Pinpointing Korotkoff During Stress Tests
Dec 11, 2009
Patient movement, mechanical vibrations and artifactual sounds often interfere with obtaining consistently accurate readings of Korotkoff sounds during ECG stress testing. When standard manual techniques are used, especially in a busy clinical setting, the problem can be compounded by observer variability.
While traditional automated monitoring devices can eliminate discrepancies resulting from observer variances, they are ineffective during ECG stress testing. Most automated BP monitoring uses oscillometric technology to detect minute arterial oscillations and can, therefore, only be used when the patient is motionless.
This fact has led experts such as Dr Marvin Ellestad to conclude that the only practical approach to blood pressure monitoring during stress testing is auscultatory technology. Even this can be problematic. What happens for instance, when foot strikes are in cadence with Korotkoff sounds?
The inability to consistently isolate and monitor Korotkoff sounds during ECG stress testing has led nurses to develop venous ad hoc techniques to overcome the masking effects of excess noise and motion. In some cases, nurses resort to physically holding the cuffed arm in an effort to dampen motion artifact while manually recording the blood pressure. Manual efforts such as these require the clinician's time and attention. As a result, overall patient care may be compromised.
Another option
A new technology that uses R-wave gated brachial sphygmomanometry and noise-reducing signal algorithms is offering clinicians an auscultatory alternative that is accurate, consistent and automated. The technology, already in use in many clinical settings worldwide, is designed to know when, how and where to listen for Korotkoff sounds while ignoring all other artifactual noises. The ability to automatically and effectively isolate, extract and
identify Korotkoff sounds is enabling clinicians to obtain accurate systolic and diastolic readings while focusing on patient performance during stress testing.
The new auscultatory technology combines R-wave gating and filtering techniques. R-wave gating is based on the timed relationship between the onset of the R-wave occurring in the heart and the propagation of the Korotkoff sounds in the arteries. The heart is an electromechanical pump.
Normally, the R-wave is the largest electrical depolarisation the heart undergoes during a cycle of one beat. Korotkoff sounds originate from the flow of blood caused by the cyclical pumping of the heart. USing the R-wave as an auscultatory cue, the technology knows when to listen for the Korotkoff sounds. Random noises generated between R-waves are ignored.
The technology also takes advantage of the low-frequency components of the Korotkoff sounds that have been found to be a dominant feature of the Korotkoff signal throughout the entire cuff deflation cycle. By isolating the frequency range specific to the Korotkoff sounds, the new technology can more accurately ensure that extracted during R-wave generation.
Mounting evidence
In a recent study conducted by members of the Baker Heart Research Institute, Alfred Heart Centre, and Monash University, in Melbourne Australia, the efficacy of the automated auscultatory technology was compared to the
industry's gold standard, intra-arterial monitoring.
During treadmill exercise ECG testing, the combined mean difference between invasive brachial artery recording and the new automated technology recording was 4.79 mmHg (± 0,14) for systolic and 6.33 mmHg (± 0,10) for diastolic.
In their report, published in Blood Pressure Monitoring, the researchers concluded that the
technology 'is tolerant to exercise and provides reliable automated BP assessment with absolute differences within an acceptable clinical range'.
Perhaps, one of the greatest unseen benefits of the new automated technology is the potential increase in patient care. Automated auscultatory monitors can be programmed to register and record a patient's blood pressure at pre-defined intervals. Generated readouts can provide clinicians and physicians with a visual report of the patient's performance during the stress test. Free from having to manually monitor and record systolic and diastolic pressures, the clinicians can focus on interacting with the patient and monitoring their overall well being
By using sequential, multi-dimensional morphology analysis combined with R-wave gating and dimensional analysis of Korotkoff sounds, a new generation of blood pressure monitoring devices is bringing a higher degree of accuracy and efficiency to the stress lab. As a result, it has the potential to substantially improve the delivery of healthcare.
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