right atrium filling from ↑ venous return c. Stretch receptors in right atria and vena cava stretched d. ↑ firing rate to brain e. Brain ↑ SNS tone f. ↑ HR and SV
How does the bainbridge reflex increase heart rate and stroke volume?
a. Increased cardiac filling elicits tachycardia b. ↑ right atrium filling from ↑ venous return c. Stretch receptors in right atria and vena cava stretched d. ↑ firing rate to brain e. Brain ↑ SNS tone f. ↑ HR and SV
What factors damage the endothelium?
o Normal microvascular wear and tear o Fibrinogen o Free radicals o High blood pressure o Turbulent flow o Atherosclerotic lesions often occur at artery intersections or curves o Blood flow speed and direction changes creating turbulence o Viral attack o Carbon monoxide
Name the common symptoms of an MI?
• Classic symptoms: intense, oppressive chest pressure radiating to left arm • Other symptoms: chest heaviness, burning radiation to jaw, neck, shoulder, back, arms. nausea, vomiting dysponea. Lightheadedness. Sweating (cold and clammy). Confusion.
Why do Q-waves develop on an ECG after an MI?
They are the result of absence of electrical activity. A myocardial infarction can be thought of as an elecrical ‘hole’ as scar tissue is electrically dead and therefore results in pathologic Q waves.
What blood tests help diagnose an MI?
Released from damaged myocytes. Cardiac troponins I & T (initial rise 4-6h; peak 12-24h post-MI) CK (4-6i; 12-24 peak) CK-MB (4-6h initial; peak 12-36h) Myoglobin (2h post) LDH (8-12i; 48-72p)
What vessels supply the anterior myocardium?
Branching from the ascending aorta Left coronary artery -[Circumflex; Left anterior descending / AIB] Right Coronary artery [Marginal artery]
What vessels supply the posterior myocardium?
Left coronary artery Circumflex Right Coronary artery Posterior interventricular artery
What is the coronary perfusion problem?
Pressure in the muscle tissue during systole opposes blood flow. The effect is maximal in the deeper layers.
What exacerbates the coronary perfusion problem?
- Tachycardia leads to decreased diastolic time. a. diastole decreases more than systole at ↑ heart rate 2. Low diastolic pressure 3. Ischaemic heart disease - large vessel or small vessel
In a normal subject, ↑ heart rate has what effect on coronary blood flow?
↑ heart rate → ↑ coronary blood flow, by autoregulatory vasodilation – In ischaemic heart disease, ability to deliver ↑ flow is limited
How many deaths from IHD in Britain in 2015?
70,000 (BHF, 2015) Biggest single killer CVD cost the country approx…. £15 billion
What proportion of people now survive heart attacks?
7 in 10 (BHF, 2015)
What are the macrophages trying to do to the LDL cholesterol?
Pro-inflammatory M2 macrophages in the vascular smooth muscle bind and transduce signals from oxLDL and thus differ from those in adipose tissue or hepatic tissue. As these macrophages ingest oxLDL to become the lipid-rich foam cells characteristic of atherosclerosis, their molecular signature changes further. Foam cells differ markedly from normal resident macrophages in healthy vessels in that foam cells are less mobile and secrete more inflammatory mediators than normal macrophages
What are foam cells?
Foam cells are the fat-laden M2 macrophages seen in atherosclerosis. … Foam cells are formed when the body sends macrophages to the location of a fatty deposit on the blood vessel walls
How does the body initially try to preserve the lumen width after plaque formation?
o Arterial enlargement around area of the stenosis can keep lumen open even with large plaque
What are the chain of events leading to an MI?
i. Atherosclerosis ii. Plaque rupture (Most likely in fatty plaques; Fibrous capped plaques more stable) iii. Platelet aggregation>Thrombus formation>Vessel occlusion iv. Vasospasm v. Distal ischaemia & Ischaemic complications
What did Naghavi et al. (2003) identify as the key stages of atherosclerosis?
- Endothelial damage 2. Stenosis 3. Formation of plaque
What is Virchow’s triad?
Virchow’s triad describes the three broad categories of factors that are thought to contribute to thrombosis. Hypercoagulability. Hemodynamic changes (stasis, turbulence) Endothelial injury/dysfunction.
What type of vessels do the majority of infarcts occur in?
o 85% of all infarct related lesions are in vessels that are less than 75% occluded o A fibrous cap makes the plaque more stable
Which coronary artery is affected with an anterior MI?
LAD
Which coronary artery is affected with a septal MI?
LAD
Which coronary artery is affected with an left lateral MI?
left circumflex
Which coronary artery is affected with an inferior MI?
RCA
Which coronary artery is affected with an right atrial MI?
RCA
Which coronary artery is affected with an posterior MI?
RCA
Which coronary artery is affected with a right ventricular MI?
RCA
If chest leads V1-4 show ST elevation, which area of the heart and coronary artery have been occluded?
Anterior LAD
If chest leads V1-2 show ST elevation, which area of the heart and coronary artery have been occluded?
Septum LAD