Vikas Kuriachan, MD, FRCP(C), Fellow, Cardiac Arrhythmia, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB.
Robert Sheldon, MD, PhD, FRCP(C), Professor, Cardiac Sciences, and Associate Dean of
Clinical Research, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB.

The implantable cardioverter defibrillator (ICD) plays an important role in primary and secondary preventions of sudden cardiac death. Several trials conducted in the past few years have shown the superiority of ICDs over drug therapy. Cardiac resynchronization therapy (CRT) is also emerging as an adjunctive treatment for heart failure, with some survival benefits as well. This article reviews the major recent clinical trials of ICD and CRT devices and summarizes their importance in contemporary cardiology.
Key words: cardioverter defibrillator, cardiac resynchronization, older adults, sudden cardiac death, cardiology.

Jeff Silverman, MD, FRCPC, Fellow in Adult Hematology, University of Toronto, Toronto, ON.
William Geerts, MD, FRCPC, Consultant in Clinical Thromboembolism, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, Toronto, ON.

Introduction
Thrombocytopenia, defined as a platelet count of less than 150 x 10⁹/L, is an important clinical problem most commonly encountered in hospitalized patients. Although the differential diagnosis is extensive (Table 1), it is essential to always consider heparin-induced thrombocytopenia (HIT) in patients with thrombocytopenia who are hospitalized or who have recently been in a hospital.^1,2

HIT is an adverse drug reaction induced by exposure to heparin that is followed by thrombocytopenia, platelet activation and a dramatic increase in thrombosis risk. Although it is one of the most common and serious drug reactions in hospitalized patients, HIT is frequently not recognized until a major thromboembolic complication has resulted. However, if diagnosed and treated promptly, the outcome is generally favourable. With the widespread use of heparin in the elderly, geriatric patients constitute the largest population at risk of developing HIT. Therefore, clinicians providing care for the elderly must be able to recognize and manage HIT effectively and efficiently.

Cynthia M. Westerhout, MSc^1,2 and Eric Boersma, PhD¹
From the ¹Department of Cardiology, Erasmus Medical Centre, Rotterdam, The Netherlands and the ²University of Alberta, Edmonton, AB.

Introduction
The chain of events leading to acute coronary syndromes (ACS), including unstable angina (UA) and non-ST-segment elevation (NSTE) or ST-segment elevation myocardial infarction (STEMI), is triggered by the disruption of an atherosclerotic plaque, which leads to the formation of a platelet-rich thrombus within a coronary artery.^1,2 The inhibition of platelet aggregation is fundamental to the treatment of these patients; however, standard antiplatelet agents such as aspirin do not completely obstruct this activity. Advances in understanding the pathophysiology of ACS have to the recognition of the activation of the glycoprotein IIb/IIIa (Gp IIb/IIIa) receptors on platelets as the final common pathway leading to platelet aggregation. With this target in mind, pharmacological treatment of ACS has been propelled into a new era with agents that completely inhibit platelet aggregation.

Anne-Sophie Rigaud, Hôpital Broca, CHU Cochin-Port-Royal, Paris, France.
Bernard Forette, Centre Claude Bernard de Gérontologie, Hôpital Sainte Périne, Paris, France.

Abstract
Diastolic blood pressure is considered an important risk factor for the development of cerebrovascular disease, congestive heart failure and coronary heart disease. However, it is now clear that isolated systolic hypertension and elevated pulse pressure play an important role in the development of these diseases, which are the major causes of cardiovascular morbidity and mortality among subjects aged 65 years and older. The benefit of antihypertensive therapy in reducing the incidence of cardiovascular and cerebrovascular complications has been shown for systolic and systolo-diastolic hypertension in all age groups. Because of the higher risk of cardiovascular disease in the elderly, the effect of antihypertensive treatment appears greater in patients over 60 or 65 years when expressed as an absolute risk reduction.

Definition
Essential (i.e. primary) hypertension is the main cause of hypertension in the elderly population. However, secondary, especially renovascular hypertension is more common in older than in younger adults. The incidence of hypertension in the elderly is high. In an ambulatory population aged 65-74, the overall prevalence is 49.6 % for stage 1 hypertension (140-159/90-99 mmHg), 18.2% for stage 2 (160-179/100-109 mmHg), and 6.

Rodrigo B. Cavalcanti, MD, FRCP(C)
Clinical Assistant, Internal Medicine, University Health Network.

Shabbir M.H. Alibhai, MD, MSc, FRCP(C)
Staff Physician, Internal Medicine and Geriatrics,
University Health Network, Lecturer, Dept. of Medicine,
University of Toronto, Toronto, ON.

Introduction
Syncope is defined as a transient loss of consciousness accompanied by a loss of postural tone, followed by complete, spontaneous recovery.¹ Population-based studies, such as the Framingham study, indicate that the overall incidence of syncope is 3% per year for men and 3.5% per year for women.² Moreover, syncopal events become more frequent with age, with the incidence rising to 6% per year in persons over 75 years of age.²

It is important to note that syncope is fundamentally a symptom, rather than a disease process, with multiple conditions giving rise to this symptom. The common step in most etiologies is a transitory compromise in cerebral blood flow. Impairment in blood flow to the reticular activating system in the brainstem results in loss of consciousness, while lack of perfusion to the corticospinal pathways impairs motor tone.

