Cardiac Physiology Flashcards
What is the primary determinant of myocardial oxygen consumption?
Heart rate
How much oxygen does the heart extract?
75-80%
What valve corresponds with the beginning of the R wave?
Closing of the mitral valve
What corresponds with the end of the QRS?
Opening of the aortic valve
What corresponds with the end of the T wave?
Closure of the aortic valve
What does mild aortic stenosis also suggest?
Diastolic dysfunction
What cardiac output dependent on in someone with diastolic dysfunction?
LV filling during diastole
What does LV filling depend on?
Proper atrial ejection (only happens in normal sinus rhythm)
Enough time to fill (HR control)
Assuming normal cardiac function, what is the relationship of partial pressures of inhaled anesthetics at equilibrium in the CNS, blood and alveoli?
Pcns=Pblood = Palveoli
What are the sympathetic cardiac innervations?
Alpha 1
Beta 1
Beta 2
What do the sympathetic fibers travel through?
The stellate ganglions
Which side has a greater effect on heart rate?
The right stellate
Which. Stellate ganglia has more effect on MAP and contractility
Left
What does beta 2 do in the heart?
Positive chronotropy > inotropy
What does alpha 1 do in the heart?
Positive inotropy
What are the sympathetic cardiac innervations?
Alpha 1
Beta 1
Beta 2
What do the sympathetic fibers travel through?
The stellate ganglions
Which side has a greater effect on heart rate?
The right stellate
Which. Stellate ganglia has more effect on MAP and contractility
Left
What does beta 2 do in the heart?
Positive chronotropy > inotropy
What does alpha 1 do in the heart?
Positive inotropy
What is phase 0 of the ventricular contraction?
Fast sodium influx
What is phase 1?
Inactivation of sodium channels
Transient leak of potassium out (partial repolarization)
What is phase 2?
The plateau where L type calcium channels open to release calcium from the sarcoplasmic reticulum
What is phase 3?
Complete repolarization by efflux of potassium by voltage gated K channel and calcium activated channels.
What is phase 4?
The resting phase maintained by K
What happens to the heart in hypocalcemia?
Less calcium is available for release so you get a slower repolarization time (wider QRS and prolonged QT)
What is the second messenger in cardiac myocytes?
IP3 which stimulates the release of cytoplasmic calcium which in turn activates the ryanodine receptors on the sarcoplasmic reticulum
What is the second messenger in cardiac myocytes?
IP3 which stimulates the release of cytoplasmic calcium which in turn activates the ryanodine receptors on the sarcoplasmic reticulum
What do T wave inversions in the precordial leads indicate?
Severe right heart dysfunction (PE)
Where do thebesian veins empty?
Into the left heart
What are the most common cardiac benign tumors in adults and where are they found?
Myxoma
Found in the left atrium and inter atrial septum
Where does RCC Mets usually end up in the heart?
Right atrium and IVC
What is normal PCWP?
6-12 mm Hg
What is a normal CI?
2.5-4L/min/m2
What is normal SVR?
800-1200 dynes X sec/cm 5
What is resynchronization therapy
Biventricular packng where the pacer wires are in the right atrium, right ventricle and coronary sinus (activates the left ventricle)
What does unipolar pacemaking require?
Farther distance for current to travel so a large stimulus artifact can be seen on ECG
What may happen with unipolar pacemakers?
Other excitable tissue may be stimulated due to the large current required
What is pulses paradoxus?
A decrease greater than 10 mmHg in systemic blood pressure during inspiration characteristic of cardiac tamponade
Why does pulses paradoxus occur?
Due to ventricular interdependence
When the right heart fills during pericardial tamponade the ventricle can’t distend to accommodate the volume so the septum bulges into the left ventricle decreasing SV and therefor systemic blood pressure by more than 10 mmHg
When is right atrial collapse seen in tamponade?
In late diastole
Early systole
When does RV collapse occur in tamponade?
In early diastole
How long since a patient had an MI should they have elective surgery delayed?
1 month
What ECG lead is most sensitive for MI?
Lead V
Where is lead V placed?
The anterior axillary line of the 5th intercostal space
What is lead II sensitive for?
P wave characteristics
Arrhythmias
What is the most common causes of MI?
Plaque ruptures
Oxygen supply imbalance
What is the most common cause of intraoperative MI
Oxygen supply imbalance
How much air entrainment does it take for a fatal air lock situation?
3-5 ml/kg
10-15 ml/kg of CO2
What does the RCA supply?
Inferior wall of the LV lateral and posterior walls of RV 1/3 of inter ventricular septum + posteromedial papillary muscle (PDA) in 85% of people AV node SA node (60%)
What does it mean if someone has a left dominant coronary system?
In 15%, the PDA comes off the LCX. This is left dominant
PDA gives off AV nodal artery
What does the LAD supply?
The anterior wall of heart
Inter ventricular septum
Bundle branches and Purlinje system
What does LCX supply?
The posterior and lateral walls of the LV
What do you do in unstable Torsades?
Unsynchronized cardioversion
What would be first line measures in a hypotension patient with HOCM?
Increase preload
Avoid inotropes and vasodilation
What cautery should be used with an active AICD?
Bipolar and short bursts
Also, place dispersive pad near the surgical field
What happens to an AICD with a magnet?
