We've long known that right ventricular pacing is not physiologic. PACE study investigators, presenting at AHA 2009, looked at the difference between RV and BiV pacing in terms of EF after one year in patients with normal or nearly normal systolic function at baseline.
By one year there was no difference in 6 minute walk performance or quality of life indicators, but patients in the RV pacing group dropped their EF (by 7%) whereas those in the BiV group did not. For a patient starting with a normal EF, a 7% drop may not seem like much, but consider the impact of a few % per year!
RV pacing leads to cardiac remodeling. BiV pacing prevents it. Based on these findings, chronic RV pacing is a bit like depriving some patients of ACE inhibitors.
If you've taken care of many patients with pacemakers you've probably seen pacemaker mediated cardiomyopathy. The hypothesis needs further study before we implant BiV pacers in all patients, but for now there is an important take home message---minimize RV pacing via rate and AV interval programming and be aware that patients in whom this is not possible, because they are RV pacer dependent, may be at special risk to develop dilated cardiomyopathy.
For details on this fascinating study: