for people with moderate to severe left ventricular systolic heart failure (nyha class ii–iv), which enhances both the strength of ventricular contraction and the heart's pumping capacity. the ccm mechanism is based on stimulation of the cardiac muscle by nonexcitatory electrical signals, which are delivered by a pacemaker-like device. ccm is particularly suitable for the treatment of heart failure with normal qrs complex duration (120 ms or less) and has been demonstrated to improve the symptoms, quality of life, and exercise tolerance. ccm is approved for use in europe, and was approved by the food and drug administration for use in the united states in 2019. about one-third of people with lvef below 35% have markedly altered conduction to the ventricles, resulting in dyssynchronous depolarization of the right and left ventricles. this is especially problematic in people with left bundle branch block (blockage of one of the two primary conducting fiber bundles that originate at the base of the heart and carry depolarizing impulses to the left ventricle). using a special pacing algorithm, biventricular cardiac resynchronization therapy (crt) can initiate a normal sequence of ventricular depolarization. in people with lvef below 35% and prolonged qrs duration on ecg (lbbb or qrs of 150 ms or more), an improvement in symptoms and mortality occurs when crt is added to standard medical therapy. however, in the two-thirds of people without prolonged qrs duration, crt may actually be harmful. surgical therapies people with the most severe heart failure may be candidates for ventricular assist devices, which have commonly been used as a bridge to heart transplantation, but have been used more recently as a destination treatment for advanced heart failure. in select cases, heart transplantation can be considered. while this may resolve the problems associated with heart failure, the person must generally remain on an immunosuppressive regimen to prevent rejection, which has its own significant downsides. a major limitation of this treatment option is the scarcity of hearts available for transplantation. palliative care people with heart failure often have significant symptoms, such as shortness of breath and chest pain. palliative care should be initiated early in the hf trajectory, and should not be an option of last resort. palliative care can not only provide symptom management, but also assist with advanced care planning, goals of care in the case of a significant decline, and making sure the person has a medical power of attorney and discussed his or her wishes with this individual. a 2016 and 2017 review found that palliative care is associated with improved outcomes, such as quality of life, symptom burden, and satisfaction with care. without transplantation, heart failure may not be reversible and heart function typically deteriorates with time. the growing number of people with stage iv heart failure (intractable symptoms of fatigue, shortness of breath, or chest pain at rest despite optimal medical therapy) should be considered for palliative care or hospice, according to american college of cardiology/american heart association guidelines. prognosis prognosis in heart failure can be assessed in multiple ways, including clinical prediction rules and cardiopulmonary exercise testing. clinical prediction rules use a composite of clinical factors such as laboratory tests and blood pressure to estimate prognosis. among several clinical prediction rules for prognosticating acute heart failure, the 'effect rule' slightly outperformed other rules in stratifying people and identifying those at low risk of death during hospitalization or within 30 days. easy methods for identifying people that are low-risk are: adhere tree rule indicates that people with blood urea nitrogen < 43 mg/dl and systolic blood pressure at least 115 mm hg have less than 10% chance of inpatient death or complications. bwh rule indicates that people with systolic blood pressure over 90 mm hg, respiratory rate of 30 or fewer breaths per minute, serum sodium over 135 mmol/l, and no new st–t wave changes have less than 10% chance of inpatient death or complications. a very important method for assessing prognosis in people with advanced heart failure is cardiopulmonary exercise testing (cpx testing). cpx testing is usually required prior to heart transplantation as an indicator of prognosis. cpx testing involves measurement of exhaled oxygen and carbon dioxide during exercise. the peak oxygen consumption (vo2 max) is used as an indicator of prognosis. as a general rule, a vo2 max less than 12–14 cc/kg/min indicates poor survival and suggests that the person may be a candidate for a heart transplant. people with a vo2 max <10 cc/kg/min have a clearly poorer prognosis. the most recent international society for heart and lung transplantation guidelines also suggest two other parameters that can be used for evaluation of prognosis in advanced heart failure, the heart failure survival score and the use of a criterion of ve/vco2 slope > 35 from the cpx test. the heart failure survival score is calculated using a combination of clinical predictors and the vo2 max from the cpx test. heart failure is associated with significantly reduced physical and mental health, resulting in a markedly decreased quality of life. with the exception of heart failure caused by reversible conditions, the condition usually worsens with time. although some people survive many years, progressive disease is associated with an overall annual mortality rate of 10%. around 18 of every 1000 persons will experience an ischemic stroke during the first year after diagnosis of hf. as the duration of follow-up increases, the stroke rate rises to nearly 50 strokes per 1000 cases of hf by 5 years. epidemiology in 2022, heart failure affected about 64 million people globally. overall, around 2% of adults have heart failure. in those over the age of 75, rates are greater than 10%. rates are predicted to increase. increasing rates are mostly because of increasing lifespan, but also because of increased risk factors (hypertension, diabetes, dyslipidemia, and obesity) and improved survival rates from other types of cardiovascular disease (myocardial infarction, valvular disease, and arrhythmias). heart failure is the leading cause of hospitalization in people older than 65. united states in the united states, heart failure affects 5.8 million people, and each year 550,000 new cases are diagnosed. in 2011, heart failure was the most common