THE EFFECTS OF ISCHEMIA ON THE ESTIMATION ACCURACY OF

A REDUCED LEAD SYSTEM

D Güldenring1, DD Finlay1, CD Nugent1, MP Donnelly1

1 1 University of Ulster, Belfast, United Kingdom

ARE 10 ELECTRODES TOO MUCH? The 12 lead ECG format is familiar to medical personal

throughout disciplines (Fischer et al. 1998; Lin Haiping et al. 2008)

The 12 lead ECG provides a detailed picture of the heart´s electrical activity

The 12 lead ECG requires the attachment of 10 Electrodes

There is a demand for electrocardiographic systems with less and/or different recording sites Access to the precordium (defibrillation, resuscitation,

echocardiography) (Feild et al. 2008; Nelwan et al. 2000)

Easy identifiable electrode locations (Feldman et al. 1997)

Reduction in costs for consumables (electrodes) (Feild et al. 2008)

Simplified maintenance for continuous monitoring (Drew et al. 2004)

Reduced lead systems aim to address this demand

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COMMERCIAL REDUCED LEAD SYSTEMSBASIS LEADS

3

TruST

#

Dräger Medical

EASI

Philips Medical Systems

12RL

GE Medical Systems Information Technologies

LEAD TRANSFORMATIONS A non recorded lead (target

lead) is typically estimated (derived) by a weighted sum of all recorded leads (basis leads) (Feild et al. 2008)

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Two different concepts for optimisation of weights a1 to a4

exist• Optimised for one specific patient (patient specific weights)

(Nelwan et al. 2004)

• Optimised over several patients of a cohort (generalised weights) (Nelwan et al. 2004)

dV3(t)= a1 * I(t) +a2 * II(t) +a3* V1(t) +a4*V5(t)

AIM

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Higher estimation accuracy has been reported for PS weights (Nelwan et al. 2000)

Negative impact of ischemia on the estimation accuracy of RLS has previously been identified (Feild et al. 2008; Nelwan et al. 2008)

However, no detailed assessment of the location of the ischemic event and its impact on the estimation accuracy of PS derived target leads has been reported.

In this study, we assesses how different ischemic events impact on the similarity between derived and recorded STT segments diagnostic classification

ECGSIM MODEL

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Geometry of torso model is defined by 300 nodes

Geometry of cardiac model is

defined by 257 nodes

Ischemic events were simulated by• delay of depolarisation time by 15ms

• reduction of action potential

duration to 80% of normal value

• reduction of transmembrane

amplitude to 80% of normal value

ISCHEMIC EVENTS

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Ischemic Event

#

Ventricular segments

1 1

2 10

3 1&2&10

4 1&2&3&4&10

5 1&2&3&4

6 1&3&4&10

…

25 9&10&11&12&14&15&17

1 1

3 1&2&10

6 1&3&4&10

10 left ventricular segments are after Galeotti et al. [11]

WAVEFORM SIMILARITY ASSESSMENT

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ECGSIM

PS weights

basis leads

GN weights

target leads

PSRMSE

GNRMSE

basis leads

PS derived target leads

GN derived target leads

Assessment of waveform similarity

• by RMSE between derived and actual target leads

• for 25 simulated ischemic events

• over STT segment

RESULTS -WAVEFORM SIMILARITY

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Simulated ischemic events increase RMSE of PS derived target to a level that is comparable to that obtained by GN derived target leads.

RMSE values for target leads V2, V4 and V6 show similar overall profile. However, the order of the ischemic events on the x-axis and their corresponding RMSE values does differ.

RMSE of PS derived V3 RMSE of GN derived V3

DIAGNOSTIC CLASSIFICATION

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PS derived target leads

GN derived target leadsECGSIM

PS weightsbasis leads

GN weights

12-lead ECG

AHA criteria

basis leads

PS derived 12-lead ECG

AHA criteria

GN derived 12-lead ECG

AHA criteria

Diagnostic classification• of (PS / GN) derived and actual 12-lead ECG

• based on AHA criteria for acute myocardial ischemia (Thygesen et al. 2007)

• search for ischemic events detected on actual 12-lead ECG and missed on (PS/GN) derived 12-lead ECG

RESULTS –DIAGNOSTIC CLASSIFICATION

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Ischemic events identified by AHA criteria for acute myocardial ischemia (Thygesen et al. 2007)

• identified by recorded 12 lead ECGs

• missed by derived (PS & GN) 12 lead ECGs

Derived ECGs missed the AHA criteria only marginally short• would be obvious human observer

• may be not detected by computerised algorithm

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GN derived

EXAMPLE OF MISSED ISCHEMIC EVENT #1

derived lead (ischemia present)

simulated lead (ischemia present)simulated lead (no ischemia present)

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EXAMPLE OF MISSED ISCHEMIC EVENT #1

derived lead (ischemia present)

simulated lead (ischemia present)simulated lead (no ischemia present)

