Iron Sufficient to Cause Hepatic Fibrosis and Ascites Does Not Cause Cardiac Arrhythmias in the Gerbil

Chronic iron overload associated with hereditary hemochromatosis or repeated red cell transfusions is known to cause cardiac failure. Cardiac arrhythmias have been incidentally noted in patients with iron overload, but often times dismissed as being caused by other co-morbid conditions. Studies with iron-loaded gerbils suggest a role for iron in the development of cardiac arrhythmias, however these studies utilized short duration recordings of anesthetized gerbils. Furthermore, we were unable to reproduce these loading protocols without significant morbidity and mortality. Our goal was to characterize iron-induced arrhythmias in the chronically instrumented, untethered, telemetered gerbil. Monitored gerbils were divided into 2 groups: iron-loaded (n=23) and control (n=8). Iron loaded gerbils received iron dextran intraperitoneally at a dose of 1.7 (n=4), 3.0 (n=5) or 6.2 (n=14) g/kg; control gerbils received dextran. Gerbils were weighed and given a physical exam weekly. Electrocardiograms were recorded for 10 seconds every 30 minutes for approximately 6 months (DSI Ponehma) and reviewed daily. Quantitative analysis was completed on 6 iron loaded (6.2g/kg) and 3 control gerbils. Heart rate and intervals were calculated and arrhythmias were characterized and counted. Cardiac and hepatic histology and tissue iron concentration were assessed.

All gerbils showed evidence of frequent sinus arrhythmia (more than one episode per hour). However, except for two control gerbils that showed frequent unifocal PVCs, no significant arrhythmias were noted in daily review. There was no difference in heart rate, P duration, PR interval, QRS duration or QT interval between groups. Neither total number of arrhythmias nor arrhythmias per minute were different between groups. One iron-loaded gerbil had a single episode (11 beats) of supraventricular tachycardia. Two iron-loaded gerbils had PVCs, one had only a single beat and the other had 9 unifocal PVCs over the duration of the study. Iron-loaded gerbils rarely showed other arrhythmias One control gerbil had 260 unifocal PVCs over the duration of the study. Other arrhythmias were noted rarely.

Body weight and heart weight was not different between groups, while liver weight increased with increasing iron dose. Cardiac and hepatic iron were significantly increased in iron loaded gerbils when compared to control. Liver weight increased as iron dose increased. Seven of 14 gerbils loaded to 6.2 g/kg developed ascites as assessed both by physical examination and necropsy.

We conclude that an iron load sufficient to cause clinical liver disease does not, in the absence of co-morbid conditions, cause cardiac arrhythmias in the gerbil model of iron overload. This suggests that iron alone is insufficient to cause cardiac arrhythmias.