How accurate are nuclear stress tests, and what does a negative result mean? no ischemia? no detectable ischemia?

Good, not perfect: You've asked an excellent question about which books are written. The accuracy depends on the likelihood that pathology is present and the prevalence of the disease in the population studied. Broadly, a negative test is 80% accurate but can lower your chance of disease from >60% to <20%. Practically, let your doc decide for you based on your unique issues whether more tests are indicated.