Cardiac electrophysiology: normal and ischemic ionic currents and the ECG

Abstract

Basic cardiac electrophysiology is foundational to understanding normal cardiac function in terms of rate and rhythm and initiation of cardiac muscle contraction. The primary clinical tool for assessing cardiac electrical events is the electrocardiogram (ECG), which provides global and regional information on rate, rhythm, and electrical conduction as well as changes in electrical activity associated with cardiac disease, particularly ischemic heart disease. This teaching review is written at a level appropriate for first- and second-year medical students. Specific concepts discussed include ion equilibrium potentials, electrochemical forces driving ion movements across membranes, the role of ion channels in determining membrane resting potentials and action potentials, and the conduction of action potentials within the heart. The electrophysiological basis for the ECG is then described, followed by discussion on how ischemia alters cellular electrophysiology and ECG recordings, with particular emphasis on changes in T waves and ST segments of the ECG.

Acute coronary syndromes in the practice of the emergency medical team

“…The criteria described above, however, do not apply to patients who may have features of left ventricular hypertrophy or left bundle branch block (LBBB). However, if you suspect acute myocardial ischemia and simultaneous presence of LBBB or RBBB (right bundle branch block), it is recommended to implement such procedures as in patients with ST segment elevation [14,15].…”

“…It should be remembered that a correct ECG recording is not a basis for exclusion of ACS. In a situation where symptoms continue or recur, it is useful to repeat the ECG recording or compare the current one with the previous ones [7,10,11,15].…”

“…• Oxygen therapy in ACS is currently not recommended as a standard treatment for any patient with ACS because it has been shown that excess oxygen can be detrimental to the patient and can increase the area of myocardial injury. It is recommended to use oxygen therapy in patients with significant hypoxemia (SpO2 < 90%) [5,15,19,20].…”

The Essentiality of Dynamic Interfaces in Human-Environment Interactions

“…In cardiovascular disease, for example, decades of research has aimed at identifying signatures of healthy and dysregulated function. The cardiac rhythm serves as the final common path for multiple neural systems, including both the endogenous pacemakers which mediate and maintain cardiac rhythm as well as the outputs of the sympathetic and para-sympathetic nervous systems[8],[9]. These so-called "fight or flight" and "rest and digest" systems, respectively, can be elicited in response to external stimuli, for example the reflexive avoidance of a collision; or, in response to our own activity, as more or less strenuous exercise requires necessary resource recruitment.…”

The effects of nicotine and cigarette smoking on cardiac electrophysiology.

“…Basic cardiac electrophysiology is fundamental in understanding rhythmic cardiac function and electrical conduction, as well as changes in electrical activity associated with cardiac disease. The primary clinical tool for assessing cardiac electrical events is the electrocardiogram (ECG) [21]. The 12-lead ECG remains the most widely available, inexpensive, non-invasive, an indispensable tool for the diagnosis and prompt initiation of therapy in patients with acute coronary syndromes.…”