Maintaining physical fitness of patients with chronic heart failure: a randomized controlled trial

Cardiac Rehabilitation and Heart Failure with Reduced Ejection Fraction: Pathophysiology, Benefits, and Precautions

Heart failure (HF) is a highly comorbid condition associated with significant mortality, despite advances in current medical management. Patients who suffer from HF represent a high needs disease care population in whom structured, long-term chronic disease care delivery models, such as cardiac rehabilitation (CR), have been shown to be highly cost effective in reducing hospitalizations and improving quality of life. HF with reduced ejection fraction affects a growing number of Canadians and health care costs secondary to this condition are increasing, with further increases over the next decade to be expected. CR is a guideline-directed medical therapy for patients living with HF with reduced ejection fraction, and with increasing numbers of HF patients across the world, there is a prescient need to revisit the benefits, safety, and the prescription of this intervention for the health care professionals who treat this condition. Certainly, there is a clinical need for HF practitioners to better understand the pathophysiological benefits of CR with respect to exercise training, as well as the prudent precautions required to facilitate the safe delivery of this highly cost-effective patient intervention.

The Effects of Aquatic Exercise Training on Functional and Hemodynamic Responses in Patients With Heart Failure: A Systematic Review and Meta-Analysis

Objective: This study aimed to investigate the impacts of water exercise training on functional and hemodynamic responses in HF patients. Methods: A systematic review and meta-analysis were conducted until February 15, 2024, using multiple databases. Mean difference (MD) with corresponding 95% confidence intervals (CIs) were calculated. Results: Sixteen studies, comprising 349 participants with HF, were included. Water exercise led to enhancements in peak VO2 (MD, 2.85 mL/kg/min; 95% CI, 1.89 to 3.80; p < .00001) and resting heart rate (MD, -4.16 bm; 95% CI, -6.85 to -1.46; p = .002) compared to no exercising controls. Water plus land exercise reduced resting heart rate (MD, -1.41 bm; 95% CI, -2.13 to -0.69; p = .0001) compared to land exercise alone. Furthermore, acute water exercises decreased resting heart rate (MD, -3.85 bm; 95% CI, -6.49 to -1.21; p = .004) and increased stroke volume (MD, 14.68 mL/beat; 95% CI, 8.57 to 20.79; p < .00001) and cardiac output (MD, 0.5 L/min; 95% CI, 0.27 to 0.73; p < .00001) compared to baseline. Conclusion: These findings suggest that water exercise holds promise as an effective intervention for enhancing functional capacity and hemodynamic parameters in individuals with HF, highlighting the importance of further research to optimize its implementation and elucidate long-term benefits.

The left ventricular assist device 'skeleton man': case report-simple tools for skeletal muscle evaluation and very early aerobic/resistance/inspiratory training in cardiac cachexia

Background

Skeletal muscle wasting (SMW) is highly prevalent in patients with heart failure (HF) at left ventricular assist device (LVAD) implantation and is associated with morbidity and mortality. At the same time, SMW is clinically under-recognized, while exercise training (ET) studies in weak LVAD patients are lacking.

Case summary

A 60-year-old man with advanced HF, SMW, cardiac cachexia, and frailty was confined in bed for 6 months initially supported with intravenous inotropes and subsequently with an intra-aortic balloon pump. His frailty was recognized as an LVAD-responsive frailty, and patient was successfully implanted with a HeartWare (Medtronic). Post-surgery, patient was very weak, unable even to move in bed without assistance. We evaluated skeletal muscle using simple tools such as the Oxford scale, mid-thigh circumference, hand-held dynamometry, and maximum inspiratory pressure. Physical performance was assessed with the sit to stand test, gait speed test, pedal bike timing, and the 6 min walk test. On top of routine physiotherapy, patient underwent an 8-week modified aerobic/resistance/inspiratory (ARIS) ET programme at moderate intensity and showed significant improvements in skeletal muscle mass and strength and physical and functional capacity.

Discussion

We want to emphasize the importance of skeletal muscle evaluation at LVAD implantation and the feasibility and effectiveness of early ARIS training in very weak patients.

Effects of exercise-based cardiac rehabilitation delivery modes on exercise capacity and health-related quality of life in heart failure: a systematic review and network meta-analysis

Background

This review aimed to compare the relative effectiveness of different exercise-based cardiac rehabilitation (ExCR) delivery modes (centre-based, home-based, hybrid and technology-enabled ExCR) on key heart failure (HF) outcomes: exercise capacity, health-related quality of life (HRQoL), HF-related hospitalisation and HF-related mortality.

