Cardiogoniometry in acute chest pain

Patients presenting with acute chest pain (ACP) remain an immediate challenge for general practitioners or physicians in emergency units, respectively, in particular when there is limited access to sophisticated, expeditious laboratory analysis. Albeit the symptomatology of patients who present in the primary care setting is in the majority of cases of benign aetiology, an acute cardiovascular cause may be life threatening and has to be excluded at short notice. In a prospective study conducted in US outpatient clinics, the majority of episodes were characterised as ‘non-organic’; approximately one-third were of a musculoskeletal origin, followed by gastrointestinal causes (19%). Of particular relevance, cardiac causes were diagnosed in 16% of all ACP patients; however, the proportion was as high as 50% in older populations (Figure 1).(1) While these numbers can be considerably different in other settings, they reflect the diagnostic challenge for primary care and emergency physicians to exclude or confirm a cardiovascular origin of ACP. Numerous medical texts emphasise the potential dangerous nature of chest pain and, despite the fact that medical guidelines provide assistance in the challenge of precise judgement,(2) a cost-effective approach is necessary to maintain a decent clinical standard.

Office evaluation of new-onset chest pain commonly includes an evaluation of the patient (for example, assessment of medical history, existing cardiac risk factors, description of the individual properties of chest pain and associated symptoms), a physical examination and a rest electrocardiogram (ECG). All of these measures can be of importance for decision making; however, they also hold important limitations. Clinical assessment is of significance to determine the so-called pre-test probability of organic chest pain.(3) Interestingly, a history chest pain is of limited value in patients presenting with an acute coronary syndrome (ACS).(4) An ECG that is generally available for most physicians who are involved in the differential diagnosis of ACP has a high sensitivity and specificity to rule out acute ST‑elevation myocardial infarction. However, there is strong evidence that a significant portion of rest ECGs may be normal in patients that are referred to a chest pain clinic for unstable angina (UA) or non ST-elevation myocardial infarction (NSTEMI). One of the largest studies conducted to this effect found a normal rest ECG in approximately half of the patients presenting with unstable angina.(5) 

Albeit exercise ECG testing is not recommended in the context of ACP, it is often performed at a subsequent stage for further diagnosis. It is generally recommended that exercise ECG should only be performed in patients with intermediate pretest probability. Bearing this in mind, approximately one-third of patients cannot undergo meaningful exercise ECG testing, for example, because of arrhythmias, physical disabilities, abnormal blood pressure or failure to reach the target heart rate.(6) A large meta-analysis showed a maximum sensitivity of 68% for the detection of significant coronary artery disease (CAD) in patients with intermediate pre-test probability undergoing exercise ECG.(7) In the context of the shortcomings of ECG testing, and in light of the fact that most primary care physicians do not have routine access to sensitive, expeditious laboratory analysis to rule out ACS by high-sensitivity troponin testing, there is a highly relevant unmet clinical need for a cost-effective, easy-to-use diagnostic tool that assesses a cardiovascular cause of ACP. The goals for a non-invasive diagnostic tool to diagnose cardiovascular disease in the context of ACP are summarised in Table 1.

Over a century ago, Einthoven paved the way for modern electrocardiography by introduction of the leads, which still carry his name and are still in use today. In contemporary medicine, ECG recordings at rest are of critical importance in the diagnosis of acute myocardial infarction (AMI), albeit it misses approximately 5–10% of acute Q-wave (transmural) myocardial infarctions. Transmural AMIs account for approximately 10% of all ACS. The major portion of ACS is comprised of NSTEMI and UA. These conditions carry an immediate risk for the patient, which can be resolved in the cardiac catheterisation lab by acute coronary revascularisation. Therefore, expedited diagnosis is critical for risk stratification. Rest ECG misses at least one-half of patients with NSTEMI and UA;8 therefore, a refined, cost-effective diagnostic tool that is readily available is needed. As mentioned above, exercise ECG is usually contraindicated in the acute setting because it can provoke clinical deterioration of the patient. 

Einthoven’s approach was based on a single vector in the middle of an isosceles triangle. However, this approach does not reflect the human electrical heart cycle entirely and three-dimensional models were developed. This was the birth of vectorelectrocardiography, which became popular during the third quarter of the last century. However, because it was difficult to interpret, time-consuming and complex, it never became routine clinical practice and the interest in this technology continuously declined. 

