10  Cardiac Stress Tests

• Prevalence of CAD

Age	Asymptomatic	Asymptomatic	Nonanginal Chest Pain	Nonanginal Chest Pain	Atypical Angina	Atypical Angina	Typical Angina	Typical Angina
	Male	Female	Male	Female	Male	Female	Male	Female
30–39	1.9	0.3	5.2	0.8	21.8	4.2	69.7	25.8
40–49	5.5	1.0	14.1	2.8	46.1	13.3	87.3	55.2
50–59	9.7	3.2	21.5	8.4	58.9	32.4	92	79.4
60–69	12.3	7.5	28.1	18.6	67.1	54.4	94.3	90.6

• LR- of a normal stress test is 0.15

  • e.g. pre-test probability of 50-59 yo M with typical angina based on prevalence in this population is 92%. If this patient has a normal stress test, his post-test probability is 63%.

\[ \frac{0.92}{1 - 0.92} = 11.5 \\11.5 \times 0.15 = 1.725 \\\frac{1.725}{1 + 1.725} = 0.633 \]

• First question to ask yourself: “Can this patient exercise?”

  • can they achieve > 5 METs

Algorithm to determine type of cardiac stress test to order.

• Indications for pharmacologic stress testing:

  • unable to exercise, i.e. unable to achieve > 5 METs

  • unable to increase HR, inc ppm

    • includes those unable to achieve 85% of max HR

  • Presence of baseline EKG abnormality, e.g. LBBB (‘VolksWagen Drivers Don’t Litter’)

Tip

EKG cannot be used if either of the following EKG abnormalities are present: V-paced rhythm, WPW, ST depression, Digoxin, LBBB (mnemonic: VolksWagen Drivers Don’t Litter) [Source](https://www.coreimpodcast.com/2019/04/24/stress-testing/)

• 3 types of stressors:

  • exercise

    • pt should be able to get HR to 85% predicted (\(\text{Predicted HR} = 220 - \text{age}\))

  • inotropes (e.g. Dobutamine)

    • Especially useful for pts w/ hx of bronchospasm (e.g. asthma) or severe carotid a. stenosis
    • Con: may precipitate arrhythmias, ∴ for pts w/ paced rhythm, hx of VT, etc., you’re pharmacologic choice will be vasodilator

  • vasodilators (e.g. regadenoson, adenosine, dipyridamole - RAD)

    • Mechanism: causes coronary vasodilation via the adenosine receptor → cAMP production → vascular smooth muscle relaxation

    • When to avoid:

      • 2^nd or 3^rd degree heart block without a pacemaker
      • severe COPD/asthma

• What is the physiologic effect of vasodilators that is used for cardiac stress testing?

  • dilate and ↑ blood flow in normal cardiac vessels; no effect in diseased areas → dilated normal vessels “steal” flow from stenotic vessels → perfusion defects in scans

  • Note: vasodilators do not act by ↑ HR (like do exercise or dobutamine)

• 5 choices for diagnostic tools:

  • EKG

  • Echocardiogram

    • exercise or pharmacologic (dobutamine is the only option)

  • Nuclear imaging

  • MRI 💰

  • PET 💰

10.1 Warranty Period for Prior Cardiac Testing

Source: Table 7 of 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR Guideline for the Evaluation and Diagnosis of Chest Pain

Test Modality	Result	Warranty Period
Anatomic	Normal coronary angiogram CCTA with no stenosis or plaque	2 years
Stress testing	Normal stress test (given adequate stress)	1 year