Cardiac stress testing and Holter monitoring

In short

Cardiac stress testing records the ECG, heart rate, blood pressure and symptoms while the heart's workload is raised by exercise (treadmill or bicycle) or by a drug, to unmask ischaemia that a resting ECG misses. Holter monitoring records a continuous ambulatory ECG for 24-48 hours (or longer with extended patch recorders) to catch arrhythmias, pauses and silent ischaemia that come and go during ordinary life. Together they are the two commonest non-invasive "beyond resting ECG" investigations a cardiac care technologist performs, and they are heavily examined in B.Sc Cardiac Care / Cardiac Technology papers on non-invasive cardiology. Employers test them at interview because the technologist independently hooks up, runs, aborts and pre-reports these studies - hospitals such as AIIMS, PGIMER, CMC Vellore, Apollo, Fortis, Narayana Health, Medanta and Max, plus diagnostic chains like Dr Lal PathLabs and Metropolis, hire for exactly this skill set. Mastery means knowing protocols, endpoints, absolute contraindications, artefact control and the arithmetic of METs, target heart rate and the Duke score.

Explained

Physiological basis and why stress testing works

• Exercise raises myocardial oxygen demand (MVO₂), which depends chiefly on heart rate, systolic wall tension and contractility; demand is tracked clinically by the rate-pressure product (HR × systolic BP).
• Coronary supply rises by coronary vasodilatation; a fixed stenosis limits flow reserve, so at a critical workload supply falls short of demand - the ischaemic cascade begins.
• Order of events: reduced perfusion → metabolic change → diastolic then systolic wall-motion abnormality → ST depression on ECG → angina. ECG change appears late, which is why imaging-based stress tests are more sensitive.
• A stenosis usually must narrow the lumen by roughly 70% or more in diameter before flow reserve is exhausted at exercise; so a normal treadmill test does not exclude non-obstructive plaque.
• Normal responses: HR rises linearly with workload; systolic BP rises; diastolic BP stays flat or falls slightly; PR, QRS and QT shorten; P wave height increases; J point and ST segment show upsloping change.
• Abnormal responses: exertional hypotension (fall of systolic BP ≥10 mmHg below baseline), chronotropic incompetence (failure to reach ~85% of age-predicted maximum), delayed HR recovery, and ventricular arrhythmia with increasing workload.

Exercise stress test: protocols and procedure

• Modalities: motorised treadmill (commonest in India), cycle ergometer (used where balance or obesity makes walking unsafe; workload set in watts), arm ergometer, and historically the Master's two-step test.
• Bruce protocol - the standard: 3-minute stages with speed and gradient both increasing. | Stage | Speed (km/h) | Grade (%) | Approx. METs | Cumulative time (min) | |---|---|---|---|---| | 1 | 2.7 | 10 | 4.6 | 3 | | 2 | 4.0 | 12 | 7.0 | 6 | | 3 | 5.4 | 14 | 10.2 | 9 | | 4 | 6.8 | 16 | 13.5 | 12 | | 5 | 8.0 | 18 | 16.0 | 15 | | 6 | 8.8 | 20 | 19.0 | 18 | | 7 | 9.7 | 22 | 22.0 | 21 |
• Modified Bruce: adds two warm-up stages at 2.7 km/h with 0% and 5% grade for elderly, deconditioned or early post-MI patients.
• Other protocols: Naughton and Balke-Ware (small increments, for heart failure and cardiac rehabilitation), Ramp protocol (continuous smooth increase, best for VO₂ estimation and for CPET).
• Electrode placement - Mason-Likar modification: limb electrodes moved onto the torso (arms to infraclavicular fossae, legs to iliac crests/lower abdomen) to cut motion artefact. It shifts the axis rightward and can create new inferior Q waves - never use a Mason-Likar baseline to diagnose an old infarct.
• Preparation: written informed consent; NPO 3-4 hours; no smoking or caffeine; comfortable shoes; chest shaved and skin abraded with alcohol; medication advice from the physician (beta blockers usually withheld 24-48 h for diagnostic tests, continued for a functional/efficacy test); a resting 12-lead ECG supine and standing, and baseline BP in both.
• During the test: ECG displayed continuously, 12-lead recorded and BP taken at the end of every stage and at peak; symptoms and Borg scale (6-20) rating noted; physician present or immediately available; crash cart, defibrillator, oxygen and emergency drugs ready.
• Recovery: monitor at least 6-10 minutes supine or seated; ST changes often appear only in recovery, so never remove electrodes early. Immediate supine position increases venous return and sensitivity.
• Endpoints - target: symptom-limited maximal test, or 85% of age-predicted maximum HR for a sub-maximal diagnostic test. A test stopped before 85% HRmax without symptoms or ECG change is inconclusive/non-diagnostic, not negative.

