Past Papers · SAQ
Vasoactive Pharmacology — Metoprolol vs GTN
2010A Q16
Exam questionDefine the mechanisms of action and adverse effects of metoprolol and glyceryl trinitrate when used to manage myocardial ischaemia.
CICMWrecks answer
Master answer
Myocardial ischaemia
- Occurs when myocardial oxygen demand is not met by oxygen delivery
- Type I
- Due to atherosclerotic disease – plaque rupture, or coronary artery spasm
- Type II
- Due to increased metabolic demand of myocardium (e.g. tachycardia, hypertensive crisis)
- Type I
- Determinants of myocardial oxygen demand
- Basal metabolism of heart
- Heart rate
- Contractility
- External work
- Wall tension
| METOPROLOL | GLYCERYL TRINITRATE | |
|---|---|---|
| β1 selective adrenoceptor antagonist | Nitrate | |
| MoA | β1 adrenoceptor = GsPCR In Myocardium – Inhibition → Decreased activation of adenylyl cyclase → Decreased intracellular [cAMP] → Decreased activation of protein kinase A → Decreased phosphorylation and activation of intracellular enzymes → Decreased intracellular [Ca2+] – Decreased inotropy and decreased chronotropy → Decreased myocardial oxygen consumption → Relief of ischaemia | Nitrate groups activated by thiols to nitric oxide In vascular smooth muscle (veins > arteries) – → Diffuses intracellularly and activated guanylyl cyclase → increased intracellular [cAMP] → Decreased intracellular [Ca2+] → decreased vascular tone → venodilation and vasodilation – → Decreased preload and decreased afterload – → Decreased myocardial O2 consumption → Relief of ischaemia |
| A/E | CVS – Bradycardia – Hypotension – Arrhythmia – Decompensation of acute heart failure → Cardiogenic shock – Rebound myocardial ischaemia on abrupt cessation Resp – Bronchospasm if reactive airways disease CNS – Vivid dreams – Lethargy Other – Dyslipidaemia – Hyperglycaemia | CVS – Hypotension – Reflex tachycardia – If preload dependent cardiac output → decreased cardiac output → shock Resp – Methaemoglobin → decreased O2 delivery – Bronchodilation → V/Q mismatch CNS – Increased cerebral blood flow Other – Tolerance |
Sakurai 2016
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2010A Q16 | Define the mechanisms of action and adverse effects of metoprolol and glyceryl trinitrate when used to manage myocardial ischaemia. | 80% |