A 44-year-old man was referred to the emergency department after attending a private clinic for his annual company medical check-up, because an alteration was detected in the ECG reported as "arrhythmic conduction of the P waves, with suspected atrioventricular block of 2nd degree".

HISTORY, CURRENT ILLNESS AND PHYSICAL EXAMINATION

Personal and family history
No known cardiovascular risk factors. Never smoked, occasionally drinks some wine or beer with meals. He is a recreational sportsman: he cycles to work and goes on longer outings at weekends, also goes hiking and occasionally plays football or paddle tennis. No known heart disease or other medical or surgical history of interest.
Mother with non-ischemic dilated cardiomyopathy, currently with moderate systolic dysfunction, pacemaker wearer since the age of 55 and with radiofrequency ablation of sustained monomorphic ventricular tachycardia (SMVT) at the age of 61.

Present illness
The patient went to a private clinic for an annual company check-up and the ECG showed what was described as "arrhythmic conduction of the P waves, suspected 2nd degree AVB" and he was referred to his health centre. His family doctor performed a new ECG and referred him to the emergency department. The patient denies any related symptoms (no dizziness, no asthenia, no syncope).
He does not understand why he is here.

Physical examination
BP 119/73 mmHg. HR 57 bpm. Ta 36°C. Good general condition. Arrhythmic cardiac auscultation by extratonos, without murmurs. Pulmonary auscultation with preservation of vesicular murmur. Abdomen and extremities normal, without oedema and with normal pulses.

COMPLEMENTARY TESTS
ECG: sinus rhythm at 90 bpm with complete atrioventricular block and escape rhythm at 45-50 bpm. EV monomorphic, with BCRDHH morphology and inferior axis (isolated, with some duplet).
CBC: glucose 89 mg/dl, urea 34 mg/dl, creatinine 0.87 mg/dl, total cholesterol 167 mg/dl, triglycerides 88 mg/dl, HDL cholesterol 32 mg/dl, LDL cholesterol 117 mg/dl, sodium 144 mEq/l, potassium 5.4 mEq/l, troponin I 0.044 (normal, < 0.01μg/l), CK 7.3, CK-MB 4.40. Haemogram: haemoglobin 14.8 g/dl, haematocrit 43.9%, MCV 83.9 fl, platelets 239,000, leucocytes 7,520.
Echocardiogram: LV slightly dilated (LVEDD 59 mm, LVEDV 183 cc) with normal wall thickness. Mild LA dilatation. Marked asynchrony of contraction at the level of the interventricular septum, with mild global hypokinesia and LVEF by volumetry of 43% (mild systolic dysfunction). Trivalve aortic valve, normal. Mitral, tricuspid and pulmonary valves of normal morphology and mobility. Mitral filling pattern with E>>A wave with no data suggesting increased LV filling pressures. Right ventricle not dilated, of normal thickness, without alterations of regional contractility and with preserved global systolic function. Mild TR with PSAP estimated at 26 mmHg. Inferior vena cava and suprahepatic veins were not dilated, with adequate inspiratory collapse, which excludes the presence of significant systemic venous hypertension.
Cardio MRI: LV of normal thickness, slightly dilated (248 mL TVD; 115 mL/m2 of CS) with slightly reduced ejection fraction (EF 48%), normal segmental contractility. RV of normal global and segmental dimensions and contractility. Linear mesocardial enhancement is identified in the basal septum, with extension to the mid-segment. Conclusions: mild LV dilatation and systolic dysfunction, with basal mesoseptal linear fibrosis extending to the mid-segment (His bundle area).
Chest X-ray (post-implantation): normal cardiothoracic index, no images of pneumothorax or other complications. Atrial and ventricular electrode well positioned and generator at left subclavicular level.
Exercise echocardiogram: 9.30 min of Bruce protocol exercise.
The test is stopped due to fatigue at 93% of maximum theoretical heart rate. Basically and up to minute 7, sinus rhythm conducted by ventricular stimulation by the pacemaker; in minute 7 there is alternation of pacemaker rhythm with own rhythm and ventricular extrasystoles, causing a marked irregularity in the heart rate; from 130 bpm it remains in own rhythm with subsequent reappearance of the pacemaker rhythm in the immediate post-exercise. Normal tension response. Contractility slightly depressed at baseline with global hypokinesia and estimated LVEF of 40-45%, with improvement of around 10 points with exercise. The test was clinically and echocardiographically negative for ischaemia, with a pattern of improvement in contractility with exercise (contractile reserve) suggesting cardiomyopathy. ECG not assessable due to baseline pacemaker rhythm.

EVOLUTION
Although the patient was completely asymptomatic and the block was detected by chance, it was decided to admit him to hospital with continuous ECG monitoring, and he remained in complete AVB at all times, although with adequate escape rhythm and totally asymptomatic. It was decided to implant a definitive bicameral pacemaker, with prior cardiac MRI. Twenty-four hours after the procedure, once complications related to the procedure had been ruled out, the patient was discharged from hospital. If familial dilated cardiomyopathy associated with atrioventricular conduction disorders is suspected, the patient is referred to the Family Cardiopathies Unit (UCF) of reference for genetic study.
Likewise, a schedule of visits is programmed for review of the device and follow-up in Cardiology consultations.
At subsequent check-ups, the patient reported feeling well. Following pacemaker implantation, he has moderated his sporting activities considerably, following medical recommendations. A stress echocardiogram was performed with the results described, so moderate physical exercise was not contraindicated. In the periodic reviews of the device, several episodes of NSVT were detected (about 10 in a year, of short duration).
We insisted on the family history and the patient commented that his maternal grandmother, who died suddenly at the age of 69, had been considered for a pacemaker implant during her lifetime, which was never carried out. She has 3 brothers, one of whom (a 47-year-old male) has just been diagnosed with a 2nd degree atrioventricular block (he lives in another Community; during follow-up, a permanent pacemaker was implanted). She has two other sisters and two children aged 12 and 8, with no evidence of heart disease after screening of family members.
Finally, more than a year after the pacemaker implantation, the results of the genetic analysis were received, in which 34 genes involved in conduction system diseases were evaluated, reporting that the patient is a heterozygous carrier of the Glu444* truncation, considered to be pathogenic or associated with disease. A defibrillator implantation is proposed, which the patient accepts.

DIAGNOSIS
Asymptomatic complete atrioventricular block.
Carrier of a definitive bicameral pacemaker.
Familial dilated cardiomyopathy with associated AV conduction disorder due to laminopathy A/C.
Mild LV systolic dysfunction (LVEF 45-50%).
Repeat NSVT, asymptomatic (detected by pacemaker).
Defibrillator implantation in primary prevention.
