Theory of the P wave detection

The algorithm first finds the  the possible positive and negative wave peaks
based on zero transition searching, then validates them with comparing
to reference P waves.

The P wave detection needs high amplitude resolution. This value is better,
than 0.6 uV / bit in the Cardiospy system.  With this resolution and
the effective filter system which uses wavelet transformation,
the Cardiospy system is able to detect P waves less than 50 uV of amplitude.

Validation of the P wave detector

The validation is carried out on 10 pcs 12 channel and 10 pcs 3 channel ECG
reference records. The reference records include the P wave  annotation.  12
of the 20 records are taken from the MitBih database, 8 records are
taken from the Labtech database (30000 – 30007). 

12 ch records

s0014lre, s0292lre, s0302lre, s0331lre, s0364lre, s0422_re, s0431_re,
s0437_re, s0549_re, s0550_re

3 ch records

mgh001, mgh007, 30000, 30001, 30002, 30003, 30004, 30005, 30006, 30007

Validation result:

Sensitivity:                       95.42%

Positive predictivity:         97.16%

Central blood pressure: current evidence

and clinical importance

Carmel M. McEniery1*, John R. Cockcroft2, Mary J. Roman3,

Stanley S. Franklin4, and Ian B.Wilkinson1

1Clinical Pharmacology Unit, University of Cambridge, Addenbrooke’s Hospital, Box 110, Cambridge CB22QQ, UK; 2Department of Cardiology,Wales Heart Research Institute, Cardiff

CF14 4XN, UK; 3Division of Cardiology,Weill Cornell Medical College, New York, NY 10021, USA; and 4University of California, UCI School of Medicine, Irvine, CA 92697-4101, USA

Received 29 April 2013; revised 27 November 2013; accepted 17 December 2013; online publish-ahead-of-print 23 January 2014

and central pressure. Therefore, basing treatment decisions on central, rather than brachial pressure, is likely to have important implications

for the future diagnosis and management of hypertension. Such a paradigm shift will, however, require further, direct evidence that selectively

targeting central pressure, brings added benefit, over and above that already provided by brachial artery pressure.

Central pressure † Blood pressure † Anti-hypertensive treatment † Cardiovascular risk

Introduction

The brachial cuff sphygmomanometer was introduced into medical

practice well over 100 years ago, enabling the routine, non-invasive,

measurement of arterial blood pressure. Life insurance companies

were among the first to capitalize on the information provided by

cuff sphygmomanometry, by observing that blood pressure in

largely asymptomatic individuals relates to future cardiovascular

risk—observations that are nowsupported by a wealth of epidemiological

data.1 The most recent Global Burden of Disease report2

identified hypertension as the leading cause of death and disability

worldwide. Moreover, data from over 50 years of randomized controlled

trials clearly demonstrate that lowering brachial pressure,

in hypertensive individuals, substantially reduces cardiovascular

events.1,3 For these reasons, measurement of brachial blood pressure

has become embedded in routine clinical assessment throughout the

developed world, and is one of the most widely accepted ‘surrogate

measures’ for regulatory bodies.

The major driving force for the continued use of brachial blood

pressure has been its ease of measurement, and the wide variety of

devices available for clinical use. However, we have known for over

half a century that brachial pressure is a poor surrogate for aortic

pressure, which is invariably lower than corresponding brachial

values. Recent evidence suggests that central pressure is also more

strongly related to future cardiovascular events4 – 7 than brachial

pressure, and responds differently to certain drugs.8,9 Appreciating

this provides an ideal framework for understanding the much publicized

inferiority of atenolol and some other beta-blockers,10 compared

with other drug classes, in the management of essential

hypertension. Although central pressure can now be assessed noninvasively

with the same ease as brachial pressure, clinicians are unlikely

to discard the brachial cuff sphygmomanometer without

robust evidence that cardiovascular risk stratification, and monitoring

response to therapy, are better when based on central rather

than peripheral pressure. Central pressure assessment and accuracy

will also have to be standardized, as it has been for brachial pressure

assessment with oscillometric devices. This review will discuss our

current understanding about central pressure and the evidence

required to bring blood pressure measurement, and cardiovascular

risk assessment into the modern era.

Physiological concepts

Arterial pressure varies continuously over the cardiac cycle, but in

clinical practice only systolic and diastolic pressures are routinely

reported. These are invariably measured in the brachial artery

using cuff sphygmomanometry—a practice that has changed little

over the last century. However, the shape of the pressure waveform

* Corresponding author. Tel: +44 1223 336806, Fax: +44 1223 216893, Email: cmm41@cam.ac.uk

Published on behalf of the European Society of Cardiology. All rights reserved. &The Author 2014. For permissions please email: journals.permissions@oup.com

European Heart Journal (2014) 35, 1719–1725　doi:10.1093/eurheartj/eht565

Pressure measured with a cuff and sphygmomanometer in the brachial artery is accepted as an important predictor of future cardiovascular risk.However, systolic pressure varies throughout the arterial tree, such that aortic (central) systolic pressure is actually lower than corresponding　brachial values, although this difference is highly variable between individuals. Emerging evidence now suggests that central pressure is better　related to future cardiovascular events than is brachial pressure. Moreover, anti-hypertensive drugs can exert differential effects on brachial　and central pressure. Therefore, basing treatment decisions on central, rather than brachial pressure, is likely to have important implications　for the future diagnosis and management of hypertension. Such a paradigm shift will, however, require further, direct evidence that selectively　targeting central pressure, brings added benefit, over and above that already provided by brachial artery pressure.As discussed earlier, a full synthesis of the available evidence concerning

central pressure and the risk of future cardiovascular events is　now required. However, it will also be necessary to determine the　clinical relevance of differences between brachial and central pressure

for the individual patient, especially given the relatively high correlation　between the two. Emerging data support the prognostic　superiority of both 24-h ambulatory blood pressure monitoring

(ABPM)79 – 81 andhomemonitoring81 in comparison with office measurements.　Interestingly, a recent study82 demonstrated that 24-h　ambulatory cuff pressures were comparable with office central pressure

measurements in the prediction of risk, although the significance　of this study awaits confirmation.83 As yet, there are no data comparing　the predictive value ofhomemonitoring vs. central pressure in the

prediction of risk. Ultimately, it will be necessary to evaluate the prognostic　value of 24-h ambulatory central pressure.With the recent development　of ambulatory central pressure systems,84,85 this is now

possible and it may be reasonable to hypothesize that 24-h central,　rather than brachial ABPM would be superior in terms of risk prediction.