1. A wearable device for real-time detection, analysis and application of heart rate variability (HRV), the device comprising: a. a chest strap integrated with one or more strap electrodes to detect a plurality of consecutive QRS waves; and b. a battery-powered and self-contained processing circuit comprising: i. a microprocessor operatively coupled to the one or more electrodes and configured to receive at least one additional input unrelated to the QRS waves detected by the strap electrodes; ii. an ECG analog front end (AFE) circuit coupled between the microprocessor and at least one strap electrodes to provide a signal gain control to a strap electrode output such that the microprocessor receives signals with a desired amplitude, wherein the ECG AFE circuit has an internal amplifier where the internal amplifier operates to output a conditioned QRS signal comprising the plurality of consecutive QRS waves; iii. an analog voltage comparator coupled between the ECG analog front end circuit and the microprocessor, wherein the analog voltage comparator operates to detect one or more specified characteristics of the conditioned QRS signal, wherein the plurality of consecutive QRS waves, detected by the one or more strap electrodes, are received by the ECG AFE circuit wherein the internal amplifier of the ECG AFE circuit operates to convert the plurality of consecutive QRS waves into a conditioned QRS signal, wherein the conditioned QRS signal is received by the analog voltage comparator where the analog voltage comparator operates to detect the one or more specified wave characteristic of the conditioned QRS signal whereupon detection of the one or more specified wave characteristics, the analog voltage comparator triggers an interrupt directly to a signal processor integrated into the microprocessor; iv. a non-volatile memory storing computer-readable instructions that, when executed by the microprocessor, cause the microprocessor to perform operations comprising A. detecting a rising edge or a declining edge of an R-wave from each of the QRS waves; B. triggering an interrupt when the rising edge or the declining edge crosses a trigger point, the trigger point for interrupt triggering being predetermined or dynamically adjusted value; C. recording a time value each time when the interrupt is triggered; D. determining an RR interval each time when the time value is recorded; E. generating a temporal RR interval array, the RR interval array being stored within the memory and comprising a plurality of determined RR intervals; F. generating an HRV measurement based on the temporal RR interval array; and G. comparing the generated HRV measurement to an HRV threshold and outputting a real-time notification when the HRV threshold is reached, the HRV threshold being determined at least by the additional input unrelated to the QRS waves; and v. a notification means to receive the real-time notification to generate a user alert, the notification means being a haptic indicator, an audio indicator or a visual indicator.