Methods and results

Randomised controlled trials (RCTs) published through 20 June 2021 were identified from six databases, and reference lists of included studies. Risk of bias and certainty of evidence were evaluated using the Cochrane tool and Grading of Recommendations Assessment, Development and Evaluation, respectively. Bayesian network meta-analysis was performed using R. Continuous and binary outcomes are reported as mean differences (MD) and ORs, respectively, with 95% credible intervals (95% CrI). One-hundred and thirty-nine RCTs (n=18 670) were included in the analysis. Network meta-analysis demonstrated improvements in VO₂peak following centre-based (MD (95% CrI)=3.10 (2.56 to 3.65) mL/kg/min), home-based (MD=2.69 (1.67 to 3.70) mL/kg/min) and technology-enabled ExCR (MD=1.76 (0.27 to 3.26) mL/kg/min). Similarly, 6 min walk distance was improved following hybrid (MD=84.78 (31.64 to 138.32) m), centre-based (MD=50.35 (30.15 to 70.56) m) and home-based ExCR (MD=36.77 (12.47 to 61.29) m). Incremental shuttle walk distance did not improve following any ExCR delivery modes. Minnesota living with HF questionnaire improved after centre-based (MD=−10.38 (−14.15 to –6.46)) and home-based ExCR (MD=−8.80 (−13.62 to –4.07)). Kansas City Cardiomyopathy Questionnaire was improved following home-based ExCR (MD=20.61 (4.61 to 36.47)), and Short Form Survey 36 mental component after centre-based ExCR (MD=3.64 (0.30 to 6.14)). HF-related hospitalisation and mortality risks reduced only after centre-based ExCR (OR=0.41 (0.17 to 0.76) and OR=0.42 (0.16 to 0.90), respectively). Mean age of study participants was only associated with changes in VO₂peak.

Conclusion

ExCR programmes have broader benefits for people with HF and since different delivery modes were comparably effective for improving exercise capacity and HRQoL, the selection of delivery modes should be tailored to individuals’ preferences.

Cardiac telerehabilitation as an alternative to centre-based cardiac rehabilitation

Multidisciplinary cardiac rehabilitation (CR) reduces morbidity and mortality and increases quality of life in cardiac patients. However, CR utilisation rates are low, and targets for secondary prevention of cardiovascular disease are not met in the majority of patients, indicating that secondary prevention programmes such as CR leave room for improvement. Cardiac telerehabilitation (CTR) may resolve several barriers that impede CR utilisation and sustainability of its effects. In CTR, one or more modules of CR are delivered outside the environment of the hospital or CR centre, using monitoring devices and remote communication with patients. Multidisciplinary CTR is a safe and at least equally (cost-)effective alternative to centre-based CR, and is therefore recommended in a recent addendum to the Dutch multidisciplinary CR guidelines. In this article, we describe the background and core components of this addendum on CTR, and discuss its implications for clinical practice and future perspectives.

The sustained effects of extending cardiac rehabilitation with a six-month telemonitoring and telecoaching programme on fitness, quality of life, cardiovascular risk factors and care utilisation in CAD patients: The TeleCaRe study

INTRODUCTION

The aim of this study was to assess the acute and sustained effects of a six-month heart-rate-based telerehabilitation programme, following the completion of cardiac rehabilitation (CR), on peak oxygen uptake (peakVO₂), quality of life (QoL), cardiovascular risk factors and care utilisation in patients with coronary artery disease (CAD).

METHODS

A total of 122 patients with CAD were randomised, after the completion of CR, to an intervention group with six months of telemonitoring and telecoaching (TELE) or a control group with a traditional six-month follow-up programme with monthly calls (CON). The primary outcome was peakVO₂ at 12 months, to assess the sustained effects of TELE. The secondary outcomes included QoL, cardiovascular risk factors (lipid spectrum), major adverse cardiovascular events (MACE) and habitual physical activity.

RESULTS

PeakVO₂ increased significantly from baseline to 12 months in TELE (+2.5 mL·kg^-1min^-1 (95% CI 1.5-3.2)) and CON (+1.9 mL·kg^-1min^-1 (95% CI 1.0-2.5)), and did not differ between groups (P = 0.28). Similarly, QoL (P = 0.31), total cholesterol (P = 0.45), MACE (P = 0.86) did not differ between groups and in time.

