Upon completion of the chapter, the reader will be able to:
Describe the phases of the cardiac action potential, cardiac myocyte ion currents corresponding to each phase, and the relationship between the cardiac action potential and the electrocardiogram (ECG).
Describe the modified Vaughan Williams classification of antiarrhythmic drugs and compare and contrast the effects of these drugs on cardiac electrophysiology.
Determine risk factors for and mechanisms, etiologies, symptoms, and goals of therapy of (a) sinus bradycardia, (b) atrioventricular (AV) block, (c) atrial fibrillation (AF), (d) paroxysmal supraventricular tachycardia (PSVT), (e) premature ventricular complexes (PVCs), (f) ventricular tachycardia (VT, including torsades de pointes [TdP]), and (g) ventricular fibrillation (VF).
Compare and contrast mechanisms of action of drugs used for ventricular rate control, conversion to sinus rhythm, and maintenance of sinus rhythm in patients with AF.
Compare and contrast the advantages and disadvantages of warfarin and the direct oral anticoagulants (DOACs) for prevention of stroke and systemic embolism in patients with AF.
Discuss nonpharmacologic methods for termination of PSVT and compare and contrast mechanisms of action of drugs used for acute termination of PSVT, as well as treatment options for long-term prevention of PSVT recurrence.
Describe the role of drug therapy for management of asymptomatic and symptomatic PVCs.
Compare and contrast mechanisms of action of drugs used for treatment of acute episodes of VT and describe options and indications for nonpharmacologic treatment of VT and VF.
Design individualized drug therapy treatment plans for patients with (a) sinus bradycardia, (b) AV block, (c) AF, (d) PSVT, (e) PVCs, (f) VT (including TdP), and (g) VF.
NORMAL AND ABNORMAL CARDIAC CONDUCTION AND ELECTROPHYSIOLOGY
The two primary functions of the heart are mechanical and electrical activity. Mechanical activity refers to atrial and ventricular contraction, the mechanism by which blood is delivered to tissues. Deoxygenated blood returns to the heart via the venous circulation and enters the right atrium. Right atrial contraction delivers blood to the right ventricle through the tricuspid valve. Right ventricular contraction pumps blood through the pulmonic valve and pulmonary arteries to the lungs, where it is oxygenated. The oxygenated blood then flows through the pulmonary veins into the left atrium. Left atrial contraction pumps blood through the mitral valve into the left ventricle (LV), contraction of which delivers blood through the aortic valve and to the body’s tissues.
The heart’s mechanical activity stems from its electrical activity. The heart possesses an intrinsic electrical conduction system (Figure 10–1). Normal function of the heart’s electrical conduction system is required for normal myocardial contraction. Atrial depolarization causes atrial contraction, and ventricular depolarization produces ventricular contraction. Perturbation of the heart’s electrical conduction system may result in dysfunctional atrial and/or ventricular contraction and reduce cardiac output.
The cardiac conduction system. (AV, atrioventricular.)