Interpretation, scoring and the stress-test family

• Positive ECG criterion: horizontal or downsloping ST depression ≥1 mm (0.1 mV) measured 60-80 ms after the J point, in two or more contiguous leads, persisting for at least three consecutive beats with a stable baseline.
• Upsloping ST depression is non-specific; ST elevation ≥1 mm in a non-infarct lead suggests transmural ischaemia or spasm and is a reason to stop. ST depression lead location does not localise the culprit artery reliably (unlike ST elevation).
• Other markers: exertional hypotension, ≥2 mm depression, depression at a low workload (<5 METs or stage 1), persistence >5 minutes into recovery, sustained VT, and a low exercise capacity - all mark a high-risk test.
• Duke Treadmill Score (Bruce protocol only): combines duration, ST deviation and angina into a prognostic score and a 5-year survival estimate.
• Diagnostic performance: exercise ECG sensitivity roughly 65-70% and specificity 70-80%. Low-prevalence populations give many false positives - Bayes' theorem explains why it is a poor screening test in asymptomatic young adults.
• False positives are common in: women, LVH, digoxin therapy, hypokalaemia, mitral valve prolapse, anaemia, hyperventilation. Uninterpretable ST baselines: LBBB, ventricular pacing, pre-excitation (WPW), ST depression ≥1 mm at rest - these need an imaging stress test instead.
• Stress imaging alternatives (named here only for contrast; detail belongs with echo and nuclear topics): exercise/dobutamine stress echocardiography (wall-motion based), myocardial perfusion imaging with technetium-99m or thallium-201 using exercise, dobutamine, adenosine, dipyridamole or regadenoson, and stress cardiac MRI.
• Pharmacological agents: dobutamine (dose stepped 5→10→20→30→40 µg/kg/min with atropine if HR inadequate) raises demand; vasodilators create flow heterogeneity (steal). Choose a drug test when the patient cannot walk (arthritis, amputation, PVD, severe COPD, deconditioning).
• Contraindications - absolute: acute MI within about 2 days, unstable angina not stabilised, uncontrolled symptomatic arrhythmia, symptomatic severe aortic stenosis, decompensated heart failure, acute PE or DVT, acute myocarditis/pericarditis, acute aortic dissection, inability to consent. Relative: obstructive HCM with high gradient, severe untreated hypertension (e.g. >200/110 mmHg), high-grade AV block, electrolyte abnormality, significant tachy- or bradyarrhythmia, mental or physical impairment.
• Indications to terminate: drop in systolic BP ≥10 mmHg with ischaemia, ST elevation ≥1 mm in non-Q leads, sustained VT, moderate-to-severe angina, signs of poor perfusion (pallor, cyanosis, ataxia, confusion), technical failure of the ECG trace, or the patient's request.
• Complications and risk: mortality roughly 1 in 10,000 tests and serious events (MI, sustained VT, resuscitation) about 1-5 in 10,000 - low, but the reason resuscitation facilities are mandatory.

Cardiopulmonary exercise testing (CPET) in brief

• Adds expired gas analysis to exercise testing: measures VO₂ peak, VCO₂, RER, VE/VCO₂ slope and the anaerobic threshold.
• RER (VCO₂/VO₂) above about 1.10 confirms a genuinely maximal effort - a key quality criterion.
• Used for heart-failure prognosis and transplant listing (VO₂ peak thresholds around 12-14 mL/kg/min), unexplained dyspnoea, and pre-operative risk.

