The Coronary Artery Calcium (CAC) scoring test is a non-invasive imaging procedure using a specialized computed tomography (CT) scan to measure calcified plaque in the coronary arteries. To ensure accurate results, preparation instructions require abstaining from stimulants, particularly caffeine and nicotine. This restriction is driven by caffeine’s physiological effects and the demanding technical requirements of the CT imaging process.
Understanding Coronary Artery Calcium Scoring
The CAC scoring test uses a CT scanner to capture images of the heart without intravenous contrast dye. The procedure detects and quantifies hardened, calcium-containing deposits that form within atherosclerotic plaques. These deposits are a direct indicator of coronary artery disease and suggest an increased risk for adverse cardiac events.
The result is reported as the Agatston score, calculated based on the area and density of the detected calcium deposits. A score of zero indicates no detectable calcified plaque and suggests a low risk of a heart attack. Higher scores, such as those exceeding 100 or 300, correlate with increasing plaque buildup and higher cardiovascular risk.
Caffeine’s Stimulatory Effect on the Cardiovascular System
Avoiding caffeine is necessary due to its potent stimulatory effect on the cardiovascular and nervous systems. Caffeine acts as a central nervous system stimulant by blocking adenosine receptors, increasing the release of catecholamines (hormones like epinephrine and norepinephrine).
The surge in these hormones triggers the “fight or flight” response, leading to physiological changes in the heart. This manifests as an elevated heart rate (tachycardia) and increased blood pressure. Even moderate doses of caffeine significantly raise the concentration of free epinephrine for several hours, temporarily altering the heart’s rhythm and pressure.
Why Motion Compromises CT Scan Results
The CT scan for calcium scoring depends on image stability, which a fast-beating heart compromises. Since the heart is constantly moving, the CT scanner must synchronize image acquisition with the cardiac cycle, a process known as cardiac gating. To achieve a clear picture, the scanner targets the diastole phase, when the heart is most relaxed and still.
If a patient’s heart rate is too fast, typically exceeding 60 to 70 beats per minute (bpm), the time window for capturing a sharp image shrinks considerably. A heart rate over 75 bpm significantly increases motion susceptibility, leading to image blurring or “motion artifact.” This blurring prevents the CT software from accurately mapping calcium deposits, resulting in an inaccurate or misleading Agatston score. The goal is to obtain a low heart rate to maximize the heart’s resting phase for precise measurement.
Required Preparation and Contingency Plans
To ensure a low heart rate, patients are instructed to abstain from all sources of caffeine for 12 to 24 hours before the test. This includes coffee, tea, soda, energy drinks, chocolate, and certain over-the-counter medications containing stimulants. Avoiding nicotine and strenuous exercise is also advised, as these activities similarly increase the heart rate.
If the heart rate remains elevated upon arrival, the medical team has contingency plans to avoid rescheduling. A technician may administer an oral or intravenous beta-blocker to temporarily slow the heart rate to the desired range. This pharmacological intervention allows the scan to proceed, ensuring sufficient image quality for an accurate coronary artery calcium score.