Routine cardiovascular imaging has dramatically increased over the last 2 decades across demographic subgroups, with marked variation in regional- and hospital-based utilization. This rapid growth and excess cost expenditure cannot be fully accounted for by changing disease rates, and it has not consistently translated into improved patient outcomes. Based on international comparative data, there is a clear disconnect between diagnostic testing frequency and clinical outcomes. In patients with low-risk non–ST-elevation acute coronary syndromes, enrolled in an international trial, stress testing was more commonly performed outside versus inside the United States, despite a lack of difference in mortality at 30 days, 6 months, and 1 year across geographical regions. Inappropriate routine testing may increase radiation exposure, false positive results, patient anxiety, downstream invasive testing, and unnecessary interventions. Efforts to better delineate appropriateness of cardiovascular diagnostics in various settings often are limited to initial encounters. Clinical decision-making regarding subsequent or serial testing is highly variable. For example, number of echocardiograms performed in a well-monitored cohort of patients with ambulatory heart failure (HF) varies widely from 1 to 30 during a span of only 3 years between the initial and final testing. Large variation in testing frequency across the United States regions suggests lack of clear guidance regarding appropriate testing intervals. For routine re-evaluation of chronic cardiovascular conditions, a test should only be performed as frequently as necessary to detect a clinically meaningful change.
The Warranty Period
As the imaging test characteristics and operator reliability of testing improves, a normal or stable examination should confer a favorable patient outcome. The durability of this low-risk status over an established timeframe has been referred to as the “warranty period.” The routine use of warranty periods in select cardiovascular settings may inform patient-level discussions, clinician ordering practices, and value-based care. For example, in single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI), a normal test translates to less than a 1% risk of myocardial infarction (MI) or cardiovascular mortality, which may vary by demographic and clinical characteristics. The warranty period of MPI therefore can be determined by observing the time from last SPECT MPI to total accrued risk of 1% MI and cardiovascular mortality. From a practical perspective however, a warranty period may be more appropriately conceptualized as the time leading up to the next test result that changes clinical management, which may ultimately alter the patient’s disease course or prognosis. Warranty periods may be applicable in select disease states when (1) they are slowly progressive in a predictable pattern; (2) routine testing is available, widely used, and offers high negative predictive value; (3) the early disease course is still amenable to future interventions (e.g., excluding advanced HF and nonintervenable coronary artery disease [CAD]); and (4) surveillance in stable patients without recent change in symptoms or clinical events. Herein, we review the available data in 2 domains of cardiovascular medicine, namely routine stress testing in CAD and echocardiography in HF.
Stress Testing in Coronary Artery Disease
SPECT MPI presently has a critical role in risk stratification of patients with suspected or known CAD. A normal stress MPI confers a better prognosis than those with abnormal results, however the durability of this low-risk status is still unknown. Serial testing of patients with suspected or known CAD could provide valuable information about future risk of MI and cardiovascular death. The American College of Cardiology/American Heart Association recommends against routine retesting in patients who have not had a change in clinical status or who are at low risk of adverse cardiovascular events. Although this recommendation is based on expert opinion, few studies have validated appropriate time intervals to repeat testing. This issue is further complicated by clinical variables that can affect risk. For example, the estimated time to reach a defined risk of nonfatal MI and cardiac death ranged widely from 145 months (95% confidence interval 125 to 175) in patients without diabetes and preserved ejection fraction (EF) to only 12 months (95% confidence interval 6 to 28) in patients with diabetes and reduced EF in 1 propensity-matched study. Risk prognostication scores could help define which clinical, historical, or index test characteristics are most valuable in affirming the duration of a warranty period. Careful implementation of warranty periods for low-, intermediate-, and high-risk populations could be useful adjuncts to clinicians seeking cost-effective methods of serially testing patients with suspected or known CAD.
Stress Testing in Coronary Artery Disease
SPECT MPI presently has a critical role in risk stratification of patients with suspected or known CAD. A normal stress MPI confers a better prognosis than those with abnormal results, however the durability of this low-risk status is still unknown. Serial testing of patients with suspected or known CAD could provide valuable information about future risk of MI and cardiovascular death. The American College of Cardiology/American Heart Association recommends against routine retesting in patients who have not had a change in clinical status or who are at low risk of adverse cardiovascular events. Although this recommendation is based on expert opinion, few studies have validated appropriate time intervals to repeat testing. This issue is further complicated by clinical variables that can affect risk. For example, the estimated time to reach a defined risk of nonfatal MI and cardiac death ranged widely from 145 months (95% confidence interval 125 to 175) in patients without diabetes and preserved ejection fraction (EF) to only 12 months (95% confidence interval 6 to 28) in patients with diabetes and reduced EF in 1 propensity-matched study. Risk prognostication scores could help define which clinical, historical, or index test characteristics are most valuable in affirming the duration of a warranty period. Careful implementation of warranty periods for low-, intermediate-, and high-risk populations could be useful adjuncts to clinicians seeking cost-effective methods of serially testing patients with suspected or known CAD.
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