Holter monitoring: equipment, hook-up and analysis

• Definition: continuous ambulatory ECG recording on a body-worn digital recorder, named after Norman Jefferis ("Jeff") Holter; standard duration 24 h, often 48 h, up to 7-14 days with patch devices.
• Channels and leads: 2-, 3- or 12-channel recorders. A 3-channel set-up uses bipolar pseudo-leads - commonly CM5 (modified V5, best for ST change and QRS size), CM1 (modified V1, best for distinguishing SVT from VT and for P waves; CC5, a chest-to-chest lead from V5R to V5, is an alternative ischaemia lead) and an inferior lead; 7 or 8 electrodes with one reference.
• Sampling typically 128-1,000 Hz per channel; data on flash memory; 12-lead Holters allow true ST analysis and QT measurement.
• Hook-up steps: 1) explain and consent; 2) shave and abrade skin, clean with alcohol, let it dry; 3) place electrodes over bony prominences (sternum, ribs, clavicle) not over muscle or breast tissue; 4) press firmly, loop the lead wires and tape them down for strain relief; 5) check the live trace on all channels; 6) enter patient ID, date and time; 7) issue a diary and explain the event button; 8) instruct no bathing or swimming (unless the device is water-resistant), no electric blanket, keep to normal activity.
• Patient diary is essential: symptom, time to the minute and activity - the report must correlate rhythm with symptom. A diary with no entries and a "normal" recording during an asymptomatic day proves nothing.
• Analysis software outputs: total beats, minimum/average/maximum HR with times, ventricular ectopic count and morphology (couplets, triplets, bigeminy, VT runs), supraventricular ectopics, atrial fibrillation burden, longest RR/pauses, AV block episodes, ST trend, QT/QTc trend, heart rate variability (SDNN, rMSSD, pNN50, and frequency-domain LF/HF) and heart rate turbulence.
• The technologist must edit the auto-analysis: software mislabels artefact as VT, tall T waves as extra QRS (double counting) and low-amplitude beats as pauses (undercounting). Every reported arrhythmia must be verified on the raw strip.
• Minimum analysable recording: aim for ≥85-90% of the time artefact-free and at least ~18-20 hours of usable data in a 24-h study; otherwise repeat.
• Indications: palpitations, unexplained syncope or presyncope, documented or suspected AF (including burden and rate control assessment, and post-ablation follow-up), pacemaker/ICD function with symptoms, suspected sick sinus syndrome, assessing antiarrhythmic efficacy or proarrhythmia, suspected silent ischaemia, HRV in diabetic autonomic neuropathy, and risk stratification after MI.
• Limitations: records only the days it is worn - useless for symptoms occurring once a month; no 12-lead diagnostic quality in 3-channel devices; artefact-prone; not a substitute for a 12-lead ECG during symptoms.

Related ambulatory devices and where Holter stops

• Event/patient-activated recorder: patient triggers recording during symptoms; good for frequent but not daily symptoms; useless if symptoms cause immediate collapse.
• Loop recorder (external): continuously overwrites a loop and freezes pre- and post-trigger data; captures the onset of a very brief arrhythmia and syncope.
• Implantable loop recorder (ILR): inserted subcutaneously, battery life about 3-4 years; the standard for infrequent unexplained syncope and cryptogenic stroke monitoring.
• Mobile cardiac telemetry / patch monitors: adhesive single-lead patches (and Indian devices in this class) transmit or store 7-14 days with automatic arrhythmia detection.
• Ambulatory blood pressure monitoring (ABPM): 24-h oscillometric BP, cycling every 15-30 min by day and 30-60 min by night; detects white-coat and masked hypertension and non-dipping (normal nocturnal fall is >10% of daytime mean).
• Choosing by symptom frequency: daily → Holter 24-48 h; weekly → patch 7-14 days or event recorder; monthly or rarer with syncope → ILR.

