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CARDIAC ANATOMY

FIGURE 1.1

Cardiac chambers, valves, and major vessels.

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.

FIGURE 1.3

Cardiac myocyte action potential.

TABLE 1.1Hemodynamic Calculations Used Clinically

DETERMINANTS OF CARDIAC FUNCTION

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

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