Undifferentiated Palpitations — Written Clinical Reasoning

SAQ 1 — The Diagnostic Approach to Undifferentiated Palpitations (20 marks, 30 minutes)

Prompt: Outline your structured approach to the patient presenting with undifferentiated palpitations, addressing: (a) the four-descriptor classification; (b) the focused history questions that discriminate between the causes; (c) the focused examination; (d) the investigations — the mandatory 12-lead ECG, the bloods, the tiered ambulatory monitoring, the echocardiogram, the EP study; (e) the high-risk features; and (f) the cause-directed management. [1]

Model Answer

(a) The four-descriptor classification (3 marks): [1]

The classification of the palpitations by the symptom character narrows the differential before any test is ordered. The four descriptors are: [1]

1. Regular fast rhythm — the differential is sinus tachycardia (the physiological response to a systemic stimulus — fever, anxiety, anaemia, thyrotoxicosis, pregnancy, hypovolaemia, sympathomimetic drugs), paroxysmal supraventricular tachycardia (AVNRT, AVRT — the re-entrant circuits involving the AV node or an accessory pathway), and ventricular tachycardia (the re-entrant circuit in the scarred myocardium or the idiopathic outflow-tract VT).
2. Irregular rhythm — the differential is atrial fibrillation (the irregularly irregular pattern with no discernible P waves), atrial flutter with variable block (the regularly irregular pattern with the grouped beating), and frequent ectopic beats (the recognisable cadence of the normal-early-pause sequence).
3. Missed beat or extra beat sensation — the cardinal feature of the ectopic beats (atrial or ventricular); the patient perceives the compensatory pause after the ectopic as the missed beat, and the next sinus beat (with the larger stroke volume after the pause) as a thud.
4. Pounding or forceful sensation in a regular rhythm — the awareness of the increased stroke volume in the sinus rhythm; the differential is anaemia, thyrotoxicosis, pregnancy, fever, aortic regurgitation, the mitral valve prolapse, anxiety, and the sympathomimetic drugs (caffeine, salbutamol, pseudoephedrine). [1]

(b) The focused history questions (4 marks): [1]

The history is the most powerful investigation in the palpitations encounter. The six structured questions are: [1]

1. The onset: sudden or gradual? The sudden onset (the patient can name the moment) points to the re-entrant tachycardia (the SVT) or the initiation of the AF. The gradual onset (the rate climbs over minutes) points to the sinus tachycardia.
2. The duration: seconds, minutes, or hours? The seconds point to the ectopics or the non-sustained tachycardia. The minutes point to the SVT or the paroxysmal AF. The hours point to the persistent AF or the sustained VT.
3. The termination: sudden or gradual? The sudden termination (the rhythm switches off) points to the re-entrant tachycardia, often terminated by the vagal manoeuvre. The gradual termination (the rate drifts down) points to the sinus tachycardia. The terminating episode followed by the brisk polyuria is the SVT discriminator — the atrial natriuretic peptide drives the diuresis [2][6].
4. The triggers and the modifiers. The exercise-provoked palpitations are a red flag — the VT, the channelopathies (the LQT1, the CPVT), the structural disease (the HCM, the aortic stenosis). The substance-provoked palpitations (the caffeine, the alcohol, the cocaine) point to the triggered arrhythmia.
5. The associated symptoms. The syncope is the red flag (the haemodynamically compromising tachycardia). The chest pain may indicate the ischaemia or the atypical MVP pain. The dyspnoea indicates the loss of the atrial contribution to the filling. The polyuria is the SVT discriminator.
6. The drug, the family, and the past cardiac history. The drug history (the sympathomimetics, the QT-prolonging drugs, the antiarrhythmics). The family history of the sudden cardiac death under 40 (the channelopathies, the cardiomyopathies). The past cardiac history (the prior infarction, the cardiomyopathy, the valve disease, the congenital heart disease).

