Mechanical Circulatory Support (eBook)

CHAPTER 1

PATIENT SELECTION, TIMING, AND INDICATIONS FOR

DURABLE LVAD IMPLANTATION

Contributors: Garrick C Stewart, Finn Gustafsson

When selecting patients for durable left ventricular assist device (LVAD) therapy, the considerable benefits of treating advanced heart failure (HF) must be weighed against significant risks and considerable costs. There is an inherent dilemma in selecting the right patients for the right device at the right time. If patients are implanted too early, outcomes after implantation may be good, but the net benefit is small since outcomes would also have been good with ongoing medical and electrical therapy. Conversely, if the device is implanted too late, outcomes may be poor, with or without device therapy (Figure 1).

Consequently, selection and timing for LVAD implant first requires accurate estimation of the patient’s prognosis in the absence of advanced therapies like LVAD or transplantation. Multiple studies describe prognostic factors in groups of patients (or in an “average” patient in that population) and may help identify relevant risk factors. However, the incremental impact of a given factor (e.g. renal dysfunction) on an individual patient within their broader risk profile is often not well understood. Studies addressing an individual patient’s prognosis with HF are less prevalent and often come with their own limitations. The selection of the optimal candidate for LVAD therapy must begin with the identification of patients on high risk heart failure trajectories who may be a candidate for an evaluation for mechanical circulatory support (MCS).

Hospitalization for acute decompensated HF (ADHF) is an extremely important marker of risk, as it identifies a highly vulnerable period in the patient’s journey with HF. Data from the United States reveal that mortality is 3-4 % in-hospital during an admission with HF, 10-12 % at 30 days following discharge, and 30-40 % after one year1. Rehospitalization rates are high and generally reported to be 45-65% within the first year1,2. Among patients with ADHF, the manner of clinical presentation may further identify patients at high risk. At one end of the spectrum, patients admitted with cardiogenic shock after myocardial infarction (MI) have a 30-day mortality greater than 40%3. In patients without shock, which represents the vast majority, admission profiles associated with risk markers include acute MI, myocardial ischemia as evidenced by abnormal ECG or elevated troponin T or I,4 low systolic blood pressure, renal insufficiency, increased heart rate, hyponatremia, reduced ejection fraction, increased B-type natriuretic peptide (BNP) or N-terminal (NT)-proBNP, older age, and presence of comorbidities5,6. Patients who require intravenous vasodilators or inotropic support have a particularly poor prognosis7. The need for inotropic support was associated with an in-hospital mortality rate of 26% in the ALARM-HF (Acute Heart Failure Global Survey of Standard Treatment) registry8. Hypertensive patients (systolic blood pressure>160 mmHg) generally have the best prognosis with a low 60-day mortality.

In stable outpatients, the most important prognostic factors are patient age and symptoms, including the New York Heart Association (NYHA) functional class. In addition, a large number of laboratory, hemodynamic, and echocardiographic measures have been examined and shown to correlate with long term survival and hospitalization risk4,9,10 (Table 1).

ANP, atrial natriuretic peptide; BUN, blood urea nitrogen; BNP, B-type natriuretic peptide; eGFR, estimated glomerular filtration rate; NYHA, New York Heart Association Class; PCWP, pulmonary capillary wedge pressure; RAAS, renin angiotensin aldosterone system; VO2, oxygen consumption.

Interestingly, simple clinical bedside examination can still provide prognostic information even in contemporary outpatient populations such as those included in the PARADIGM-HF (Prospective Comparison of ARNI with ACEI to Determine Impact on Global Mortality and Morbidity in Heart Failure) trial. In this study, jugular venous distention, edema, rales, and third heart sound were found to provide prognostic information independent of symptoms and natriuretic peptide levels11. Left ventricular systolic function as measured by ejection fraction (LVEF) is an important predictor of outcome. It has been well documented that patients with HF and preserved ejection fraction have a better prognosis compared with patients with reduced LVEF (HFrEF)12. However, in patients with HFrEF, the degree of impairment in LVEF, a load dependent marker of cardiac performance, may be a less robust marker of outcome. Also, it is important to realize that the inter- and intra-observer variability in LVEF using echocardiography in clinical practice is approximately 10% (absolute values). Hence, serial measurements must be interpreted with caution and a measured decline in LVEF from 25 to 15 % may not, by itself, represent a major prognostic change.

The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) classification describes characteristics of patients with advanced HF, both hospitalized and ambulatory. Patients with advanced HF are categorized among 7 different profiles with specific focus on potential timing for advanced therapies, especially MCS (Table 2)13.