Atrial fibrillation and CHF are close companions. Either it precipitates CHF or follows it.In advanced heart failure of any etiology the incidence of AF can be up to 40% .Medical therapy of AF is fairly effective in patients with normal LV function .But when associated with refractory cardiac failure it becomes too complex to control .
Currently CRT with ICD is becoming the standard OF care for advanced CHF. The efficacy of CRT is being rigorously being assessed . Even as the controversy about the wideness of QRS is being settled , the issue of optimal timing of CRT has risen . Now , the MADIT-CRT has answered this issue “Earlier it is better , it can be indicated even for class 1 patients”
While MADIT -CRT will increase the number of CRT implants , we have no clear cut answer for the efficacy of CRT in patients with AF .( Of course , the MUSTIC and CARE HF sub group analysis suggested AF has no significant impact on CRT efficacy )
Why is AF important in CRT ?
There are two issues that need analysis
- A patient who has chronic AF at the time of CRT
- Development of new onset AF after CRT implantation.
Impact of AF during CRT
- Inter atrial synchrony is lost. ( Significance not clear . . . makes AF permanent)
- AV synchrony is lost
- Rapid AV conduction : May trigger too much of Bivi pacing if sensed by LV lead
Presence of AF at the time of CRT gives us an opportunity to tackle this issue.
How to tackle sudden AF induced CRT response ?
There are variety of algorithms available to
- Ventricular sense response
- Conducted AF response
- Atrial tracking recovery
In dual chamber pacing mode switching converts DDD into VVI .This happens at the cost of loss of AV synchrony .This may have profound implication in CRT .
Then the big question comes . What is the use of having Intraventricular and interventricular synchrony without AV synchrony ?
When nothing works .The best strategy is ( Rather deemed to be best ! )
- To ablate the AV node pace the atrium and ventricle (RV & LV) .
Note : Ablation of AV node and putting a dual chamber pacing can never guarantee a physiological pacing as the atrium continues to fibrillate and AV synchrony is rarely there .
Final message
For CRT is to be successful , there should be maximal Bi-Vi capturing , of course this capture has to optimally timed , and must reverse the three pathological asynchronies , namely intraventricular , Interventricular and atrio ventricular asynchronies.
It is obvious , presence of AF complicates the issue as it demands constant monitoring and programming of the device (Of course now most of them are automated) . It may require knocking down of AV node , which not only carries a risk of SCD * , it also make these patients permanently dependent on the RV pacing . This adds on , another risk , for an acute complication if the RV lead fails for some reason.
Reference :
EP experts generally take too much liberty in adopting this strategy for the simple reason it solves the nuisance of atrial impulses interfering with ventricular leads function that result in inappropriate ventricular capture fusion or ultimately poor BiVi pacing . But it is not an easy decision atleast for the patient ! This article , emphasises the dangers involved in ablate and pace strategy for uncontrolled AF.
Further reading
- Fung, J. W H, Yip, G. W K, Yu, C.-M. (2008). Does atrial fibrillation preclude biventricular pacing?. Heart 94: 826-827 [Full Text]
- Khadjooi, K, Foley, P W, Chalil, S, Anthony, J, Smith, R E A, Frenneaux, M P, Leyva, F (2008). Long-term effects of cardiac resynchronisation therapy in patients with atrial fibrillation. Heart 94: 879-883 [Abstract]
- Buck, S., Rienstra, M., Maass, A. H., Nieuwland, W., Van Veldhuisen, D. J., Van Gelder, I. C. (2008). Cardiac resynchronization therapy in patients with heart failure and atrial fibrillation: importance of new-onset atrial fibrillation and total atrial conduction time. Europace 10: 558-565 [Abstract] [Full Text]
Dr.S.Venkatesan MD 