DISCUSSION

Extending CR with a heart-rate-based telerehabilitation programme did not yield additional sustainable health benefits compared with regular care with monthly telephone calls. These observations highlight that both telerehabilitation and regular care with monthly telephone calls may prevent the typically observed reductions in peakVO₂ following the completion of a CR programme.Trial registration: Dutch Trial Register NL4140 (registered 6 December 2014).

Impact of a Graded Exercise Program on V˙O2peak and Survival in Heart Failure Patients

INTRODUCTION

Although exercise therapy has the potential to improve health outcomes of patients with chronic heart failure (CHF), less than 50% of patients adhere to prescribed physical activity guidelines 1 yr after cardiac rehabilitation. We aimed to assess the effects of an extended cardiac rehabilitation program with 12 months of graded exercise therapy (GET) and resistance exercise training (RT) on exercise capacity and long-term survival in patients with CHF.

METHODS

This prospective cohort study included 60 CHF patients between 2009 and 2010. The GET-RT program consisted of exercise sessions at 6 d·wk. Total training time of aerobic exercises increased incrementally every other week without changing exercise intensity. Resistance exercise training consisted of 8 exercises with a durable resistance band. Guidance consisted of a step-down approach from in-hospital to home-based training. Cardiopulmonary exercise tests were performed at baseline, 3, 6, and 12 months. Subsequently, patients were propensity score matched on a 1:2 ratio with controls (n = 117) from a CHF registry of patients from the same clinic receiving usual out-patient care and the incidence of all-cause mortality was compared between both groups.

RESULTS

Baseline V˙O2 peak was 15.0 mL·min·kg and significantly elevated at 3 months (+1.1 mL·min·kg (95% CI, 0.4-1.8), 6 months (+2.9 mL·min·kg (95% CI, 1.1-2.9) and 12 months (+2.6 mL·min·kg (95% CI, 1.4-3.8). During 8 yr of follow-up 23 (38.3%) patients of the GET-RT program died versus 63 (53.8%) patients of the control group (P = 0.063).

CONCLUSIONS

The 12-month GET-RT program was associated with an improved fitness during 1-yr follow-up, whereas a tendency toward better survival rates was observed during long-term follow-up.

Exercise Training in Heart Failure Patients With Persistent Atrial Fibrillation: a Practical Approach

Persistent AF is present in at least 20 % of patients with chronic heart failure (CHF) and is related to a poor prognosis and more severe cardiac arrhythmias. CHF and AF share a common pathophysiology and can exacerbate one another. Exercise programmes for people with CHF have been shown to improve aerobic capacity, prognosis and quality of life. Given that patients with both CHF and AF show greater impairment in exercise performance, exercise training programmes have the potential to be highly beneficial. Optimal clinical evaluation using a cardiopulmonary exercise test should be performed before starting a training programme. Heart rate should be calculated over a longer period of time In patients with CHF and AF than those in sinus rhythm. The use of telemetry is advised to measure HR accurately during training. If telemetry is not available, patients can be safely trained based on the concomitant workload. An aerobic exercise training programme of moderate to high intensity, whether or not combined with strength training, is advised in patients with CHF and AF. Optimal training modalities and their intensity require further investigation.

The influence of training characteristics on the effect of exercise training in patients with coronary artery disease: Systematic review and meta-regression analysis

BACKGROUND

Although exercise-based cardiac rehabilitation improves exercise capacity of coronary artery disease patients, it is unclear which training characteristic determines this improvement. Total energy expenditure and its constituent training characteristics (training intensity, session frequency, session duration and programme length) vary considerably among clinical trials, making it hard to compare studies directly. Therefore, we performed a systematic review and meta-regression analysis to assess the effect of total energy expenditure and its constituent training characteristics on exercise capacity.

METHODS

We identified randomised controlled trials comparing continuous aerobic exercise training with usual care for patients with coronary artery disease. Studies were included when training intensity, session frequency, session duration and programme length was described, and exercise capacity was reported in peakVO₂. Energy expenditure was calculated from the four training characteristics. The effect of training characteristics on exercise capacity was determined using mixed effects linear regression analyses. The analyses were performed with and without total energy expenditure as covariate.

RESULTS

Twenty studies were included in the analyses. The mean difference in peakVO₂ between the intervention group and control group was 3.97ml·min^-1·kg^-1 (p<0.01, 95% CI 2.86 to 5.07). Total energy expenditure was significantly related to improvement of exercise capacity (effect size 0.91ml·min^-1·kg^-1 per 100J·kg, p<0.01, 95% CI 0.77 to 1.06), no effect was found for its constituent training characteristics after adjustment for total energy expenditure.