Indian practice, standards and regulation

• Medical electrical equipment is regulated as a device under the Drugs and Cosmetics Act, 1940 read with the Medical Devices Rules, 2017 (CDSCO); ECG, treadmill and Holter systems are notified medical devices requiring import/manufacture licences and, for Class B/C devices, conformity with the Quality Management System in those Rules.
• Safety and performance are referenced to the IS/IEC 60601 family - the general standard for medical electrical equipment safety plus the particular standards for electrocardiographic monitoring and ambulatory electrocardiographic systems; quote the clause only from the edition in hand, as these are revised periodically. Electrical installation of the lab follows the CEA (Measures relating to Safety and Electric Supply) Regulations, 2023.
• Leakage-current limits, defibrillation-proof (type CF) applied parts, equipotential earthing and periodic electrical-safety testing are the audit items in a cardiology lab.
• NABH hospital and NABL (ISO 15189 for labs) accreditation drive SOPs, calibration records, consent forms, crash-cart checklists and competency files; NABH accreditation is voluntary but is required for many insurer and government scheme empanelments. Treadmill, BP instrument and defibrillator calibration traceable to NPL-India is expected at accredited sites.
• Biomedical waste (electrodes, gel, razors) is handled under the Bio-Medical Waste Management Rules, 2016 as amended; e-waste from retired recorders under the E-Waste (Management) Rules, 2022.
• Patient data on Holter software is personal health data; until the Data Fiduciary duties under the DPDP Rules, 2025 take effect on 13 May 2027, the IT Act section 43A and the SPDI Rules govern sensitive personal data security practices, and hospital privacy policy plus NABH information-management standards apply throughout.
• Cost reference (varies widely by city and institution): TMT roughly ₹800-2,500 and a 24-h Holter roughly ₹1,500-5,000 in 2026; CGHS and Ayushman Bharat (PM-JAY) package rates are lower and are revised from time to time.
• Qualification: a B.Sc Cardiac Care / Cardiovascular Technology graduate works as Cardiac Care Technologist; registration requirements follow the National Commission for Allied and Healthcare Professions Act, 2021 and state allied-health councils, which are being rolled out progressively.

Key points

• Stress test purpose - raise myocardial oxygen demand to expose flow-limiting coronary disease that rest cannot reveal.
• Ischaemic cascade - perfusion defect precedes wall-motion change, which precedes ST depression, which precedes angina.
• Bruce protocol - 3-minute stages, starts 2.7 km/h at 10%, ~1 MET gained per minute on average; modified Bruce adds 0% and 5% warm-up stages.
• Mason-Likar placement - torso limb electrodes to reduce artefact; it alters the frontal axis, so it cannot be used to read old infarcts.
• Positive ECG response - ≥1 mm horizontal or downsloping ST depression 60-80 ms after the J point in ≥2 contiguous leads.
• High-risk findings - exertional hypotension, ≥2 mm depression at low workload, ST elevation, sustained VT, exercise capacity <5 METs, slow HR recovery.
• 85% of age-predicted HRmax - the threshold below which a negative test is called inconclusive, not normal.
• 1 MET = 3.5 mL O₂/kg/min, the resting metabolic rate; exercise capacity in METs is the single strongest prognostic output.
• Absolute contraindications - recent MI (~2 days), unstable angina, symptomatic severe AS, decompensated failure, acute PE, myocarditis, dissection, uncontrolled arrhythmia.
• Uninterpretable baseline - LBBB, paced rhythm, WPW, resting ST depression; use stress imaging instead.
• Pharmacological stress - dobutamine raises demand; adenosine/dipyridamole/regadenoson cause flow maldistribution; used when the patient cannot exercise.
• Recovery monitoring - at least 6 minutes; many positive responses appear only after exercise stops.
• Holter monitoring - continuous 24-48 h ambulatory ECG, 2-12 channels, for intermittent arrhythmia, silent ischaemia and HRV.
• Pseudo-leads CM5 and CM1 - CM5 best for ST change and QRS amplitude, CM1 for P waves and SVT-versus-VT discrimination.
• Patient diary - mandatory; a report without symptom-rhythm correlation is incomplete.
• Device choice by symptom frequency - Holter for daily, patch/event recorder for weekly, implantable loop recorder for rare syncope.
• Artefact control - shave, abrade, bony-prominence placement, lead loops; artefact mimics VT, pauses and AF on auto-analysis.
• Regulation - Medical Devices Rules, 2017 under CDSCO; IS/IEC 60601 safety family; NABH/NABL SOP and calibration discipline.

Formulas and examples

Example 1 - target heart rate and chronotropic response. A 52-year-old man, resting HR 78/min, is sent for a diagnostic TMT.

• Predicted HRmax = 220 − 52 = 168 beats/min.
• 85% target = 0.85 × 168 = 142.8 ≈ 143 beats/min (the minimum for a diagnostic negative test).
• He stops at Bruce stage 3 with HR 131/min and no symptoms or ST change. 131 < 143, so the test is inconclusive, not negative.
• Chronotropic index = (131 − 78)/(168 − 78) = 53/90 = 0.59 - below 0.80, so chronotropic incompetence is present (he was not on a beta blocker).
• At 1 minute of recovery HR is 122/min → HRR1 = 131 − 122 = 9 beats/min, abnormal (≤12), an adverse prognostic marker.

