Frequency of arrhythmias

Hypotension Hypotension (postural) occurs regularly in about 50% of patients while they are supine, manifested by dizziness, light-headedness, vertigo, or faintness. Tolerance occurs unpredictably but may be present after several days. Hypotension with supine systolic pressure above 75 mm Hg need not be treated unless symptomatic. If supine systolic pressure falls below 75 mm Hg, infuse dopamine or norepinephrine to increase blood pressure use dilute solution and monitor blood pressure closely because pressor effects are enhanced by bretylium. Perform volume expansion with blood or plasma and correct dehydration where appropriate. Transient hypertension and increased frequency of arrhythmias Transient hypertension and increased frequency of arrhythmias may occur due to initial release of norepinephrine from adrenergic postganglionic nerve terminals. 

Gokce M, Karahan B, Yilmaz R, Orem C, Erdol C, Ozdemir S. Long term effects of hormone replacement therapy on heart rate variability, QT interval, QT dispersion and frequencies of arrhythmia. Int J Cardiol 2005 99 373-9. 

Catecholamines increase conduction rate in excitable tissue and bring the membrane potential closer to threshold. Thus, an excess of catecholamines, or sensitivity of the heart to catecholamines (e.g., by thyroid hormone) will increase the frequency of arrhythmias. 

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