PATHOPHYSIOLOGY

Temporary cardiac pacing, whether transcutaneous, transvenous, or epicardial, is a potentially lifesaving technique for patients with arrythmias which cause hemodynamic instability.

Etiology of malignant rhythms may be due to structural heart disease, most often and commonly associated with ischemia or infarction, but can also include adult congenital heart disease, infiltrative cardiomyopathies (amyloidosis, lymphoma), infection or inflammation (viral myocarditis, infectious endocarditis, Lyme disease, Chagas disease, diphtheria, toxoplasmosis, sarcoidosis, malaria, Dengue fever, viral hemorrhagic fevers, etc.), post-surgical (post coronary artery bypass grafting, valvular surgeries) or thoracic blunt force trauma. Nonstructural or extrinsic causes of arrythmias may include electrolyte and endocrine abnormalities, hypothermia, whether accidental or purposeful (targeted temperature management), drug or toxin effects (organophosphates, medication overdoses), and neurogenic shock.

When the cardiac conduction system suffers an insult, such as described above, the loci of cardiac impulse generation, in the sinoatrial (SA) node, and the pathway of electrical impulses downward through the intraatrial conduction pathways, atrioventricular (AV) node, bundle of His, bundle branches, and terminating with the Purkinje fibers, are all potential locations of dysfunction, resulting in a variety of dysrhythmias.

Of the resulting arrythmias and the associated hemodynamic compromise and end organ dysfunction that may present with those arrhythmias, those that benefit from cardiac pacing are bradycardia, symptomatic 2nd degree, type I (Wenckebach’s) block, 2nd degree, type II (Mobitz type II) block, 3rd degree (complete) block, sick sinus syndrome, and junctional (escape) rhythms. In some cases, tachyarrhythmias (such as Torsades de pointes and ventricular tachycardias) benefit from providing external electrical stimulus to overcome the native dysfunction (i.e. overdrive pacing). Most patients that require cardiac pacing suffer from symptomatic bradycardia or either 2nd - or 3rd -degree heart block.