(c) The focused examination (3 marks): [1]

The examination has two goals: to identify a structural cardiac cause, and to identify a systemic cause. The examination is the full cardiovascular examination plus the thyroid. [1]

The vital signs — the pulse rate and rhythm (the apex-radial deficit of the AF), the blood pressure (the wide pulse pressure of the aortic regurgitation), the respiratory rate, the temperature, the oxygen saturation. The cardiovascular examination — the pulse character (the collapsing water-hammer of the aortic regurgitation), the apex beat (the location and the character — the thrusting volume-loaded apex, the pressure-loaded sustained apex, the double impulse of the HCM), the right ventricular heave, the heart sounds and the murmurs (the pansystolic of the MR, the early diastolic of the AR, the mid-systolic click and the late systolic murmur of the MVP, the mid-diastolic rumble of the MS). The thyroid examination — the goitre, the bruit, the eye signs of the Graves orbitopathy (the exophthalmos, the lid retraction, the lid lag, the ophthalmoplegia). The general examination — the pallor of the anaemia, the tremor of the thyrotoxicosis, the signs of the chronic disease. [1]

(d) The investigations (4 marks): [1]

The 12-lead ECG is mandatory for every patient with palpitations, no exceptions. The ECG may be normal between episodes in up to half of the patients with a documented arrhythmia, but it may reveal the substrate: the delta wave and the short PR of the WPW, the long QT (over 470 ms in a male, 480 ms in a female), the Brugada pattern (the coved ST elevation in V1 to V3), the left ventricular hypertrophy, the pathological Q waves of the old infarction, the right precordial T-wave inversions and the epsilon wave of the ARVC, the U waves of the hypokalaemia. [1]

The bloods — the full blood count (anaemia), the TSH with the free T4 (thyrotoxicosis), the urea and electrolytes with the magnesium (the electrolyte disturbances), the glucose, the drug levels if indicated. [1]

The ambulatory ECG monitoring is matched to the frequency of the symptoms. The 24 to 48-hour Holter for the daily symptoms. The patient-activated event monitor or the 14-day patch recorder for the weekly symptoms. The implantable loop recorder for the monthly or the rarer symptoms, or the unexplained syncope. A Holter for the infrequent palpitations is wasted effort [9].

The transthoracic echocardiogram is indicated for the suspected structural heart disease (the abnormal findings, the abnormal ECG, the high-risk history). It is not indicated for the patient with the normal history, the normal examination, and the normal ECG. [1]

The electrophysiology study is indicated for the confirmation and the ablation of the SVT, the induction and the mapping of the VT, and the risk stratification of the WPW (the antegrade ERP of the accessory pathway). [1]

(e) The high-risk features (3 marks): [1]

The five high-risk features that mandate the urgent cardiology referral are: [1]

1. The syncope or the near-syncope during the palpitations — the cerebral hypoperfusion from the haemodynamically compromising tachycardia.
2. The exertional symptoms — the VT, the channelopathies (the LQT1, the CPVT), the structural disease (the HCM).
3. The family history of the sudden cardiac death under the age of 40 — the channelopathies, the cardiomyopathies.
4. The structural heart disease — the prior infarction, the cardiomyopathy, the heart failure.
5. The abnormal ECG — the long QT, the Brugada, the epsilon wave, the right precordial T-wave inversions, the pathological Q waves, the LVH with the strain. [1]

(f) The cause-directed management (3 marks): [1]

The management is directed by the cause. The sinus tachycardia — treat the underlying cause. The SVT — the acute termination with the modified Valsalva manoeuvre, the adenosine (6 mg then 12 mg then 12 mg), the verapamil; the long-term management with the catheter ablation (the preferred definitive treatment, over 95 per cent success for the AVNRT and the AVRT) or the AV nodal blockers. The AF — the rate or the rhythm control, the anticoagulation guided by the CHA2DS2-VASc and the HAS-BLED, the direct oral anticoagulants preferred over the warfarin for the non-valvular AF. The ectopic beats — the reassurance and the trigger avoidance in the normal heart, the beta-blocker for the highly symptomatic, the cardiology referral for the ectopy burden over 10 to 15 per cent or the structural heart disease. The VT — the urgent cardiology referral, the synchronised DC cardioversion if unstable, the intravenous amiodarone if stable, the ICD for the secondary prevention. The channelopathies — the specialist evaluation, the beta-blockade, the left cardiac sympathetic denervation, the ICD for the high-risk. [1]

SAQ 2 — Interpreting a Complex Palpitation Case (10 marks)

Prompt: A 28-year-old woman has a 2-year history of intermittent palpitations. The episodes occur every two to three weeks, last 10 to 20 minutes, start and stop abruptly, and are followed by a brisk diuresis. She had one episode of near-syncope during a particularly fast episode. She takes no regular medications. The 12-lead ECG in the clinic is normal. (a) What is the most likely diagnosis? (b) What is the most appropriate investigation to confirm it, and why? (c) What is the definitive management? (d) What are the safety considerations for the pharmacological termination of the episodes? [1]

Model Answer

(a) The most likely diagnosis (2 marks): [1]