Cardiogoniometry is a spatiotemporal vectocardiographic advancement of the above-described principle. This novel technology was introduced recently(9) and verified in patients with stable CAD undergoing invasive coronary catheterisation.(10) The methodology was further developed by a systematic development of a stenosis-specific parameter set(11) in this study of several stenosis-specific CGM parameters, which was clinically validated and which described the spatiotemporal variability of R vectors, R-T angles, the geodistribution of R-T vectors and ST-T segment alterations. Using this concept, a CGM device was developed that has the size of an ordinary ECG apparatus. Five leads are connected to the resting patient and an automated diagnosis is provided within minutes, stating whether the patient is likely to suffer from myocardial abnormalities, for example ischaemia, or if the finding is inconspicuous. Further insights of CGM are provided in Figure 2.

An illustrated clinical case is depicted in Figure 3. A 62-year-old male was admitted to the emergency room with UA; serial ECG and troponin T assessments were within normal limits. However, CGM recording suggested myocardial ischaemia. Cardiac catheterisation revealed an ostial LAD stenosis, which was successfully revascularised by stent placement.

Completed and ongoing prospective studies using CGM 

The CGM@ACS trial was a multicentre, prospective observational trial conducted in interventional centres in Germany.(12) A total of 216 patients who presented with ACP without ST elevation underwent cardiac catheterisation within 72 hours of presentation in the hospital. All patients were screened by CGM, troponin laboratory test and 12-lead ECG at rest before cardioangiography. CGM revealed a considerably higher sensitivity for detection of angiographically-determined relevant coronary stenosis compared with ECG (74% vs 28%), albeit specificity was lower (54% vs 78%). Accuracy for the correct detection of angiographical coronary artery stenosis with immediate revascularisation was 40% for ECG, 50% for first troponin, 62% for serial troponin, 65% for CGM and 76% for the combination of CGM and troponin. The results of this study suggest that CGM might play an important role in the diagnosis of ACP in the clinical setting. Importantly, CGM performed considerably better in terms of accuracy compared to ECG. Further studies are currently under way.

The CGM@MRT study compares prospectively the significance of CGM compared with the non-invasive gold-standard, adenosine perfusion MRT, for the detection of myocardial ischaemia in stable patients with suspected CAD. The CGM@DIABETES trial investigates the value of CGM compared with 12-lead ECG at rest and exercise ECG for detection of significant CAD in asymptomatic, intermediate risk patients with type II diabetes. Patients with conspicuous findings in any of these diagnostic tools suggestive of myocardial ischaemia will be undergoing coronary angiography.

The initial clinical results are encouraging but there are limitations to the application of CGM in certain patient subsets. Patients with atrial fibrillation, active stimulation by a pacemaker, as well as patients with significant arrhythmias, are not recommended to undergo CGM at the current stage because particular algorithms for these patients have not been prospectively validated to date.

Conclusions 

Owing to the increasing prevalence of CAD in an ageing society and the worldwide rise of conditions that increase the risk to develop coronary plaques, such as diabetes mellitus, there is an obvious clinical need to improve the diagnostic armamentarium, in particular in the preclinical setting, to reliably diagnose and risk-stratify patients with ACP and/or suspected CAD. The standard 12-lead ECG is inevitable in the diagnosis of AMI but it has its limitations in NSTEMI-ACS, including UA.

The same is the case for exercise ECG in the diagnostic setting of suspected, stress-dependent myocardial ischaemia. CGM is just entering the clinical setting and will be refined further in the near future. However, at the current stage, it is tempting to speculate that this novel diagnostic tool will extend its clinical importance in the near future because of reasonable cost, ease of operation and diagnostic accuracy, as suggested in the CGM@ACS trial. Fields of application will most likely include the primary care sector as well as emergency rooms. Assuming that CGM ascertains accuracy and reliability in these settings, considering further routes of applications, as for example in the ambulance, pre-operative screening or surveillance during non-cardiac or cardiac surgery settings, respectively, will be worthwhile.(1)

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