CONCLUSIONS

We conclude that the design of an exercise programme should primarily be aimed at optimising total energy expenditure rather than on one specific training characteristic.

Aquatic Exercise Training is Effective in Maintaining Exercise Performance in Trained Heart Failure Patients: A Randomised Crossover Pilot Trial

BACKGROUND

Providing flexible models and a variety of exercise options are fundamental to supporting long-term exercise participation for patients with heart failure (HF). The aim of this pilot study was to determine the feasibility and efficacy of aquatic exercise training during a maintenance phase for a clinical heart failure population.

METHODS

In this 2 x 2 crossover design trial, individuals who had previously completed HF rehabilitation were randomised into either a land-based or aquatic training program once per week for six weeks, after which time they changed to the alternate exercise training protocol for an additional six weeks. Six-minute walk test (6MWT), grip strength, walk speed, and measures of balance were compared for the two training protocols.

RESULTS

Fifty-one participants (43 males, mean age 69.2 yrs) contributed data for the analysis. Both groups maintained function during the follow-up period, however improvements in 6MWT were greater in the land-based training group (95% CI: 0.7, 22.5; p=0.038), by a mean difference of 10.8 metres. No significant difference was observed for other parameters when the two training protocols were compared.

CONCLUSION

Attending an aquatic exercise program once per week is feasible for patients with stable HF and may provide a suitable option to maintain functional performance in select patients.

The influence of training characteristics on the effect of aerobic exercise training in patients with chronic heart failure: A meta-regression analysis

Although aerobic exercise training has shown to be an effective treatment for chronic heart failure patients, there has been a debate about the design of training programs and which training characteristics are the strongest determinants of improvement in exercise capacity. Therefore, we performed a meta-regression analysis to determine a ranking of the individual effect of the training characteristics on the improvement in exercise capacity of an aerobic exercise training program in chronic heart failure patients. We focused on four training characteristics; session frequency, session duration, training intensity and program length, and their product; total energy expenditure. A systematic literature search was performed for randomized controlled trials comparing continuous aerobic exercise training with usual care. Seventeen unique articles were included in our analysis. Total energy expenditure appeared the only training characteristic with a significant effect on improvement in exercise capacity. However, the results were strongly dominated by one trial (HF-action trial), accounting for 90% of the total patient population and showing controversial results compared to other studies. A repeated analysis excluding the HF-action trial confirmed that the increase in exercise capacity is primarily determined by total energy expenditure, followed by session frequency, session duration and session intensity. These results suggest that the design of a training program requires high total energy expenditure as a main goal. Increases in training frequency and session duration appear to yield the largest improvement in exercise capacity.

[Exercise training as a key component of heart failure therapy]

Physical exercise has been recognized as a standard therapy in the guidelines for secondary prevention of chronic heart failure. In clinical practice its benefits are widely underestimated. It is still too rarely applied as a therapeutic component, despite overwhelming scientific evidence, including meta-analyses illustrating the positive effect on exercise capacity, quality of life and hospitalization. It is crucial that patients undergo a thorough clinical investigation, including exercise testing and are in a clinically stable condition for at least 6 weeks under optimal guideline-conform medicinal therapy before exercise training is initiated. Moreover, it is important that only approved exercise regimens should be prescribed and exercise sessions should be appropriately monitored. Both moderate continuous endurance training and recently developed interval training have been shown to be safe and effective in chronic heart failure. Ideally, endurance training should be combined with moderate resistance training. Current evidence clearly demonstrates a dose-response relationship in the way that beneficial effects of exercise training are strongly related to factors such as exercise duration and intensity. Development of strategies that support long-term adherence to exercise training are a crucial challenge for both daily practice and future research.