Example 2 - METs and VO₂ from the treadmill setting. Bruce stage 2 is 4.0 km/h at 12% grade; patient weighs 70 kg.

• Speed = 4.0 km/h = 4000 m / 60 min = 66.67 m/min; G = 0.12.
• VO₂ = 0.1 × 66.67 + 1.8 × 66.67 × 0.12 + 3.5 = 6.667 + 14.400 + 3.5 = 24.57 mL/kg/min.
• METs = 24.57 / 3.5 = 7.02 METs - matches the ~7 METs tabulated for Bruce stage 2.
• Absolute VO₂ = 24.57 × 70 / 1000 = 1.72 L/min.
• If he completes 6:00 of Bruce, functional capacity ≈ 7 METs - adequate for most daily activities but below the ~10 METs associated with a good prognosis.

Example 3 - Duke Treadmill Score. A 60-year-old woman exercises 7 minutes on the Bruce protocol, develops 2 mm horizontal ST depression in V4-V6 and non-limiting angina.

• Angina index = 1 (angina present but not test-limiting).
• DTS = 7 − (5 × 2) − (4 × 1) = 7 − 10 − 4 = −7.
• −7 lies between +4 and −10 → intermediate risk; typical annual cardiac mortality in this band is about 1-3%, and further evaluation (stress imaging or angiography, per the physician) is usual.
• Had she stopped at 7 minutes with the same ST change but angina forcing termination: DTS = 7 − 10 − 8 = −11 → high risk.

Example 4 - Holter beat count and PVC burden. A 24-hour Holter reports 102,816 total QRS complexes and 11,310 PVCs.

• Average HR = 102,816 / (24 × 60) = 102,816 / 1,440 = 71.4 beats/min.
• PVC burden = (11,310 / 102,816) × 100 = 11.0%.
• A burden above roughly 10-15% sustained over time is linked with PVC-induced cardiomyopathy, so the report must flag the burden, the dominant morphology and whether it is monomorphic.
• The same recording lists "2 episodes of VT, 4 beats, HR 240/min" at 07:40 while the diary says "brushing teeth" - verify on the raw strip: toothbrush artefact typically shows no change in the underlying RR interval and the sinus beats march through, whereas true VT interrupts them.

Example 5 - rate-pressure product and ischaemic threshold. Baseline HR 72/min, BP 130/80 mmHg. At peak (stage 3) HR 148/min, BP 180/84 mmHg, with 1.5 mm downsloping ST depression in II, III, aVF.

• Resting RPP = 72 × 130 = 9,360.
• Peak RPP = 148 × 180 = 26,640 (a normal peak is roughly 25,000-30,000).
• Ischaemic threshold is reported as the RPP at which ST depression first reached 1 mm - say HR 136, BP 170 → 136 × 170 = 23,120; this is the figure used to judge anti-anginal therapy at a repeat test.
• Systolic BP rose by 50 mmHg - a normal response. A fall of 10 mmHg or more instead would have mandated stopping.

Where it is used

• Hospital non-invasive cardiology labs: AIIMS, PGIMER, SCTIMST, CMC Vellore and corporate chains (Apollo, Fortis, Max, Manipal, Narayana, Medanta) run daily TMT and Holter lists staffed by cardiac care technologists.
• Diagnostic chains and standalone cardiac clinics: Dr Lal PathLabs, Metropolis, SRL and city polyclinics offer TMT, Holter and ABPM packages; home Holter hook-up is a growing service line.
• Pre-employment, insurance and fitness-to-work medicals: TMT is routine in executive health checks, aviation and railway medical boards, and pre-employment screening for safety-critical jobs.
• Cardiac rehabilitation and sports science: sub-maximal and CPET protocols set exercise prescriptions after MI, CABG or valve surgery; HRR and METs track progress.
• Device and consumable industry: sales, application and service roles with BPL Medical Technologies, Schiller Healthcare India, Allengers, Nasan, Recorders & Medicare Systems, and the Indian arms of GE HealthCare, Philips and Mortara/Hillrom - installation, demo and software training.
• Research and telecardiology: ICMR and institutional studies on HRV in diabetic autonomic neuropathy, AF screening programmes, and tele-ECG/Holter reporting hubs serving district hospitals.