reason for hospitalization for adults aged 85 years and older, and the second-most common for adults aged 65–84 years. an estimated one in five adults at age 40 will develop heart failure during their remaining lifetimes and about half of people who develop heart failure die within 5 years of diagnosis. heart failure is much higher in african americans, hispanics, native americans, and recent immigrants from eastern europe countries such as russia. this high prevalence in these ethnic minority populations has been linked to high incidence of diabetes and hypertension. in many new immigrants to the u.s., the high prevalence of heart failure has largely been attributed to lack of preventive health care or substandard treatment. nearly one of every four people (24.7%) hospitalized in the u.s. with congestive heart failure are readmitted within 30 days. additionally, more than 50% of people seek readmission within 6 months after treatment and the average duration of hospital stay is 6 days. heart failure is a leading cause of hospital readmissions in the u.s. people aged 65 and older were readmitted at a rate of 24.5 per 100 admissions in 2011. in the same year, people under medicaid were readmitted at a rate of 30.4 per 100 admissions, and uninsured people were readmitted at a rate of 16.8 per 100 admissions. these are the highest readmission rates for both categories. notably, heart failure was not among the top-10 conditions with the most 30-day readmissions among the privately insured. united kingdom in the uk, despite moderate improvements in prevention, heart failure rates have increased due to population growth and ageing. overall heart failure rates are similar to the four most common causes of cancer (breast, lung, prostate, and colon) combined. people from deprived backgrounds are more likely to be diagnosed with heart failure and at a younger age. developing world in tropical countries, the most common cause of heart failure is valvular heart disease or some type of cardiomyopathy. as underdeveloped countries have become more affluent, the incidences of diabetes, hypertension, and obesity have increased, which have in turn raised the incidence of heart failure. sex men have a higher incidence of heart failure, but the overall prevalence rate is similar in both sexes since women survive longer after the onset of heart failure. women tend to be older when diagnosed with heart failure (after menopause), they are more likely than men to have diastolic dysfunction, and seem to experience a lower overall quality of life than men after diagnosis. ethnicity some sources state that people of asian descent are at a higher risk of heart failure than other ethnic groups. other sources however have found that rates of heart failure are similar to rates found in other ethnic groups. history for centuries, the disease entity which would include many cases of what today would be called heart failure was dropsy; the term denotes generalized edema, a major manifestation of a failing heart, though also caused by other diseases. writings of ancient civilizations include evidence of their acquaintance with dropsy and heart failure: egyptians were the first to use bloodletting to relieve fluid accumulation and shortage of breath, and provided what may have been the first documented observations on heart failure in the ebers papurus (around 1500 bce); greeks described cases of dyspnea, fluid retention and fatigue compatible with heart failure; romans used the flowering plant drimia maritima (sea squill), which contains cardiac glycosides, for the treatment of dropsy; descriptions pertaining to heart failure are also known in the civilizations of ancient india and china. however, the manifestations of failing heart were understood in the context of these peoples' medical theories – including ancient egyptian religion, hippocratic theory of humours, or ancient indian and chinese medicine, and the current concept of heart failure had not developed yet. although shortage of breath had been connected to heart disease by avicenna round 1000 ce, decisive for modern understanding of the nature of the condition were the description of pulmonary circulation by ibn al-nafis in the 13th century, and of systemic circulation by william harvey in 1628. the role of the heart in fluid retention began to be better appreciated, as dropsy of the chest (fluid accumulation in and round the lungs causing shortage of breath) became more familiar and the current concept of heart failure, which brings together swelling and shortage of breath due to fluid retention, began to be accepted, in the 17th and especially in the 18th century: richard lower linked dyspnea and foot swelling in 1679, and giovanni maria lancisi connected jugular vein distention with right ventricular failure in 1728. dropsy attributable to other causes, e.g. kidney failure, was differentiated in the 19th century. the stethoscope, invented by rené laennec in 1819, x-rays, discovered by wilhelm röntgen in 1895, and electrocardiography, described by willem einthoven in 1903, facilitated the investigation of heart failure. 19th century also saw experimental and conceptual advances in the physiology of heart contraction, which led to the formulation of the frank-starling law of the heart (named after physiologists otto frank and ernest starling), a remarkable advance in understanding mechanisms of heart failure. one of the earliest treatments of heart failure, relief of swelling by bloodletting with various methods, including leeches, continued through the centuries. along with bloodletting, jean-baptiste de sénac in 1749 recommended opiates for acute shortage of breath due to heart failure. in 1785, william withering described the therapeutic uses of the foxglove genus of plants in the treatment of edema; their extract contains cardiac glycosides, including digoxin, still used today in the treatment of heart failure. the diuretic effects of inorganic mercury salts, which were used to treat syphilis, had already been noted in the 16th century by paracelsus; in the 19th century they were used by noted physicians like john blackall and william stokes. in the meantime, cannulae (tubes) invented by english physician reginald southey in 1877 was another method of removing excess fluid by directly inserting into swollen limbs. use of organic mercury compounds as diuretics, beyond their role in syphilis treatment, started in 1920, though it was limited by their parenteral route of administration and their side-effects. oral mercurial diuretics