Heart Failure
Figure 4: Graph Showing Superior Outcome When the Left Ventricular Lead Is Positioned in Segment with Significant Electrical Delay
0.0 0.2 0.4 0.6 0.8 1.0
02 4 6 Months
Left ventricular lead electrical delay (LVLED) with the sensed signal on the LV lead further than 50% into the QRS width (LVLED ≥50%).
Figure 5: Multispeciality Approach Needed in the Care of the Heart Failure Patient with an Implanted Cardiac Resynchronisation Therapy Device
8 LVLED ≥50% LVLED <50% 10 12
Follow-up Strategies
A new genre of ambulatory heart failure patients with implanted devices has resulted from the high prevalence of heart failure and increasing patient population eligible for device therapy. This is a frail group of patients needing care from their primary cardiologist, electrophysiologist and heart failure specialist, often with additional input from an imaging (echocardiography) specialist (see Figure 5). Most centres lack a form of structured cross-talk between the cardiac sub-specialties and often several weeks may pass between individual sub-speciality evaluations, resulting in disjointed and often sub-optimal medical care. Current post- device-implant care is deficient on many fronts, namely consideration of device diagnostic information and utilisation of such data to titrate medications, enhance device response in patients and, more importantly, enable early identification and treatment of non-responders. There is a certain level of reticence when it comes to proactively optimising the atrio-ventricular and inter-ventricular timings of these devices to maximise the stroke volume. Several studies have now demonstrated that device optimisation facilitates functional improvement and increases the extent of reverse remodelling.28–31
Cardiac arrhythmia service
Patient
Echocardiography and imaging
Heart failure service
improved long-term outcome (see Figure 4).24 Recent work has also
suggested that site-specific pacing over the segments with dyssynchrony may be associated with a better clinical outcome.18 Another important aspect of LV lead placement relates to physical separation between the two pacing electrodes.25
However, there is
still no conclusive study delineating whether the best lead implantation approach is targeting the most electrically delayed segment, lead placement over the most mechanically delayed segment, anatomical lead positioning in the lateral and postero- lateral segment or maximising physical separation between the RV and LV leads.
Similar to the native LBBB, RV pacing causes abnormal activation and consequently dyssynchronous contraction of the LV.26
Upgrading
chronically RV-paced cardiomyopathy patients (who meet all other criteria for CRT) can improve heart failure by virtue of reduction in the variation of LV myocardial segmental contractility, reduction in isovolumic contraction time, improved myocardial performance index and improved global systolic function. Another less well- understood entity is the impact of RV pacing lead location on the LV depolarisation wavefront and its consequent impact on resynchronisation. Previous work has demonstrated that shifting the RV pacing lead can alter the LV activation sequence.26
An interesting
question that could benefit from further investigation is the interaction between the RV and LV pacing lead location and its impact on response. Another matter that needs to be examined is the effect of scar on ventricular remodelling, as determined by the proximity of the pacing lead to the akinetic (scar) segment.27
86
Non-responsive patients usually come to attention via a heart failure exacerbation or a hospitalisation, and one of the goals of an integrated healthcare delivery programme is to detect problems early, with proactive modification of the drug regimen or device settings to prevent acute disease decompensation. Having all the disciplines work together can facilitate better patient selection, CRT device optimisation and careful titration of medical therapy in the post- implantation period. A multidisciplinary clinic provides an ideal structure for consultation between different specialties to allow these data to be used more efficiently in the care of these patients. Although it appears intuitive that this multispeciality model would translate into better patient care, the impact of such integrated services still needs to be prospectively assessed.
CRT devices record and provide detailed information pertinent to patient activity, heart rate, autonomic activity and transthoracic impedance, and in the near future they will also provide realtime haemodynamic data.32
The
recent advent of remote monitoring of these devices has enabled the realtime automatic transmission of ambulatory information regarding heart rate, physical activity, development of incipient pulmonary oedema (transthoracic impedance measure), etc., via the Internet. Although this may result in a risk of information overload, it provides the opportunity to enhance the quality of patient care and identify non-responders well before they actually decompensate. Also, ongoing work to enhance sensor technology has enabled over-the-web transmission of other important parameters such as blood pressure, weight, oxygen saturations, etc. Web-based monitoring of these patients and their devices provides the option for the different sub-specialists to share patient data and individualise treatment, and consequently reduce hospitalisations.
Conclusion
Although CRT has had a large impact on the field of heart failure, its complete potential has not been realised. Over the next few years, our understanding of ventricular mechanical dyssynchrony along with substrate- and pacing-site-specific response will improve, enabling wider application of multisite pacing of the ventricle(s). There is a clear benefit of device therapy in the symptomatic patient refractory to conventional medical therapy, and recent evidence from the Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy (MADIT-CRT) and Resynchronization
EUROPEAN CARDIOLOGY
Event-free survival
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