Aerobic exercise effect on prognostic markers for systolic heart failure patients: a systematic review and meta-analysis

From previous systematic reviews and meta-analyses, there is consensus about the positive effect of exercise training on exercise capacity for systolic heart failure (HF); however, the effect on actual prognostic markers such as NTproBNP and minute ventilation/carbon dioxide production (VE/VCO2) slope has not been evaluated. The primary aim of the proposed study is to determine the effect of aerobic exercise training (AEX) on the VE/VCO2 slope and NTproBNP. The following databases (up to February 30, 2013) were searched with no language limitations: CENTRAL (The Cochrane Library 2013, issue 2), MEDLINE (from January 1966), EMBASE (from January 1980), and Physiotherapy Evidence Database (PEDro) (from January 1929). We screened reference lists of articles and also conducted an extensive hand search of the literature. Randomized controlled trials of exercise-based interventions with 2-month follow-up or longer compared to usual medical care or placebo were included. The study population comprised adults aged between 18 and 65 years, with evidence of chronic systolic heart failure (LVEF < 45 % and baseline NTproBNP > 300 pg/ml). Two review authors independently extracted data on study design, participants, interventions, and outcomes. We assessed the risk of bias using PEDro scale. We calculated mean differences (MD) or standardized mean differences between intervention and control groups for outcomes with sufficient data; for other outcomes, we described findings from individual studies. Eight studies involving a total of 408 participants met the inclusion criteria across the NTproBNP (5 studies with 191 patients) and VE/VCO2 slope (4 studies with 217 patients). Aerobic exercise significantly improved NTproBNP by a MD of -817.75 [95 % confidence interval (CI) -929.31 to -706.19]. Mean differences across VE/VCO2 slope were -6.55 (95 % CI -7.24 to -5.87). Those patients' characteristics and exercise were similar (frequency = 3-5 times/week; duration = 20-50 min/day; intensity = 60-80 % of VO2 peak) on the included studies. Moreover, the risk of bias across all studies was homogeneous (PEDro scale = 7-8 points). However, based on the statistical analysis, the heterogeneity among the studies was still high, which is related to the variable characteristics of the studies. Aerobic exercise may be effective at improving NTproBNP and the VE/VCO2 slope in systolic HF patients, but these effects are limited to a specific HF population meeting specific inclusion criterion in a limited number of studies. Future randomized controlled studies including diastolic and HF overleap with pulmonary diseases are needed to better understand the exact influence of AEX.

Cardiac rehabilitation is associated with lasting improvements in cognitive function in older adults with heart failure

OBJECTIVE

Heart failure (HF) is a known risk factor for cognitive impairment. Cardiac rehabilitation (CR) may attenuate poor neurocognitive outcomes in HF via improved physical fitness--a significant promoter of cognitive function. However, no study has examined the possible acute and lasting benefits of CR on cognitive function in persons with HF.

METHODS AND RESULTS

Fifty-two patients with HF completed a 12-week Phase II CR program. All participants were administered neuropsychological testing and completed a brief physical fitness assessment at baseline, completion of CR (i.e. 12 weeks), and 12-month follow-up. Repeated measures analyses showed a significant time effect for both attention/executive function and memory (P < 0.05). Attention/executive function performance increased from baseline to 12 weeks and these gains remained up to 12 months; memory was unchanged from baseline to 12 weeks, but then improved between the 12-week and 12-month time points. Physical fitness improved from baseline to 12 weeks and these benefits were maintained 12 months later. Changes in physical fitness and cognitive function over time did not reach a statistically significant association, though poorer physical fitness was associated with decreased cognitive performance at the baseline and 12-month time points.

CONCLUSIONS

CR is associated with both acute and lasting cognitive benefits in patients with HF. Prospective studies with extended follow-ups are needed to clarify the mechanisms that underpin cognitive improvements following CR (e.g., improved cerebral perfusion) and whether CR can ultimately reduce risk for cognitive decline and conditions like Alzheimer's disease in HF.

Implementing a community-based model of exercise training following cardiac, pulmonary, and heart failure rehabilitation

PURPOSE

Encouraging patients to continue regular activity beyond the period of formal cardiac, heart failure, or pulmonary rehabilitation is a challenge faced by all program coordinators. The purpose of this study was to evaluate the feasibility of a community model run by fitness instructors as long-term maintenance for patients exiting a disease-specific rehabilitation program.

METHODS

Heartmoves programs were established in close proximity to all major tertiary hospitals in Brisbane, Queensland, Australia, and all eligible patients were offered supported referral to a program. Referred patients and rehabilitation staff were surveyed regarding perceived barriers to attendance. Referral rates and individual attendance rates for the first 12 weeks were recorded.

RESULTS

Over 12 months, 241 patients were referred to a community Heartmoves class, of whom 141 (59%) attended at least once and 76 (32% of referrals, 54% of initial attendees) attended more than 6 of the first 12 weeks. Preattendance surveys identified concerns about quality and safety, as well as social and logistic barriers. The programs proved to be sustainable, as evidenced by the growth of programs from 18 at the end of the project to 31 over a 18-month period.

