Many patients with angina have no obstructive coronary artery disease at the time of angiography. This is also known as INOCA. Here, we present a comprehensive gold standard protocol for testing structural and functional disorders of the coronary circulation.
This technique comprises two components, the diagnostic guidewire study, as well as the acetylcholine provocation test. Together, they provide additional information to help distinguish between the INOCA endotypes. This technique is therefore useful for investigating patients for potential microvascular angina and/or vasospastic angina.
This then allows for personalization of therapies according to diagnosis. Performing the procedure with us today is Professor Colin Berry. It's my pleasure to introduce Professor Berry, who is a professor of cardiology at the University of Glasgow and a consultant cardiologist at the Golden Jubilee National Hospital.
Before starting, review the clinical case and plan the procedure with the catheter laboratory team. Prepare medication and equipment in case of adverse events. To begin the procedure, obtain arterial access using the standard Seldinger technique.
Administer modest doses of intra-arterial, short-acting nitrate to reduce the propensity of radial artery spasm. Then, record the left ventricular and diastolic pressure and perform standard coronary angiography to obtain orthogonal views of all main coronary artery branches. Engage the coronary artery with a guide catheter.
Then, with the guide catheter engaged and coaxial, administer 200 micrograms of glyceryl trinitrate to attenuate any epicardial coronary spasm. Ensure that the activated clotting time is approximately 250 seconds before instrumentation of the coronary artery. Then, move the sensor to the tip of the guide catheter while avoiding handling the diagnostic guidewire sensor.
Then, flush the guide catheter to avoid contrast pressure damping. Wait 30 seconds for resting conditions to return before equalizing the pressure with the invasive aortic root pressure. Advance the diagnostic guidewire to the distal third of the coronary artery.
With the diagnostic guidewire in a suitable position within the vessel, flush the guide catheter with room-temperature saline and wait 30 seconds for resting physiology to return. Record resting pressure indices, including resting PdPa and RFR. Next, use a three-milliliter syringe to administer brisk three-milliliter boluses of room-temperature normal saline via the guide catheter.
Repeat the three-milliliter boluses of room-temperature normal saline as required. Inspect the recorded transit times and replace any outlier readings. Set up the linked diagnostic software and commence IV adenosine infusion at 140 micrograms per kilograms per minute via a large peripheral venous cannula.
Monitor for signs of hyperemia. Document fractional flow reserve at stable hyperemia. While the adenosine infusion is ongoing, the software is switched back to the thermodilution CFR/IMR page to complete hyperemic thermodilution measurements.
Repeat rapid three-milliliter boluses of room-temperature normal saline via the guide catheter to record hyperemic thermodilution transit times. Then, stop the IV adenosine. Acquire 1, 10, and 100 micromolar solutions of acetylcholine and keep at four degrees Celsius.
Choose an angiographic projection that allows visualization of the coronary artery, with minimal foreshortening and overlap. Then, acquire a resting angiogram. Check that the guide catheter is coaxially intubated for the acetylcholine infusion.
Next, connect a long, sterile IV line to a three-way tap and flush the system with normal saline. Connect the sterile IV line to a 60-milliliter syringe containing one micromolar acetylcholine. Purge the IV line and guide catheter with four milliliters of acetylcholine solution.
With the guide catheter still coaxial, commence the infusion at two milliliters per minute for two minutes. Monitor the patient for vital signs and ECG for effects of acetylcholine. If encountering safety concerns, stop the acetylcholine infusion immediately.
After each acetylcholine infusion, acquire an ECG and assess the patient for symptoms. Gently purge the guide catheter system with contrast. Repeat the coronary angiogram in the same projection as at rest.
Closely monitor the vital signs and ECG of the patient while the angiographic images are assessed for vasospasm, TIMI flow, and myocardial blush. Next, connect a 60-milliliter syringe to infuse 10 micromolar acetylcholine solution. Commence the infusion at two milliliters per minute for two minutes.
After infusion, acquire an ECG and assess the patient for symptoms. Repeat the coronary angiogram, then perform an acetylcholine infusion using 100 micromolar acetylcholine solution at two milliliters per minute for two minutes. Acquire an ECG, and repeat the coronary angiogram.
With the guide catheter still coaxial, perform manual infusion of acetylcholine for over 20 seconds. This dose is usually 100 micrograms for the left coronary artery, or reduced to 50 micrograms in the right or dominant coronary artery. Repeat the coronary angiogram in the same projection as at rest.
Ensure sufficient time to assess myocardial blush and TIMI frame counts over three heartbeats. After this, administer 300 micrograms of intra-coronary glyceryl trinitrate, and allow 30 seconds for it to take effect. Finally, pull back the diagnostic guidewire and ensure signal drift of less than or equal to 0.03.
Check a final angiogram to exclude distal guidewire injury. The interventional diagnostic procedure is used to differentiate patients according to their clinical endotypes and institute appropriate management. The diagnostic guidewire test measures the parameters of coronary flow limitation.
If the index of microvascular resistance is greater than 25, or if the coronary flow reserve value is less than 2 in the absence of obstructive epicardial disease, it is indicative of microvascular angina. Another example is seen here. Using the acetylcholine provocation test, microvascular spasm is diagnosed with the reproduction of angina, ST-segment deviation, less than 90%change in epicardial lumen diameter, or TIMI flow reduction, as seen in this case.
Vasospastic angina is diagnosed when there is more than 90%reduction in coronary luminal diameter along with reproduction of anginal symptoms and ischemic ECG changes. An example is seen here. There are a few important considerations when performing this technique.
First, beware of hydrodissection or air emboli during injections. Second, ensure that there's close monitoring during the acetylcholine infusions. And finally, ensure that the guide catheter is gently purged after each infusion to avoid a sudden bolus during the next injection.
So, in conclusion, this technique helps to guide the stratification and management of patients with INOCA. Research studies that have utilized this technique include the CorMicA pilot, the Cor-CTCA study, and the ongoing iCorMicA trial.
