Which of the following is most associated with tachycardia?
ECG
You need a basic understanding of ECG's for the exams. Don't spend too much time on this as it's a very complex area and you do not need a detailed knowledge.
Rate
Normal rate is 60-100. Less than 60 is called bradycardia and more than 100 is called tachycardia.
PR interval
A normal PR interval is between 0.12 and 0.2 seconds. A PR interval consistently longer than 0.2s is referred to as first degree heart block.
ST segment
An upsloping ST segment (referred to as ST elevation) is indicative of a myocardial infarction. A depressed ST segment suggests myocardial ischaemia.
QTc interval
The normal range for the QTc interval is 0.35-0.45 seconds.
T waves
Are peaked in hyperkalemia, flat and prolonged in hypokalemia, and inverted in normal in some leads and also in ischemia and infarction.
U waves
Can be normal but also can be found in hypokalemia.
The following table illustrates some of the ECG changes associated with psychotropic drugs:
| ECG finding | Associated medication |
|---|---|
| Tachycardia | Clozapine TCAs MAOIs Antiparkinsonian Antipsychotics (generally the older ones) |
| Bradycardia | SSRIs Lithium Cholinesterase inhibitors |
| Heart blocks | TCAs |
| Repolarisation changes (ST segment & T wave changes) | Thioridazine Chlorpromazine |
| QTc prolongation | Wide range of antipsychtiics and antidepressants |
| Torsades/VF | Haloperidol Thioridazine Mesoridazine Chlorpromazine |
