Cardiology   Student Notes
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Cardiology Student Notes

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Cardiology   Student Notes Cardiology Student Notes Presentation Transcript

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  • Why Valves?
    • Valves provide a means to ensure that fluids ( e.g. , blood) only flows in one direction – when heart chambers contract, valves prevent blood from flowing backward.
    • Heart valves are passive – i.e. , they have no intrinsic opening or closing mechanism –they close from initial currents caused by pressure gradients , and also open by these.
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  • Two different kinds of Valves:
    • Atrio-ventricular (A-V) valves – between these chambers – the tricuspid (right), and the bicuspid or Mitral (left), are flimsy, and are supported by Chordae tendinae to prevent reversal and leakage.
    • Semilunar valves ( aortic and pulmonary ) are more robust and are able to resist backflow because of well developed edges on the cusps.
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  • Ventricular (left vs right) imbalance
    • This is usually described as heart failure – not a sudden “heart attack” ( most commonly an “infarct” due to deprived blood flow ) but rather an acute weakening of the myocardium ( a consequence of an infarct or other pathology ) and its output capacity – and almost always also clarified as either left side or right side heart failure (since rarely are both sides of the heart equally damaged)
  • Ventricular (left vs right) imbalance
    • If the right ventricle is damaged and cannot keep up (viz. flow rate ) with the left vent.:
  • Ventricular (left vs right) imbalance
    • If the right ventricle is damaged and cannot keep up (viz. flow rate ) with the left vent.:
    • If the left ventricle is damaged and cannot keep up with the right ventricle:
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  • Cardiac Cycle
    • Atrial press wave- a-wave - atrial contraction c-wave - ventricular contraction (A-V valves bulge) v-wave - flow of blood into atria
  • Ventricular Pressure and Volume Curves
    • Diastole
          • Isovolumic relaxation
          • A-V valves open
          • Rapid inflow
          • Diastasis - slow flow into ventricle
          • Atrial systole - extra blood in and this just follows P wave.
  • Ventricular Pressure and Volume Curves (cont’d)
    • Systole
          • Isovolumic contraction
          • A-V valves close (ventricular press > atrial press)
          • Aortic valve opens
          • Ejection phase
          • Aortic valve closes
    • During the latter part of the ejection phase how can blood still leave the ventricle if pressure is higher in the aorta?
    • Total energy of blood = P + mV 2 / 2 = pressure + kinetic energy
    • Total energy of blood leaving ventricle is greater than in aorta.
    Ventricular Pressure and Volume Curves (cont’d)
  • Aortic Pressure Curve
    • Aortic pressure starts increasing during systole after the aortic valve opens.
    • Aortic pressure decreases toward the end of the ejection phase.
    • After the aortic valve closes, an incisura occurs because of sudden blockage of back-flow toward left ventricle by the closed valve.
    • Aortic pressure decreases slowly during diastole because of the elasticity of the aorta.
  • 50 100 150 200 50 100 150 200 0 Intraventricular Pressure (mmHg) Left Ventricular Volume (ml) Period of Filling Isovolumic Relaxation Period of Ejection Isovolumic Contraction End Systolic Volume End Diastolic Volume Work Output of the Heart
  • Work Output graph variations:
    • Increased Preload : extends to the right (increased pressure) because there is more venous return (volume and pressure), and this increases the swelling of the atrium and ventricle (more volume = right shift, more pressure, shift higher), increasing the mass of blood to be ejected.
    • Increased Afterload : extends the diagram upward because there is greater than normal pressure in the aorta. Thus the semilunar valve cannot open at the usual pressure level (at the corner, #2), and blood cannot be ejected until the ventricle’s pressure rises higher to match the Aorta’s – thus its opening is delayed , and the curve rises higher on the diagram. However, the left side is shifted to the right because as the ventricle relaxes and ventricular pressure drops, the higher aortic pressure causes the semilunar valve to close earlier (normally, the corner, #3). Less blood is ejected, and more blood remains inside (smaller ejection fraction)!
