David J. Wright

An Entirely Subcutaneous Implantable Cardioverter–Defibrillator

BACKGROUND Implantable cardioverter-defibrillators (ICDs) prevent sudden death from cardiac causes in selected patients but require the use of transvenous lead systems. To eliminate the need for venous access, we designed and tested an entirely subcutaneous ICD system. METHODS First, we conducted two short-term clinical trials to identify a suitable device configuration and assess energy requirements. We evaluated four subcutaneous ICD configurations in 78 patients who were candidates for ICD implantation and subsequently tested the best configuration in 49 additional patients to determine the subcutaneous defibrillation threshold in comparison with that of the standard transvenous ICD. Then we evaluated the long-term use of subcutaneous ICDs in a pilot study, involving 6 patients, which was followed by a trial involving 55 patients. RESULTS The best device configuration consisted of a parasternal electrode and a left lateral thoracic pulse generator. This configuration was as effective as a transvenous ICD for terminating induced ventricular fibrillation, albeit with a significantly higher mean (+/-SD) energy requirement (36.6+/-19.8 J vs. 11.1+/-8.5 J). Among patients who received a permanent subcutaneous ICD, ventricular fibrillation was successfully detected in 100% of 137 induced episodes. Induced ventricular fibrillation was converted twice in 58 of 59 patients (98%) with the delivery of 65-J shocks in two consecutive tests. Clinically significant adverse events included two pocket infections and four lead revisions. After a mean of 10+/-1 months, the device had successfully detected and treated all 12 episodes of spontaneous, sustained ventricular tachyarrhythmia. CONCLUSIONS In small, nonrandomized studies, an entirely subcutaneous ICD consistently detected and converted ventricular fibrillation induced during electrophysiological testing. The device also successfully detected and treated all 12 episodes of spontaneous, sustained ventricular tachyarrhythmia. (ClinicalTrials.gov numbers, NCT00399217 and NCT00853645.)

Cardiopulmonary exercise testing and its application

Cardiopulmonary exercise testing CPET has become an important clinical tool to evaluate exercise capacity and predict outcome in patients with heart failure and other cardiac conditions. It provides assessment of the integrative exercise responses involving the pulmonary, cardiovascular and skeletal muscle systems, which are not adequately reflected through the measurement of individual organ system function. CPET is being used increasingly in a wide spectrum of clinical applications for evaluation of undiagnosed exercise intolerance and for objective determination of functional capacity and impairment. This review focuses on the exercise physiology and physiological basis for functional exercise testing and discusses the methodology, indications, contraindications and interpretation of CPET in normal people and in patients with heart failure.

Physiological cardiac reserve: development of a non-invasive method and first estimates in man

Objective To investigate whether physiological cardiac reserve can be measured in man without invasive procedures and whether it is a major determinant of exercise capacity. Design Development of method of measurement and an observational study. Setting A regional cardiothoracic centre. Subjects 70 subjects with a wide range of cardiac function, from heart failure patients to athletes. Methods Subjects underwent treadmill, symptom limited cardiopulmonary exercise tests to measure aerobic exercise capacity (represented by V˙o 2max) and cardiac reserve. Cardiac output was measured non-invasively using the CO 2 rebreathing technique. Results Cardiac power output (CPOmax) at peak exercise was found to be significantly related to aerobic capacity: CPOmax(W) = 0.35 + 1.5V˙o 2max (l/min),r = 0.87, p < 0.001. It also correlated well with exercise duration (r = 0.62, p < 0.001), suggesting that cardiac reserve is a major determinant of exercise capacity. In the study, cardiac reserve ranged from 0.27 to 5.65 W, indicating a 20-fold difference between the most impaired cardiac function and that of the fittest subject. Conclusions A non-invasive method of estimating physiological cardiac reserve was developed. The reserve was found to be a major determinant of exercise capacity in a population of normal subjects and patients with heart disease. This method may thus be used to provide a clearer definition of the extent of cardiac impairment in patients with heart failure.