It will disable the anti-tachy arrhythmia therapy
- must interrogate after surgery!
What increases UOP in CPB?
Mannitol in the priming solution
Pulsation perfusion
Maintaining MAP
What are the whole blood concentration of heparin sufficient for CPB?
3-4 U/ml
What is a normal ACT?
110-140 seconds
What is adequate ACT for CPB?
400-480 seconds
What factors decrease the reliability of an ACT?
Hypothermia
Hemo dilution
Who is resistant to heparin?
Those with anti thrombin 3 deficiency
Those who have had 2-4 units of FFP
What does cardioplegic solution do to the resting membrane potential of the cardiac myocytes?
Makes it more positive and makes cells depolarize
After depolarization, the potassium rich solution establishes a new resting value that is less negative than before so cells cannot fully repolarize. This inactivates voltage gated sodium channels
What phase does cardioplegic arrest the heart in?
Diastole
What does blood based cardioplegic solution do?
Enhances oxygen carrying capacity and free radical scavenging so enhanced recovery of ventricular function and less periop MIs
How much does myocardial oxygen consumption decrease by with hypothermia?
50% for every 10 degrees
What else does hypothermic cardioplegic solution do?
Increases the time the myocardium can tolerate ischemia
What are the adverse effects of hypothermia?
Myocardial edema Phrenic nerve injury Citrate toxicity Impaired oxygen dissociation Increased plasma viscosity Decreased RBC formability
What has been shown about warm cardioplegic
Less atrial fib, use of balloon pump, low CO syndrome, periop MI
What is retrograde cardioplegia?
Placing a balloon tipped catheter in the coronary sinus
What is ante grade cardioplegia?
Putting it in between the aortic cannula and the aortic valve OR
putting it in the coronary ostia
In what conditions may retrograde cardioplegia need to be used?
Aortic insufficiency
AV surgery
Severely stenosis coronary arteries
What is the drawback of retrograde cardioplegia?
Inadequate delivery to the free wall of the RV and posterior third of the septum
What is the resting membrane potential of a normal cardiac myocyte?
-90mV
What is the resting membrane potential of a cardioplegic cardiac myocyte?
-60 mV
What is McConnell’s sign on TEE?
RV mid-free wall akinesia with spared apex
Finding of PE
What are some TEE findings of pulmonary embolism?
Dilated coronary sinus, right atrium, hepatic veins, RV, tricuspid regurg, bulging/flattening of septum
What is a type III protamine reaction?
Pulmonary HTN + RV FAILURE mediated by heparin-protamine complexes and TXA2
What is a type I protamine reaction?
Direct histamine or nitric oxide release
Happens with rapid administration
What is a type II protamine reaction?
IgE mediated anaphylaxis
A - true anaphylaxis
B- immediate anaphylactoid reaction
C - delayed anaphylactoid reaction
What patients may be at increased risk for type II protamine reaction?
Diabetics taking NPH
Fin fish allergy
Prior protamine exposure
What is the treatment for type III protamine reaction?
Cessation of protamine infusion Reinstate CPB Intropes (milrinone, isoproterenol) Nitric oxide for the Pulm HTN Small dose of heparin to reduce the heparin-protamine complex sizes
What does fenoldopam do?
Increases renal and splanchnic blood flow
Decreases peripheral vascular resistance
Diuresis and natriuresis
Increase intraocular
What are the contraindications to IABP?
Aortic regurgitation Aortic dissection Aortic stent Aortic aneurysm Severe bilateral PVD Aortic or Ilio-femoral bypass grafts Tachyarrythmias Uncontrolled sepsis Uncontrolled bleeding
What are the indications for IABP?
Improved coronary perfusion (increases diastolic pressure, decreases afterload)
Cardiogenic shock Refractory ventricular arrhythmias Refractory unstable angina Decompensated systolic heart failure Cardio support for procedure Decompensated aortic stenosis
How does IABP work?
It inflates during diastole and deflates right before systole so it augments diastolic pressure and therefore coronary perfusion pressure and decreases afterload
This decreases myocardial workload and oxygen consumption
When should the IABP be deflated on ECG.
At the peak of the R wave which signals the start of systole
When should the balloon inflate?
The start of diastole, so the middle of the T wave (right after closure of the aortic valve)
Who should get antibiotic prophylaxis?
- Prosthetic valves
- Previous endocarditis
- Palliative shunts and conduits
- Unrepaired cyanotic heart lesions
- Repaired congenital heart problems with residual defects
- Cardiac transplant with valvular disease
- Respiratory tract procedures that break the mucosa
What are the absolute contraindications to TEE probe placement?
Esophageal webs/strictures Esophageal tumor Scleroderma Malloryl-Weiss tear Zenker diverticulum Recent esophageal variceal bleeding Active upper GI bleeding Recent upper GI surgery Esophagectomy Perforated viscus
What is the medication of choice to prevent arrhythmia in patients with prolonged QT?
Beta blockers
What is the treatment for patients with prolonged QT that are refractory to medication?
Pacemakers
How long of a QT is an indication for an ICD.
Greater than 550
Why are centrifugal pumps preferred over roller pumps?
Less blood destruction, lower risk of air emboli, lower line pressures, elimination of wear and spallation
What is Beck’s triad?
Hypotension
Increased venous pressure
Muffled heart sounds