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Chapter 1-01: Anatomy and Physiology in Cardiology

CARDIAC ANATOMY

FIGURE 1.1

Cardiac chambers, valves, and major vessels.

An image shows the structure of cardiac chambers, valves and major values present in the human heart. A cylindrical tube slightly bulged at center is present at the left side of the structure along with three outlet tubes at the top. An inverted c shaped structure was attached to the top of the tube with three outlets as tube on the top. In the gap of that structure a horizontal tube was attached to the first left outlet and below the center. Over all a slanting oval shaped structure is placed with four major segments. Below that tube was attached which is extended from C shaped structure.
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CARDIAC ELECTROPHYSIOLOGY

  • Cardiac electrical conduction system: Sinoatrial (SA) node (1° pacemaker) → Atrioventricular (AV) node (stalls conduction; can also act as a backup pacemaker with rate of 40–60 bpm) → Bundle of His → Right/left bundle → Purkinje fibers → Ventricle

  • Pacemaker cells (SA/AV node cells) automatically create electrical impulses that trigger myocyte cells (atrial/ventricular cells)

    • - Pacemaker action potential is described using three phases (Phases 0, 3, and 4). It is automatic and initiated by a slow inward Ca2+ current. The maximum diastolic potential (analogous to resting membrane potential) is ∼−55 mV (Figure 1.2)

    • - Myocyte action potential is described using five phases (Phases 0–4). It is automatic and triggered by a fast inward Na+ current. The resting membrane potential is −90 mV, determined by K+ conductance and equilibrium potential (Figure 1.3)

FIGURE 1.2

Cardiac pacemaker cell action potential.

An image shows the cardiac pacemaker cell action potential. The horizontal axis shows time and the vertical axis denotes the voltage, as zero, minus thirty five and minus fifty five M V was indicted from top and x axis denotes the time. From fifty five the line starts gradually raising and reaches the peak above zero and reduces and again reaches fifty five. The curve is labeled as 4 in the beginning 0 in the left side of the peak and 3 in the right side of the perk. The data are as follows: 0 - Upstroke/rapid depolarization: calcium flows in slowly (as fast voltage-gated sodium channels are inactive). 3 - Repolarization: Inactivation of calcium channels. Activation of potassium challenge right arrow potassium efflux. 4- Depolarization: sodium influx increases right arrow depolarization. Upstroke determines HR. Below that, two lines indicate the membrane at center. The passing is indicated by upward and downward arrows. The sodium leak channels shows a group of downward sodium arrows. The slow-opening calcium channels shows a group of downward calcium arrows. The delayed outward rectifier shows a group of upward potassium arrows. The inactive fast-opening sodium channel is followed by potassium, ATP, sodium, ATP and calcium.
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FIGURE 1.3

Cardiac myocyte action potential.

An image shows the cardiac myocyte action potential. The horizontal axis represents time and the vertical axis denotes the voltage, from plus twenty to minus eighty five M V from top to bottom and x axis denotes the time. The straight line from minus eighty five to plus twenty is drawn and gradually decreased and forms the L shaped curved. The curve is labeled from 0 to 4 at each point. The data are as follows: 0- Upstroke/rapid depolarization: sodium flows rapidly through the voltage-gated sodium channel. 1- Initial repolarization: Sodium channels inactivate. Potassium channels open and potassium flows out. 2- Plateau: Calcium channels open right arrow calcium influx balances potassium efflux. Calcium influx triggers additional calcium release from sarcoplasmic reticulum, causing myocyte contraction. 3 - Repolarization: Potassium channels open right arrow massive potassium efflux, calcium channels close. 4- Resting potential: High potassium permeability. Below that there are two rectangle boxes indicating sodium and calcium channels. Below that, two lines indicate the membrane at center. The passing is indicated by upward and downward arrows. The fast-opening sodium channel shows downward sodium arrow. The slow-opening calcium channels shows downward calcium arrows. The potassium delayed outward rectifier shows upward potassium arrows and followed by sodium/potassium ATPase, sodium/calcium antiporter, Calcium pump.
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TABLE 1.1Hemodynamic Calculations Used Clinically
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TABLE 1.1 Hemodynamic Calculations Used Clinically

Volume Calculations

SV = EDV – ESV

SV = CO/HR

EF = SV/EDV = (EDV − ESV)/EDV. Normal 55–70%.

Pressure Calculations

MAP = (SBP + [2 × DBP])/3. Normal 65–100 mmHg.

MAP = CO × SVR

mPAP = (PASP + [2 × PADP])/3. Normal <20 mmHg.

Resistance Calculations

Ohm’s Law: V = IR; R = V/I

SVR = (MAP − RAP) × 80/CO. Normal 800–1200 dynes × cm−5.

PVR = (mPAP − PCWP)/CO. Normal <3 Wood units.

Flow Calculations

CO = HR × SV. Normal 4–8 L/min.

CO = VO2/(CaO2 − CvO2)

CO = VO2/(Hgb × 13.6 × [PaO2 − MvO2]). Fick Principle.

CI = CO/BSA. Normal 2.4–4 L/min/m2.

Abbreviations: Stroke volume (SV), End-diastolic volume (EDV), End-systolic volume (ESV), Cardiac output (CO), Heart rate (HR), Ejection fraction (EF), Mean arterial pressure (MAP), Systolic blood pressure (SBP), Diastolic blood pressure (DBP), Systemic vascular resistance (SVR), Mean pulmonary artery pressure (mPAP), Pulmonary artery systolic pressure (PASP), Pulmonary artery diastolic pressure (PADP), Voltage (V), Current (I), Resistance (R), Right atrial pressure (RAP), Pulmonary vascular resistance (PVR), Pulmonary capillary wedge pressure (PCWP), Heart rate (HR), Stroke volume (SV), Oxygen consumption (VO2), Arteriovenous oxygen difference (CaO2 − CvO2), Hemoglobin (Hgb), Partial pressure of oxygen (PaO2), Myocardial volume oxygen (MvO2), Cardiac index (CI), Body surface area (BSA)

DETERMINANTS OF CARDIAC FUNCTION

  • Preload: Myocardial stretch before contraction (i.e., the end-diastolic length of the cardiac fibers), which ...

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