The most likely diagnosis is the paroxysmal supraventricular tachycardia (PSVT). The four discriminating features are the sudden onset and the sudden offset (the patient can name the moment — the hallmark of a re-entrant tachycardia), the short duration (minutes), the regular fast rhythm during the episode (implied by the abrupt onset and the near-syncope at the fast rate), and the brisk polyuria after the termination (the atrial natriuretic peptide released during the tachycardia drives the diuresis — a highly specific feature of the SVT). The near-syncope during one episode indicates a haemodynamically compromising fast rate, which is a red flag that elevates the priority of the definitive management. The normal ECG between episodes is expected — up to half of the patients with the documented SVT have a normal resting ECG [2][6].

(b) The most appropriate investigation (3 marks): [1]

The most appropriate investigation to confirm the diagnosis is the ambulatory ECG monitoring matched to the frequency of the symptoms. Given that the episodes occur every two to three weeks (too infrequent for the 24-hour Holter, and at the upper limit of the practicality for the 14-day patch recorder), the patient-activated event monitor (the external loop recorder) or the 14-day patch recorder (the Zio XT) is the appropriate choice. The event monitor records the rhythm when the patient activates it during an episode, and the recorded tracing is transmitted to the cardiac service for the analysis. The patch recorder (the Zio) records continuously for up to 14 days and requires no patient activation — the diagnostic yield for the infrequent symptoms is higher with the extended monitoring. If the event monitor or the patch recorder is unsuccessful over the reasonable period, the implantable loop recorder (the ILR, monitoring for up to three years) is the next step [9].

The investigation strategy is designed to capture the ECG during an episode, which confirms the diagnosis and characterises the arrhythmia (the AVNRT with the invisible or the pseudo R-prime in V1, the AVRT with the retrograde P waves, the atrial tachycardia, or the atypical presentation of the AF). [1]

(c) The definitive management (3 marks): [1]

The definitive management of the symptomatic recurrent PSVT is the catheter ablation — for the AVNRT (the ablation of the slow pathway, the success rate over 95 per cent, the risk of the AV block requiring a pacemaker at 1 per cent or less), the AVRT (the ablation of the accessory pathway, the success rate over 95 per cent), the atrial tachycardia, or the atypical atrial flutter. The ablation offers the prospect of the cure and the freedom from the long-term medication, and it is the preferred strategy for the young woman of the reproductive age who wishes to avoid the medication in the future pregnancies [1][2].

The alternatives for the patient who declines the ablation or who is not a candidate: the AV nodal blocking agents (the verapamil, the diltiazem, the beta-blockers, the digoxin) for the prophylaxis, and the pill-in-the-pocket flecainide (the single oral dose at the onset of the episode) for the infrequent well-tolerated SVT in the patient with the structurally normal heart. The flecainide is contraindicated in the structural heart disease and the ischaemic heart disease (the pro-arrhythmic risk — the CAST trial finding). [1]

Given the episode of the near-syncope, the ablation is the preferred strategy — the recurrent haemodynamically compromising SVT warrants the definitive treatment rather than the long-term medication. [1]

(d) The safety considerations for the pharmacological termination (2 marks): [1]

The intravenous adenosine (6 mg then 12 mg then 12 mg as a rapid bolus with the saline flush) is the standard first-line pharmacological agent for the acute SVT termination, but the safety considerations are: [1]

• The patient must be warned of the unpleasant sensation (the chest tightness, the breathlessness, the flushing, the sense of doom) and the transient asystole (2 to 5 seconds).
• The adenosine is contraindicated in the asthmatic (the bronchospasm), the severe aortic stenosis, and the hypertrophic cardiomyopathy (the profound hypotension).
• The adenosine must not be given if the broad-complex tachycardia could be the VT — the adenosine may provoke the VF in the VT patient, and the adenosine-induced vasodilatation in the poor cardiac reserve can precipitate the collapse.
• The defibrillator must be at the bedside when the adenosine is administered. [1]

The intravenous verapamil (5 to 10 mg over 2 minutes) is the alternative, but it must not be given immediately after the beta-blocker (the risk of the complete heart block and the asystole from the combined AV nodal blockade), and it must not be given if the broad-complex tachycardia could be the VT. The modified Valsalva manoeuvre (the REVERT technique — the 15-second blow to 40 mmHg in the semi-recumbent position, then the immediate supine repositioning with the passive leg raise) is the first manoeuvre and has a 43 per cent success rate versus 17 per cent for the standard Valsalva [4].