Currently, it is estimated that between 2-6% of all hospital admissions are for evaluation of syncope or treatment of associated falls, 80% of which are in persons aged 65 years or older.

When to Use a Pacemaker

Naushad Hirani, BSc, MD
Medical Writer,
Geriatrics & Aging.

For over four decades, permanent implantable pacemakers have been routinely used for the treatment of bradyarrhythmias. In that time, the sophistication, capabilities and potential usefulness of pacemakers for a wide variety of indications have grown tremendously. Most pacemaker recipients are elderly; it is estimated that, currently, more than 70% of pacemaker recipients are over the age of 70. The reasons for this preponderance include the changes in the conduction system associated with normal aging, as well as the increased prevalence of coronary artery disease and primary conduction system disease that is observed as age increases.

Approximately two billion beats are required from an average heart over a typical lifetime. Most of these are initiated in the sinus node. With increasing age, the "P" cells that are the main component of the sinus node are progressively replaced by collagen. In addition, the distal portions of the conduction system, the His bundle and the bundle branches show an age-related loss in conducting cells without a concomitant increase in collagen.

Diagnosis and Management of Acute Coronary Syndromes

Nariman Malik, BSc, MD
Medical Writer,
Geriatrics & Aging

Coronary heart disease (CHD) is one of the leading causes of death in individuals over the age of 65¹ and, through a variety of syndromes, is responsible for symptomatic and asymptomatic functional abnormalities. The prevalence of cardiovascular disease increases with age and is a major cause of death and disability in the elderly population.² CHD is the most prevalent cardiac illness in this population: it accounts for 85% of all deaths due to heart disease in persons over the age of 65.³ By age 70, 15% of men and 9% of women have coronary artery disease (CAD) and are at an increased risk of suffering an acute coronary syndrome (ACS).⁴ By age 80, the severity of lesions becomes nearly equal for men and women.⁴ An estimated 40% of all individuals over the age of 80 have symptomatic cardiac disease.²

Despite advances in cardiology, CHD is still the leading cause of death in older individuals, especially those aged over 75.¹ Nevertheless, there is wide variation in the severity of coronary illness and in the functional status of elderly patients.

Endocarditis Prophylaxis

D'Arcy Little, MD, CCFP
Director of Medical Education,
York Community Services,
Toronto, ON.

Introduction
Endocarditis is a relatively uncommon but potentially life-threatening infection.¹ The condition was first described by Lazare Rivere in 1646, although William Osler's name has a more current association given that the clinical feature, "Osler's nodes," bears his name.² Prior to the development of antibiotics, endocarditis was almost universally fatal; despite recent advances in diagnosis and treatment, the condition continues to have a 37% mortality rate.^1,3 Endocarditis is also associated with significant morbidity, including the development of valvular dysfunction, congestive heart failure, and focal neurologic or septic complications associated with embolic phenomena.^1,3

Due to the considerable morbidity and mortality associated with endocarditis, where possible, primary prevention is the optimal goal. Although the details are controversial, endocarditis prophylaxis with antibiotics is directed towards this goal. However, studies have revealed that compliance with endocarditis prophylaxis guidelines is less than complete.⁴ The following article will review some of the controversies associated with, and the details of, endocarditis prophylaxis.

Congestive Heart Failure

Nariman Malik, BSc, MD
Contributing Author,
Geriatrics & Aging.

Congestive heart failure (CHF) is a condition that affects individuals of all ages but is predominantly a medical condition of the elderly. In the elderly, it reflects the consequences of age-related changes in the cardiovascular system compounded by an increasing prevalence of hypertension, coronary artery disease and valvular heart disease.¹ Heart failure is a complex clinical syndrome characterized by cardiac function that is inadequate to meet the circulatory demands of the body or only does so at abnormally elevated filling pressures.^2,3 The ventricular dysfunction is either systolic or diastolic. A wide variety of etiologies is involved in heart failure; however, the underlying cause is an inability of the heart to properly fill or empty the ventricle. In general, the etiologies of heart failure in the elderly are the same as those in younger patients, although the clinical presentation can be quite different.³

CHF is the leading cause of admissions to hospital in individuals over the age of 65.^2,4 In the United States, it is considered the most expensive cardiovascular disorder because of its high incidence and intensive use of medical resources; estimated costs related to this condition are in excess of $20 billion per year.

Stable Coronary Artery Disease

D'Arcy Little, MD, CCFP
Director of Medical Education,
York Community Services, Toronto, ON.

Introduction
A recent, large, retrospective study concluded that anti-ischemic therapy in nursing home patients with coronary artery disease (CAD) is often suboptimal. When the medical regimens of 72,263 patients aged 65 years or older with a diagnosis of CAD were evaluated, beta-adrenergic blockers were the least likely anti-ischemic agent (of nitrates, calcium channel blockers and beta-adrenegic blockers) to be administered regardless of age, gender, cognitive or physical function.¹ The following article will review the management of coronary artery disease in this population with the goal of providing the busy clinician with a practical, evidence-based approach.

Epidemiology
Coronary artery disease is a major clinical problem in the elderly,² and the prevalence is increasing as the population ages.⁴ It is the leading cause of death in Canada, responsible for 56% of deaths related to cardiovascular disease, and 21% of all deaths.³ The incidence of CAD increases significantly in both sexes above the age of 65 years.