Short PR Interval - AAIM

1 145 JOURNAL OF INSURANCE MEDICINEC opyrightQ2005 Journal of Insurance MedicineJ Insur Med2005;37:145 152 ECG CASE STUDYS hort PR IntervalRoss MacKenzie, MDA Short PR Interval may be associated with an otherwise normalelectrocardiogram or a myriad of bizarre electrocardiographic ab-normalities. Clinically, the individual may be asymptomatic or ex-perience a variety of complexarrhythmias, which may be disablingand rarely cause sudden death. In life insurance applicants, it isimportant to recognize these abnormalities and to assess their :Ross MacKenzie Consult-ing, 2261 Constance Drive, Oakville,Ontario, L6J 5L8, Canada; MacKenzie,MD, FRCP(C), FACC; Division ofCardiology, Toronto General words:Electrocardiography,prognosis, differential diagnosis, PRinterval, :March 17, 2005 CASE SCENARIOA 34-year-old businesswoman is applyingfor a large life insurance policy.

2 She is asymp-tomatic at the time of her university 14 years ago, she hadtwo episodes of tachycardia . Both occurredwhen she had been drinking an excessiveamount of coffee while cramming for finalexaminations. Both episodes lasted less thanan hour and had disappeared by the time shearrived in the localemergency room. Afterher examinations that year, the universitymedical clinic referred her to a cardiologist inher hometown for follow-up assessment. Shewas told she had a benign arrhythmia anddid not require medications.

3 She has had norecurrences and has tolerated 3 pregnanciesduring the of this history, the underwriter as-sessing her application requested an attend-ing physician s statement(APS) from the car-diologist and ordered an electrocardiogram(ECG). The APS disclosed that she had anor-mal cardiovascular examination at that investigations, which included a restingand exercise ECG, a 24-hour ambulatory ECGand an echocardiogram, were all reported ECG done as part of thecurrent riskselection process for her application is con-tained in the Figure.

4 What do you think? Isit normal or abnormal? The underwriterthinks she may have had a previous myocar-dial infarction, do youagree? How do youaccount for her previous normal ECG anddoes the change have any prognostic value?ECG INTERPRETATION AND ANALYSISThe prevailing rhythm is sinus in originwith an average ventricular rate of 62 beatsper minute. The PR Interval is very Short ( ) and in most leads, no clear-cut PRJOURNAL OF INSURANCE MEDICINE146 Applicant s is visible. The QRS complexes areabnormally wide and measure leads I, II, AVL, and V3 V6, the wide QRScomplexesrise directly from the end of the Pwave, eliminating the PR segment.

5 These QRScomplexes are deformed by a broad slur onthe initial part of the upstroke of the R ST segment and T waves appear a Short PR Interval may be anor-mal variant, it also has been noted in a num-ber of clinical conditions including: hypertro-phic cardiomyopathy, Ebstein s anomaly, tri-cuspid valve atresia, corrected transpositionof the great vessels, mitral valve prolapse,Duschenne muscular dystrophy, Pompe s dis-ease and Fabry s disease. These conditions areusually obvious on clinical grounds.

6 A shortPR Interval is also seen in a number of elec-trophysiological disorders including: AVjunctional rhythms, ectopic atrial rhythmsand preexcitation AV junctional rhythms with retrogradeatrial activation, theretrograde P-waves mayoccur before the QRS complexwith a shortPR Interval . In this situation, the negative P-waves in II, III and AVF point to the correctdiagnosis. In isorhythmic AV dissociation, theP-waves are dissociated from the QRS com-plexes but frequently the P and QRS rates aresimilar resulting in thephenomenon of accro-chage with the P-wave marching back andforth across the QRS complex and at timescreating the appearance of a sinus P-wavewith a Short PR Interval .

7 Ectopic atrialrhythms originating near the AV node mayhave a Short PR Interval because atrial acti-vation is originating from near the AV node,however the P-wave morphologywill be dif-ferent from the sinus subsets of the preexcitation syndromeare associated with a Short PR Interval . TheLown-Ganong-Levine syndrome (LGL) has ashort PR Interval but is associated with anor-mal QRS complex . In our applicant, the shortPR Interval , the wide QRS complexes and thebroad slur on the upstroke of the R wave tak-MACKENZIE Short PR INTERVAL147en together are characteristic ECG featuresfound in individuals with the commonestform of ventricular preexcitation.

8 The ep-onym for these findings is the Wolff-Parkin-son-White (WPW) pattern. This will be thefocus of our case PR Interval starts from the beginningof the P-wave (SA node depolarization) andincludes the whole P-wave, ie, the whole ofatrial depolarization. There is then a flatseg-ment as depolarization reaches the AV nodecreating an electrical interlude. The AV nodedelays conduction of the electrical impulselong enough for the ventricles to be filled byatrial contraction before they themselves PR Interval ends as ventricular depo-larization begins (the start of the QRS com-plex).

9 Thus the PR Interval represents thetime it takes for the atria to depolarize andpass its message to the ventricles. It is mea-sured from the beginning of the P-wave to thebeginning of the QRS complex . The normalPR Interval measures to seconds , it is important to remem-ber that normal PR intervals are distributedon a bell-shaped curve so that 1% 2% ofnor-mal individuals will have a PR Interval lessthan the normal heart, electrical impulsesoriginate in the sinus node located in theright atrium and spread throughout the atrialtissue, eventually arriving at the AV the AV node.

10 Physiologic slowing ofthe impulse occurs followed by conductionthrough the bundle of His, bundle branchesand Purkinje system to the ventricular mus-cle. Preexcitation occurs when the atrial im-pulse activates ventricular muscle earlier thanwould be expected if the impulse traveledonly by way of the normal specialized con-duction system. This premature activation iscaused by muscular connections composed ofworking muscular fibers that exist outside thespecialized conducting system and connectthe atrium and the ventricle while bypassingAV nodal conduction additionalor alternative pathways are called accessorypathways or connections.