CONCLUSIONS

A supported referral pathway to Heartmoves provides a feasible and acceptable model for maintenance exercise following cardiac, heart failure, and pulmonary rehabilitation. Strategies that recognize and address barriers perceived by participants and by rehabilitation program staff should be part of the supported referral process.

Endurance exercise intensity determination in the rehabilitation of coronary artery disease patients: a critical re-appraisal of current evidence

In the care of coronary artery disease (CAD) patients, the benefits of exercise therapy are generally established. Even though the selected endurance exercise intensity might affect medical safety, therapy adherence and effectiveness in the rehabilitation of CAD patients in how to determine endurance exercise intensity properly remains difficult. The aim of this review is to describe the available methods for endurance exercise intensity determination in the rehabilitation of CAD patients, accompanied with their (dis)advantages, validity and reproducibility. In general, endurance exercise intensity can objectively be determined in CAD patients by calculating a fraction of maximal exercise tolerance and/or determining ventilatory threshold after execution of a cardiopulmonary exercise test with ergospirometry. This can be translated to a corresponding training heart rate (HR) or workload. In the absence of ergospirometry equipment, target exercise HR can be calculated directly by different ways (fraction of maximal HR and/or Karvonen formula), and/or anaerobic threshold can be determined. However, the use of HR for determining exercise intensity during training sessions seems complicated, because many factors/conditions affect the HR. In this regard, proper standardization of the exercise sessions, as well as exercise testing, might be required to improve the accuracy of exercise intensity determination. Alternatively, subjective methods for the determination of endurance exercise intensity in CAD patients, such as the Borg ratings of perceived exertion and the talk test, have been developed. However, these methods lack proper validity and reliability to determine endurance exercise intensity in CAD patients. In conclusion, a practical and systematic approach for the determination of endurance exercise intensity in CAD patients is presented in this article.

Adherence of heart failure patients to exercise: barriers and possible solutions: a position statement of the Study Group on Exercise Training in Heart Failure of the Heart Failure Association of the European Society of Cardiology

The practical management of heart failure remains a challenge. Not only are heart failure patients expected to adhere to a complicated pharmacological regimen, they are also asked to follow salt and fluid restriction, and to cope with various procedures and devices. Furthermore, physical training, whose benefits have been demonstrated, is highly recommended by the recent guidelines issued by the European Society of Cardiology, but it is still severely underutilized in this particular patient population. This position paper addresses the problem of non-adherence, currently recognized as a main obstacle to a wide implementation of physical training. Since the management of chronic heart failure and, even more, of training programmes is a multidisciplinary effort, the current manuscript intends to reach cardiologists, nurses, physiotherapists, as well as psychologists working in the field.

Integration target site selection for retroviruses and transposable elements

When a retrovirus infects a cell, its RNA genome is reverse transcribed into a double-stranded DNA, which is then permanently integrated into the host chromosome. Integration is one of the essential steps in the retroviral life cycle. Many transposable elements also move around and integrate into the host genome as part of their life cycle, some through RNA intermediates and some through 'cut and paste' mechanisms. Integration of retroviruses and transposable elements into 'sensitive areas' of the genome can cause irreparable damage. On the other hand, because of their ability to integrate permanently, and the relatively efficient rates of transgenesis, retroviruses and transposable elements are widely used as gene delivery tools in basic research and gene therapy trials. Recent events in gene therapy treatments for X-linked severe combined immunity deficiencies (X-SCID) have highlighted both the promise and some of the risks involved with utilizing retroviruses. Nine of 11 children were successfully treated for X-SCID using a retrovirus carrying the gene mutated in this disease. However, later two of these children developed leukemias because of retroviral integrations in the putative oncogene LMO2 [1]. A third child has also been demonstrated to have an integration in LMO2, but is as of yet nonsymptomatic [2]. It is a bit difficult to explain the high frequency of integrations into the same gene using a random model of retroviral integration, and there has been evidence for decades that retroviral integrations may not be random. But the data were somewhat limited in their power to determine the precise nature of the integration biases. The completion of the human genome sequence coupled with sensitive polymerase chain reaction techniques and an ever-decreasing cost of sequencing has given a powerful new tool to the study of integration site selection. In this review, we describe the findings from several recent global surveys of target site selection by retroviruses and transposable elements, and discuss the possible ramifications of these findings to both mechanisms of action and to the use of these elements as gene therapy vectors.