Maximizing Patient Benefit From Cardiac Resynchronization Therapy With the Addition of Structured Exercise Training : A Randomized Controlled Study

OBJECTIVES We evaluated the benefits of additional exercise training after cardiac resynchronization therapy (CRT). BACKGROUND Cardiac resynchronization therapy results in improved morbidity and mortality in appropriate patients. We hypothesized that a structured exercise training program in addition to CRT would maximize the improvements in exercise capacity, symptoms, and quality of life (QOL). METHODS Fifty patients referred for CRT were recruited. Patients were assessed before and 3 and 6 months after CRT. Functional class and QOL scores were recorded, and exercise tests were performed with hemodynamic measurements. Peak lower limb skeletal muscle torque was measured during extension, and echocardiography was undertaken at each visit. At 3 months, patients were randomized with a simple sealed envelope method to exercise training (n = 25) or control group (n = 25). The exercise group underwent an exercise program consisting of 3 visits/week for 3 months. Paired sample t tests were used to look for in-group differences and independent sample t tests for between-group differences. RESULTS Three months after CRT there were significant improvements in all functional, exercise hemodynamic, and echocardiographic measures. After randomization the exercise group showed further significant improvements in functional, exercise hemodynamic, and QOL measures compared with the control group. There were also significant in-group improvements in peak skeletal muscle function and ejection fraction that did not reach statistical significance on intergroup analysis. CONCLUSIONS Exercise training leads to further improvements in exercise capacity, hemodynamic measures, and QOL in addition to the improvements seen after CRT. Therefore, exercise training allows maximal benefit to be attained after CRT.

How many patients fulfil the surface electrocardiogram criteria for subcutaneous implantable cardioverter-defibrillator implantation?

AIMS To determine the number of patients with a primary or secondary prevention implantable cardioverter-defibrillator (ICD) indication who are eligible for subcutaneous ICD (S-ICD) implantation according to the S-ICD manufacturers surface electrocardiogram (ECG) screening template. METHODS AND RESULTS One hundred and ninety-six ICD patients with a non-paced ventricle were assessed using erect and supine ECG limb lead recordings to simulate the three S-ICD sensing vectors. Each ECG lead was scrutinized by two independent observers. Subcutaneous ICD eligibility required two or more leads to satisfy the S-ICD screening template in both erect and supine positions. Overall, 85.2% of patients [95% confidence interval (CI): 80.2-90.2%] fulfilled surface ECG screening criteria. The proportion of patients with 3, 2, 1, and 0 qualifying leads were 37.2% (95% CI: 30.4-44.0%), 48.0% (95% CI: 41.0-55.0%), 11.2% (95% CI: 6.8-15.6%), and 3.6% (95% CI: 1.0-6.2%). The S-ICD screening template was satisfied more often by Lead III (primary vector, 83.7%, 95% CI: 78.5-88.9%) and Lead II (secondary vector, 82.7%, 95% CI: 77.4-88.0%) compared with Lead I (alternate vector, 52.6%, 95% CI: 45.6-59.6%). A prolonged QRS duration was the only baseline characteristic independently associated with ineligibility for S-ICD implantation. There was 92.9% agreement between the two independent observers in assessment of eligibility using the S-ICD screening template. CONCLUSION About 85.2% of patients with an indication for a primary or secondary prevention ICD have a surface ECG that is suitable for S-ICD implantation when assessed with an S-ICD screening template. There is minor inter-observer variation in assessment of eligibility using the S-ICD screening template.

A prospective longitudinal evaluation of the benefits of epicardial lead placement for cardiac resynchronization therapy

AIMS Cardiac resynchronization therapy (CRT) is a recognized treatment for appropriate patients. However, placement of the transvenous left ventricular lead is unsuccessful in 5-10% of patients and a further 20% fail to respond. For these groups, epicardial left ventricular lead placement is one alternative. We prospectively evaluated the effects of epicardial vs. transvenous placed CRT. METHODS AND RESULTS Twenty-three subjects with unsuccessful transvenous coronary sinus lead placement underwent epicardial implantation. The subjects underwent clinical evaluation, cardiopulmonary exercise testing, and echocardiography before 3 and 6 months after. The results were compared with a control group (n = 35) who had received transvenous CRT. In both groups, there were significant improvements in all measures at 3 and 6 months. The improvement in peak VO(2) was delayed in the epicardial group compared with the transvenous group. At 6 months, the improvements seen in all variables showed no difference between the groups. CONCLUSION Epicardial lead placement is a viable option for patients with unsuccessful coronary sinus lead placement. The improvements in most variables were of a similar magnitude and over a similar time scale compared with transvenous placement. Improvements in peak VO(2) were delayed in the epicardial group, probably as a result of a prolonged recovery time.

