Cause

The definition of tachycardia is a heart rate greater than 100 beats per minute (bpm). Supraventricular tachycardia (SVT) is an abnormally fast heart rhythm arising from improper electrical activity in the upper part of the heart. 

SVT starts from either the atria or atrioventricular node. It is generally due to one of two mechanisms: re-entry or increased automaticity. The other type of fast heart rhythm is ventricular arrhythmias—rapid rhythms that start within the ventricle.

Sinus tachycardia originates from the sinus node, also called Sinoatrial node or SA node. It is caused by the SA node firing at a rate of greater than 100 bpm. All other electrical conduction after the SA node is normal.

Symptoms

Symptoms may include palpitations, feeling faint, sweating, shortness of breath, or chest pain.

Sources:

Landiolol: A Review in Tachyarrhythmias. Syed YY Drugs. 2018 Mar 78(3):377-388. doi: 10.1007/s40265-018-0883-9 
Pharmacokinetics and pharmacodynamics of two different landiolol formulations in a healthy Caucasian group. Krumpl G; Ulc I; Trebs M; Kadlecová P; Hodisch J Eur J Pharm Sci. 2016 Sep 20;92:64-73.