Implantable cardioverter-defibrillators

Control of action potential duration alternans in canine cardiac ventricular tissue

Cardiac electrical alternans, characterized by a beat-to-beat alternation in action potential waveform, is a naturally occurring phenomenon, which can occur at sufficiently fast pacing rates. Its presence has been putatively linked to the onset of cardiac reentry, which is a precursor to ventricular fibrillation. Previous studies have shown that closed-loop alternans control techniques that apply a succession of externally administered cycle perturbations at a single site provide limited spatially-extended alternans elimination in sufficiently large cardiac substrates. However, detailed experimental investigations into the spatial dynamics of alternans control have been restricted to Purkinje fiber studies. A complete understanding of alternans control in the more clinically relevant ventricular tissue is needed. In this paper, we study the spatial dynamics of alternans and alternans control in arterially perfused canine right ventricular preparations using an optical mapping system capable of high-resolution fluorescence imaging. Specifically, we quantify the spatial efficacy of alternans control along 2.5 cm of tissue, focusing on differences in spatial control between different subregions of tissue. We demonstrate effective control of spatially-extended alternans up to 2.0 cm, with control efficacy attenuating as a function of distance. Our results provide a basis for future investigations into electrode-based control interventions of alternans in cardiac tissue.

Wound management and restrictive arm movement following cardiac device implantation - evidence for practice?

BACKGROUND

The rate of cardiac device implantation has risen significantly secondary to an increase in the number of indications. Wound infection and lead displacement are two common and potentially life-threatening complications. No national/international guidelines address postoperative care and controversy exists regarding wound management and arm movement following cardiac device implantation.

AIMS

We aimed to explore and review the evidence behind current practice but found that certain aspects of established practice.

METHODS

An electronic search of the databases EMBASE, British Nursing Index, CINAHL, Cochrane and PubMed to identify evidence regarding wound management and lead displacement.

FINDINGS

We found that certain aspects of established practice are based on tradition rather than evidence. Recent guidelines on wound management published by The National Institute for Health and Clinical Excellence in the UK recommend covering the wound postoperatively for 48 h with a low-adherent transparent dressing and letting patients shower thereafter. Since specific guidelines for cardiac device patients are lacking, we suggest that further research address whether or not the NICE guidelines can be extrapolated to this area. Studies showed that early mobilisation and allowing a full range of arm movements following device implantation is safe. Further research must validate these findings.

CONCLUSION

We discuss the reasons behind these gaps in the evidence base and support the idea that nursing education has not placed enough emphasis on how to critically appraise research. This accounts for the very small proportion of nurses that get involved in conducting research and generating guidelines. Additionally, we argue that nurses can play a key role in identifying and addressing research questions that lead to improved patient outcome. Thus, we support proposals to enhance nurses' opportunities to pursue academic careers to achieve adequate research skills.

Pacemakers and implantable cardioverter defibrillators

An increasing number of patients are now treated cardiac pacemakers and implantable cardioverter defibrillators and the technology of these is constantly changing. It is vital to have a good understanding of how they function and what the real risks are. Understanding how the device should work when functioning normally, and the possible effects of electromagnetic interference, is paramount to their safe management in the peri-operative period. Knowing when a device should be disabled or reprogrammed requires careful consideration. Information from the patient's pacemaker clinic should be sought whenever possible and can be invaluable. In addition, the Medicines Healthcare products Regulatory Agency have published the first set of UK guidelines on the management of implantable devices in the presence of surgical diathermy and this will undoubtedly provide a firm foundation on which anaesthetists can base much of their practice.

Long-term quality of life and uncertainty in patients living with an implantable cardioverter defibrillator

PURPOSE

This study describes the quality of life (QOL) and uncertainty in patients who have an implantable cardioverter defibrillator (ICD) and predicts QOL at long-term follow-up.

METHODS

Long-term follow-up was defined as 6.9 years +/- 1 year (range 4.11-8.7 years). QOL was measured with the Quality of Life Index, and uncertainty was measured with the Mishel Uncertainty in Illness Scale.

RESULTS

The overall QOL and health/functioning were unchanged over time. QOL in the socioeconomic (P = .002) and psychologic/spiritual domains (P = .012) decreased in the first year. From baseline to long-term follow-up, the QOL in the family domain (P = .011) and uncertainty (P = .002) decreased. Uncertainty was a predictor of low QOL.

CONCLUSION

QOL was reasonably good 6.9 years post-ICD implantation. Patients felt less uncertain once they had passed the first year of their illness.

Implantable cardioverter-defibrillators, induced anxiety, and quality of life

Since its approval in 1985, the implantable cardioverter-defibrillator (ICD) has supplanted antiarrhythmic drugs as the standard of care for patients with potentially lethal ventricular arrhythmias. The increased popularity of ICDs stems primarily from their safety and tolerability compared with commonly used medications notorious for adverse drug reactions. As ICD indications have broadened, the number of implantations has increased substantially, and more attention has been directed to sequelae of implantation, particularly after ICD firing. Although scant, studies of quality of life and psychiatric symptoms in patients with ICDs consistently report assorted psychiatric disturbances affecting up to 87% of recipients. Depression and anxiety predominate: up to 38% of patients experience symptoms that meet diagnostic criteria for an anxiety disorder. Psychological theories such as the classic conditioning model, learned helplessness model, and cognitive appraisal model have been invoked to conceptualize these new-onset ICD-induced anxiety disorders. Small trials of psychosocial interventions, including support groups and cognitive behavioral therapy, have had mixed results. Little is known about preexisting anxiety disorders in ICD recipients, particularly which premorbid features predict a worse prognosis, other than suggestions that younger patients and those receiving multiple shocks are at greater risk. Prospective studies of the psychopathology of patients with ICDs, both before and after implantation, are warranted.

Doppler tissue imaging for assessing left ventricular diastolic dysfunction in heart transplant rejection

OBJECTIVE

To test the hypothesis that diastolic mitral annular motion velocity, as determined by Doppler tissue imaging and left ventricular diastolic flow propagation velocity, is related to the histological degree of heart transplant rejection according to the International Society of Heart and Lung Transplantation (ISHLT).

METHODS

In 41 heart transplant recipients undergoing 151 myocardial biopsies, the following Doppler echocardiographic measurements were performed within one hour of biopsy: transmitral and pulmonary vein flow indices; mitral annular motion velocity indices; left ventricular diastolic flow propagation velocity.

RESULTS

Late diastolic mitral annular motion velocity (A(DTI)) and mitral annular systolic contraction velocity (SC(DTI)) were higher in patients with ISHLT < IIIA than in those with ISHLT >/= IIIA (A(DTI), 8.8 cm/s v 7.7 cm/s (p = 0.03); SC(DTI), 19.3 cm/s v 9.3 cm/s (p < 0.05)). Sensitivity and specificity of A(DTI) < 8.7 cm/s (the best cut off value) in predicting significant heart transplant rejection were 82% and 53%, respectively. Early diastolic mitral annular motion velocity (E(DTI)) and flow propagation velocity were not related to the histological degree of heart transplant rejection.

CONCLUSIONS

Doppler tissue imaging of the mitral annulus is useful in diagnosing heart transplant rejection because a high late diastolic mitral annular motion velocity can reliably exclude severe rejection. However, a reduced late diastolic mitral annular motion velocity cannot predict severe rejection reliably because it is not specific enough.