Cost–consequence analysis of daily continuous remote monitoring of implantable cardiac defibrillator and resynchronization devices in the UK

Aims The need for ongoing and lifelong follow-up (FU) of patients with cardiac implantable electric devices (CIED) requires significant resources. Remote CIED management has been established as a safe alternative to conventional periodical in-office FU (CFU). An economic model compares the long-term cost and consequences of using daily Home Monitoring® (HM) instead of CFU. Methods and results A cost–consequence evaluation comparing HM vs. CFU was performed using a Markov cohort model and data relating to events and costs identified via a systematic review of the literature. The model is conservative, without assuming a reduction of cardiovascular events by HM such as decompensated heart failure or mortality, or considering cost savings such as for transportation. Also cost savings due to an improved timing of elective device replacement, and fewer FU visits needed in patients near device replacement are not considered. Over 10 years, HM is predicted to be cost neutral at about GBP 11 500 per patient in either treatment arm, with all costs for the initial investment into HM and fees for ongoing remote monitoring included. Fewer inappropriate shocks (−51%) reduce the need for replacing devices for battery exhaustion (−7%); the number of FU visits is predicted to be halved by HM. Conclusion From a UK National Health Service perspective, HM is cost neutral over 10 years. This is mainly accomplished by reducing the number of battery charges and inappropriate shocks, resulting in fewer device replacements, and by reducing the number of in-clinic FU visits.

Selective site right ventricular pacing

The right ventricular apex (RVA) has been the elective site for placing endocardial pacing leads since 1959 when Furman described the use of the transvenous route for pacemaker implantation. This site was used because it is easily accessible, readily identified and associated with a stable position and reliable chronic pacing parameters. It was recognised, however, that pacing from the RVA did not reproduce normal ventricular conduction or contraction. With the advent of reliable active fixation leads, alternative right ventricular sites became accessible and began to be explored. In this review, the detrimental effects of RVA pacing are outlined, the right ventricular outflow tract is defined and the evidence for selective site pacing is discussed.

Cardiac resynchronisation therapy: Evidence based benefits and patient selection

Despite the improvement in pharmacologic treatment of heart failure, many patients continue to have severe persistent symptoms, and their prognosis remains poor. One of the most recent advances in heart failure management is the concept of cardiac resynchronization therapy (CRT) with right and left ventricular pacing. Large clinical trials have demonstrated morbidity and mortality benefits of CRT in patients with moderate to severe drug refractory heart failure (New York Heart Association (NYHA) functional class III or IV), and ejection fraction < or = 35% with QRS duration > or = 120 ms. Despite the documented benefits, 20-30% of patients selected to have CRT do not respond to this treatment. Echocardiography will probably play a more important role in better selecting patients with mechanical dyssynchrony who are more likely to respond to CRT. This article reviews the available evidence for CRT as well as the way to select responders to this rather invasive therapy.

Wound haematoma following defibrillator implantation: incidence and predictors in the Shockless Implant Evaluation (SIMPLE) trial

Aims Pocket haematoma is a common complication after defibrillator [implantable cardioverter defibrillator (ICD)] implantation, which is not only painful, but also increases the risk of device-related infection, and possibly embolic events. The present study seeks to evaluate the rate and predictors of clinically significant pocket haematoma. Methods and results This study included 2500 patients receiving an ICD in the SIMPLE trial. A clinically significant pocket haematoma was defined as a haematoma that required re-operation or interruption of oral anticoagulation (OAC) therapy. Clinically significant pocket haematoma occurred in 56 of 2500 patients (2.2%) of which 6 (10.7%) developed device-related infection. Patients who developed pocket haematoma were older (mean age 67.6 ± 8.8 years vs. 62.7 ± 11.6 years, P < 0.001), were more likely to have permanent atrial fibrillation (30.4 vs. 6.7%, P < 0.001) and a history of stroke (17.9 vs. 6.7%, P = 0.004), or were more likely to receive peri-operative OAC (50.0 vs. 28.4%, P < 0.001), unfractionated heparin (16.1 vs. 5.2%, P = 0.003), or low-molecular-weight heparin (37.5 vs. 17.5%, P < 0.001). Independent predictors of wound haematoma on multivariable analysis included the use of heparin bridging (OR 2.65, 95% CI 1.48-4.73, P = 0.001), sub-pectoral location of ICD (OR 2.00, 95% CI 1.12-3.57, P =0.020), previous stroke (OR 2.47, 95% CI 1.20-5.10, P = 0.015), an upgrade from permanent pacemaker (OR 2.52, 95% CI 1.07-5.94, P = 0.035), and older age (OR 1.03, 95% CI 1.00-1.06, P = 0.049). Conclusion Pocket haematoma remains an important complication of ICD implantation and is associated with a high risk of infection. Independent predictors of pocket haematoma include heparin bridging, prior stroke, sub-pectoral placement of ICD, older age, and upgrade from a pacemaker.