Acetylcholine (ACh) is too rapidly hydrolyzed and inactivated by acetylcholinesterase (AChE) to be of any therapeutic use; however, its action can be mimicked by other substances, namely direct or indirect parasympathomimetics (cholinomimetics).
There are numerous conditions that cause ST-segment elevation (STE) on an ECG that are not attributable to an acute coronary syndrome. In order to avoid errors in diagnosis or management, it is important for the EP to know the differential diagnosis for STE.
Heart murmurs are due to vibrations caused by turbulent flow within the heart. The most common causes are due to left-sided valvular heart disease and tricuspid regurgitation.
Substances acting antagonistically at the M-cholinoceptor are designated parasympatholytics (prototype: the alkaloid atropine; actions shown in red in the panels). Therapeutic use of these agents is complicated by their low organ selectivity.
Approximately 1% to 2% of patients with hypertension will present with a hypertensive emergency, defined as organ dysfunction due to an elevated blood pressure. Importantly, there is no specific blood pressure threshold that identifies a patient with a hypertensive emergency.
Hematemesis is the vomiting of fresh (bright red) or altered ("coffee ground") blood. Melena is the production of black, tarry stools and is due to bleeding from the upper gastrointestinal (GI) tract of more than 100 mL of blood.
Antiadrenergics are drugs capable of lowering transmitter output from sympathetic neurons, i.e., “sympathetic tone”. Their action is hypotensive (indication: hypertension) however, being poorly tolerated, they enjoy only limited therapeutic use.
When an acute inferior myocardial infarction is diagnosed, a right-sided ECG should be obtained to exclude the presence of a concomitant right ventricular myocardial infarction (RVMI). RVMIs can complicate 30% to 50% of acute IMIs.
Beta-Sympatholytics (Beta Blockers) are antagonists of norepiphephrine and epinephrine at β- adrenoceptors; they lack affinity for alpha-receptors. Beta-Blockers protect the heart from the oxygen wasting effect of sympathetic inotropism by blocking cardiac beta-receptors; thus, cardiac work can no longer be augmented above basal levels (the heart is “coasting”). This effect is utilized prophylactically in angina pectoris to prevent myocardial stress that could trigger an ischemic attack.
The goal of a cardiac stress test is to identify the patient with obstructive coronary artery disease (CAD), typically defined as stenosis of 50% or more of a coronary artery on angiography.