    • Increased Contractility : The ventricle contracts more forcibly (raising the curve upward to a higher pressure when the semilunar valve opens). Also, this increased contraction ejects more blood (higher ejection fraction), so the curve also extends farther left (to a lower volume for the start of isovolumic relaxation).
  • Ejection Fraction
    • End diastolic volume = ___ ml
    • End systolic volume = __ ml
    • Ejection volume (stroke volume) = __ ml
    • Ejection fraction = 70ml/120ml = __% (normally __%)
    • If heart rate (HR) is 70 beats/minute, what is cardiac output?
    • Cardiac output = HR * stroke volume = 70/min. * __ ml = ____ml/min.
  • Beats per minute 50 160 200 Output per individual “beats” Heart Output ( measured as … ) ?
  • Beats per minute 50 160 200 Output per unit time ( e.g., minute ) Heart Output ( measured as … ) ?
  • Ejection Fraction (cont’d)
    • If HR =100, end diastolic volume = 180 ml, end systolic vol. = 20 ml, what is cardiac output?
    • C.O. = ___/min. * ___ ml = _____ ml/min .
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  • Bipolar Limb Leads
    • Bipolar means that the EKG is recorded from two electrodes on the body.
    Figure 11-6; Guyton & Hall
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  • Bipolar Limb Leads (cont’d)
    • Lead I - The negative terminal of the electrocardiogram is connected to the right arm, and the positive terminal is connected to the left arm.
    • Lead II - The negative terminal of the electrocardiogram is connected to the right arm, and the positive terminal is connected to the left leg.
  • Bipolar Limb Leads (cont’d)
    • Lead III - The negative terminal of the electrocardiogram is connected to the left arm, and the positive terminal is connected to the left leg.
    • Einthoven’s Law states that the electrical potential of any limb equals the sum of the other two (+ and - signs of leads must be observed).
    • If lead I = 1.0 mV, Lead III = 0.5 mV, then Lead II = 1.0 + 0.5 = 1.5 mV
  • Principles of Vectorial Analysis of EKG’s
    • The current in the heart flows from the area of depolarization to the polarized areas, and the electrical potential generated can be represented by a vector, with the arrowhead pointing in the positive direction .
    • The length of the vector is proportional to the voltage of the potential .
    • The generated potential at any instance can be represented by an instantaneous mean vector.
    • The normal mean QRS vector is 59 o .
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  • Principles of Vectorial Analysis of EKG’s (cont’d)
    • The axis of lead I is zero degrees because the electrodes lie in the horizontal direction on each of the arms.
    • The axis of lead II is +60 degrees because the right arm connects to the torso in the top right corner, and left leg connects to the torso in the bottom left corner.
    • The axis of lead III is 120 degrees.
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  • Principles of Vectorial Analysis of EKG’s (cont’d)
    • When the vector representing the mean direct current flow in the heart is perpendicular to the axis of one of the bipolar limb leads, the voltage recorded in the electrocardiogram in this lead will be very low.
    • When the vector has approximately the same direction as the axis of one of the bipolar limb leads, nearly the entire voltage will be recorded in this lead.
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  • Other EKG Leads (cont’d)
      • Augmented Unipolar Limb Leads aVR, aVL,
    • and aVF are also in use. For aVR the +
    • electrode is the right arm, and the -
    • electrode is the left arm + left leg; aVL +
    • electrode is left arm; aVF + electrode is left
    • foot.
  • Axes of the Unipolar Limb Leads + + + I aVL aVR aVF -
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  • Principles of Vectorial Analysis of EKG’s (cont’d) Axes of the Three Bipolar and Augmented Leads + _ _ _ + + 60 o 120 o 0 o I I III II III II + _ -30 o aVL aVL + _ 210 o aVR aVR + _ aVF aVF 90 o
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  • Ventricular Fibrillation
    • Some parts of ventricle contract while others relax, thus little blood flows out of the heart.
    • Caused by electrical shock or cardiac ischemia.
    • Also called circus movements .
    • If pathway is long (dilated heart)
    • If conduction velocity is decreased (blockade of Purkinje system, ischemia of muscle, and high K + levels)
    • If refractory period is shortened (epinephrine)
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