Interview questions

• Q: What makes an exercise ECG positive for ischaemia? A: Horizontal or downsloping ST depression of at least 1 mm measured 60-80 ms after the J point, in two or more contiguous leads, over at least three consecutive beats with a steady baseline.
• Q: A patient reached only 70% of predicted maximum heart rate with no ECG change. Is the test negative? A: No - it is inconclusive or non-diagnostic, because the heart was not stressed to the 85% threshold needed to exclude ischaemia.
• Q: Why are the limb electrodes moved to the torso in a treadmill test, and what is the cost of doing so? A: The Mason-Likar position reduces motion artefact from the arms and legs; it shifts the frontal-plane axis and can create artificial inferior Q waves, so it must not be used to diagnose a previous infarct.
• Q: Name four absolute contraindications to a treadmill test. A: Acute myocardial infarction within about two days, unstable angina not yet stabilised, symptomatic severe aortic stenosis and decompensated heart failure (also acute PE, myocarditis, dissection, uncontrolled symptomatic arrhythmia).
• Q: The systolic BP falls from 150 to 135 mmHg at peak exercise. What do you do? A: Stop the test - exertional hypotension of 10 mmHg or more below baseline with exercise suggests severe ischaemia or left ventricular dysfunction; put the patient supine, continue monitoring and inform the physician immediately.
• Q: Why must recovery be monitored for at least six minutes? A: Ischaemic ST changes and arrhythmias frequently appear or deepen only after exercise stops, and heart rate recovery at one minute is itself a prognostic measurement.
• Q: Which patients need a pharmacological or imaging stress test rather than a plain exercise ECG? A: Those who cannot exercise adequately, and those with an uninterpretable ST baseline - left bundle branch block, ventricular pacing, pre-excitation or resting ST depression.
• Q: Which Holter pseudo-lead do you choose to tell SVT from VT, and why? A: CM1 (modified V1), because it shows P waves and QRS morphology best for a right-versus-left activation pattern; CM5 is reserved for ST change and QRS amplitude.
• Q: The Holter software reports 30 seconds of ventricular tachycardia. How do you confirm it? A: Open the raw strip: in artefact the underlying sinus QRS complexes march through at an unchanged RR interval and the "beats" are irregular and non-physiological, whereas true VT replaces the rhythm with wide uniform complexes and is followed by a compensatory pause.
• Q: A patient had a completely normal 24-hour Holter but still has palpitations once a month. What next? A: Holter only covers the days worn - escalate to a 7-14 day patch or event/loop recorder, or an implantable loop recorder if the episodes cause syncope.
• Q: What is 1 MET and why is exercise capacity in METs important? A: One MET is resting oxygen uptake, 3.5 mL O₂/kg/min; exercise capacity in METs is the strongest prognostic variable from the test - below 5 METs marks high risk, above about 10 METs a good outcome.
• Q: How do you prepare a hirsute, sweaty patient so the Holter trace stays clean for 24 hours? A: Shave the sites, abrade the skin lightly, degrease with alcohol and let it dry fully, place electrodes over bony prominences away from muscle, press firmly for several seconds, loop the lead wires and tape them for strain relief, then verify all channels live before releasing the patient.

Common mistakes

• Calling a sub-maximal test "normal" when the patient never reached 85% of predicted maximum heart rate.
• Measuring ST depression at the J point itself instead of 60-80 ms after it, or reporting non-specific upsloping depression as positive.
• Reading Q waves or axis from a Mason-Likar baseline tracing as evidence of an old infarction.
• Removing electrodes as soon as the treadmill stops, losing the recovery ST changes and the one-minute heart rate recovery.
• Mixing up the two drug classes of pharmacological stress - dobutamine increases demand, adenosine and dipyridamole redistribute flow; and forgetting that caffeine blocks the vasodilators.
• Signing off a Holter from the software summary without editing artefact, double-counted T waves and undercounted low-amplitude beats, and without matching the diary times to the strips.
• Reporting a PVC or AF burden without the denominator (total analysed beats and analysable hours), so a 60%-artefact recording looks like a complete study.
• Unit slips in the MET and VO₂ formulas - treadmill speed must be in m/min and grade as a fraction, not a percentage.

Related topics

Electrocardiography (ECG): recording and interpretation · Echocardiography basics · Cardiac catheterisation lab: angiography and angioplasty · Pacemakers and implantable cardiac devices · Arrhythmias and their management · Cardiac rehabilitation and exercise physiology