25mm/s; 10mm/mV

CONCLUSION

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Our simulations indicate• In absence of ischemic events PS derived leads are superior

to GN derived ones

• Superiority of PS approach is largely compromised in the presence of ischemic events

Findings raise questions about the superiority of PS approach used for continuous monitoring

Findings indicate the importance of evaluation of such systems on data that reflects pathological changes

Follow-up research based on real patient data is currently under way

REFERENCESS. D. Fisher, A. K. Loeffler, C. L. Green, N. M. Wildermann, J. E. Pope and M. W. Krucoff, "Device implementation, validation, and application assessment of two continuous 12-lead ECG monitors during percutaneous transluminal coronary angioplasty: Description of the validation method and implications for clinical trials," J. Electrocardiol., vol. 30, pp. 149-154, 1998.

Lin Haiping and Xiang Kui, "T-Wave Alternans Analysis in Portable ECG Monitor," Computational Intelligence and Industrial Application 2008, 2008, pp. 710-713.

D. Q. Feild, S. H. Zhou, E. D. Helfenbein, R. E. Gregg and J. M. Lindauer, "Technical challenges and future directions in lead reconstruction for reduced-lead systems," J. Electrocardiol., vol. 41, pp. 466-473, 12, 2008.

S. P. Nelwan, J. A. Kors and S. H. Meij, "Minimal lead sets for reconstruction of 12-lead electrocardiograms," J. Electrocardiol., vol. 33, pp. 163-166, 2000.

C. L. Feldman, G. MacCallum and L. H. Hartley, "Comparison of the standard ECG with the EASIcardiogram for ischemia detection during exercise monitoring," in Computers in Cardiology 1997, 1997, pp. 343-345.

B. J. Drew, R. M. Califf, M. Funk, E. S. Kaufman, M. W. Krucoff, M. M. Laks, P. W. Macfarlane, C. Sommargren, S. Swiryn, G. F. Van Hare, American Heart Association and Councils on Cardiovascular Nursing, Clinical Cardiology,and Cardiovascular Disease in the Young, "Practice standards for electrocardiographic monitoring in hospital settings: an American Heart Association scientific statement from the Councils on Cardiovascular Nursing, Clinical Cardiology, and Cardiovascular Disease in the Young: endorsed by the International Society of Computerized Electrocardiology and the American Association of Critical-Care Nurses " Circulation, vol. 110, pp. 2721-2746, Oct 26, 2004.

S. P. Nelwan, S. W. Crater, C. L. Green, “Assessment of derived 12-lead electrocardiograms using general and patient-specific reconstruction strategies at rest and during transient myocardial ischemia,“ Am. J. Cardiol., vol. 94, pp. 1529-1533, 2004.

S. P. Nelwan , J. A. Kors, S. W. Crater, S. H. Meij, T. B. van Dam, M. L. Simoons, et al. “Simultaneous comparison of 3 derived 12-lead electrocardiograms with standard electrocardiogram at rest and during percutaneous coronary occlusion,” J. Electrocardiol., vol. 41, pp.230-237, 2008.

A. van Oosterom ,T. F. Oostendrop, “ECGSIM: an interactive tool for studying the genesis of QRST waveforms,” Heart, vol. 90, pp. 165-168, 2004.

S. P. Nelwan, “Evaluation of 12-Lead Electrocardiogram Reconstruction Methods for Patient Monitoring,” Ph.D. dissertation, Erasmus MC, Rotterdam, The Netherlands, 2005.

L. Galeotti, D. G. Strauss, J. F. Ubachs, O. Pahlm, E. Heiberg, “Development of an automated method for display of ischemic myocardium from simulated electrocardiograms,” J. Electrocardiol., vol. 42, pp. 204-212, 2009.

K. Thygesen, J. S. Alpert, H. D. White, “Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction,” Eur. Heart J., vol. 28, pp. 2525-2538, 2007.

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QUESTIONS?

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WEIGHTS

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ECGSIM(van Oosterom et al.

2004)

normal 12 lead ECG OLS

regression

PSweights

GN weights (Nelwan 2005)

OLSregression

12 lead ECG

1242 subjects

dV3(t)= a1 * I(t) +a2 * II(t) +a3* V2(t) +a4*V5(t)

A non recorded lead (target lead) is typically estimated (derived) by a weighted sum of all recorded leads (basis leads) (Feild et al. 2008)

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GN derived

EXAMPLE OF MISSED ISCHEMIC EVENT #6

derived lead (ischemia present)

simulated lead (ischemia present)simulated lead (no ischemia present)

LIMITATIONS

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Findings solely based on simulations• Further research on real patient data is required

Simulations are limited in that• Only 25 ischemic events have been simulated

• Only one torso and heart geometry was used

• Severity of simulated ischemia was not varied