The goal of this observational study is to learn about the factors which determine how well ventricular tachycardia (VT) is tolerated. The main questions it aims to answer are:

1. What impact does coronary artery disease have on the ability for a patient to tolerate VT?
2. Does treatment of coronary artery disease with stents improve the tolerability of VT?

Participants who are undergoing a clinically indicated coronary angiogram or coronary angioplasty procedure will have measurements of blood pressure, coronary pressure and coronary flow made during pacing at a range of heart rates.

Ventricular tachycardia (VT) is a common and life-threatening arrhythmia that occurs in people with heart problems. Some patients who develop this arrhythmia remain very stable with very little symptoms while others become unstable with low blood pressure or even sudden death. It is not known why some people tolerate the arrhythmia well and others do not.

If VT is not tolerated then current practice is to offer an implantable cardioverter defibrillator (ICD) which can deliver a shock to the heart if dangerous heart rhythms are detected. While shocks can be life-saving, they are also harmful, including causing psychological distress. ICDs also frequently deliver shocks when they are not needed.

If research could identify which factors predispose a person to be stable or unstable in VT, this would allow doctors to help them in a range of ways. One way would be to treat patients to improve the tolerance of VT, so avoiding the need for an ICD. Another would be to assess the the risk of instability and so allow a patient-centred decision on whether an ICD is needed.

In this study the investigators plan to recruit patients who are referred for a coronary angiogram. During the angiogram, the investigators will stimulate the heart at a range of fast heart rates and measure their blood pressure and flow in their coronary arteries. In patients who undergo stenting for a coronary stenosis, the investigators will also make these measurements after stenting so they can see if there is any difference. By recruiting a range of different cardiology patients, the investigators will be able to assess which factors contribute to stability during VT.

Inclusion Criteria:

• Able to give valid consent
• Referred for coronary angiography or coronary angioplasty
• Suitable for percutaneous physiological interrogation and PCI when clinically indicated

Exclusion Criteria:

• Unable to give valid consent
• Pregnant or breastfeeding women
• Unstable coronary artery disease (acute coronary syndrome)
• Severe multivessel coronary artery disease suitable for coronary artery bypass grafting
• Severe heart valve disease
• Severe (NYHA IV) heart failure

Adults referred for coronary angiography or coronary angioplasty.